Highly stereoselective dearomative [3 + 2] cycloadditon of cyclic pyridinium ylides to access spiro-indolizidine scaffolds

Abstract

Spiro-indolizidine scaffolds are attractive structural motifs in natural alkaloids and pharmaceuticals. Herein, we described a highly stereoselective dearomative [3 + 2] cycloaddition between cyclic pyridinium ylides and nitroolefins. A novel type of cyclic pyridinium salts, which bear an electron-withdrawing group on the pyridine ring, have been developed as the ylide precusors and successfully applied in this cyclization. This protocol features a series of advantages inculding broad substrate scope, mild conditions, short reaction time and high level of yield and stereoselectivity, thus providing a concise and efficient method for the construction of spiro-indolizidine scaffolds.