Synthesis of cis-2,cis-4-vitamin A acid by a Wittig condensation
Abstract
cis-2 Vitamin A acid and the hitherto unknown cis-2,cis-4 vitamin A acid are obtained by condensation of 3-methyl-5-(1,3,3-trimethylcyclohexenyl)penta-trans-2,trans-4-dienylidenephosphorane (IV) with cis-β-formyl-crotonic acid (II). Controlled stereomutation of the cis-2,cis-4-acid yielded cis-2- and all-trans vitamin A acid. cis-β-Formylcrotonic acid is isomerised to the trans-acid (I) by treatment with base.