Divergent Assembly of Functionalized Pyrazolo[1,5‐a]pyridine Derivatives via [3+2] Cyclization of N‐Aminopyridinium Salts with Various Unsaturated Hydrocarbons

Abstract

Comprehensive SummaryTwo reaction modes for metal‐free [3 + 2] cyclization of N‐aminopyridinium derivatives with β‐alkoxyvinyl trifluoromethylketones have been described through selective C—O or C—O/C—C bond cleavage. This strategy can also be extended to the [3 + 2] cyclization of N‐aminopyridinium derivatives with enaminones and bromoalkynes. A broad range of N‐aminopyridinium, N‐aminoquinolinium, and N‐aminoisoquinolinium salts are well tolerated, enabling the divergent synthesis of trifluoroacylated, non‐substituted, acylated, and brominated pyrazolo[1,5‐a]pyridine derivatives (62 examples).