GB605772A - A process for the manufacture of pentaenes - Google Patents

Abstract

Pentaenes are obtained by heating, in order to split off acid, a compound of the general formula <FORM:0605772/IV(b)/1> (where R is an acyl, alkyl, aryl or aralkyl group and R1 is an acyl group), preferably in the presence of a basic agent, e.g. an alkali acetate or tertiary potassium amylate in tertiary amyl alcohol, or in an inert solvent in the presence of phthalic anhydride. The compound above is obtained by condensing 4-(21, 61, 61-trimethylcyclohexene - (11) - yl) - 2 - methyl - butene - (2) - al-(1) with a Grignard compound of 1-hydroxy-3 - methyl - pentene - (2) - yne - (4) or an ether thereof (both these starting materials being obtainable as described in Specification 605,208) and subjecting the 1-hydroxy-3 : 7-dimethyl-6-hydroxy - 9 - (21,61,61 - trimethyl - cyclohexenyl) - nonadiene-(2 : 7)-yne-(4) or the ether thereof thus formed to hydrogenation in the presence of a hydrogenation catalyst until 1 mol. of hydrogen has been added to the triple bond of of said ether or hydroxy compound, or (b) to esterification and allyl rearrangement by treating with an acylation agent, e.g. phthalic or acetic anhydride and by heating and subjecting the resulting ester to hydrogenation until one molecule of hydrogen has been added to the triple bond of said ester. Anti-oxidants, e.g. tocopherols, are preferably present during the synthesis. In examples: (1) 4-(21,61,61-trimethyl-cyclohexene-(11)-yl) -2-methyl-butene-2-al-(1) is condensed by means of ethyl magnesium bromide with 1 - methoxy - 3 - methyl - pentene - (2) - yne - (4) to produce 1 - methoxy - 3 : 4 - di - methyl - 6 - hydroxy - 9 - (21,61,61-trimethyl - cyclo - hexene - (11) - yl) - nonadiene - (2,7) - yne-(4) which is hydrogenated using palladised charcoal on which quinoline had been previously adsorbed to produce 1 - methoxy - 3 : 7 - dimethyl - 6 - hydroxy - 9 - (21,61,61 - trimethyl - cyclohexene - (1) - yl) - nonatriene - (2 : 4 : 7) which is refluxed in acetic anhydride with potassium acetate; a concentrate of Vitamin A methyl ether is obtained from the residue by chromatographic adsorption; (2) 1-methoxy-(3,7)-dimethyl-6-hydroxy-9-(21,61, 61-trimethyl-cyclohexene-(11)-yl)-nonotriene-(2 : 4 : 7) (obtained as in (1)) is refluxed with sodium acetate in acetic anhydride and the product boiled with potassium in tertiary amyl alcohol to produce Vitamin A methyl ether; (3) 1-methoxy-(3 : 7)-dimethyl-6-hydroxy-9-(21,61, 61-trimethyl-cyclohexene-(11)-yl)-nonadiene-(2 : 7)-yne-(4) (obtained as in (1)) is heated with potassium acetate in acetic anhydride and the product hydrogenated using palladised charcoal on which quinoline had been previously adsorbed as catalyst; the hydrogenated compound heated with potassium in tertiary amyl alcohol yields Vitamin A methyl ether; (4) as in (3) carrying out the acylation using benzoyl chloride instead of acetic anhydride; (5) 1-methoxy-3 : 7-dimethyl-6 - hydroxy - 9 - (21,61,61 - trimethyl - cyclohexene - (11)-yl)-nonatriene-(2 : 4 : 7) prepared as in (1)) is refluxed in xylene passing in dry phosgene to produce Vitamin A methyl ether; (6) 1-methoxy-3 : 7 - dimethyl - 6 - hydroxy - 9 - (21 : 61 : 61 - tri - methyl - cyclohexene - (11) - yl) - nonatriene - (2 : 4 : 7) (prepared as in (1)) in benzene is refluxed with phthalic anhydride in the presence of dl-a -tocophenol whilst introducing nitrogen to produce Vitamin A methyl ether; (7) 1 - butoxy - 3 - methyl - pentene - (2) - yne - (4) is condensed with 4 - (21,61,61 - trimethyl - cyclo - hexene - (11) - yl) - 2 - methyl - butene - 2 - al - (1) and hydrogenated as in (1) to produce 1-butoxy 3 : 7 - dimethyl - 6 - hydroxy - 9 - (21 : 61 : 61 - tri - (methyl-cyclohexene-(11)-yl)-nonatriene-2 : 4 : 7 which is treated with phthalic anhydride in benzene as in (6) to produce Vitamin A butyl ether. A sample furnished under Sect. 2 (5) was prepared by condensing 1-hydroxy-3-methyl-pentene-(2)-yne-(4) by means of ethyl magnesium bromide with 4-(2 : 61 : 61-trimethylcyclohexene-(11)-yl)-2-methyl-butene-(2) -al-(1) to produce 1 : 6 - dihydroxy - 3 : 7 - dimethyl - 9 - 2 : 61 : 61 - trimethyl - cyclohexene - (11) - yl) - nona - diene - (2 : 7) - yne - (4) which is treated in (1) above to produce Vitamin A acetate, which gave free Vitamin A when boiled with potassium.