Carotenoids and related compounds. Part XXVI. Synthesis of methyl natural bixin
A stereochemically controlled synthesis of the cis-(Z)-4-isomer (26; R = Me) of methylbixin is described, which involves 5-methoxycarbonyl-3-methylpenta-cis-(Z)-2,trans-(E)-4-dien-1-al (6) as the key intermediate. The product is shown to be identical with the methyl ester of natural bixin.