Abstract
Aminig to develop a new biogenetic-type cyclization of acyclic terpene derivatives which is applicable to the asymmetric synthesis of optically active terpenes, a novel acidcatalyzed cyclization of the dienamines (7) easily prepared with citral (1) and several kinds of secondary amines, was studied. Treatment of citral-pyrrolidine enamine (7a) with a mixture of concd. sulfuric acid and water, followed by hydrolysis, was found to exclusively afford α-cyclocitral (2) in 41% yield. Detailed studies on the structure of 7 and the reaction mechanism for the new cyclization reaction were also carried out.
