Synthesis of anthracyclinones. Part 1. Regioselective alkylation of 5-hydroxyquinizarin

Abstract

Condensation of leuco-5-hydroxyquinizarin with aldehydes under Marschalk conditions (sodium hydroxide – water) gives 2-alkyl-5-hydroxyquinizarins with high regioselectivity, while the 3-alkyl compounds are obtained under Lewis conditions (piperidinium acetate – isopropanol). Reaction of the quinone with nitronate anions in methanol yields 2-alkyl derivatives exclusively.