Utilization of hypervalent iodine in organic synthesis: A novel and facile two-step protocol for the synthesis of new derivatives of 1H-imidazo[1,2-b] pyrazole by the cyclocondensation involving α-tosyloxyacetophenones

Abstract

A series of new 2-aryl-7-cyano/ethoxycarbonyl-6-methylthio-1H-imidazo[1,2- e]pyrazoles (5) have been synthesized in moderate to good yields, via a two-step cyclocondensation procedure of 5-amino-4-cyano/ethoxycarbonyl-3-methylthio-1H- pyrazole (1) and α-bromoacetophenones (3) or α-tosyloxyacetophenones (2), which were prepared by the reactions of acetophenones with [hydroxy(tosyloxy)iodo]benzene (HTIB). The intermediates, 5-amino-1- (aroylmethyl)-4- cyano/ethoxycarbonyl-3-methylthio-1H-pyrazoles (4), have been isolated, serving as evidence for the regioselectivity. When utilizing α-tosyloxy-acetophenones, the reactions were more eco-friendly, the reaction time was significantly reduced and the synthetic procedure was more convenient and easier to manipulate. Surprisingly, using potassium carbonate to displace sodium carbonate in the synthesis of 4, in the case of 1 (R = CN), two novel cyclocondensation products have been isolated and fully characterized, followed by the proposal of a plausible mechanism.