Vilsmeier formylation of vinylcyclopropanes: 1. Formylation of thujopsene

Abstract Thujopsene(1) can be formylated in the 3‐position in 80% yield by use of one equivalent of the Vilsmeier reagent. The resulting 3‐formylthujopsene(4) is useful for the synthesis of other 3‐substituted derivatives (CH2OH, COOH, COCH3). With an excess of the reagent higher formylation products are formed. Two such products have been isolated and characterized and a mechanism for their formation is put forward.