The Formal [4+3] Cycloaddition between Donor−Acceptor Cyclobutanes and Nitrones

The formal [4+3] cycloaddition of 2-alkoxy-1,1-dicarboxylate activated donor−acceptor cyclobutanes with nitrones is disclosed. The reaction forms structurally unique oxazepines in moderate to high yield with a wide scope of nitrones. In most cases either a diastereomeric mixture or a single diastereomer may be formed, depending on the reaction conditions.