Abnormal Diels-Alder Reaction of 5-Alkoxyoxazoles with Tetracyanoethylene and X-Ray Crystal Structure of an Adduct

Article abstract of DOI:10.1246/bcsj.65.1771

The reaction of 2-alkyl- or 2-aryl-substituted 5-methoxy-4-(p-nitrophenyl)oxazoles with tetracyanoethylene gave methyl esters of 5-substituted 3,3,4,4-tetracyano-2-(p-nitrophenyl)-3,4-dihydro-2H-pyrrole-2-carboxylic acid as formal <3+2> cycloadducts through oxazole ring opening.Zwitterionic mechanisms were proposed on the basis of the solvent effect on the reaction.The molecular structure of 2-isopropyl-substituted product was determined by means of X-ray crystallography.Crystals of the cycloadduct are orthorhombic with space group Pcab having unit-cell dimensions of a=17.998(2), b=27.188(6), c=15.833(3) Angstroem, and Z=16, which contains two crystallographically independent molecules.The final R value is 0.070 for 4629 observed reflections.