Studies on the Carbon Zip Reaction of 2‐Oxocycloalkane‐1‐carbonitriles

Abstract As a part of continuing interest in the zip reaction, we present the results on a carbon ring‐enlargement reaction of activated ketones with a CN group as a charge stabilizer. Two series of (1‐cyano‐2‐oxocy‐cloalkyl)alkanoates were prepared from 8‐ and 12‐membered cyano‐ketones 1 and 2 , respectively, namely the propanoates 3 and 4 , the butanoates 6 , 8 and 9 as well as the pentanoates 12 and 15 . While treatment with t ‐BuOK of the former two homologous esters resulted in both ring enlargement and competitive transesterification, the pentanoates 12 and 15 afforded mostly the diastereoisomeric mixtures of bicyclic alcohols 20a – c and 31a , b , respectively, which remained intact on further exposure to base. It was shown that – apart from the base used ( t ‐BuOK) vs. Li(i‐Pr) 2 N – the distribution of products was greatly influenced by the ring size of substrates. This is further illustrated by treatment of ketones 34 and 35 with t ‐BuOK. While the former rearranged smoothly to diketone 36 , no reaction at all took place with the latter. The behavior of the substrates is discussed in terms of steric and energetic reasons.