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

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.

Automated summary

A novel iodine promoted reaction was developed for the synthesis of 1H-pyrazolo[3,4-b]pyridines. This transition metal-free catalysis method has simple reaction conditions and good substrate compatibility and has been demonstrated in the transformation of various enaminones. Mechanistic studies revealed involvement of two different cyclization pathways leading to the same target product through selective cleavage of the acyl group.