Steric redirection of alkylation in 1H-pyrazole-3-carboxylate esters

Abstract The alkylation of ethyl 1 H -pyrazole-3-carboxylate with a variety of alkylating agents in the presence of K 2 CO 3 was found to largely favor the formation of ethyl 1-substituted pyrazole-3-carboxylates. The alkylation could be sterically redirected by the use of a triphenylsilyl group (ethyl 3-(triphenylsilyl)-1 H -pyrazole-5-carboxylate) to provide synthetically useful yields of ethyl 1-substituted-3-(triphenylsilyl)-1 H -pyrazole-5-carboxylates. The triphenylsilyl group could be removed with Bu 4 NF. Other triorganosilyl groups (TMS, TES, TBDMS) failed to provide significant redirection, while TIPS proved refractory to protodesilylation.