Reactions of dimethyl acetylenedicarboxylate-II: reaction with phenacylamines

Abstract

Dimethyl acetylenedicarboxylate reacts with phenacylanilines to give simple 1:1 adducts, arising out of a Michael type of addition. NMR studies of these adducts reveal that they have the maleate geometry. Chemical shift non-equivalence of the diastereotopic phenacyl methylene protons in some of these adducts has been observed and this is attributed to the restricted rotation about the aryl nitrogen bond. Under the influence of an acid catalyst and in some cases without any catalyst, the Michael adducts are cyclyzed to dimethyl 1-aryl-4-phenylpyrrole-2,3-dicarboxylates. The Michael adducts, under basic conditions, undergo a Dieckmann-type of cyclization to give methyl 1-aryl-5-benzoyl-4-hydroxypyrrole-2-carboxylates.