The Use of Vinyl Sulfonium Salts in the Stereocontrolled Asymmetric Synthesis of Epoxide- and Aziridine-Fused Heterocycles: Application to the Synthesis of (-)-Balanol

摘要

The asymmetric synthesis of epoxides fused to carbo- or heterocycles by epoxidation methods is inherently challenging because the two enantiotopic faces of the corresponding cyclic (cis) alkene are poorly differentiated. The use of chiral sulfur ylides offers a complementary method for preparing epoxides, but this method has essentially only been employed to make acyclic epoxides.[1] We considered the possibility of extending sulfur ylide reactions to make fused bicyclic epoxides, and in particular to the challenging substrates described above. We were particularly attracted by the possibility of designing a general asymmetric annulation process for the synthesis of N-heterocycles through the reaction of a bifunctional aminoaldehyde with a chiral vinyl sulfonium salt (Scheme 1). This type of reaction has been studied by Jimenez and co-workers in relation to the synthesis of mitomycins[2] but has not been explored beyond that.