Copper-Catalyzed Formal [4+1] Annulation toward Diverse Trifunctionalized Indolizines from Pyridinium 1,4-Zwitterionic Thiolates and Diazos

Pyridinium 1,4-zwitterionic thiolates were regarded aspowerfuland versatile building blocks to prepare nitrogen- and sulfur-containingheterocycles. Herein, we reported a copper-catalyzed formal [4 + 1]annulation of pyridinium 1,4-zwitterionic thiolates and diazo compoundswithout any additives to access a library of trifunctionalized indolizinesin good yields. Besides, isoquinolinium 1,4-zwitterionic thiolatesand imidazolium 1,4-zwitterionic thiolates were also applied to thisformal [4 + 1] annulation reaction. Of particular note is that variousfunctional groups such as -CO2R, -CO2NR2, -CF3, -CN, and -(O)-P-(OR)(2) could be easily introduced into cycloaddition products indolizinesby this strategy.