Chiral Lewis Acid Catalysis in Nitrile Oxide Cycloadditions

摘要

Nitrile oxide cycloaddition to olefins is an important synthetic transformation.1,2 Diastereoselective nitrile oxide cycloadditions have been investigated extensively, and successful methods are at hand.3 However, the development of enantioselective variants using chiral Lewis acids has been hampered by the use of coordinative amine bases for the generation of the nitrile oxide, by the high donor ability of the oxygen atom of the dipole,4 and by the propensity of the dipole to dimerize.2 Ukaji and Inomata have reported examples of enantioselective nitrile oxide cycloadditions with allylic alcohols using chiral catalysts.5 In this contribution we describe examples of highly regio- and enantioselective nitrile oxide cycloadditions to electron-deficient alkenes using substoichiometric amounts of a chiral Lewis acid.