Theoretical study of the solvent effects on the mechanisms of addition of dimethyl acetylenedicarboxylate to 1-methyl-2-vinylpyrrole

The molecular mechanisms for the addition of dimethyl acetylenedicarboxylate to 1-methyl-2-vinylpyrrole have been investigated using PM3 semiempirical procedure and ab initio method at HF/3-21G basis set level both in vacuo and CHCl3 solvent. Two competitive mechanisms can exist in vacuo: an asynchronous concerted and a stepwise mechanism. The solvent reaction field was found to have a noticeable effect on the reaction pathways and, in CHCl3 solvent, the two steps mechanism is preferred, suggesting that the solvent is capable of modulating the two possible molecular mechanisms. Copyright (C) 1996 Elsevier Science Ltd