On the reaction of 3,5-dimethylpyrazole with acetylenic esters

Abstract

Addition of 3,5-dimethylpyrazole (1) to the triple bond of dimethyl acetylenedicarboxylate (DMAD) is highly stereoselective in aprotic solvents, yielding almost exclusively the supra-addition product (2-E). In protic solvents, the reaction is less stereoselective, giving as the major product the antara-addition adduct (2-Z). Addition of (1) to the olefinic esters (2-E) and (2-Z) yields the diastereoisomers (3) and (4). being the supra-addition product predominant in both protic and aprotic solvents.