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

Abstract

Comprehensive Summary Two 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).

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