Z and E Isomers of 1:1 Michael-Type Adducts from 2-Addition of Pyrroles to Dimethyl Acetylenedicarboxylate. Stereochemistry and Spectra

The 1:1 Michael-type adducts derived from reaction of pyrroles (1) having an open 2-posltlon with dimethyl acetylenedicarboxylate (DMAD) In the presence of a source of active hydrogen (usually provided by their own NH groups, If present, or by sufficient acetic acid) can exist as Z(3) and E (4) stereoisomers. Both 3 and 4 were obtained from the following pyrroles, with the exceptions noted: pyrrole (1a), 1-methyl-(1b), 2-methyl- (1c), 1,2-dlmethyl- (1d), 1,3-dlmethyl- (1e, gave dimethyl (Z)-1,3-dlmethyL2-pyrrolyl-2-butenedloate (3e) but no 4e), 2,4-dimethyl- (1f), 1-butyl- (11), 1-(1-methylpropyl)- (1J), l-(dlmethylethyl)- (1k), 1-benzyl- (11), 1-phenyl- (1m), 1-(4-methoxyphenyl)- (1n), 1-(4-bromophenyl)- (1o), 1 -(2-methylphenyI)- (1p), 1-(2,6-dlmethylphenyl)- (1q and 3q only), 1-(4-nltrophenyl)- (1r, no 3r or 4r), 1-acetyl- (1s, 4s only). The stereochemistry has been determined from the NMR, UV, and IR spectra. Extensive spectral data, Including mass spectra, have been tabulated and Interpreted for 15 adducts of type 3 and 14 of type 4.