An efficient one-pot synthesis of aryl-substituted 1-(thiazol-2-yl)-1H- pyrazole-3-carboxylates via a hantzsch synthesis-knorr reaction sequence

The treatment of α-bromoalkyl aryl ketones and 2-(propan-2-ylidene) hydrazine carbothioamide afforded 4-aryl-2-(2-(propan-2-ylidene)hydrazinyl) thiazoles via a Hantzsch-thiazole synthesis, which reacted with 4-aryl-2,4-diketoesters via a sequential Knorr-pyrazole reaction to deliver a variety of aryl-substituted ethyl 1-(thiazol-2-yl)-1H-pyrazole-3-carboxylates in a one-pot fashion with moderate to high yields. The key intermediates 4-aryl-2,4-diketoesters, existing as its enolic lithium salt, were synthesized in situ by a high-yield tert-BuOLi-mediated Claisen condensation of alkylphenones and diethyl oxalate. This class of elegant molecule comprises aryl groups on the two different heterocyclic cores, and the configurations of two representative molecules were determined by single crystal X-ray crystallography. The treatment of α-bromoalkyl aryl ketones and 2-(propan-2-ylidene)hydrazine carbothioamide afforded 4-aryl-2-(2-(propan-2- ylidene)hydrazinyl)thiazoles via a Hantzsch-thiazole synthesis, which reacted with 4-aryl-2,4-diketoesters via a sequential Knorr-pyrazole reaction to deliver a variety of aryl-substituted ethyl 1-(thiazol-2-yl)-1H-pyrazole-3-carboxylates in a one-pot fashion with moderate to high yields.