Sulfur Ylide-Mediated [2 + 1] Annulation for the Synthesis of Spiro[cyclopropane-indolizine] Derivatives

High Resolution Image Download MS PowerPoint Slide A diastereoselective synthesis of spiro[cyclopropane-indolizine] derivatives via a [2 + 1] annulation reaction has been developed. This Michael-initiated ring closure of 7-arylmethylidene-6,7-dihydroindolizin-8(5 H )-ones with acyl-stabilized sulfur ylides furnishes a diverse array of densely functionalized spirocyclopropanes in moderate to excellent yields (up to 94%) with generally high to excellent diastereoselectivity (up to >20:1 dr). Further derivatization of these tricyclic scaffold-containing products has been accomplished via free-radical C–N bond coupling or sequential cyclopropane ring-opening followed by heteroatom-mediated 1,5-dicarbonyl cyclization.