AU2002253387A1

AU2002253387A1 - Uncatalysed addition reactions

Info

Publication number: AU2002253387A1
Application number: AU2002253387A
Authority: AU
Inventors: Michael Casner; Theodore Maurice Resnick; Lee Jonathan Silverberg
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2001-05-25
Filing date: 2002-05-09
Publication date: 2003-05-08
Anticipated expiration: 2022-05-09

Description

UNCATALYSED ADDITION REACTIONS

The present invention relates to novel synthetic processes wherein (+)-2-carene epoxide (1) is coupled with a variety of reagents in the absence of acid or base catalyst.

(+)-2-Carene epoxide (1) is a useful chiral intermediate that has been used as a precursor to tetrahydrocannabinoids. The acid-catalysed and base-catalysed rearrangements of (+)-2-carene epoxide (1) have been extensively studied. What these studies have in common is that mixtures of products are invariably obtained, and the yield of the desired compound is modest at best.

Bledsoe and co workers found that by treating (+)-2-carene epoxide (1) with metatitanic acid, the rearranged product (+)-/?-menthadienol (2) was obtained in 85% yield (US 3,814,733). The present inventors have not achieved reproduction of Bledsoe's work. More typical is Bulliard's report of 44% yield of (2) when treating (1) with pyridinium /?αrø-toluenesulfonic acid (PPTS) in cyclohexane (Bull. Soc. Chim. Fr. 1991, 128, 222). Bledsoe also reports that treatment of (+)-2-carene epoxide (1) with 2% sulfuric acid in water gives a mixture containing 50% (+)-/?-menth-2-ene-l,8-diol (3).

(1) (2) (3)

Arata, Bledsoe and Tanabe have published a study of the isomerisation of (+)-2- carene epoxide (1) over solid acids and bases (J. Org. Chem. 1978, 43, 1660). Clark has noted a different rearrangement of (1) using ZnBr₂ (J. Org. Chem. 1978, 43, 519). (+)-p- Menthadienol (2) and (+)-/?-menth-2-ene-l,8-diol (3) are often major products in the catalysed rearrangements. The dienol (2) and the diol (3) have both been used to produce tetrahydrocannibinoids, particularly (-)-Δ⁹-Tetrahydrocannibinol (Δ⁹-THC). A synthetic route using the dienol (2) is disclosed by Razdan et al in US 4,025,516, and a synthetic route using the diol (3) is disclosed by Stoss et al in US 5,227,537.

Δ⁹-THC has also been synthesised directly by acid-catalysed reaction of (+)-2- carene epoxide (1) with olivetol (4), albeit in low yields. Razdan et al propose that this reaction is achieved via a ring-opened intermediate (scheme 1) (J. Amer. Chem. Soc.

1970, 43, 519). Crombie et al propose a mechanism involving a cyclopropylcarbinyl cation (scheme 2) (J. Chem. Soc. Perkin. Trans. 1, 1988, 1243).

S

Scheme 2. Crombie mechanism

cannibidiol

Mixtures of products and low yields generally result from the acid catalysed reactions of (+)-2-carene epoxide (1). This is probably due to the very high lability of the vicinal cyclopropyl-epoxy moiety to acid, which releases the strain energy of two three- membered rings and leads to the very stable cyclopropylcarbinyl cation. Base catalysed rearrangements similarly produce mixtures of products and low yields. The present inventors have devised a synthetic route whereby (+)-2-carene epoxide (1) can be reacted cleanly and in high yield to produce useful, chiral products. The synthetic route requires neither acid nor base catalysts, as employed in prior art methods. Accordingly, the present invention provides a process for the producing a compound of general formula (5):

(5)

wherein X is a nucleophilic moiety and Y is an electrophilic moiety; comprising the reaction of (+)-2-carene epoxide (1) with a compound of general formula X-Y wherein X and Y are as hereinbefore defined,

characterised in that the reaction 7 mixture consists essentially of a source of (+)-2-carene epoxide (1), a compound of general formula X-Y, optionally an inert solvent and optionally a pH buffer.

In the context of this invention, the term "nucleophilic moiety" is used to describe a chemical group containing an electron rich centre. The term "electrophilic moiety" is used to describe a chemical group containing an electron deficient centre. Examples of

X, a nucleophilic moiety, include OH and OR wherein R is alkyl, aryl, acyl or silyl.

Examples of Y, an electrophilic moiety, include H and silyl. Suitably the compound of general formula X-Y is water, an alcohol, a phenol, a carboxylic acid, a silanol, a silylated alcohol, a silylated phenol, a silylated carboxylic acid, a carbon acid, a thiol, a phosphite, or a phosphate. In a preferred embodiment of the invention, compound X-Y is water and the product of the process is (+)-p-menth-2-ene-

1,8-diol (3):

(1)

(3)

The direct reaction of (+)-2-carene epoxide (1) with water proceeds more cleanly than the prior art acid catalysed reactions of (+)-2 -carene epoxide (1).

In a further embodiment of the invention, compound X-Y is an alcohol, a phenol or a carboxylic acid. In an especially preferred embodiment, compound X-Y is olivetol (4) and the product of the process is an ether (6):

The ether (6) is proposed as an intermediate in the Razdan mechanism (scheme 1 above) but has not previously been isolated. Furthermore the Razdan mechanism is for an acid- catalysed reaction whereas there is no acid catalyst in the process of the present invention. The ether can be further converted to (-)-Δ⁹-Tetrahydrocannibinol (Δ -THC) by a ring closure reaction. Reagents that will bring about the ring closure include BF₃.(OEt)₂ and t-BuOH. Therefore the present invention also provides a novel synthesis of Δ⁹-THC, comprising a first step wherein (+)-2-carene epoxide (1) is reacted with olivetol to produce an ether according to the process of the present invention, and a second step wherein the ether undergoes ring closure.

(+)-2-Carene epoxide (1) can be prepared by any of the methods known in the art.

Suitable methods include epoxidation of (+)-2-carene (7) with perbenzoic acid, peracetic acid or w-CPBA. A preferred method is epoxidation using Jacobs' version of Sharpless' method (Tet. Lett. 1998, 39_^ 8521) wherein the reagents are CH₃ReO catalyst, pyridine, hydrogen peroxide and CH₂C1₂.

In the process of the present invention the reaction mixture contains a source of (+)-2-carene epoxide (1). The source of (+)-2-carene epoxide (1) may be distilled (+)-2- carene epoxide (1). The crude product of epoxidation can also be used as the source of (+)-2 -carene epoxide (1). Another source of (+)-2-carene epoxide (1) is a mixture of (+)- 2-carene epoxide (1) and (+)-3-carene epoxide. (+)-3-Carene (8) is an inexpensive component of turpentine. A catalytic isomerisation is generally used to produce (+)-2- carene (7). The isomerisation gives a 40:60 mixture of (+)-2-carene (7) and (+)-3-carene (8) and separation of the components is difficult because they have very similar boiling points. However, the inventors have found that if the mixture of isomers undergoes epoxidation, the mixture of epoxide isomers ((+)-2-carene epoxide (1) and (+)-3 -carene epoxide) can be used as the source of (+)-2-carene epoxide in the present invention. This is because the (+)-3-carene epoxide does not undergo the addition reaction with compound X-Y and can be easily removed from the product of general formula (5). Therefore in a particular embodiment of the invention, the source of (+)-2-carene epoxide is a mixture of (+)-2-carene epoxide and (+)-3 -carene epoxide.

An inert solvent may be used in the process of the invention, but often compound X-Y will provide the only solvent needed (even though the reaction mixture may initially be heterogeneous). Suitable inert solvents include dichloromethane, 1,3-dioxolane and ethyl acetate.

A pH buffer is optionally included in the reaction mixture. The pH buffer is suitably employed when crude (+)-2-carene epoxide is used as the source of (+)-2-carene epoxide (1). Impurities present in the crude reagent can cause the pH to drop during the course of the reaction. A pH buffer can maintain the pH and the reaction proceeds more efficiently. A buffer is not required when distilled (+)-2-carene epoxide is used. When compound X-Y is water, a preferred pH range for the reaction is 5.7-5.9.

Suitably the process is carried out at room temperature or above, preferably between 10°C to 150°C. The process is suitably carried out at atmospheric pressure.

The product of the process can be separated from the reaction mixture using methods known to those in the art. One suitable method is to use a separating funnel and extract the product using a solvent such as ethyl acetate or heptane. Methods of purification of the product include chromatography and, if the product is a solid, recrystallisation from organic solvents.

Preferably the reaction proceeds with a yield of at least 40%, more preferably with a yield of at least 50%.

The reaction suitably proceeds with retention of the stereochemistry at the two chiral centres.

The reactions of the present invention are significantly cleaner than similar reactions using acid catalysts. When acid catalysts are used, the cyclopropylcarbinyl cation is rapidly formed, which can rearrange to numerous products. We believe that when no acid catalyst is used, weak acids such as water and methanol react by a more concerted mechanism of the type proposed by Razdan (Scheme 1 above). The present invention provides synthetic processes that may be used in industrial synthesis. (+)-p-Menth-2-ene-l,8-diol (3) is an important industrial precursor of Δ⁹- THC, and the present invention provides a clean, high-yielding synthesis from (+)-2- carene epoxide (1). Also, the present invention provides a process for the production of an ether (6), that may also be a useful intermediate in the industrial production of Δ⁹- THC.

The invention will now be described by way of example only:

General Experimental Details

(+)-2-Carene (97%) was purchased from Aldrich Chemical Company (Milwaukee, WI, USA). Samples of (-)-Δ⁹- and Δ⁸-THC were purchased from RBI/Sigma (Natick, MA, USA). Anhydrous solvents were purchased from Aldrich Chemical Company. 1,3-Dioxolane was purchased from Ferro/Grant Chemical Co. (Cleveland, OH, USA). TLC plates (silica gel GF, 250micron, 10 x 20 cm) were purchased from Analtech (Newark, DE, USA). TLCs were visualized under short wave UV, and then with I or by spraying with eerie ammonium nitrate/sulfuric acid and heating. Column chromatography was carried out using TLC grade silica gel purchased from Aldrich Chemical Company. NMR spectra were obtained on a Bruker 300 MHz instrument.

Preparation of (+)-2-carene epoxide 900mg methyl trioxorhenium was dissolved in 35% aqueous hydrogen peroxide and cooled to 0°C internal in a 21, 3 -necked flask. A solution was separately prepared from methylene chloride (0.71), (+)-2-carene (95.2g, 0.698mol), and pyridine (11.7g). While stirring the aqueous solution vigorously, the methylene chloride solution was added over a two-hour period, keeping the exothermic reaction at 0-5°C. After three hours (when HPLC indicated disappearance of (+)-2-carene), the mixture was poured in to a separating funnel and the layers were separated. The organic layer was washed once with water (300ml). The combined aqueous layers were extracted twice with methylene chloride (300ml each). The organic layers were combined, dried with Na₂SO and concentrated in vacuo (30°C, 30mm) to give the product as a pale yellow mobile liquid (lOOg). 1H NMR was consistent with published reports. R_f (5% EtOAc/hexane): 0.37. Distillation of (+)-2-carene epoxide

Crude (+)-2-carene epoxide prepared as outlined above (9.76g) was fractionally distilled under vacuum. The only major fraction was collected as a colourless liquid at 70.5-71.5°C at 8mm (8.01g, 82.0% recovery). 1H NMR (CDC1₃): δ (ppm): 2.97 (d, 1H), 1.85 (quint., 1H), 1.63 (t, 2H), 1.53 (m, 1H), 1.22 (s, 3H), 1.02 ( s, 3H), 1.00 (s, 3H), 0.61 (m, 1H). ¹³C NMR (CDCI₃): δ (ppm) 58.11, 57.85, 28.92, 27.14, 23.74, 21.94, 21.06, 20.69, 16.55, 16.39.

EXAMPLE 1:

Reaction of crude (+)-2-carene epoxide with water

Crude (+)-2-carene epoxide prepared as outlined above (60g, 0.34mol) was suspended in aqueous pH 5.8 buffer solution (1200ml) and stirred vigorously. The internal temperature was warmed to 40°C and held until starting material had disappeared by TLC and HPLC (3-6 hours): The reaction was cooled to room temperature, transferred to a separating funnel and washed once with heptane (300ml). NaCl (180g) was added to the aqueous layer and this was extracted with ethyl acetate (1 x 11, 2 x 500ml). The ethyl acetate extracts were combined, dried over Na₂SO , and concentrated in vacuo to give a white solid. Recrystallization from 5% EtOAc/heptane (300ml) gave (+)-p-menth-2-ene-l,8-diol as flocculent white crystals (31.5g, 51.3% from (+)-2-carene). Melting point: 112-113°C (lit.l 14.5°C). 1H NMR matched literature values. ¹³C NMR (CD₃OD): δ (ppm) 137.1, 129.0, 73.3, 70.2, 39.1, 28.8, 27.6, 26.0, 24.4. R_f (50% EtOAc/hexane): 0.16. IR (KBr, cm^"1): 3383 (OH stretch), 3024 (alkene C- H stretch).

EXAMPLE 2: Epoxidation of (+)-2-carene and subsequent reaction with water 131mg methyl trioxorhenium was dissolved in 30% aqueous hydrogen peroxide (23.6ml) and cooled to 0°C internal in a 21, 3 -necked flask. A solution was separately prepared from 1,3-dioxolane (100ml), (+)-2-carene (13.6g, 0.1 mol), and pyridine (12ml). This was also cooled to 0°C internal. While stirring the cold aqueous solution vigorously, the cold dioxolane solution was added over 70 minutes, keeping the exothermic reaction at 0-5°C. After three hours (when TLC indicated disappearance of (+)-2-carene), the mixture was poured in to a separating funnel and the layers were separated. Saturated NaCl solution (20ml) was added to the aqueous layer and more separation occurred. The layers were separated again. The aqueous layer was extracted once more with dioxolane (10ml). The organics were combined. Aqueous pH 5.8 buffer solution (304ml) was 5 added and stirred vigorously at room temperature until (+)-2-carene epoxide had disappeared by TLC and HPLC (4 hours). The reaction was transferred to a separating funnel and washed once with heptane (75ml). NaCl (45g) was added to the aqueous layer and this was extracted with ethyl acetate (3 x 125ml, 1 x 100ml). The ethyl acetate extracts were combined, dried over Na₂SO₄, and concentrated in vacuo to ~ 150ml.

10 200ml heptane was added and the solution was concentrated to ~ 150ml. 5- 10ml of EtOAc was added to dissolve the solid. It was allowed to cool with stirring and then cooled to 0°C. The solid was collected by vacuum filtration and washed twice with cold 5% EtO Ac/heptane. After drying under vacuum, 11.857g of (+)-/?-menth-2-ene-l,8-diol (69.8% yield from (+)-2-carene) was obtained. NMR showed some residual heptane.

15 Elemental Analysis: 70.6% C, 10.6% H.

EXAMPLE 3 Isomerisation of (+)-3-carene followed by epoxidation and reaction with water

A 100ml roundbottom flask with a stir bar was dried with a heat gun, fitted with 0 septa, and cooled under N₂. Potassium t-butoxide (lOg, 0.09mol) was added. Anhydrous dimethylsulfoxide (25ml) was added and stirred. (+)-3-Carene (13.6g, O.lmol) was added. The mixture was heated to 100°C and stirred overnight. After cooling, hexane (50ml). was added and stirred. Water (50ml) was added and stirred. The layers were separated. The aqueous layer was extracted with hexane (2 x 250ml). The hexane layers 5 were combined and washed with water, dried over Na₂SO , filtered, and concentrated in vacuo to oil (l lg). NMR analysis showed 58% (+)-3-carene and 42% (+)-2-carene.

lOOmg methyl trioxorhenium was dissolved in 30% aqueous hydrogen peroxide (19ml) and cooled to 0°C internal in a 250ml, 3-necked flask. A solution was separately 0 prepared from 1,3-dioxolane (89ml), the carene mixture (l lg), and pyridine (9ml). This was also cooled to 0°C internal. While stirring the cold aqueous solution vigorously, the cold dioxolane solution was added over 70 minutes, keeping the exothermic reaction at 0- 5°C. After three hours, NaCl solution (20ml) was added and the layers were separated. The aqueous layer was extracted once with dioxolane (25ml). The organics were combined. Aqueous pH 5.8 buffer solution (275ml) was added and stirred vigorously at room temperature for 1 hour, then 30°C for 2.5 hours. The reaction was transferred to a separating funnel and washed once with heptane (100ml). NaCl (43 g) was added to the aqueous layer and stirred for 30 min. The aqueous layer was extracted with ethyl acetate (1 x 100ml, 2 x 250ml). The ethyl acetate extracts were combined, dried over Na₂SO₄, and concentrated in vacuo to solid (2g). The solid was dissolved in hot ethyl acetate. Heptane was added and the solution was allowed to cool with stirring and then cooled to 0°C. The solid was collected by vacuum filtration and washed with hexane. After drying under vacuum, lg (+)-p-menth-2-ene-diol (6.5% yield from (+)-3-carene) was obtained.

EXAMPLE 4: Reaction of distilled (+V2-carene epoxide with water

Fractionally vacuum-distilled (+)-2-carene epoxide (l.OOg) was suspended in distilled water (30ml). The internal temperature was warmed to 40°C and held there for 6 hours. The reaction was cooled to room temperature, transferred to a separating funnel and washed once with heptane. The aqueous layer was extracted with ethyl acetate (7 x 75ml). The ethyl acetate extracts were combined, washed with saturated NaCl solution, and concentrated in vacuo to give (+)-p-menth-2-ene-diol as a white crystalline powder (0.92g, 82.3%).

EXAMPLE 5: Reaction of (+)-2-carene epoxide with methanol

A 50ml roundbottom flask with a stir bar was oven-dried, fitted with septa, and cooled under N₂. Distilled (+)-2-carene epoxide (l.OOg) was added. Anhydrous methanol (40ml) was added and stirred. A condenser was added and the solution was warmed to reflux for 28 hours. The solvent was removed in vacuo. The colourless oil was chromatographed on 30g TLC mesh silica. 10% EtOAc/hexane eluted a UV active spot (25.5mg), which appeared by NMR to be a methoxy diene. 30% EtOAc/hexane eluted a mixture of two spots (0.1836g), which by NMR was partly dieneol. 40% EtOAc/hexane eluted a methyl ether corresponding to a compound of general formula (5) (0.8722g, 72.1%). ^lU NMR (CDC1₃): δ (ppm) 5.63 (s, 2H), 3.16 (s, 3H), 2.33-2.28 (m, 1H), 1.97-1.84 (m, 1H), 1.80-1.58 (m, 2H), 1.4-1.3 (m, 1H), 1.24 (s, 3H), 1.07 (s, 3H), 1.04 (s, 3H). ¹³C NMR (CDC1₃): δ (ppm) 136.63, 128.17, 76.57, 69.53, 48.77, 43.45, 38.45, 28.22, 22.95, 22.15, 21.98. Elemental Analysis: 67.12% C, 10.61% H. R_f(40% EtOAc/hexane): 0.31. [α]_D ²⁵ = +37.1° (c = 1.045, CHC1₃).

EXAMPLE 6:

Reaction of (+)-2-carene epoxide with acetic acid

A 250ml roundbottom flask with a stir bar was dried with a heat gun, fitted with septa, and cooled under N₂. Distilled (+)-2-carene epoxide (2.00g) was added. Glacial acetic acid (80ml) was added and stirred. TLC after one minute showed complete reaction. The acetic acid was removed under vacuum at 30°C. The colourless oil (2.355g) was chromatographed on 50g TLC mesh silica. 30-40% EtOAc/hexane eluted a monoacetate corresponding to a compound of general formula (5) (1.48g, 53.2%). A minor product was also isolated (0.13 lg, 6.55% yield) and the NMR matched that of (+)-/?-menthadienol (compound 2). Η and ¹³C NMR of the monoacetate matched literature values. Elemental Analysis: 62.35% C, 8.84% H. R_f (50% EtOAc/hexane): 0.40. [α]_D ²⁵ = +32.1° (c = 0.535, CHC1₃).

EXAMPLE 7; Reaction of (+)-2-carene epoxide with allyl alcohol

A 100ml roundbottom flask with a stir bar was dried with a heat gun, fitted with septa, and cooled under N₂. Distilled (+)-2-carene epoxide (l.OOg) was added. Allyl alcohol (40ml) was added and stirred. A condenser was added and the solution was warmed to 60°C for one day, then 80°C for one day, then reflux for three days. The solvent was removed in vacuo. The colourless oil was chromatographed on 30g TLC mesh silica. 40% EtOAc/hexane eluted an allyl ether corresponding to a compound of general formula (5) (62mg, 4.5%). Η NMR (CDC1₃): δ (ppm) 5.87 (octet, IH), 5.67 (dq, 2H), 5.28-5.21 (td, IH), 5.11-5.06 (td, IH), 3.88 (m, 2H), 2.34 (m, IH), 1.92-1.86 (m, IH), 1.85-1.7 (m, IH), 1.7-1.6 (dt, IH), 1.43 (m, IH), 1.25 (s, 3H), 1.11 (s, 3H), 1.09 (s, 3H). ¹³C NMR (CDC1₃): δ (ppm) 135.99, 135.56, 128.40, 115.40, 7690, 69.63, 62.23, 44.08, 38.51, 28.22, 23.01, 22.77, 22.56. R_f(20% EtOAc/hexane) 0.16. EXAMPLE 8:

Reaction of (+)-2-carene epoxide with ethylene glvcol

A 100ml roundbottom flask with a stir bar was dried with a heat gun, fitted with 5 septa, and cooled under N₂. Distilled (+)-2-carene epoxide (l.OOg) was added. Ethylene glycol (40ml) was added and stirred. A condenser was added and the solution was warmed to 60°C for 2.5 hours. Water (40ml) was added. The solution was poured in to a separating funnel and washed twice with hexane (20ml each). The aqueous layer was then extracted with ethyl acetate (5 x 40ml). The EtOAc extracts were combined and

10 washed with saturated NaCl solution (20ml), dried over Na₂SO , and filtered in vacuo. The colourless oil was chromatographed on 30g TLC mesh silica. EtOAc eluted a glycol ether corresponding to a compound of general formula (5) (0.825g, 58.6%). Η NMR (CD₃OD): δ (ppm) 5.73-5.69 (td, IH), 5.63- 5.58 (td, IH), 3.60 (t, 2H), 3.44 (t, 2H), 2.40- 2.34 (m, IH), 1.86-1.64 (m, 3H), 1.5-1.3 (m, 2H), 1.23 (s, 3H), 1.12 (s, 3H), 1.09 (s, 3H).

15 ¹³C NMR (CD₃OD): δ (ppm) 136.91, 129.02, 78.02, 70.27, 63.69, 63.08, 45.38, 39.13, 28.80, 24.223, 23.34, 22.90, 21.04. Elemental Analysis: 64.49% C, 10.39% H. R_f (EtOAc): 0.38. [α]_D ²⁵ = +34.4° (c = 0.956, CHC1₃).

EXAMPLE 9 0 Reaction of (+)-2-carene epoxide with t-butyldimethylsilanol

A 5 ml roundbottom flask with a stir bar was oven-dried, fitted with septa, and cooled under N₂. Distilled (+)-2-carene epoxide (lOOmg) was added. t-Butyldimethylsilanol (1ml) was added and stirred. A condenser was added and the 5 solution was warmed to 125°C for 20 hours, then 140°C (reflux) for three days. After cooling, hexane was added and the solids were filtered off. The hexane solution was chromatographed on 5g TLC mesh silica gel. A silyl ether corresponding to a compound of general formula (5) was obtained as a colourless oil (4.5mg, 2.4%). 1H NMR (CDC1₃): δ (ppm) 5.79-5.74 (dd, IH), 5.65-5.60 (dd, IH), 2.2-2.1 (m, IH), 1.9-1.8 (m, 2H), 1.7-1.3

30 (m, 2H), 1.26 (s, 3H), 1.19 (s, 3H), 1.13 (s, 3H), 0.85 (s, 9H), 0.08 (s, 6H). ¹³C NMR (CDC1₃): δ (ppm) 135.2, 129.2, 77.2, 75.2, 69.7, 48.3, 38.6, 29.7, 28.1, 27.7, 26.4, 25.8, 23.2, 18.1, 1.0, -0.06, -2.1. R_f (20% EtOAc/hexane): 0.32. EXAMPLE 10: Reaction of (+)-2-carene epoxide with olivetol

A 5ml reactivial with a stir bar was oven-dried, capped and cooled under N₂. 5 Distilled (+)-2-carene epoxide (l.OOg) was weighed in. Olivetol (1.77g, 1.5 eq.) was added. The mixture was stirred at room temperature for 30 minutes, then warmed to 45°C in an oil bath for 18 hours. The thick, light yellow oil was allowed to cool and then dissolved in ethyl acetate, evaporated onto silica gel, and chromatographed on 40g TLC mesh silica gel. Fractions 29-35 contained clean olivetol ether corresponding to

10 compound (6) (0.2373g, 10.9%). Fractions 23-28 and 36-37 also contained some of the olivetol ether but at lower purity (0.3098g, 14.2%). The olivetol ether was a colourless oil (total weight 0.5468g, 25.0% yield). 1H NMR (CDC1₃): δ (ppm) 6.39 (dd„ 2H), 6.33 (ds, IH), 5.89 (d, IH), 5.3 (d, 2H), 2.46 (t, 2H), 2.0-1.3 (m, ~11H), 1.29 (s, 3H), 1.19 (s, 3H), 1.16 (s, 3H), 0.86 (t, 3H). ¹³C NMR (CDC1₃): δ (ppm) 156.08, 155.88, 144.88,

15 135.70, 128.49, 116.60, 110.74, 108.60, 82.47, 70.00, 45.44, 38.36, 35.80, 31.40, 30.82, 28.22, 24.44, 23.32, 23.25, 22.48, 13.99. Elemental Analysis: 72.22% C, 10.34% H. R_f(50% EtOAc/hexane): 0.45. [α]_D ²⁵ = +25.2° (c - 0.159, CHCI3).

EXAMPLE 11: 0 Conversion of olivetol ether to Δ⁹-THC

A 5ml roundbottom flask with a stir bar was oven-dried, fitted with septa and cooled under N₂. The olivetol ether (6.4mg) in anhydrous methylene chloride (0.8ml) was added. Magnesium sulphate (30mg) was added and stirred. The slurry was cooled to 5 -40°C. BF₃ (OEt)₂ (5μl) was added. TLC after five minutes showed three spots. The top spot cospotted with genuine Δ⁹-THC.

EXAMPLE 12: Reaction of crude (+)-2-carene epoxide with olivetol in t-BuOH 0

A 5ml roundbottom flask with a stir bar was oven-dried, fitted with septa, and cooled under N₂. Crude (+)-2-carene epoxide (lOOmg) was added and the flask was evacuated and filled with N₂ three times. Olivetol (118mg) was added. t-Butanol (1ml) was added. A condenser was connected and the solution was warmed to 50°C in an oil bath. TLC after two hours showed the olivetol ether forming. After three days, TLC showed the reaction had not changed. The temperature was turned up to reflux. After 10 minutes, TLC showed the olivetol ether had disappeared and two higher spots had formed. The top spot cospotted with genuine Δ⁹-THC. The solution was refluxed for one day, then allowed to cool. Chromatography on 5g TLC mesh silica gel eluted three fractions of Δ⁹-THC (27.2mg, 13.2%) yield from (+)-2 -carene epoxide) and five fractions of mixed Δ⁹- and Δ⁸-THC (15.0mg, 7.3% yield). 1H NMR agreed with published reports and commercial sample.

EXAMPLE 13 Reaction of (+)-2-carene epoxide with trimethylsilyl methanol

A 10ml roundbottom flask with a stir bar was oven-dried, fitted with septa, and cooled under N₂. Distilled (+)-2-carene epoxide (lOOmg) was added. Trimethylsilyl methanol (2ml) was added and stirred. A condenser was added and the solution was warmed to 100°C for 30hours. After cooling, the solvent was removed under vacuum. A yellowish oil was obtained (0.0929g, 55.1% yield). NMR showed that the compound corresponded to general formula (5), but it was not pure. ^!H NMR (CDC1₃): δ (ppm) 5.63 (m, 2H), 2.83 (s, IH), 2.25 (m, IH), 1.9-1.5 (m, 3H), 1.5-1.1 (m, 2 H), 1.23 (s, 3H), 1.00 (s, 3H), 0.97 (s, 3H), -0.02 (s, 9H). ^,3C NMR (CDC1₃): δ (ppm) 135.11, 128.87, 110.83, 69.65, 52.30, 44.05, 42.49, 38.57, 28.89, 28.19, 27.74, 22.98, 21.90, 21.54, 21.09, 0.93, - 3.19. R_f (20% EtOAc/hexane): 0.52. [α]_D ²⁵ = +17.0° (c = 0.586, CHC1₃).

Table 1 summarises the reactants (compound X-Y) and the products (compound

(5)) of the examples: Table 1

Claims

CLAIMS 17

1. A process for the producing a compound of general formula (5)

characterised in that the reaction mixture consists essentially of a source of (+)-2-carene epoxide (1), a compound of general formula X-Y, optionally an inert solvent and optionally a pH buffer.

2. A process according to claim 1 wherein compound X-Y is water, an alcohol, a phenol, a carboxylic acid, a silanol, a silylated alcohol, a silylated phenol, a silylated carboxylic acid, a carbon acid, a thiol, a phosphite, or a phosphate.

3. A process according to claim 2 wherein compound X-Y is water.

4. A process according to claim 2 wherein compound X-Y is an alcohol, a phenol or a carboxylic acid.

5. A process according to claim 4 wherein compound X-Y is olivetol.

6. A synthesis of (-)-Δ⁹-Tetrahydrocannibinol comprising a first step which is a process according to claim 5 and a second step which is a ring closure step.