Patent ID: 7067703

Claim:
A process for the manufacture of retinal, of the formula comprising reacting a 5-(2,6,6-trimethyl-cyclohex-1-enyl)-1,4-pentadiene derivative of the general formula or a 5-(2,6,6-trimethyl-cyclohex-2-enyl)-1,4-pentadiene derivative of the general formula or a 5-(2,6,6-trimethyl-2-cyclohexen-1-ylidene)-1-pentene derivative of the general formula or a 5-(2,6,6-trimethyl-cyclohex-1-enyl)-penta-1-en-4-yne derivative of the general formula or a 5-(2,6,6-trimethyl-cyclohex-2-enyl)-penta-1-en-4-yne derivative of the general formula wherein R 1 signifies hydroxyl or a group OR 3 , R 2 signifies chlorine, bromine, C 1-6 -alkoxy, C 1-6 -alkylthio, aryloxy, aryithio, (C 1-6 -alkyl)carbonyloxy, aroyloxy, tri(C 1-6 -alkyl)silyloxy, di(C 1-6 -alkyl)phosphonyloxy, (C 1-6 -alkyl)sulphonyloxy, arylsulphonyloxy, (C 1-6 -alkyl)sulphonyl, arylsulphonyl; di(C 1-6 -alkyl)amino, N-aryl-(C 1-6 -alkyl)amino or diarylamino, and R 3 signifies C 1-6 -alkyl, (C 1-6 -alkyl)carbonyl, aroyl, (C 1-6 -alkoxy)carbonyl, tri-(C 1-6 -alkyl)silyl, di(C 1-6 -alkyl)phosphonyl, diarylphosphonyl, (C 1-6 -alkyl)sulphonyl or arylsulphonyl, with a 1,3-butadiene derivative of the general formula wherein R 4 signifies C 1-6 -alkyl, (C 1-6 -alkyl)carbonyl or tri(C 1-6 -alkyl)silyl, in the presence of a Lewis or Brönsted acid and subjecting the so-obtained compound of the general formula (starting from the 5-substituted 1,4-pentadiene derivative of the formula IIa) or (starting from the 5-substituted 1,4-pentadiene derivative of the formula IIb) or (starting from the 5-substituted 1-pentene derivative of the formula IIc) or (starting from the 5-substituted penta-1-en-4-yne derivative of the formula IId) or (starting from the 5-substituted penta-1-en-4-yne derivative of the formula IIe) to basic or acidic conditions to eliminate therefrom the moiety R 2 H and thus produce, from the compound of the formula IVa, retinal of the formula I, or, from the compound of the formula IVb, the compound of the formula or, from the compound of the formula IVc, the compound of the formula or, from the compound of the formula IVd, the compound of the formula or, from the compound of the formula IVe, the compound of the formula and, where a compound of the formula Va or Vb has been produced, hydrogenating this to produce retinal of the formula I or the compound of the formula I′ respectively, and in each case where a compound of the formula I′ or I″ has been produced, isomerizing this under basic or acidic conditions or in the presence of a metal catalyst to the desired retinal of the formula I.