Development of a Scalable Process for the Insecticidal Candidate Tyclopyrazoflor. Part 1. Evaluation of [3 + 2] Cyclization Strategies to 3-(3-Chloro-1<i>H</i>-pyrazol-1-yl)pyridine

Abstract

The evaluation of [3 + 2] cyclization strategies to prepare a key intermediate, 3-(3-chloro-1H-pyrazol-1-yl)pyridine, for the insecticidal candidate tyclopyrazoflor (1) is described. Among the validated strategies, the route involving [3 + 2] cyclization of 3-hydrazinopyridine·2HCl with methyl acrylate was selected for further optimization. This route provided ready access to 3-(3-chloro-1H-pyrazol-1-yl)pyridine in three steps via cyclization, chlorination, and oxidation. Further functionalization of 3-(3-chloro-1H-pyrazol-1-yl)pyridine via nitration, reduction, and amide formation with 3-((3,3,3-trifluoropropyl)thio)propanoic acid followed by ethylation rendered 1 in a total of seven steps.