Silylation of bicyclic six-membered nitronates. Ring—chain tautomerism of intermediate N,N bis(oxy)iminium cations

Abstract

Silylation of bicyclic six membered nitronates was studied as a possible route to conjugated enoximes with a distant carbonyl group. Apart from the target enoximes, this reaction yielded nitro compounds. The ratio of these two types of products and the configurations of their stereogenic centers depend on the nature and configurations of the starting nitronates and the silylation conditions. The results obtained were interpreted in terms of ring-chain tautomer ism of intermediate N,N bis(oxy)iminium cations.

Enumeration of Ring–Chain Tautomers Based on SMIRKS Rules

“…A few structures were excluded from our analysis due to their type of ring–chain tautomerism. Specifically, nine compounds were classified as not applicable because their transformation involved halogen anions, , alkaline solution, intermediate reaction forms, − or the molecule did not have the nucleophilic center required for a ring–chain transformation process, i.e., were not tautomeric transformations in the strict sense relative to our definition. We were able to predict the documented ring–chain tautomers for 57 out of the remaining 62 compounds.…”