‘One-pot’ synthesis of 4-substituted 1,5-diaryl-1H-pyrazole-3-carboxylates via lithium tert-butoxide-mediated sterically hindered Claisen condensation and Knorr reaction

A concise ‘one-pot’ synthesis of a variety of 4-substituted 1,5-diaryl-1H-pyrazole-3-carboxylates has been developed in moderate to good yields with excellent regioselectivity. Less cost lithium tert-butoxide has been identified as a base for sterically hindered Claisen condensation to efficiently generate the labile 3-substituted 4-aryl-2,4-diketoesters. Furthermore, extensive studies lead to a ‘one-pot’ process by combination of the Claisen condensation and the Knorr reaction for the synthesis of highly valuable 4-substituted 1,5-diaryl-1H-pyrazole-3-carboxylates.