The rates of diene formation are remarkably different among the four dienes. Conjugated dienes 3, 13, and 17 are formed relatively fast with one isomer always predominating, whereas unconjugated diene 8, which consists of three isomers, is formed as slowly as 2- acetoxy-3-methylacrylonitrile Therefore, we assume that both the formation of the monoenolate and the consecutive formation of bisenolate proceeded much faster with 2, ...