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 (CH 2 OH, COOH, COCH 3 ). 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.