Independent of the nature of alkyne substitution, hydrazides of 4-arylethynyl-5-carboxylic acid annealed at the pyrazole scaffold undergo a regioselective base-catalyzed 6-endo-dig cyclization with the formation of pyrazolo [3,4-c]pyridine-7-ones. This behavior contrasts the observation of selective 5-exo closures in the analogous benzannelated systems and illustrates selective destabilization of the reaction path leading to the formation of a smaller ring. Computational analysis also reveals an important role of prototropic equilibria in rendering the overall cyclization feasible in the strained heterocyclic systems. The switch to the formation of a larger cycle suggests that strategic incorporation of strain can be used as a tool for the efficient control of regiochemistry of nucleophilic cyclizations.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry