I2-Promoted site-selective C–C bond cleavage of aryl methyl ketones as C1 synthons for constructing 5-acyl-1H-pyrazolo[3,4-b]pyridines

Abstract

A novel iodine promoted [1 + 3 + 2] cleavage cyclization reaction for the synthesis of 1H-pyrazolo[3,4-b]pyridines from aryl methyl ketones, 5-aminopyrazoles and enaminones has been established. This transition metal-free catalysis method has simple reaction conditions and good substrate compatibility, and has been demonstrated in the transformation of alkyl and natural molecule-derived enaminones. Mechanistic studies showed that two cyclization pathways affording different key intermediates were involved, but affording the same target product after site-selective cleavage of the unstrained C–C bond of the acyl group.