Base-Promoted Regioselective Annulation of Pyridinium Ylides and Bromoalkynes for the Chemodivergent Synthesis of Indolizines.

A base-promoted regioselective formal [3 + 2] annulation of pyridinium ylides with bromoalkynes is reported, producing a series of substituent-diverse indolizines in generally good yields. A mild KCO-promoted three-component formal [3 + 2] cyclization of pyridinium ylides and bromoalkynes at a 2:1 molar ratio delivered C2-acylmethylated indolizines, whereas C2-brominated indolizines were generated starting from pyridinium ylides bearing strong electron-withdrawing groups at the pyridinium unit by using 2,2,6,6-tetramethyl-1-piperidinyloxy as a dehydrogenating reagent. The current synthetic methodology offers a controllable and modular approach to access indolizines with different substitution patterns, featuring a wide substrate scope, good functional group compatibility, and complete regioselectivity without the demand of any transition-metal catalysts.