Synthetic approach towards cuparene-type sesquiterpenes via highly regioselective epoxide opening under acid catalysis

Abstract

Abstract: Obtaining cuparene-type sesquiterpenes is a significant synthetic challenge mainly because of the construction of the sterically hindered quaternary centres. We report herein the successful construction of such quaternary moiety by a highly regioselective opening of (+/−)-2,5-dimethoxy-4-methyl-α-methylstyrene oxide by the acetone silyl enol ether catalysed by Lewis acid. Additionally, an efficient epoxidation of the highly activated 2,5-dimethoxy-4-methyl-α-styrene was accomplished by modifications on the dioxirane-promoted epoxidation protocol. Intensive optimisations for both key steps allowed the synthesis of the desired branched homo-aldol adduct, proposed as a key intermediate for a short synthetic alternative towards enokipodins. Graphical abstract: [Figure not available: see fulltext.]. © 2018, Springer-Verlag GmbH Austria, part of Springer Nature.