Enantioselective organocatalytic formal [3+2]-cycloaddition of isatin-derived ketimines with benzylidenemalononitriles and benzylidineindanones

Abstract

The biological and medicinal importance of oxindole-derived spirocycles is now well-established, and has inspired the development of numerous creative synthetic strategies. Here we report an efficient formal [3+2]-cycloaddition of isatin-derived N-trifluoroethyl ketimines with a series of benzylidinemalononitrile and benzylidineindandione dipolarophiles catalysed by a cinchona-derived thiourea catalyst. The reaction affords a series of functionalized spiro-pyrrolidinoxindole products with up to four contiguous stereocentres in excellent yields, ee and d.r. (up to 98% yield, 97% ee, and >100 : 1 d.r.). These products share a common core scaffold with compounds previously found to have anti-tumour, anti-microbial and anti-inflammatory activities.