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Organocatalytic Asymmetric Ring Expansion of Cyclobutanones
F. Capitta, A. Frongia*, J. Ollivier, P. P. Piras*, F. Secci
Università di Cagliari, Monserrato, Italy and Université Paris-Sud, Orsay, France
16 February 2011 (online)
A secondary amine catalyzed ring expansion of substituted cyclobutanones with nitrosobenzene is reported. Surprisingly, none of the expected α-aminoxylation products was isolated and the ring-expanded products were obtained in reasonable yields, diastereo- and enantioselectivities. The proposed mechanism involves an enamine formation, followed by a formal nitroso aldol reaction (1). However, intermediate 2 cyclizes, presumably directed by the catalyst, and leads to bicyclic intermediate 3, which undergoes a rearrangement and hydrolysis, thus liberating the catalyst and product.