GB2279072A - Synthesis of substituted triphenylenes useful for discotic liquid crystals - Google Patents

Abstract

Substituted triphenylenes, required in the synthesis of polymeric discotic liquid crystals, are made using an oxidising agent (eg FeCl3 or NOBF4) to couple suitably substituted benzenes with suitably substituted benzenes or biphenyls. The coupling is followed by treatment with a reducing agent (eg methanol). For example, iron (III) chloride in organic solvent at room temperature may be used to effect the oxidative coupling of 1,2-dialkoxybenzenes to 3,3',4,4'-tetraalkoxybiphenyls. The same oxidation-reduction protocol also proves effective in the trimerisation of 1,2-dialkoxybenzenes.

Description

SYNTHESIS OF SUBSTITUTED TRIPHENYLENES.

USEFUL AS DISCOTIC LIOUID CRYSTALS This invention relates to a method of synthesising pure (i.e. isomer-free) substituted, e.g. unsymmetrically substituted, triphenylenes and includes the compounds so made. Hitherto, such synthesis undesirably yielded isomers in plenty. These compounds, which form a good feedstock for polymerisation, may find application as discotic liquid crystals, which may be of low or high molar mass.

The method makes it possible to prepare polymeric discotic liquid crystals of defined structure because, without unsymmetrically substituted triphenylenes, homogeneous polymers of defined structure based on this nucleus cannot be made. The method is also useful for liquid crystal systems of low molar mass in which the triphenylene nucleus may be symmetrically or unsymmetrically substituted. It allows these compounds to be made pure, cheaply and in large quantities.

Discotic liquid crystals based on the triphenylene nucleus show promise particularly because they form ordered hexagonal columnar phases, and triphenylene based polymers in particular are likely to be especially important. Potential applications are likely to be based on building functionality into these systems to create conducting and/or photosensitive materials for use in xerography, laser printing, electronic photography, information storage, sensors (especially chemical sensors), etc. For example when hexaalkoxytriphenylenes are doped with an oxidant they are converted into semiconductors in which the preferred direction of conduction is along the columns of the hexagonal columnar phases, the aromatic core of the columns providing a conducting pathway with the annul us of hydrocarbon chains forming an insulating sheath.

Since Chandrasekhar's original paper (1) reporting the first synthesis of a discotic liquid crystal there has been an ever-increasing interest in the preparation of new discotic mesogens. Progress has, however, been held back by synthetic difficulties which have restricted the availability of the requisite large amounts of highly pure materials.

Hexasubstituted triphenylenes are a widely synthesised class of discotic liquid crystals. Their synthesis traditionally involves the oxidative trimerization of 1,2-dimethoxybenzene (veratrole) 1 in 67Z sulphuric acid using the quinone chloranil as oxidant t2,3]. This reaction is more or less limited to the production of hexamethoxytriphenylene 2 and if, for example, hexahexyloxytriphenylene (HAT6) 4 is required it is necessary to replace the alkoxy groups OMe; the methyls can be removed either by using hydrogen bromide/acetic acid or boron tribromide.The resulting hexahydroxytriphenylene is then alkylated with hexyl bromide

Although the chloranil/sulphuric acid mixture can be used to trimerize 1,2-dihexyloxybenzene directly to form HAT6, purification of the HAT6 involves repeated chromatography and repeated recrystallisation, and the yield is low. For this reason the indirect route via compounds 2 and 3 is usually more economical.

The need to replace the alkoxy substituent in the "chloranil" route is, however, a wasteful step and synthesis of hexaalkoxytriphenylenes in this way involves two lengthy chromatographic separations (firstly to separate compound 2 from chloranil and secondly to purify the final product) which makes the whole process rather time-consuming and which limits the overall scale of production. In our experience it is not easy to prepare more than about 10 g of any pure mesogen such as HAT6, in a single batch.

An alternative route which has been explored is electrochemical oxidation (4-7]. For example, Bechgaard and Parker (4] have shown that anodic oxidation of veratrole in trifluoroacetic acid/dichloromethane with tetrabutylammonium tetrafluoroborate as the supporting electrolyte gives the hexamethoxytriphenylene 2.

The anode potential required to bring about the reaction is also sufficiently positive to remove an electron from the triphenylene and so the observed product from such an oxidation is not the triphenylene itself but the radical cation salt 5 (R=Me).

Salts of this type are decomposed by reaction with nucleophiles such as water (which is in part the reason why such reactions are carried out in acidic solvents) and so the workup procedure is crucial to the outcome of the reaction. However if the mixture is worked up reductively a good yield of hexamethoxytriphenylene is obtained. Such a reductive workup can be achieved either by chemical or electrochemical methods (6]. If the reaction is carried out under carefully controlled conditions the radical cation-salt 5 crystallises out on the anode surface (electrocrystallisation). However, we have found that the electrochemical route is slow and the workup relatively tedious so that we have not succeeded in making more than ca. 1 g quantities at a time in this way and in most cases we do not regard it as a serious competitor to the "chloranil" route.

Another alternative oxidation reagent in these reactions is ferric chloride 8]. Bengs et al. have described a reaction procedure in which l,2-bishexadecyloxybenzene was treated with ferric chloride in 70X sulphuric acid at 80C followed by an ice/water workup to give a 20% yield of 2,3,6,7,10,11-hexakishexa- decyloxytriphenylene and have used a similar procedure for making mixed trimers in low but unspecified yield.

According to the present invention, a method of synthesising a substituted triphenylene comprises coupling

the biphenyl derivative

using an oxidising agen followed by a reducing agent, where A, B, C, D, E and F are independently chosen from among hydrogen, halogen, alkyl, alkoxy, hydroxy, acyloxy and aryloxy and G, H, I, J, K and L are independently chosen from among hydrogen, halogen, alkyl, alkoxy, hydroxy, acyloxy and aryloxy, or A and B together and/or G and H together, are

Usually A = G, B = H etc. When synthesising the triphenylene where A B and C = F and D = then using

with

offers a route yielding very little triphenylene other than the desired one.

Preferably, the oxidative coupling is performed in an organic solvent. The oxidising agent can comprise a transition metal, such as Fe(III) or V or Cr, e.g. the compound FeC13. The oxidising agent may be accompanied by a base such as K2C03 preferably insoluble in the organic solvent (preferably in excess, to mop up arising acid) or by not more than 1 weight % acid, such as H2S04, and preferably at below 400C (more preferably below 300C), e.g. 15-250C. Alternatively a one-electron oxidant such as NOBF4 can be employed or a one-electron oxidant can be employed in combination with a transition metal, for example NOBF4 can be employed in combination with FeC13. The oxidative coupling is followed by workup with a reducing agent, for example an alcohol such as methanol or ethanol. Methanol is an example of a mild reducing agent. If ferric chloride is used as the oxidising agent, methanol also has the function of dissolving ferrous iron Fe(II) while not being a solvent for the desired product, and when oxidised, it forms a volatile aldehyde.

It should be noted that the oxidative trimerization of ortho disubstituted derivatives of benzene always goes through a biphenyl intermediate, one which normally has only a fleeting existence.

However, when attempts are made to trimerize mixtures of ortho disubstituted benzene derivatives a complex mixture of triphenylenes normally results. In the reaction mentioned previously where a preformed biphenyl is coupled to a benzene derivative and where A=B (or if AsB, C=F and D=E], only a single cross-coupling product (one specific isomer) is produced, and the only separation needed is that from the triphenylene product(s) of the competing trimerization

In performing the benzene/biphenyl coupling reactions it is sometimes advantageous to use a stepwise procedure. This involves oxidising the biphenyl (e.g. with 1-2 moles of FeC13), then adding the benzene derivative, then excess of the oxidising agent, followed by a reductive workup.

results in an improvement of yield from 5% to 35% (compared to simply adding excess Fecal3 to a mixture of the two reagents).

Also, using this procedure, competing trimerization is eliminated.

In a modification of the starting materials used in the invention, the compound

may be substituted in one or both adjacent positions

in which G and H are as previously defined and N and M are independently chosen from among hydrogen, halogen, alkyl, alkoxy, hydroxy, acyloxy and aryloxy.

Examples of this modification are: G = H = -O-nC6H13, M = CH3, N = hydrogen G = H = -OCH3, M = halogen e.g. F (fluorine), N = hydrogen G = H = CH3, M = -OCH3, N = hydrogen G = hydrogen, H = M = -OCH3, N = hydrogen G = H = hydrogen, M = N = -O-nC6H13 In all these versions of this modification, one a position of the resulting triphenylene derivative product is substituted with M Such a-substituted triphenylenes are new and part of this invention, having been hitherto impossible to make. Similar variations in the number, nature and positions of substituents on the biphenyl portion can be chosen to expand the range of triphenylene derivatives accessible by this route.

For symmetrical products (A to L all identical, M = N = hydrogen) trimerization of the ortho disubstituted benzene is normally more efficient than the benzene/biphenyl coupling reaction but the reagents/reaction conditions described above represent a significant improvement on those used heretofore.

We have found, for example, that oxidation of veratrole (ortho-dimethoxybenzene) can be achieved using FeC13 in ca. 0.3% (w/v) sulphuric acid in dichloromethane at 15-25"C for 2 hours.

The product is a dark green solid which is certainly an oxidised form of the triphenylene, most probably the radical cation salt 5.

This is then filtered off and reduced on the filter pad with methanol.

Formaldehyde is liberated and hexamethoxytriphenylene thus obtained directly and virtually pure.

We have repeated this reaction using a range of different acids (0.3 g/100 ml in each case) but best yields were obtained using sulphuric: Acid Yield % Trifluoroacetic 73 Triflic 78 Chlorosulphonic 76 Conc. sulphuric 86 In truth the HC1 liberated as a by-product in the reaction is probably the "major" acid in all cases. A reasonable yield is obtained even if the acid is totally omitted. In some cases (as detailed below) it is advantageous to add base.

This route to hexamethoxytriphenylene is both quicker and easier than any other route and has the advantage that it is easy to perform on a relatively large sale. It also has the advantage over the chloranil route that most 1,2-dialkoxybenzenes can be trimerized directly to give good yields. The reaction can be performed using a variety of FeIII salts but in particular ferric chloride has been used.

Thus, we have discovered that the use of an FeIII salt in a much less acid medium, followed by a reductive workup procedure (e.g. with methanol) allows the trimerization reaction to be achieved in much higher yield than before and on a larger scale.

For example:

R = CH3 yield 86% (CH2)2CH3 77% (CH2)3CH3 65% (CH2)5CH3 73X (CH2)7CH3 60% (CH2)8CH3 55X This reaction can be used as a step towards preparing discotic liquid crystals of the hexaacyloxy type 6 by the following route:

Lyotropic discotic liquid crystals of the type shown in formula 7 can also be made as shown in the above scheme. Attempts to prepare these by trimerization of the corresponding benzene derivatives using FeC13/acid/CH2C12 have failed. However for the trimerization of related acid-sensitive substrates, the reaction is successful, if an excess of an insoluble base (FeC13/K2C03/CH2C12) is added to the reaction mixture.

In some cases these reaction conditions can be used to effect mixed trimerization reactions which, in favourable circumstances (e.g. as to product and reactant solubility) can be separated from positional isomers, allowing unsymmetrical derivatives to be prepared:

Taken together these reactions are particularly important since they allow triphenylenes of the type required for elaboration into liquid crystalline polymers of both the main chain and side-chain types to be made. For example:

Previous work on the synthesis of polymeric discotic systems 9,l0] has suggested that these are likely to be more important than their low molar mass counterparts but had failed to develop a route that could make these materials pure and free from positional isomers and on a large scale.

Although applications of discotic liquid crystals have yet to be developed, they are likely to be based on building functionality into systems and particularly based on polymeric systems.

Polymeric materials have the advantages over their low molar mass counterparts of ease of processability, in particular, to make supramolecularly aligned fibres or films. Cross-linking can impart elastomeric properties, opening up applications requiring strain-dependent conductivity. Polymeric materials are also more "tolerant" to incorporation of dopants into the hydrocarbon chain matrix, permitting doping to significantly higher concentrations and hence functionalisation of these materials as p- or n-type semiconductors by the incorporation of, respectively, oxidants or reductants into the hydrocarbon chain matrix as taught in European Patent 364185.

The oxidant or reductant could be replaced with a photosensitiser so that electron transfers can be induced ohotochemi call v:

where the electron acceptor A would be for example trinitrofluorenone, tetrachloro-p-benzoquinone or TCNQ-F4, in which case the direct transfer is induced photochemically, or cyanine or triphenylmethane cationic dyes, where the photoexcited state of the dye would act as the oxidant. These doped materials are likely to have interesting photoconductivity and electroluminescence properties. The former would find applications in, for example, xerography, laser printing, electronic photography, image/information storage, and the latter in large area displays, TV, etc.

This invention is illustrated by the following examples.

Unless otherwise stated, all steps were performed at room temperature.

It was not previously possible to synthesise, or at least not in pure form, many of the products referred to in these examples.

Accordingly, the present invention provides within its scope not only the above described new method of synthesis, but also the new products of such a synthesis.

The abbreviation Hx (hexyl) means n-hexyl unless otherwise indicated.

Synthesis ot hexamethoxytripnenytene.

Synthesis of other symmetrical hexaalkoxytriphenylenes such as hexahexyloxytriphenylene.

Synthesis of TP6E02M.

Synthesis of 2,3-dimethoxytetrahexyloxytriphenylene.

Synthesis of 2-methoxypentahexyloxytriphenylene.

Synthesis of 2,7-linked polymer The corresponding 3,6-dihydroxy compound has been used to make the analogous 3,6-linked polymer

3,4-dihexyloxybiphenyl 28

2.3.6.7.l0.01-Hexarnethoxytriphenvlene Compound 2 Veratrole (23 g, 0.166 mol) was added slowly to a well stirred suspension of iron (III) chloride (81 g, 0.5 mol) in dichloromethane (500 ml) and concentrated sulphuric acid (1.6 g). As the veratrole was added hydrogen chloride gas was given off and the temperature rose until the dichloromethane was refluxing (400C). The reaction mixture was stirred for a further 2 hours and then filtered.

Methanol was carefully added to the solid on the filter pad which changed colour from dark green to grey with copious washings. Heat and formaldehyde were liberated and it is advised that this step is performed in a well ventilated fume-cupboard. The remaining solid was dried under vacuum to yield hexamethoxytriphenylene 2 as a grey solid (19.7 g, 86%), mp > 3000C.

1,2-Dihexvloxvbenzene Bromohexane (4.92 ml, 0.0375 mol) was added to a vigorously stirred solution of catechol (1.1 g, 0.01 mol) and potassium carbonate (6.2 g) in ethanol (100 ml) under nitrogen. The reaction mixture was stirred under reflux for 16 hours and filtered through Celite with copious washings of ethanol. The filtrate was concentrated Th vacuo and subjected to column chromatography on silica eluting with 1:1 dichloromethane:light petroleum to give the product as a pale yellow oil (2.6 g, 95%).

In a similar manner were prepared: 1,2-dipropyloxybenzene (reaction time 4.5 hours1 yield 89X); 1,2-dibutyloxybenzene (4.5 hours, 91%); 1,2-dioctyloxybenzene (16 hours, 79%, mp 240C, lit. C153 23-260C; and 1,2-dinonyloxybenzene (8 hours, 86%, mp 370C, lit. tl53 370C).

2.3.6.7.l0.ll-Hexahexvloxvtriphenvlene (HAT6. 4] 1,2-Dihexyloxybenzene (1.5 g, 0.0055 mol) was added to a vigorously stirred suspension of iron (III) chloride (2.66 g, 0.0165 mol) in dichloromethane (20 ml) with concentrated sulphuric acid (2 drops). The reaction occurred with vigorous evolution of gas and was quenched with methanol (60 ml) after 45 minutes. The reaction mixture was filtered and the filtrate concentrated in vacuo to give a black solid which was subjected to column chromatography eluting with 1:1 dichloromethane:light petroleum to give the product as a pale yellow solid which was recrystallised from ethanol (1.09 g, 73Z) K-D 670C, D-l 99.50C. (lit. 16] 680C, 970C).

In a similar manner were prepared: 2,3,6,7,10,11-Hexapropyloxytriphenylene, HAT3 (77X), K-l 176.50C, (lit. 16) 1770C); 2,3,6,7,10,11-hexabutyloxy- triphenylene, HAT4 (65%), K-D 880C, D-l 143.50C, (lit. (16) 88.60C, 145.60C); 2,3,6,7,10,11-hexaoctyloxytriphenylene, HAT8 (60%), K-D 65.80C, D-l 84.80C, (lit. [16) 66.80C, 85.60C); and 2,3,6,7,10,11-hexanonyloxytriphenylene, HAT9 (55%), K-D 56.50C, D-l 780C, (lit. (16) 570C, 77.60C).

Improved Procedure for the Svnthesis of 2.3.6.7.10.11-Hexa-(1.4.7- trioxaoctvl)-triphenvlene 7 (TP6E02M) 2,3,6,7,10,11-Hexahydroxytriphenylene (1.11 g, 0.0034 mol) was added, under nitrogen, to l-bromo-2-(2-methoxyethoxy)-ethane (5.1 g, 0.028 mol) in ethanol (82 ml). Potassium carbonate (5.27 g) was added and the mixture was well stirred under reflux in an atmosphere of nitrogen for 20 hours. The mixture was allowed to cool before being filtered through Celite and the filtrate was evaporated in vacuo to give the crude product. This material was purified by column chromatography on Keiselgel eluting first with dichloromethane followed by 2X methanol in dichloromethane and finally 4% methanol in dichloromethane. Repeated recrystallisation of the product from ether at 0 C gave pure TP6E02M as white needles (1.05 g, 37X) mp 53.4-53.70C (lit. (3] 51-530C).

2.3-Dimethoxv-6.7.10.11-tetrahexvioxytriphenylene Compound 8 A solution of 1,2-dihexyloxybenzene (10 g, 0.036 mol) and veratrole (10 g, 0.074 mol) in dichloromethane (40 ml) was added to a stirred mixture of iron (III) chloride (70 g, 0.434 mol) and concentrated sulphuric acid (1 ml) in refluxing dichloromethane (250 ml) at such a rate that a gentle reflux was maintained. The mixture was stirred for a further 1 hour and poured onto methanol (400 ml). The dichloromethane was removed in vacuo and the solid filtered and purified by column chromatography on silica eluting with benzene. The white solid was recrystallised from dichloromethane/methanol to give the product (2.7 g, 22%), mp 1020C. Anal.

Found C (76.6X), H (9.4%), C44H6406 requires C (76.7Z), H (9.4Z).

2-Methoxv-3.6.7.l0.l l-pentahexvloxytriphenvlene Compound 9 1,2-Dihexyloxybenzene (10 g, 0.036 mol) and 2-hexyloxyanisole (7.5 g, 0.036 mol) were added to a suspension of iron (III) chloride (35 g, 0.217 mol) in refluxing dichloromethane and concentrated sulphuric acid (0.5 ml) over 1 hour. The mixture was stirred for a further 1 hour under reflux and poured onto methanol (250 ml). The solid was filtered, washed with methanol and separated on a silica column (benzene eluant) to afford 2-methoxy-3,6,7,10,1l-penta- hexyloxytriphenylene (2.4 g, 18%) K-D 530C, D-l 720C.

4-Iodo-2-hexvloxvanisole 5-Iodo-2-methoxyphenol (50 g, 0.2 mol), hexyl bromide (38 g, 0.23 mol) and potassium carbonate (42 g) were stirred in refluxing ethanol (150 ml) for 6 hours. Light petroleum ether was added to the cooled mixture and the solid filtered and washed with light petroleum ether. The organic solvents were removed in vacuo and the residual oil distilled under reduced pressure to yield 4-iodo-2-hexyloxyanisole (58 g, 875), bp 130-1320C/0.75 mm Hg.

3.3'Dihexyloxy-4,4'-dimethoxybiphenyl 4-Iodo-2-hexyloxyanisole (20 g, 0.06 mol) and copper powder (20 g) were thoroughly mixed together and heated to 2700C for 10 minutes. The mixture was cooled and extracted repeatedly with chloroform. The solvent was removed in vacuo and the residue crystallized from ethanol to afford 3,3'dihexyloxy-4,4'dimethoxybiphenyl (5.9 g, 48%) mp 75.5-76.50C.

2.7-Dimethoxy-3.6.10.11-tetrahexyloxytriphenylene Compound 10 A mixture of iron (III) chloride (45 g, 0.279 mol), concentrated sulphuric acid (0.5 ml), 3,3'-dihexyloxy-4,4'dimethoxybiphenyl (8 g, 0.019 mol) and 1,2-dihexyloxybenzene (22.8 g, 0.082 mol) was stirred in dichloromethane (150 ml) for 1 hour. The reaction mixture was carefully poured onto methanol (500 ml) and after cooling in ice the resultant precipitate was filtered and washed with methanol. Separation on silica (benzene eluant) afforded 2,7-dimethoxy-3,6,10,ll-tetra- hexyloxytriphenylene (6 g, 45%), mp 980C.

Anal. Found: C, 76.7X; H, 9.4%; C44H6406 requires C, 76.7%; H, 9.4X.

2.7-Dihvdroxv-3.6.10.11-tetrahexvioxytriphenylene A solution of diphenylphosphine (0.9 g, 4.84 x 10-3 mol) in dry THF (40 ml) was stirred under argon in an ice bath.

Butyllithium (2.8 ml, 2.5 M in hexanes, 7 x 10-3 mol) was added and the solution stirred for 10 minutes. 2,7-Dimethoxy-6,7,10,11- tetrahexyloxytriphenylene (1 g, 1.45 x 10-3 mol) was added and the solution stirred at room temperature for 2 hours and at 450C for 1.5 hours causing a precipitate to form. The reaction mixture was poured onto dilute sulphuric acid and extracted twice with dichloromethane. The organic solution was washed twice with dilute sulphuric acid and evaporated in vacuo. The white product was recrystallized twice from ethanol to afford 2,7-dihydroxy-3,6,10,11- tetrahexyloxytriphenylene (0.7 g, 73%), mp 1860C.

Polvmerization of 2.7-dihvdroxv-3.6.10.ll-tetrahexvloxv- triphenylene Compound 11 2,7-Dihydroxy-3,6,10,11-tetrahexyloxytriphenylene (400 mg, 6.06 x 10-4 mol) and caesium carbonate (390 mg, 1.2 x 10-3 mol) were dissolved in N-methylpyrrolidone (NMP) (1.3 ml). l,ll-Dibromoundecane (190 mg, 6.05 x 10-4 mol) in NMP (1 ml) was added and the mixture immediately submerged in an oil bath at 110 C. The mixture was stirred for 1 hour at 1100C and cooled. Water was added and the resulting solid repeatedly washed with water and ethanol. The solid was precipitated from dichloromethane with ethanol to give two polymers as white solids.

1) Mw = 16000, mp 100-1150C.

2) Mw = 25000, mp 100-1150C.

2-Hexvl oxvphenol A mixture of catechol (50 g, 0.45 mol), bromohexane (75 g, 0.45 mol) and potassium carbonate (100 g) were stirred in refluxing ethanol (250 ml) for 12 hours. The mixture was cooled and dichloromethane (250 ml) added. The solid was filtered off and the filtrate concentrated in vacuo. Distillation at 150-1600C/14 mm Hg afforded 2-hexyloxyphenol (60 g, 69%) as a colourless oil.

Anal. C, 73.95%; H, 9.3%; C12H1802 requires C, 74.19%; H. 9.34%.

2-Hexvioxvphenyl acetate Acetyl chloride (35 g, 0.45 mol) was added to 2-hexyloxyphenol (65 g, 0.34 mol) with stirring over 1 hour and the mixture stirred for a further 24 hours. Dichloromethane (200 ml) was added and the solution washed with dilute potassium carbonate until the aqueous layer was basic. The organic solution was dried (MgS04) and the solvent removed in vacuo. Distillation of the residue at 100-1060C/0.8 mm Hg afforded 2-hexyloxyphenyl acetate as a colourless oil (75 g, 94%).

2-Hexvioxv-5-iodophenol 2-Hexyloxyphenyl acetate (24 g, 0.10 mol) was dissolved in chloroform (150 ml) and cooled to 80C. Iodine monochloride (20 g, 0.12 mol) in chloroform (50 ml) was added dropwise maintaining the reaction temperature between 8-130C. The mixture was stirred at room temperature overnight, washed with sodium metabisulfite until the iodine colour disappeared and then with water. The organic solution was separated and the solvent removed in vacuo. The residual red/brown oil was dissolved in ethanol (20 ml) and a solution of sodium hydroxide (35 g, 0.86 mol) in ethanol (50 ml) and water (40 ml) was added. The solution was refluxed for 1 hour, allowed to cool and carefully acidified with 40% sulphuric acid. The mixture was extracted with dichloromethane (2 x 150 ml) and the organic solutions dried (MgS04). Removal of solvent in vacuo followed by distillation of the residue at 140-1450C/1.2 mm Hg gave a yellow oil which crystallized overnight. Recrystallization from light petroleum afforded 2-hexyloxy-5-iodophenol (20.5 g, 64%) mp 29-300C.

2-Hexvloxv-5-iodoanisole 2-Hexyloxy-5-iodophenol (15.1 g, 0.047 mol) and sodium hydroxide (2 g, 0.05 mol) were stirred in ethanol (100 ml) for 10 minutes. Methyl iodide (10 g, 0.07 mol) was added and the solution was stirred at room temperature for 3 days. The mixture was acidified with dilute sulphuric acid and extracted with dichloromethane (2 x 100 ml). The solvents were removed in vacuo and the residue crystallized from ethanol to give 2-hexyloxy-5-iodoanisole (12.2 g, 78Z), mp 44-44.50C.

Anal. C, 46.9%; H, 5.95%; I, 37.95%; C13H19I02 requires C, 46.72%; H, 5.95X; I, 37.97X.

4.4'-Dihexyloxy-3.3'-dimethoxvbiphenvl 2-Hexyloxy-5-iodoanisole (15 g, 0.45 mol) was mixed intimately with copper powder (17 g). The mixture was heated carefully to 2700C where an exothermic reaction took place causing the temperature to rise to 3200C. After cooling the mixture was extracted repeatedly with dichloromethane (-350 ml). The solvent was removed in vacuo and the residue crystallized from methanol to give 4,4'-dihexyloxy-3,3'-dimethoxybiphenyl (6.1 g, 66Z), mp 82.5-830C.

Anal. C, 75.4X; H, 9.45X; C26H3804 requires C, 75.32%; H, 9.24%.

2.7.10.1 l-Tetrahexvloxv-3.6-dimethoxvtriphenvlene Compound 12 4,4'-Dihexyloxy-3,3'-dimethoxybiphenyl (3.6 g, 8.7 mmol) and 1,2-dihexyloxybenzene (7.25 g, 26 mmol) were stirred in dichloromethane (50 ml) and iron (III) chloride (18 g, 111 mmol) was added. After stirring for 1 hour the mixture was poured onto methanol (100 ml) and the resulting solid immediately filtered off and dried in a desiccator. Purification by column chromatography (silica, benzene/light petroleum 4:1) afforded 2,7,10,11-tetrahexyloxy-3,6-dimethoxytriphenylene (4.6 g, 77%), mp 116.50C.

Anal. C, 76.85X; H, 9.5X; C44H6406 requires C, 76.70%; H, 9.36X.

2.7.l0.ll-Tetrahexv1oxv-3.6-dihvdroxytrihenvlene Diphenylphosphine (1.7 g, 9.2 mmol) was dissolved in dry THF (60 ml) and cooled in an ice bath under argon. Butyllithium (2.5 M in hexanes, 5 ml, 12.5 mmol) was added over 10 minutes.

Solid 2,7,10,11-tetrahexyloxy-3,6-dimethoxytriphenylene (1.7 g, 2.5 mmol) was added and the solution stirred at 50-600C for 4 hours and at room temperature overnight. The mixture was poured onto dilute sulphuric acid and extracted with ethyl acetate (3 x 70 ml). The solvent was removed in vacuo and the residue precipitated from dichloromethane with methanol. The precipitate was filtered off, dried and purified by column chromatography (silica, benzene) to give 2,7,10,11-tetrahexyloxy-3,6-dihydroxy- triphenylene (1.2 g, 74%), mp 1050C.

Anal. C, 76.15%; H, 9.1%; C42H6006 requires C, 76.32%; H, 9.15%.

Polvmerization of 2.7.10.l1-tetrahexvioxv-3.6-dihvdroxvtriphenviene 2,7,10,11-Tetrahexyloxy-3,6-dihydroxytriphenylene (0.576 g, 0.872 mmol) was stirred in N-methylpyrrolidone (2 ml) and degassed with argon. Caesium carbonate (0.5 g) was added and the mixture stirred for 5 minutes. l,ll-Dibromoundecane (274 mg, 0.872 mmol) in N-methylpyrrolidone (0.5 ml) was added and the flask immediately immersed in an oil bath at 850C. A two-phase mixture was immediately formed which was stirred at 850C for 2 days and poured onto water.The solid was filtered, reprecipitated from dichloromethane with ethanol, and separated by column chromatography (silica, benzene then dichloromethane) to give monomer (60 mg), mp 730C, dimer (35 mg), K-D 1300C D-I 1400C, and polymer (450 mg), Mw-9000, K-D 930C, D-I 1200C.

2.3.6.7-Tetrahexvloxv-l0-hvdroxv-ll-methoxvtriphenvlene Compound 13 3,3',4,4'-Tetrahexyloxybiphenyl (100 mg, 0.18 mmol) and guaicol acetate (250 mg, 1.5 mmol) were stirred in dichloromethane (20 ml). Iron (III) chloride (0.5 g, 3.1 mmol) was added, the mixture stirred for 2 hours and poured onto methanol (30 ml).

The solid was filtered off, washed with methanol, dried and purified by column chromatography (silica, benzene) to give 2,3,6,7-tetrahexyloxy-10-hydroxy-11-methoxytriphenylene (57 mg, 47%), mp 1120C.

Methvl-2.3.6.7.10.1l-tetrahexvloxvtriphenvlene Compound 14 3,3',4,4'-Tetrahexyloxybiphenyl (1 g, 1.8 mmol) and 2,3-dihexyloxytoluene (1 g, 3.4 mmol) were stirred in dichloromethane (30 ml). Iron (III) chloride (2 g, 12 mmol) was added, the mixture stirred for 2 hours and poured onto methanol (100 ml). The solid was filtered off, dried, purified by column chromatography (silica, benzene/light petroleum 1:1) and recrystallized from ethanol to give methyl-2,3,6,7,10,11- tetrahexyloxytriphenylene (1.1 g, 73X), mp 600C.

Anal. C, 78.252; H, 10.3; C55H8606 requires C, 78.34%; H, 10.28%.

Fluoro-6.7.10 tetrahexyloxy-2.3-dimethoxytriphenylene Compound 15 3,3',4,4'-Tetrahexyloxybiphenyl (1 g, 1.8 mmol) and 3-fluoroveratrole (1 g, 6.4 mmol) were stirred in dichloromethane.

Iron (III) chloride (5 g, 30 mmol) was added and the mixture was stirred for 1.5 hours and poured onto methanol (150 ml).

The precipitate was filtered off, washed with methanol, dried and purified by column chromatography (silica, benzene) to give fluoro-6,7,10,11-tetrahexyloxy-2,3-dimethoxytriphenylene (0.85 g, 67Z) as a white solid, mp 950C.

2.3.6.7.10.11-Hexakis-((2-chloroethoxv)ethoxv)triDhenvlene Compound 16 1,2-Bis-((2-chloroethoxy)ethoxy)benzene (14 g, 0.043 mol) was stirred in dichloromethane (200 ml) with solid potassium carbonate (80 g). Iron (III) chloride (30 g, 0.19 mol) was added and the mixture stirred for 1 hour. Methanol (50 ml) was added carefully and the solids filtered off and washed with dichloromethane. The filtrate was concentrated in vacuo and methanol (150 ml) added.

After standing for 30 minutes the precipitate was filtered off, dried and purified by column chromatography (silica, dichloromethane then dichloromethane/ethyl acetate 85:15). The combined yellow product fractions were stirred with activated charcoal (30 g) for 5 minutes and filtered. Removal of the solvents in vacuo and recrystallisation from dichloromethane/methanol gave 2,3,6,7,10,11-hexakis-((2-chloroethoxy)ethoxy)triphenylene as a white solid (5 g, 36X), mp 95.50C.

Anal. C, 52.15%; H, 5.4%; C1, 21.95; C42H54C16012 requires C, 52.35%; H, 5.65X; C1, 22.08X.

4-Iodo-l .2-di hexvloxvbenzene Iodine monochloride (102 g, 0.63 mol) was added to dihexyloxybenzene (176 g, 0.63 mol) in chloroform (500 ml) and stirred for 1.5 hours. The solution was decanted and washed with sodium metabisulphite solution, water and then concentrated in vacuo. The residue was distilled to give 4-iodo-1,2-dihexyloxybenzene (175"C/1.5 mm Hg) as an orange oil (144 g, 56X).

3.3'.4.4'-Tetrahexyloxybiphenyl 4-Iodo-1,2-dihexyloxybenzene (16 g, 0.04 mol) was added to copper powder (30 g) with stirring and then heated to -3000C (exotherm noted at 2400C). The suspension was allowed to cool and extracted with dichloromethane (100 ml). The extract was then concentrated in vacuo and crystallised from ethanol (5.5 g, 501.).

mp 68-700C.

2.2'-(4-Sniro-3-methoxvcvclohexadienone)-4.4' .5.5'-tetrahexvloxv- biphenyl Compound 17 1,3-Dimethoxybenzene (0.49 g, 0.0036 mol) and 3,3',4,4'-tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) were added to a stirred suspension of iron (III) chloride (2.2 g, 0.0135 mol) in dichloromethane (30 ml). The reaction was quenched with methanol after 50 minutes and left to stand overnight. The crude solid product was filtered off and subjected to column chromatography (silica, ethyl acetate/petroleum ether 1:3). The product was collected and recrystallised from ethanol to give white needles (0.25 g, 42%).

mp 173-1750C (Found: C, 76.55Z; H, 9.0%, C43H6206 requires C, 76.52%; H, 9.25%).

l-Methoxv-3-acetyloxv-6.7.10.1l-tetrahexvloxvtriphenvlene Compound 18 The spiro-compound described previously (0.55 g, 0.0008 mol) was added to acetic anhydride (20 ml) and concentrated sulphuric acid (3 drops). This mixture was then warmed for 30 minutes and poured onto ice and left overnight. The solid was filtered off and subjected to column chromatography (silica, dichloromethane/light petroleum 55:45) and recrystallised from ethanol to give l-methoxy-3-acetyloxy-6,7,10,11-tetrahexyloxytriphenylene as white needles (0.1 g, 18%).

mp 116-1180C (Found: C, 75.2%; H, 9.05X; C45H6407 requires C, 75.39%; H, 8.99X).

2.3.6.7.9.12-Hexahexvioxvtriphenvlene Compound 19 3,3',4,4'-Tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) and 1,4-dihexyloxybenzene (1 g, 0.0036 mol) were added to a stirred suspension of iron (III) chloride (2.63 g, 0.016 mol) in dichloromethane (20 ml). The reaction was quenched with methanol after 80 minutes and the solid product filtered off and subjected to column chromatography (silica, dichloromethane/petroleum ether 2:5) to give 2,3,6,7,9,12-hexahexyloxytriphenylene as a white solid (0.1 g, 13%).

mp 82-840C (Found: C, 78.05%; H, 10.2X; C54H8406 requires C, 78.21Y; H, 10.21X).

2-Methoxv-6.7.10.11-tetrahexyloxvtriphenvlene Compound 20 3,3',4,4'-Tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) and anisole (0.9 g) were added to a stirred suspension of iron (III) chloride (2.71 g) in dichloromethane (15 ml). The reaction mixture was stirred for 40 minutes and quenched with methanol (100 ml). A dark grey solid precipitated after the mixture was concentrated and then this crude product was subjected to column chromatography (silica, dichloromethane/petroleum ether 45:55). Recrystallisation from ethanol gave 2-methoxy-6,7,10,11-tetrahexyloxytriphenylene as white platelets (0.03 g, 5Z).

(Found: M+ 658.45898; C43H6205 requires M+ 658.45973).

1.2-Dimethvl-3-methoxy-6.7.10.11-tetrahexvloxytriphenylene Compound 21 3,3',4,4'-Tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) and 2,3-dimethylanisole (1.5 g, 0.011 mol) were added to a stirred suspension of iron (III) chloride (2.71 g) in dichloromethane (15 ml). The mixture was stirred for 45 minutes, quenched with methanol, concentrated and left to stand overnight. The resulting solid was filtered and subjected to column chromatography (silica, dichloromethane) and recrystallised from ethanol to give 1,2-dimethyl-3-methoxy-6,7,10,11-tetrahexyloxytriphenylene as white needles (0.19 g, 31%).

mp 79-800C (Found: C, 78.55%; H, 9.7Z; C45H6605 requires C, 78.68%; H, 9.68%).

2-Methvl-3-methoxv-6.7.l0.ll-tetrahexvloxvtriphenvlene Compound 22 3,3',4,4'-Tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) and 2-methylanisole (1.32 g, 0.011 mol) were added to a stirred suspension of iron (III) chloride (2.65 g, 0.016 mol) in dichloromethane (15 ml). The mixture was stirred for 70 minutes then quenched with methanol (100 ml) and left to stand overnight.

The crude product was filtered, dried, subjected to column chromatography (silica, dichloromethane/petroleum ether 6:4) and recrystallised from ethanol to give 2-methyl-3-methoxy-6,7,10,11tetrahexyloxytriphenylene as white platelets (0.38 g, 63X).

mp 118-1190C (Found: C, 78.55%; H, 9.65%; C44H6405 requires C, 78.53X; H, 9.58%).

2.3-Dimethvl-6.7.10.11-tetrahexvloxvtriphenvlene Compound 23 3,3',4,4'-Tetrahexyloxybiphenyl (0.3 g, 0.0005 mol) was dissolved in o-xylene (5 ml) and added to a stirred suspension of iron (III) chloride (1.85 g) in o-xylene (10 ml). The mixture was stirred for 2 hours then quenched with methanol (100 ml) and left to stand overnight. The resulting solid was subjected to column chromatography (silica, dichloromethane/petroleum ether 6:4) and recrystallised from ethanol to give 2,3-dimethyl-6,7,10,11tetrahexyloxytriphenylene as white platelets (0.154 g, 43%).

mp 133-1350C (Found: C, 80.2%; H, 9.6X; C44H6404 requires C, 80.4%; H, 9.8%).

2-Methoxv-67,10.11-tetrahexyloxytriphenylene Compound 20 (stepwise route) 3,3',4,4'-Tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) was added to a stirred suspension of ferric chloride (0.29 g, 0.0018 mol) at OOC and stirred for 30 minutes. Anisole (methoxybenzene) (0.097 g, 0.0009 mol) was then added and the reaction mixture was stirred for 45 minutes at room temperature. An excess of ferric chloride was added and stirred for a further 10 minutes then quenched with methanol and left to stand overnight. The resulting solid was subjected to column chromatography (silica dichloromethane/petroleum ether 45:55) and recrystallised from ethanol to give 2-methoxy-6,7,10,11-tetrahexyloxytriphenylene as white crystals (0.21 g, 35%).

mp 97-990C.

2.3-Dihexvl-6.7.10.ll-tetrahexvloxvtriphenvlene Compound 24 3,3',4,4'-Tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) and 1,2-dihexylbenzene (6 g, 0.024 mol) were added to a stirred suspension of ferric chloride (2.63 g) in dichloromethane (6 ml).

The mixture was stirred for 1 hour 45 minutes then quenched with methanol (100 ml) and left to stand overnight. The resulting crude solid was subjected to column chromatography (silica, dichloromethane/petroleum ether 5:5) and recrystallised from ethanol to give 2,3-dihexyl-6,7,10,11-tetrahexyloxytriphenylene as white platelets (0.25 g, 35%).

mp 91-930C (Found: C, 81.42%; H, 10.4%; C54H8404 requires C, 81.36%; H, 10.625).

2-Hexvloxvtol uene A mixture of p-cresol (20 g, 0.19 mol), l-bromohexane (43 g, 0.26 mol) and potassium carbonate (50 g) were stirred in refluxing ethanol (200 ml) for 24 hours. The mixture was then cooled and dichloromethane (200 ml) added. The solid was filtered off and the filtrate concentrated in vacuo. Distillation at 1040C/40 mm Hg afforded 2-hexyloxytoluene as a colourless oil (23 g, 635).

2-Methvl-3.6.7.10.11-pentahexyloxytriphenylene Compound 25 3,3',4,4'-Tetrahexyloxybiphenyl (0.5 g, 0.0009 mol) and 2-hexyloxytoluene (2.1 g, 0.011 mol) were added to a stirred suspension of ferric chloride (2.65 g) in dichloromethane (20 ml).

The mixture was stirrred for 45 minutes then quenched with methanol and left to stand for 4 hours. The crude product was filtered off, allowed to dry then subjected to column chromatography (silica, dichloromethane/petroleum ether 4:6) and recrystallised from ethanol. This gave 2-methyl-3,6,7,10,11-pentahexyloxytriphenylene as white crystals (0.32 g, 48%).

mp 105-1060C (Found: C, 79.2X; H, 10.2%; C49H7405 requires C, 79.2it; H, 10.03%).

Compound 26 3,3',4,4'-Tetrahexyloxybiphenyl (0.3 g, 0.0005 mol) and dibenzo-p-dioxin (0.6 g, 0.0033 mol) were added to a stirred suspension of ferric chloride (0.9 g) in dichloromethane (15 ml) and stirred for 1 hour 15 minutes. The reaction was then quenched with methanol (100 ml) and left to stand for 3 hours. The resulting crude solid was filtered off, dried, subjected to column chromatography (silica, dichloromethane/petroleum ether 4:6) and recrystallised from ethanol. This gave compound 26 as white crystals (0.1 g, 25%).

mp 162-1640C.

2-Bromo-3-methoxv-6 .7.10.1 l-tetrahexvioxvtri phenvlene Compound 27 2-Bromoanisole (4.0 g, 0.021 mol) and 3,3',4,4'-tetrahexyloxybiphenyl (1 g, 0.0018 mol) were added to a stirred suspension of ferric chloride (5.3 g) in dichloromethane (25 ml) and stirred for 3 hours. The reaction was then quenched with methanol (200 ml), concentrated and left to stand overnight. The resulting solid was subjected to column chromatography (silica, dichloromethane/petroleum ether 7:3) and the crude product was collected as a yellow solid. This solid was subjected to further column chromatography (silica, dichloromethane/petroleum ether 50:50 or 1:1) and recrystallised from ethanol to give 2-bromo-3-methoxy-6,7,10,11-tetrahexyloxytriphenylene as white crystals (0.55 g, 41%).

mp 136-1390C.

3 .4-Di hexvloxvbi phenvl 1,2-Dihexyloxy-4-iodobenzene (10 g, 0.025 mol) and iodobenzene (5 g, 0.025 mol) were added to copper powder (20 g) and heated to 2500C. After cooling the reaction mixture was extracted with dichloromethane (4 x 50 ml), filtered and concentrated in vacuo.

Ethanol was then added to initiate crystallisation of unwanted symmetrical biphenyls which were then removed by filtration, the residue then being concentrated in vacuo again. This residue was then subjected to column chromatography (silica, dichloromethane/petroleum ether 3:7) and 3,4-dihexyloxybiphenyl was collected as a pale yellow oil (1.6 g, 18X).

2.3.6.7-Tetrahexvioxvtriphenvlene Compound 28 3,4-Dihexyloxybiphenyl (0.33 g, 0.0009 mol) and l,2-dihexyloxybenzene (1.3 g, 0.0047 mol) were added to a stirred suspension of ferric chloride (1.82 g) in dichloromethane (15 ml) and stirred for 2 hours. The reaction mixture was then quenched with methanol (100 ml) and left to stand for 3 hours. The resulting solid was then subjected to column chromatography (silica, dichloromethane/petroleum ether 35:65) and recrystallised from ethanol to give 2,3,6,7-tetrahexyloxytriphenylene as a white solid (0.28 g, 40%).

mp 114-1160C.

2-Methoxv-6.7.10.l1-tetrahexvloxvtriohenvlene Compound 29 (stepwise route using alternative oxidant) 3,3',4,4'-Tetrahexyloxybiphenyl (1 g, 0.0018 mol) was added to a stirred suspension of nitrosonium tetrafluoroborate (0.35 g, 0.0032 mol) in dry dichloromethane (20 ml) at OOC and stirred for 10 minutes. Anisole (0.22 g, 0.0020 mol) was then added and the reaction mixture was stirred for 30 minutes at room temperature. An excess of ferric chloride was added and stirred for a further 30 minutes before the reaction was quenched with methanol (150 ml). The crude solid that resulted from concentration in vacuo was subjected to column chromatography (silica, dichloromethane/petroleum ether 45:55) and recrystallised from ethanol to give 2-methoxy-6,7,10,11-tetrahexyloxytriphenylene as a white solid (0.41 g, 35%).

mp 96-980C.

REFERENCES (1) CHANDRASEKHAR, S., SADASHIVA, B.K. and SURESH, K.A., 1977, Pramana, 9, 471.

(2) MATHESON, I.M., MUSGRAVE, O.C. and WEBSTER, C.J., 1965, Chem. Commum., 278.

(3] BODEN, N., BUSHBY, R.J., FERRIS, L., HARDY, C. and SIXL, F., 1986, Liq. Crystals, 1, 109.

(4] BECHGAARD, K. and PARKER, V.D., 1972, J. Am. Chem. Soc., 94, 4749.

(5] RONLAN, A., AALSAD, B. and PARKER, V.D., 1982, Acta. Chem. Scand., B36, 317; LE BERRE, V., ANGELY, L., SIMONET-GUEGUEN, N. and SIMONET, J., 1985, Nouv. J. Chem., 9, 419.

6] LE BERRE, V., ANGELY, L., SIMONET-GUEGUEN, N. and SIMONET, J., 1987, J. Chem. Soc. Chem. Commun., 984.

(7] LE BERRE, V., SIMONET, J. and BATAIL, P., 1984, J. Electroanal. Chem., 169, 325.

8] BENGS, H., KARTHAUS, O., RINGSDORF, H., BAEHR, C., EBERT M.

and WENDORFF, J.M., 1991, Liq. Crystals, 10, 161; PIATTELLI, M., FATTORUSSO, E., NICOLAUS, R.A. and MAGNO, S., 1965, Tetrahedron, 3229.

(9] KARTHAUS, O., RINGSDORF, H., TSUKRUK, V.V. and WENDORFF, J.H., 1992, Langmuir, 8, 2279.

(10] KREUDER, W. and RINGSDORF, H., 1983, Makromol. Chem. Rapid Commun., 4, 807; WENZ, G., 1985, Makromol. Chem. Rapid Commun., 6, 577.

[11] BODEN, N., BUSHBY, R.J. and HARDY, C., 1985, J. Phys. Lett. Paris, A4, L325; BODEN, N., BUSHBY, R.J., HARDY, C. and SIXL, F., 1986, Chem. Phys. Lett., 123, 359; BODEN, N., BUSHBY, R.J., JOLLEY, K., HOLMES, M.C. and SIXL, F., 1987, Molec. Cryst. Liq. Cryst., 152, 37.

[12] GOLGFARB, D., LUZ, Z. and ZIMMERMANN, H., 1981, J. Phys., 42, 1303.

(13] ZIMMERMAN, H., POUPKO, R., LUZ, Z. and BILLARD, J., 1989 Liquid Crystals, , 151.

(14) ZIMMERMAN, H., 1989 Liquid Crystals, 4, 591.

15] BEILSTEIN, F.K., "Handbuch der organischen Chemie", Band VI, Supplement III (Springer Verlag, Berlin, 1967).

[16] DESTRADE, C., TINH, N.H., GASPAROUX, H., MALTHETE, J. and LEVELUT, A.M., 1981, Molec. Cryst. Liq. Cryst., 71, 111.

Claims (19)

1. A method of synthesising a substituted triphenylene

comprising coupling

or with the biphenyl derivative

using an oxidising agent followed by a reducing agent, where A, B, C, D, E and F are independently chosen from among hydrogen, halogen, alkyl, alkoxy, hydroxy, acyloxy and aryloxy and G, H, I, J, K and L are independently chosen from among hydrogen, halogen, alkyl, alkoxy, hydroxy, acyloxy and aryloxy, or A and B together and/or G and H together are

2. A method according to Claim 1, wherein some or all of the following apply: A = G, B = H, C = I, D = J, E = K, F = L.

3. A method according to Claim 1 or 2, wherein A B and C = F and D = E, and wherein

is coupled with

4. A method according to any preceding claim, wherein the oxidising agent comprises a transition metal.

5. A method according to any preceding claim, wherein the oxidising agent is a one-electron oxidant.

6. A method according to any preceding claim, wherein the coupling using the oxidising agent is performed in an organic solvent.

7. A method according to any preceding claim, wherein the oxidising agent is accompanied by a base.

8. A method according to Claim 7 when dependent on Claim 6, wherein the base is insoluble in the organic solvent.

9. A method according to Claim 7 or 8, wherein the base is present in excess.

10. A method according to any of Claims 1 to 6, wherein the oxidising agent is accompanied by acid of a concentration of not more than 1 weight %.

11. A method according to any preceding claim, wherein the oxidation is performed at below 400C.

12. A method according to any preceding claim, wherein the reducing agent is an alcohol.

13. A method according to Claim 12, wherein the oxidising agent is ferric chloride or NOBF4 or both and wherein the reducing agent is methanol.

14. A method according to any preceding claim, wherein the biphenyl derivative is used, in which the biphenyl derivative is treated with the oxidising agent, then the ortho-G,H-benzene is added, then excess of the oxidising agent, followed by the reducing agent.

15. A method according to any preceding claim, in which the compound

is substituted in one or both adjacent positions viz

in which N and M are independently chosen from among hydrogen, halogen, alkyl, alkoxy, hydroxy, acyloxy and aryloxy.

16. A substituted triphenylene when made according to the method of any preceding claim.

17. An a-substituted triphenylene when made according to the method of Claim 15.

18. An alkyl-, halo- or oxyalkyl- a-substituted triphenylene.

19. A methyl, fluoro or oxymethyl- a-substituted triphenylene.