Gold(i)-catalyzed asymmetric [3 + 2]-cycloadditions of γ-1-ethoxyethoxy-propiolates and aldehydes

Abstract

A gold-catalyzed asymmetric intermolecular [3 + 2]-cycloaddition of γ-1-ethoxyethoxy-propiolate and aldehydes by the use of the chiral phosphoramidite (S,R,R)-5a is developed, which provides facile access to highly substituted 2,5-dihydrofurans in up to 84% yield with up to 97% ee. Control experiments support the result that this transformation indeed proceeds via an all-carbon gold 1,3-dipole with an open carbocation rather than a S_N2 type reaction.