Amino acid derived phosphine-catalyzed enantioselective 1,4-dipolar spiroannulation of cyclobutenones and isatylidenemalononitrile

Abstract

Cyclobutenones have been explored as a new type of chiral 1,4-dipole four-carbon synthon, which readily undergoes organophosphine-mediated C-C bond cleavage and asymmetric intermolecular 1,4-dipolar spiroannulation with isatylidenemalononitrile in the presence of amino acid-derived chiral phosphine catalyst to furnish enantioenriched 3-spirocyclohexenone 2-oxindoles in good yield with up to 87% ee. To our knowledge, this is the first example of asymmetric transformation of cyclobutenones and the phosphine-catalyzed asymmetric 1,4-dipolar cycloaddition consisting of C-C bond activation is unprecedented.

Keywords: CC bond activation; organocatalysis; oxindoles; phosphanes; spiroannulation.