Michael-Induced Ring Closure to 2-Azidocyclopropane-1,1-dicarboxylates and their Staudinger Reduction to 5-Alkoxy-3(alkoxycarbonyl)pyrrolidin-2-ones

An easy and short synthesis of new (beta)-azidocyclo­propanedicarboxylates, a rather unexplored class of conformationally constrained N-protected (beta)-aminocyclopropanecarboxylic acid derivatives, is described. Michael-induced ring closure (MIRC) Aof sodium azide to 2-bromoalkylidenemalonates in alcoholic solvents leads to 3,3-dialkyl-2-azidocyclopropane-1,1dicarboxylates, whereas other polar solvents give increasing amounts of competitive 2-azidoalkylidenemalonates. The reactivity of the azidocyclopropanes was investigated under reducing conditions, giving an easy access to diastereomeric mixtures of 5alkoxy-3-(alkoxy­carbonyl)pyrrolidin-2-ones.