INTRAMOLECULAR REACTIONS OF NITROOLEFIN-BETA-DIKETONE MICHAEL ADDUCTS - FORMATION OF 3-OXO-2,3-DIHYDRO-4H-1,2-BENZOXAZINE AND 4(5H)-BENZOFURANONE DERIVATIVES

1,3-Cyclohexanedione (3) undergoes Michael addition to β-nitrostyrene in methanolic sodium methoxide to form 3,5-dioxo-4-phenyl-2,3,5,6,7,8-hexahydro-4H-1,2-benzoxazine (5a). With 1-nitropropene 3 forms the corresponding 4-methyl derivative (5b). These substances had been designated as 4-substituted 5-oxo-5,6,7,8-tetrahydro-4H-1,2-benzoxazine-2-oxides (4a, b) by other workers. 5,5-Dimethyl-1,3-cyclohexanedione (9) under similar conditions adds to β-nitrostyrene to form 2-(2-nitro-1-phenylethyl)-5,5-dimethyl-1,3-cyclohexanedione (10); 9 and 2-nitro-1-phenylpropene yield 3-phenyl-2,6,6-trimethyl-6,7-dihydro-4(5H)-benzofuranone (12). In other reactions various β-diketones add to nitroolefins to yield normal Michael adducts, 4-nitro-1-alkanones (1, 2). Molecular ion fragmentation patterns and mechanisms of formation of the abnormal addition products are presented and their rationalizations discussed. © 1969.