Stereochemical implications in the synthesis of 3,3′-spirocyclopropyl oxindoles from β-aryl/alkyl-substituted alkylidene oxindoles

3,3'-Spirocyclopropane oxindoles were synthesized in good to excellent yield and diastereoselectivity employing a Kukhtin Ramirez reaction between readily accessible E-alkylidene oxindoles, commercially available P(NMe2)(3), and alpha-keto esters. The stereoselectivity in the cyclopropanation event can be traced to the starting alkylidene geometry and the propensity of the exocyclic alkene to undergo isomerization in the presence of an electron rich phosphine. (C) 2015 Elsevier Ltd. All rights reserved.