Erich Widmer

Preparation of (9Z, 11Z) - Vitamin A

Abstract Starting from (7E,9Z)-C 15 -aldehyde 4 , the syntheses of (9Z, 11Z)-vitamin A acetate and palmitate are reported. The construction strategy is based on treatment of 4 with Zn-PPh 3 /CBr 4 , addition of acetaldehyde followed by a Wittig-Horner reaction to give the (9Z, 11Z)-C 20 -nitrile 7 which was reduced with DIBAH to the corresponding aldehyde 8 and then to the title compound 1 . The thermal instability of 1 is discussed.

Strategies for Building the Carbon Skeleton

Modern synthetic organic chemistry would permit the preparation of carotenoids by an almost countless number of strategies. In reality, however, the few methods and strategies that became established early in this century have since been used repeatedly and some of these have been developed to the scale of industrial syntheses. The aim of this Chapter is to provide a guide to the simplest route to a particular target carotenoid.

Preparation of (7Z) - and (7Z,11Z) - vitamin A

An efficient access to (7Z)- and (7Z,11Z)-vitamin A is described. Following the addition of a C6-acetylenic building block to 2,6,6-trimethylcyclohexanone (2), dehydration of the tert. alcohol 3 and formation of the C15-Wittig salt, the (7Z)-geometry was introduced by partial hydrogenation of the triple bond over Raney-nickel. Following Wittig reaction with (E)-2-methyl-4-acetoxy-2-butenal gave a mixture of the title compounds 8 and 9 which could easily be separated.