Reaction of oxazoles. Formation of abnormal Diels–Alder adducts of 5-methoxy-4-(p-nitrophenyl)oxazoles with tetracyanoethylene, and X-ray crystal structure of one of the products
The reaction of 2-alkyl or -aryl substituted 5-methoxy-4-(p-nitrophenyl)oxazoles (1) with tetracyanoethylene gave 2-substituted methyl 3,3,4,4-tetracyano-5-(p-nitrophenyl)-4,5-dihydro-3H-pyrrole-5-carboxylates (2) as formal [3 + 2] cycloadducts; these were produced via a zwitterionic mechanism involving oxazole ring opening.
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) A, and Z = 16
2-烷基-或2-芳基-取代的5-甲氧基-4-(对硝基苯基)恶唑与四氰基乙烯反应得到5-取代的3,3,4,4-四氰基-2-(对硝基苯基)甲酯)-3,4-二氢-2H-吡咯-2-羧酸作为正式的[3 + 2]环加合物通过恶唑开环。基于溶剂对反应的影响提出了两性离子机理。2-异丙基取代产物的分子结构通过X-射线晶体学确定。环加合物的晶体是正交的,空间群 Pcab 的晶胞尺寸为 a = 17.998 (2)、b = 27.188 (6)、c = 15.833 (3) A 和 Z = 16,其中包含两个晶体学独立的分子。对于 4629 次观察到的反射,最终的 R 值为 0.070。