GB2245560A - Process for the preparation of trihalogenobutadienes of controlled region and stereo-chemistry and intermediates for use therein - Google Patents

Abstract

The invention relates to trihalogenobutadienes of controlled regio- and stereo-chemistry having the formula <IMAGE> where R is H, or a hydrocarbyl or substituted hydrocarbyl group free from non-aromatic unsaturation and/or interfering substituents (i.e. substituents which are not inert under the conditions of the reaction), and Ha is halogen e.g. Br or Cl. These compounds are prepared by thermolysis of the appropriate 1,1,2,3-tetrahalogenocyclopropane of the formula <IMAGE> The intermediate compounds of formula (III) are also per se.

Description

PROCESS FOR THE PREPARATION OF TRIHALOGENOBUTADIENES OF CONTROLLED REGIO- AND STEREO-CHEMISTRY AND INTERMEDIATES FOR USE THEREIN This invention relates to a process for the preparation of trihaiogeno- butadienes of controlled regio- and stereo-chemistry, and intermediate tetrahalogenocyclopropanes for use therein.

Trihalogenobutacienes and tetrahalogenocyclopropanes both have potential utility as chemical precursors and possibly as agrochemicals. In either application the stereochemistry of the compound or the product may be of importance, thus processes for the manufacture thereof which provide for controlled regio- and stereo-chemistry are potentially of great interest.

In accordance with the present invention, trihalogenated butadienes of the formulae

where R is H, or a hydrocarbyl or substituted hydrocarbyi group free from non-aromatic unsaturation and/or interfering substituents (i.e. substituents which are not inert under the conditions of the reaction), and Ha is halogen e.g. Br or C1, and which are of controlled regio- and stereo-chemistry are prepared by thermolysis of the appropriate 1,1,2,3-tetrahalogenocyclopro- pane of the formula

where R and Ha are as above defined, such thermolysis resulting in dehydrohalogenation and opening of the cyclopropane ring to provide either a 1,1,3-trihalogenobutadiene (I) or a 1,2,3-trihalogenobutadiene (II).

Within the above formulae, the two R groups need not be the same, nor the Ha groups, each of which can be either Cl, Br or F. When R is hydrocarbyl or substituted hydrocarbyl there is no theoretical maximum to the size of the group although, of course, the size and configuration (i.e.

straight, branched or cyclic) will be subject to limitations imposed by steric hindrance. For these and other reasons the process is most generally applicable to hyrocarbyl groups of from 1 to 10 carbon atoms, more usually lower alkyl groups of 1 to 6 carbon atoms, e.g. -CH3, -CZH5 etc. and aryl, alkaryl an aralkyl groups of from 6 to 10 carbon atoms, e.g. phenyl, benzyl, tolyl etc.

Compounds of formulae I and II prepared in accordance with this invention are as follows, the three halogen substituents Ha1, Ha2, Ha3 being in the following positions:

Table 1 Compond No. Formula R Ha1 Ha2 Ha3 1 I H Br C1 C1 2 I Me Br Cl Cl 3 I Et Br Cl Cl 4 I H Cl Cl C1 5 I Me Cl Cl C1 6 I Et C1 C1 Cl 7 II H Cl C1 Br 8 II Me C1 C1 Br 9 II EL Cl Cl Br Thermolysis is conveniently carried out by heating the halogenated cyclopropane III in a base, preferably an aromatic base such as quinoline, at a temperature of from 100 to 250 C, preferably from 150 to 200 C, for about 30 to 160 minutes.Where cyclopropanes are employed as starting material containing both chlorine and bromine substituents, dehydrobromination occurs in preference to dehydrochlorination. Further heating of compounds I and II in the base can result in further dehydrohalogenation to yield dihaloalkynes, e.g.::

The I ,1,2,3-tetrahalogenocyclopropanes used as starting materials in the process of the present invention are, in many cases, believed to be novel compounds, and are prepared by alternative routes depending on the particular substituents Ha and R in the compound m, but broadly speaking such compounds can be prepared by the reaction of a non-terminal vicinally substituted alkene with a dichloro- or dibromocarbene generated under phase transfer conditions, or in the case of certain brominated compounds by thermolysis of phenyltribromomethyl mercury. For example, the dichloro- and dibromo-alkenes (IV) react with dichlorocarbene generated under phase transfer conditions to produce the 1,1-dichlorocyclopropanes ma, viz.

where Ha and R are as above defined.

Dichloroalkenes (compounds IV, Ha = Cl) also react under similar conditions with bromoform and a base under phase transfer conditions to produce 1,1-dibromo compounds Eb, viz.

The above phase transfer reactions are best carried out at about 200C in the presence of a strong base, e.g. 25M NaOH, and a suitable phase transfer catalyst, e.g. cetrimide.

The 1,1-dibromo compounds IIIb and their 2,2-dibromo- and 2-5romo- 3-chloro-analogues may also be prepared by reacting the dichloro-, dibromo- and chlorobromo-alkenes (IV) with phenyltribromomethyl mercury under reflux conditions in the presence of benzene, viz.

where Ha and IL are as defined above.

Specific tetrahalogenocyclopropanes produced and used as intermediates in accordance with this invention are listed below, the positioning of the halogen substituents in compounds of formula III being as follows:

Table 2 Comoond No. Formula R Ha1 Ha, Ha3 Ha4 10 III H Cl Cl Br Br 11 III Me Cl Cl Br Br 12 III Et Cl Cl Br Br 13 III H Cl Cl Cl Cl 14 III Me Cl Cl Cl Cl 15 III Et Cl Cl Cl Cl 16 III H Br Br Cl Cl 17 III Me Br Br Cl Cl 18 III Et Br Br Cl Cl 19 III H Br Br Br Er 20 III Me Br Br Br Er 21 III H Cl Cl Br Cl 22 III Me Cl Cl Br Cl 23 III Et Cl Cl Br Cl The processes and products of the present invention are illustrated by the following Examples.

Unless otherwise stated all new compounds were homogeneous by t.l.c. and/or g.l.c.; n.m.r. spectra were run in CDCl3 solution and recorded for 1H at 200 or 300 MHz on Bruker instruments, and 13c spectra were recorded at the corresponding carbon frequency on the same instruments.

Infra-red spectra were obtained on a Nicolet 205X, while mass spectra were measured on an AEI MS9 or a Kratos MS80 using the E.I. method; where mass measurements are quoted for chlorine containing species, they refer to 35Cl isotope peaks. Melting points are uncorrected. All experiments involving methyl lithium were carried out under dry nitrogen. Petrol refers to the fraction boiling between 40 and 60 C. Organic layers were dried with MgSO4 before removal of the solvent. Column chromatography was carried out over silica.

Preoaration of intermediate 1.1.2.3-tetrahalogenocyclopropanes Examole 1 The 1,1,2,3-tetrahalogenocyclopropanes listed below were all prepared by the following general procedure: An aqueous solution of NaOH (6 ml, 25M) was added dropwise to a mixture of dihaloalkene (4.72 mmol) and cetrimide (0.1 g, 0.28 mmol) in CHCl3 (13 ml) over 10 minutes with vigorous stirring. The mixture was stirred efficiently over 5 days and then poured into brine (50 ml). Extraction into CH2C12 (2 x 25 ml), followed by washing with brine (2 x 50 ml), drying (MgSO4) and concentration in vacuo gave the crude product. Ether (50 ml) was added, any insoluble material filtered, and the filtrate was concentrated under reduced pressure.

2,3-dibromobut-2-ene gave 2,3-dibromo-1 ,1-dichloro-2 ,3-dimethyl- cyclopropane, compound No. 10, (0.76 g, 55%), m.p. 83-850C (recrystallised from MeCN) (Found: C, 20.38; H, 1.99. C5H6Br2Cl2 requires C, 20.23; H, 2.04%) which showed H 2.1 (6H, s); C 28.7 (q), 49.4 (s), 70.6 (s); max 2934m, 2855m, 1440s, 1377s, 1217m, 1046s, 883s, 708s cm~1.

3,4-dibromohex-3-ene gave 2,3-dibromo-1,1-dichloro-2,3-diethylcyclopropane, compound No. 11, (0.74 g, 53%), m.p. 121-1230C (recrystallised from MeOH) (Found: C, 25.77; H, 3.01. C7H10Br2C12 requires C, 25.88; H, 3.10%) which showed 1.2 (6H, t, J 7Hz), 2.2 (4H, q, J 7Hz); max 2978s, 2878m, 1456s, 1379m, 1201m, 1092m, 838s, 787m cm~1.

4,5-dibromo-oct-4-ene gave 2,3-dibromo-1,1-dichloro-2,3-dipropylcyclopropane, compound No. 12, which was purified by flash chromatography with light petroleum and ether (10:1) as eluant (0.93 g, 67%), (Found: C, 30.44; H, 3.96. CgH14Br2C12 requires C, 30.63; H, 4.0%) which showed H 0.99 (6H, t, J 7Hz), 1.67 (4H, sextet, J 7Hz); 1.97-2.24 (4H, complex multiplet); C 13.6 (q), 21.1 (t), 42.3 (t), 55.5 (s), 71.0 (s); max 2917s, 2849s, 1471m, 1378 m, 1221m, 1090m, 912m, 778m cm~1.

2, 3dichlorobut-2ene gave 2 ,3dimethyl-1 ,1,2 ,3-tetrachlorocyclopro- pane, compound No. 13, (0.55 g, 57%), m.p. 68-700C (recrystallised from EtOH) (Found: C, 28.77; H, 2.80. C5H6Cl4 requires C, 28.88; H, 2.91%) which showed max 2938m, 2880m, 1444s, 1379m, 1216m, 1056s, 898s, 759s cm~1; H 1.9 (6H, s); C 23.2 (q), 55.3 (s), 70.1 (5).

3 ,4-dichlorohex-3-ene gave 2,3-diethyl-1,1,2,3-tetrachlorocyclopro- pane, compound No. 14, which was purified by flash column chromatography as above (0.61 g, 55%) (Found: C, 35.46; H, 4.05. C7H10C14 requires C, 35.63; H, 4.27%) which showed H 1.1 (6H, t, J 7Hz), 2.1 (4H, q, J 7Hz); max 2938m, 2881m, 1459s, 1380m, 1201m, 1016m, 858s, 731m cm-1.

4 ,5-dichloro-octA-ene gave 2,3-dipropyl-1,1,2 ,3-tetrachlorocyclopro- pane, compound No. 15, which was purified by flash chromatography as above (0.75 g, 6196), (Found: C, 40.76; H, 5.21. C9H14Cl4 requires C, 40.94; H, 5.34%) which showed #;H 0.98 (6H, t, J 7Hz), 1.56-1.75 (4H, complex multiplet), 2.05 (4H, multiplet); Se 13.7 (q), 19.5 (t), 37.8 (t), 59.8 (s), 71.1 (s); max 2965m, 2874m, 1470s, 1380m, 1260m, 1015m, 878m, 759s cm-1.

2-bromo-3-chlorobut-2-ene gave 3-bromo-2,3-dimethyl-1,1,2-trichlorocyclopropane, compound No. 21, (0.67 g, 57%), m.p. 79-810C (recrystallised from EtOH) (Found: C, 23.62; H, 2.31. C5H6BrCl3 requires C, 23.80; H, 2.4%) which showed#H 1.8 (3H, s), 1.9 (3H, s); sC 20.2 (q), 23.2(q), 46.3 (s), 55.3 (s), 70.1 (s); Smax 2938m, 1440s, 1380m, 1215m, 1055s, 891s, 760s cm-1.

3-bromo-4-chlorohex-3-ene gave 3-bromo-2,3-diethyl-1,1,2-trichlorocyclopropane, compound No. 22, which was purified by flash chromatography as above (0.72 g, 55%) (Found: C, 29.79; H, 3.39. C7H10BrCl3 requires C, 29.98; H, 3.59%) which showed < H 1.23 (6H, t, J 7Hz), 2.15 (2H, q, J 7Hz); 2.20 (2H, q, J 7Hz); 3 max 2977m, 2880m, 1458s, 1381m, 1050m, 852m, 787s cm1.

4-bromo-5-chlor-oct-4-ene gave 3-bromo-2,3-dipropyl-1,1,2-trichlorocyclopropane, compound No. 23, which was purified by flash chromatography as above (0.77 g, 53%), (Found: C, 34.91; H, 4.39. CgH14BrCl3 requires C, 35.04; H, 4.57%) which showed H 0.98 (3H, t, J 7Hz), 0.99 (3H, t, J 7Hz), 1.55-1.75 (4H, complex multiplet); 1.97-2.23 (4H, complex multiplet); max 2980s, 2880m, 1460m, 1379m, 1047m, 847m, 785m cm~1.

Example 2 The following dibromo-dichlorocyclopropanes listed below were all prepared by the following general procedure: An aqueous solution of NaOH (6 ml, 25M) was added dropwise to the dichloroalkene (8 mmol), bromoform (1.1 ml, 12 mmol) and cetrimide (0.1 g, 0.28 mmol) in CH2Cl2 (15 ml) over 10 minutes with vigorous stirring. The mixture was stirred efficiently for 5 days and then poured into brine (50 ml).

Extraction into CH2C12 (2 x 25 ml), followed by washing with brine (2 x 50 ml), drying (MgSO4) and concentration in vacuo gave the crude product.

Ether (50 ml) was added, any insoluble material filtered, and the filtrate was concentrated under reduced pressure.

2,3-dichlorobut-2-ene gave l,l-dibromo-2,3-dichloro-2,3aimethyl- cyclopropane, compound No. 16, (42%), m.p. 85-870C (recrystallised from EtOH) (Found: C, 20.04; H, 1.92. CsH6Br2Cl2 requires C, 20.23; H, 2.04%) which showed max 2982m, 2932m, 1440s, 1375m, 1215m, 1050s, 820s, 760s cm-1; H 1.99 (6H, s); C 22.9 (q), 55.4 (s), 47.7 (s).

3,4dichlorohex-3-ene gave l,l-dibromo-2,3-dichloro-2,3-diethyl- cyclopropane, compound No. 17, (71%), m.p. 123-1250C (recrystallised from EtOH) (Found: C, 25.67; H, 2.93. C7H1oBr2Cl2 requires C, 25.88; H, 3.10%) which showedsmax 2975s, 2879m, 1458s, 1379m, 1100m, 880m, 796s cm-1; H 1.21 (6H, t, J 7Hz), 2.18 (4H, q, J 7Hz); Sc C 10.5 (q), 31.9 (t), 46.9 (s), 60.7 (s).

4,5-dichloro-oct-4-ene gave, after work up and flash chromatography as above, 1,1-dibromo-2,3-dichloro-2,3-dipropylcyclopropane, compound No.

18, (1.49 g, 53%) as a colourless oil, (Found: C, 30.43; H, 3.91.

C9H14Br2C12 requires C, 30.63; H, 4.0%) which showed smax 2964s, 2874m, 1461s, 1380m, 1110m, 806m, 744m cm~1; sH 0.99 (6H, t, J 7Hz), 1.67 (4H, sextet, J 7Hz); 1.85-2.20 (4H, complex multiplet); #C 13.7 (q), 19.7 (t), 39.9 (t), 47.5 (s), 59.8 (s).

Example 3 The bromocyclopropanes listed below were prepared by the following general procedure: The bromoalkene (2.36 mmol) was added to the phenyltribromomethyl mercury (2.5 g, 4.72 mmol) in dry benzene (10 ml) and refluxed for 3 days.

The mixture was filtered through silica gel (Merck 7736) via a sinter column and the column was washed with light petroleum (2 x 10 ml). The combined filtrate was concentrated in vacuo to afford the corresponding tetrabromocyclopropane.

2,3-dibromobut-2-ene gave 1,1 ,2,3-tetrabromo-2 ,3-dimethylcyclopro- pane, compound No. 19, (0.62 g, 6996), m.p. 125-1270C (recrystallised from benzene and light petroleum) (Found: C, 15.41; H, 1.39. CsH6Br4 requires C, 15.57; H, 1.57%) which showed 4 max 2929m, 2852m, 1439s, 1376s, 1212m, 1047s, 766m, 656s cm-1; SH 2.1 (6H, s).

3,4-dibromohex-3-ene gave 1,1,2,3-tetrabromo-2,3-diethylcyclopro pane, compound No. 20, (0.65 g, 67%), m.p. 163-1650C (recrystallised from benzene and light petroleum) (Found: C, 20.16; H, 2.31. C7H10Br4 requires C, 20.32; H, 2.44%) which showed #H 0.9 (6H, t, J 7Hz), 2.2 (4H, q, J 7Hz).

2,3-dichlorobut-2-ene gave 1, 1-dibromo-2 ,3-dichloro-2 ,3 dim ethyl- cyclopropane, compound No. 16, (0.53 g, 77%) identical to that obtained above.

3,4-dichlorohex-3-ene gave 1,1-dibromo-2,3-dichloro-2,3-diethyl cyclopropane, compound No. 17, (0.57 g, 75%) identical to that obtained above.

Preparation of trihalogenobutadienes Example 4 Following the same general procedure as follows, the 1,1,2,3-tetrahalogenocyclopropanes prepared above were subjected to thermolysis to yield product trihalogenobutadienes.

The tetrahalogenocyclopropane (2 mmol) was added to the quinoline (7 ml) and heated at 160-2000C for 1-2.5 hours, as specified below. The mixture was then poured into dil. HCl (15 ml), extracted into ether (2 x 10 ml) and washed in succession with sat. NaHCO3 solution (10 ml), water (10 ml) and brine (10 ml), dried (MgSo4) and concentrated in vacuo to afford the corresponding trihalogenodienes. When more than one isomer was produced, they were separated by preparative g.l.c.

Compound No. 10 gave 3bromo-1 , 1-dichloro-2-methylbuta-1,3-diene (compound No. 1) in 30 minutes at 1600C (0.28 g, 65%) (Found: M+, 213.9345. C5H5BrC12 requires M, 213.9356) which showed 4 max 2923m, 1632m, 1598m, 1218m, 1083m, 914s, 787s cm1; 8 H 2.04 (3H, s), 5.78 (1H, d, J 2.1Hz), 5.75 (1H, d, J 2.1Hz); se 20.4 (q), 120.5 (s), 121.6 (s), 126.9 (t), 134.8 (s).

Compound No. 11 gave 5,5-dichloro-4-ethylpent-4-en-2-yne and 3 bromo-1,1-dichloro-2-ethyl-4-methylbuta-1,3-diene (compound No. 2) (ratio of ca. 1:1 by g.l.c.), in 75 minutes at 1800C (0.20 g, 63%). The alkyne (Found: M+, 162.0018. C7HgC12 requires M, 162.0003) which showed max 2976m, 2225w, , 1578m, 1461m, 1376m, 1068w, 890m, 786s cam~1; sH 1.11 (3H, t, J 7Hz), 2.04 (3H, s), 2.32 (2H, q, J 7Hz); C 13.6 (q), 36.5 (t), 40.5 (q), 77.2(s) 100.2 (s), 121.6 (s), 140.2 (s). The diene (Found: M+, 241.9268.

C7HgBrC12 requires M, 241.9265) showed max 2975m, 1594m, 1458m, 1216m, 1107m, 910m, 786s cm~1; H 1.0 (3H, t, 7Hz), 1.8 (3H, d, J 6Hz), 2.4 (2H, q, J 7Hz), 5.8 (1H, q, J 6Hz); SC 13.6 (q), 20.4 (t), 26.4 (q), 121.7 (s), 127.4 (d), 140.8 (s). The above reaction was repeated, and followed by g.l.c.

At short reaction times two peaks were observed, corresponding to the starting material and the diene (compound No. 2); after 1 hour the starting material had disappeared and the peak for the alkyne was present. After 4 hours at 1800C, the g.l.c. showed that all the diene had been consumed and only the alkyne remained. Work up as above gave the crude alkyne (76%) which was purified by flash distillation.

Compound No. 12 gave 6,6-dichloro-5-propylhex-5-en-3-yne and 3 bromo-1,1Zichloro-4-ethyl-2Sropylbuta-1,3-diene (compound No. 3) (ratio ca. 1:1 by g.l.c.), in 60 minutes at 2000C (0.26 g, 6796). The alkyne (Found: M+, 190.0318. C9H12Cl2 requires M, 190.0316) showedSmax 2964s, 2874m, 2225w, 1580m, 1460m, 1318m, 927s, 880m cm'l; H 0.94 (3H, t, J 7Hz), 1.20 (3H, t, J-7Hz), 1.57 (2H, sextet, J 7Hz), 2.20-2.44 (4H, complex multiplet); C 13.6 (q), 13.9 (q), 21.1 (t), 36.4 (t), 42.8 (t), 77.1 (s), 100.5 (s), 121.9 (s), 140.3 (s).The diene (Found: M+, 269.9580. C9H13BrCl2 requires M, 269.9578) showedsmax 2964s, 2873m, 1696m, 1460m, 918m cm-1; #H 0.93 4p (3H, t, J 7Hz), 1.05 (3H, J 7Hz), 1.47 (2H, sextet, J 7Hz), 2.24 (2 H, q, J 7Hz), 2.35 (2H, J 7Hz), 5.8 (1H, t, J 7Hz); #C 13.7 (q), 13.8 (q), 21.2 (t), 26.4 (t), 28.6 (t), 121.8 (s), 127.3 (d), 140.2 (s).

Compound No. 21 gave 2-methyl-1,1,3-trichlorobuta-1,3-diene (compound No. 4) in 45 minutes at 1600C (0.22 g, 64%) (Found: M+, 169.9305.

C5H5Cl3 requires M, 169.9307) which showedmax 2924w, 1630m, 1600s, 1221s, 1089m, 1033m, 912s, 670m cm-1; H 2.04 (3H, s), 5.75 (1H, d, J 2.1Hz), 5.78 (1H, d, J 2.1Hz); SC 19.9, 117.6, 121.0, 133.3, 136.9.

Compound No. 22 gave 2-ethyl-4-methyl-l,l,3-trichlorobuta-l ,3- diene (compound No. 5) in 60 minutes at 1800C (0.24 g, 61%) (Found: Mi, 197.9766. C7H9C13 requires M, 197.9770) which showed #max 2975m, 2875m, 1658w, 1596m, 1459m, 1220m, 923s, 878s cm-1; H 1.04 (3H, t, J 7Hz), 1.83 (3H, d, J 7Hz), 2.42 (2H, q, J 7Hz), 5.74 (1H, q, J 7Hz); bC 11.4, 14.3, 26.6, 120.7, 127.0, 127.1, 139.8.

Compound No. 23 gave 4-ethyl-2-propyl-1,1,3-trichlorobuta-1,3-diene (compound No. 6) in 90 minutes at 2000C (0.3 g, 67%) (Found: M+, 226.0081.

C9H13Cl3 requires M, 226.0083) which showed #max 2968s, 2875m, 1610w, 1460m, 1375m, 920m, 780m cm'l; #H 0.97 (6H, t, 7Hz), 1.66 (2H, sextet, J 7Hz), 2.39 (4H, t, J 7Hz), 5.66 (1H, t, J 7Hz); #C 12.3 (q), 13.3 (q), 20.4 (t), 22.3 (t), 35.0 (t), 121.1 (s), 127.5 (d) 133.9 (s), 138.5 (s).

Compound No. 13 gave three products in ratio ca. 10:1:1 in 90 minutes at 2000C (0.17 g, 51%). The major product was 2-methyl-1,1,3-trichlorobuta-1,3-diene (compound No. 4) identical to that obtained above.

The minor products were characterised as the isomeric 2,3,4-trichloropenta- 2,4-dienes, although their n.m.r. data were too similar to allow a simple distinction to be made. The second isomer (M+, 169.9473) showed #H 2.32 (3H, s), 5.59 (1H, d, J 1.7Hz), 5.67 (1H, d, J 1.7Hz). The third isomer (M+, 169.9467) showed #H 2.31 (3H, s), 5.50 (1H, d, J 1.5Hz), 5.64 (1H, d, J 1.5Hz).

Compound No. 14 gave three products in ratio ca. 1:2:0.75 by g.l.c. in 120 minutes at 2000C (0.22 g, 55%). The first compound was identical to 2ethyl-4-methyl-1,1,3-trichlorobuta-1,3-diene obtained above compound No.

5. The second compound (M+, 197.9794) showed max 2 990m, 1615m, 1460m, 1180w, 1130, 940s, 785s, 710 cm'l; SH 1.17 (3H, t, J 7.5Hz), 1.86 (3H, d, J 6.8Hz), 2.63 (2H, q, J 7.5Hz), 6.0 (1H, q, J 6.8Hz). The third isomer (M+, 197.9795) showed *max 2980m, 1610m, 1460m, 1190w, 935s, 815s, 780, 685 cm-1;#H 1.16 (3H, t, J 7.4Hz), 1.86 (3H, d, J 6.7Hz), 2.53 (2H, q, J 7.4Hz), 5.94 (1H q, J 6.7Hz).

Compound No. 15 gave a mixture of 4-ethyl-2-propyl-1,1,3-trichloro- buta-1,3-diene (compound No. 6) and Z,E- and Z,Z4,5,6-trichlorononadienes (ratio ca. 1:6:1 by g.l.c. and n.m.r.) in 160 minutes at 2000C (0.26 g, 57%).

The mixture (M+, 226.0083. CgH13Cl3 requires M, 226.0083) showed 2967s, 2875m, 1609w, 1460m, 1380w, 917m, 787m cm1;6 H all the sgna1S for compound No. 6 plus common signals at 0.97 (3H, t, J 7Hz), 1.06 (3H, t, J 7Hz), 1.66 (2H, sextet, J 7Hz), 2.29 (2H, t, J 7Hz), 2.59 (2H, t, J 7Hz), and two triplets at 5.86 (1H, t, J 7Hz) and 5.91 (1H, t, J 7Hz) in ratio 1:6.

Compound No. 16 gave E- and Z-1-methyl-2-bromo-1,3-dichlorobuta1,3-diene (compound No. 7) (ratio ca. 1:1 by g.l.c.) in 30 minutes at 1800C (0.26 g, 61%). One isomer (Found: M+, 213.8955. C5H5BrCl2 requires M, 213.8952) showed max 2920m, 1630m, 1590m, 1214m, 1079m, 914s, 781s cm-1;#h 2.35 (3H, s), 5.56 (1H, d, J 1.7Hz), 5.61 (1H, d, J 1.7Hz). The other isomer (Found: M+, 213.8958. C5H5BrCl2 requires M, 213.8952) showed max 2923m, 1627m, 1590m, 1216m, 1080m, 914s, 780s cm-1;#H 2.30 (3H, s), 5.49 (1H, d, J 1.5Hz), 5.59 (1H, d, J 1.5Hz).

Compound No. 17 gave Z,E- and Z,Z-4-bromo-3,5-dichlorohepta-2,4- diene (compound No. 8) (ratio ca. 2.5:1 by g.l.c.) in 30 minutes at 1800C (63%). The first isomer (Found: M+, 241.9297. C7HgBrCl2 requires M, 241.9265) showed max 2980m, 1615m, 1460m, 1380, 1285m, 1175, 1125m, 940s, 800, 795s, 695 cm-1;#H 1.17 (3H, t, J 7.4Hz), 1.84 (3H, d, J 6.8Hz), 2.66 (2H, q, J 7.5Hz), 5.97 (1H, q, J 6.7Hz); de 11.3, 14.6, 32.3, 114.4, 129.3, 129.6, 136.5. The second isomer (Found: M+, 241.9390) showed max 2980m, 1600m, 1460m, 1380, 1280m, 1180, 1120m, 930s, 805, 750s 680 cm-l; #H 1.16 (3H, t, J 7.4Hz), 1.85 (3H, d, J 6.7Hz), 2.54 (2H, q, J 7.4Hz), 5.93 (1H, q, J 6.7Hz);#C 12.9, 14.7, 30.6, 117.6, 128.6, 130.0, 142.4.

Compound No 18 gave Z,E- and Z,Z-5-bromo-4,6-dichloronona-3,5- dienes (compound No. 9) (ratio ca. 1:1 as determined by g.l.c.) in 45 minutes at 2000C (0.35 g, 65%). The first isomer (Found: M+, 269.9574.

C9Hi3BrCl2 requires M, 269.9578) showed #max 2967s, 2874m, 1606m, 1460m, 1164w, 909m, 739s cm-1; #H 1.02 (3H, t, J 7Hz), 1.06 (3H, t, J 7Hz), 1.67 (2H, sextet, J 7Hz), 2.26 (2H, p, J 7Hz), 2.63 (2H, t, J 7Hz), 5.98 (1H, t, J 7Hz). The second isomer (Found: M+, 269.9568.C9H13BrCl2 requires M, 269.9578) showed #max 2967s, 2874m, 1601m, 1460m, 1170w, 908m, 736s cm-1; dH 0.92 (3H, t, J 7Hz), 1.05 (3H, t, J 7Hz), 1.65 (2H, sextet, J 7Hz), 2.27 (2H, p, J 7Hz), 2.51 (2H, t, J 7Hz), 5.84 (1H, t, J 7Hz); #C 12.5,- 133, 21.3, 22.5, 38.7, 118.1, 128.6, 141.0, 135.5.

Although the mechanism of the thermolytic reaction described above has not been fully established, it is believed to involve the loss of a halide anion and concerted ring opening to form a halo-alkyl cation, followed by deprotonation in the presence of quinoline, e.g.

Alternatively, the following diradical process is possible.

but whichever mechanism is operable, the above described thermolysis of 1,1,2,3-tetrahalogenocyclopropanes does allow ready access to single stereoisomers of 1,1-dichloro-3-bromo-alka-1,3-dienes and to E/Z-mixtures of 1 ,2,3-trihalogenoalkadienes.

In summary: according to the invention it has been found that the thermolysis tetrahalogenocyclopropanes of the formula

where R and Ha are as defined, provide a substantially controlled stereoand regio-specific route to controlled stereo- and regio-specific trihalobutadienes of the formulae

Specific reactions and reaction products identified herein are summarised in the following Table 3, the halogen substituents being in the numbered positions hereinbefore identified: Table 3

Reactant cyclopropane Thermolysis Product Butadiene Yield CPd Form- Time Temp Cpd Form- (%) Noc ula R Ha1 Ha2 Ha3 Ha4 (min) ( C) No. ula R Ha1 Ha2 Ha3 10 III Cl Cl Br Br 30 160 1 I H Br Cl Cl 65 11 III CH3 Cl Cl Br Br 75 180 2 I CH3 Br Cl Cl 631 12 III C2H5Cl Cl Br Br 60 200 3 I C2H5Br Cl Cl 671 21 III H Cl Cl Br Cl 45 160 4 I H Cl Cl Cl 64 22 III CH3 Cl Cl Br Cl 60 180 5 I CH3 Cl Cl Cl 61 23 III C2H5Cl Cl Br Cl 90 200 6 I C2H5Cl Cl Cl 67 .16 III H Br Br Cl Cl 30 180 7 II H Cl Cl Br 612 17 III CH3 Br Br Cl Cl 30 180 8 U CH3 Cl Cl Br 633 18 III C2H5Br Br Cl Cl 45 200 9 II C2H5Cl Cl Br 654 13 III @ Cl Cl Cl Cl 90 200 4 I @ Cl Cl Cl 515 14 III CH3 Cl Cl Cl Cl 120 200 5 I CH3 Cl Cl Cl 556 15 III C2HsC1 Cl Cl Cl 160 200 6 I C2H5C1 Cl Cl 577 Footnotes 1. Total yield of diene and corresponding dehydrohalogenated dihaloalkyne derivatives as ca. 1:1 mixture 2. Total yield of E and Z isomers as ca. lfl mixture 3. Total yield of Z,E and Z,Z, isomers as ca. 2.5:1 mixture 4. Total yield of Z,E and Z,Z, isomers as ca. 1:1 mixture 5. Total yield as 10:1:1 isomeric mixture with isomeric 2,3,4 trichloropenta -2,4-dienes 6. Total yield as 1:2:.075 isomeric mixture with Z,E-and Z,Z-4,5,6 trichloromadienes

Claims (1)

1. CLAIMS 1. A process for the preparation af trihalogenated butadienes of controlled stereo- and regio-chemistry of the formulae

   where R is H, or a substituted or unsubstituted hydrocarbyl group free from non-aromatic unsaturation and/or interfering substituents, and Ha is halogen, the R substituents and the halogen substituents not necessarily all or both being the same, which comprises the thermolysis of a tetrahalogenocyclopropane of the formula

   where R and Ha are as defined above.

   2. A process according to claim 1, which comprises heating the tetrahalogenocyclopropane in the presence of an aromatic base.

   3. A process according to claim 2, wherein the aromatic base is quinoline.

   4. A process according to claim 1, 2 or 3, wherein each R is an unsubstituted or substituted hydrocarbyl group free of non-aromatic unsaturation and/or interfering substituents, and containing up to 10 carbon atoms.

   5. A process according to claim 4, where each R is C1-C6 alkyl or C6 -C 10 aryl, alkaryl or aralkyl.

   6. A process according to claim 5, where each R is methyl or ethyl.

   7. A process according to any one of claims I to 6, where each Ha is Br or Cl.

   8. Trihalogenobutadienes of the formulae defined in claim 1.

   9. Compounds according to claim 8, being the specific compounds identified hereinbefore under compound numbers I to 9.

   10. Tetrahalogenocyclopropanes of the formula defined in claim 1.

   11. Compounds according to claim 10, being the specific compounds identified hereinbefore under compound numbers 10 to 23.

   12. A process for the preparation of compounds according to claim 10, which comprises reacting an alkene of the formula

   where R and Ha are as defined in claim 1, with a dihalocarbene generated under phase transfer conditions.

   13. A process according to claim 12, wherein the dihalocarbene is a dichloro- or dibromo-carbene.

   14. A process for the preparation of compounds according to claim 10, which comprises reacting an alkene of the formula

   where R is as defined in claim 1 and Ha is Br or Cl, which comprises reacting the alkene with chloroform or bromoform in the presence of strong alkali.

   15. A process for the preparation of compounds according to claim 10, being geminal dibromo compounds, which comprises reacting an alkene of the formula

   where R is as defined in claim 1 and Ha is Br or CI, with phenyltribromomethyl mercury.

   16. A process according to claim 15, which comprises reacting the alkene with phenyltribromomethyl mercury in benzene under reflux conditions.

   17. A process according to any one of claims 12 to 16, where each R-is is an unsubstituted or substituted hydrocarbyl group free of non-aromatic unsaturation and/or interfering substituents, and containing up to 10 carbon atoms.

   17. A process according to claim 13, where each R is C1 -06 alkyl or C6 -C10 aryl, alkaryl or aralkyl.

   19. A process according to claim 14, where each R is methyl or ethyl.