Synthesis of coenzyme On and quinonoid antibiotics by using allyltrialkyltins: control of regio- and stereochemistry in fluxional pentadienyltins and their application to chiral anthracyclinone synthesis

Abstract

Abstract Pentadienyl anions, unsymmetrically substituted at the 2-position, were trapped using Me SiCI and Me SnCI to give the corresponding pentadienylmetals which show marked differences in their regioselectivity. The tin electrophile gave (Z)-2-substituted isomers in high selectivity up to 96 per cent regardless of the nature of the substituents. On the other hand, the silicon electrophile gave (Z)-4-substituted products with moderate to high selectivity. The difference is explicable in terms of the preferential 1,5-Me Sn sigmatropic shift in the pentadienyltin systems towards the thermodynamically more stable s-trans isomers.