This presentation will describe the development of an efficient and scalable route to 4 as shown in the scheme below. Highlights of this talk include the development of (1) telescoped difluoromethylation and Claisen condensation to afford enolate 2, (2) one-pot nitrosation of 2 followed by condensation with hydrazine to form nitrosopyrazole 3, and (3) subsequent reduction of the nitroso group using sodium borohydride and catalytic copper(I) chloride to produce target compound 4. The optimized process delivered highly pure 4 (99.9 A% by HPLC) in overall 28% yield over 5 steps.

Development of a novel protecting-group-free synthesis of a 3-aryl-4-aminopyrazole at kilogram scale

ACS Fall 2021

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