Patent GB-786003-A (GB)
Title: Novel dehydro-betacarotene and the manufacture and conversion thereof
Filed: 1955-12-21
Abstract: The invention comprises 3,4; 31,41-15,151-trisdehydro - b  - carotene and 15,151 - monocis3,4; 31,41 - bisdehydro - b  - carotene and the preparation thereof by condensing acetylene with 8 - [21,61,61 - trimethyl - cyclohexadiene-11,31 - yl - 11] - 2,6 - dimethyl - octatriene - 2,4,6-al - 1 or 8 - [21,61,61 - trimethyl - cyclohexen 21 - ylidene - 11] - 2,6 - dimethyl - octatriene-2,4,6 - al - 1 in a metal organic reaction subjecting the resulting 1,18-di-[21,61,61 -trimethylcyclohexadiene - 11,31 - yl - 11] - 3,7,12,16 - tetramethyl - 8,11 - dihydroxyoctadecahexaene-(2, 4,6,12,14,16) - ine - 9 or 1,18 - di[21,61,61 - trimethyl - cyclohexen - 21 - ylidene - 11] - 3,7,12, 16 - tetramethyl - 8,11 - dihydroxy - octadecahexaene - (2,4,6,12,14,16) - ine - 9 to bilateral allyl rearrangement and dehydration and, if desired, partially hydrogenating the resulting 3,4; 31,41; 15,151 - trisdehydro - b  - carotene at the triple bond to obtain 15, 151-monocis 3,4; 31,41 - bisdehydro - b  - carotene. The condensation may be effected stepwise by first condensing acetylene with approximately one molar proportion of the aldehyde initial material in a metal-organic reaction and condensing the product with a further molar proportion of the said material in a metal-organic reaction.  The bilateral allyl rearrangement and dehydration of the diol product of the first stage may be effected by heating in an inert solvent with about two molar proportions of phosphorus oxychloride in the presence of an organic tertiary base or by reacting same with a hydrogen halide at a low temperature.  The hydrogenation may be effected in the presence of a hydrogenation catalyst e.g. palladium/calcium carbonate deactivated with lead and quinoline.  The 15,151-monocis 3,4; 314-bisdehydro-b -carotene may be isomerized to the corresponding all-trans compound by treatment with iodine, by irradiation or by heat. Starting compounds.  8 - [21,61,61-Trimethylcyclohexadien - (11,31) - yl - 11] - 2,6 - dimethyloctatriene - 2,4,6 - al - 1 is obtained by treating 4 - [216161 - trimethyl - cyclohexen - 11 - yl - 11]-2 - methyl - buten - 2 - al - 1 with N - bromosuccimide and quinoline to produce 4 - [2161,61-trimethyl - cyclohexen - 21 - ylidene - 11] - 2-methylbuten - 2 - al - 1 which with isopropenyl acetate and subsequent hydrolysis yields 4-[21,61,61 - trimethyl - cyclohexadiene - 11,31 - yl-11] - 2 - methyl - buten - 2 - al - 1, which with ethyl orthoformate yields 4 - [21,61,61 - trimethyl - cyclohexadien - 11,31 - yl - 11] - 2-methyl - 1,1 - diethoxy - buten - 2, which with ethyl vinyl ether yields 6-[21,61,61-trimethylcyclohexadien - 11,31 - yl - 11] - 4 - methyl - 1,1,3-triethoxy - hexene - 4, which with glacial acetic acid and sodium acetate yields 6-[21,61,61-trimethyl - cyclohexadien - 11,31 - yl - 11] - 4-methyl - hexadien - 2,4- al - 1, which with ethylorthoformate yields 6-[21,61,6-trimethyl-cyclohexadien - 11,31 - yl - 11] - 4 - methyl - 1,1 - diethoxy - hexadiene - 2,4, which with ethyl propenyl ether yields 8 - [21,61,61 - trimethylcyclohexadiene - 11,31 - yl - 11] - 2,6 - dimethyl1,1,3 - triethoxy - octadiene - 4,6 which with sodium acetate and glacial acetic acid yields 8-[21,61,61 - trimethyl - cyclohexadien - 11,31 - yl-11] - 2,6 - dimethyl - octatriene - 2,4,6 - al - 1. 8 - [21,61,61 - Trimethyl - cyclohexen - 21 - ylidene-11] - 2,6 - dimethyl - octatriene - 2,4,6 - al - 1 is obtained in a similar manner starting from 4-[21,61,61 - trimethyl - cyclohexen - 21 - ylidene-11] - 2 - methyl - buten - 2 - al - 1.