1,3-Dipolar cycloaddition of chalcones and arylidene-1,3-dicarbonyls with diazosulfone for the regioselective synthesis of functionalized pyrazoles and pyrazolines

A convenient method for the synthesis of 3-acylpyrazoIes and pyrazole-3-carboxylates using diazosulfone as a reactive 1,3-dipole and a diazomethane equivalent is reported here. Chalcones, arylidenemalonates and other arylidene-1,3-dicarbonyls performed well as the dipolarophiles in the reaction with the diazosulfone which took place under simple base mediated conditions (CS2CO3 or NaOEt in EtOH). In few cases, the initial cycloadducts, the intermediate pyrazoline derivatives, could also be isolated and characterized. The pyrazoline derivatives undergo an alkoxide mediated 1,4-elimination, viz. decarboxylation-detosylation to afford the pyrazole derivatives. (C) 2018 Elsevier Ltd. All rights reserved

Regioselective synthesis of pyrazole and pyridazine esters from chalcones and alpha-diazo-beta-ketoesters

Base mediated deacylation of alpha-diazo-beta-ketoester generates diazoester anion, a reactive 1,3-dipole, which undergoes [3+2] annulation with chalcones to afford pyrazole ketoesters. Under similar conditions, the 1,3-dipole takes part in a [3+3] annulation with chalcone epoxides to provide pyridazine esters. Despite moderate yields, high regioselectivity, mild conditions, and functional group diversity are the salient features of this novel methodology. (C) 2016 Elsevier Ltd. All rights reserved