CYCLOADDITIONS OF 6H-1,3,4-OXADIAZIN-6-ON ES (4,5-DIAZA-ALPHA-PYRONES) .13. DIELS-ALDER REACTIONS WITH 6H-1,3,4-OXADIAZIN-6-ONES AS DIENOPHILE

2,5-Diphenyl-1,3,4-oxadiazin-6-one (1b) reacted as dienophile with 2,3 -dimethyl-1,3-butadiene to afford the pyridooxadiazinone 5. Analogousl y, the oxadiazinoisoquinolines 7 c- e were formed on treatment of 2-(4 -nitrophenyl)- (1 c), 2-(4-tolyl)- (1 d), and 2-(4-bromophenyl)-5-phen yloxadiazinone (1 e) with 1,2-bis(methylene)cyclohexane (6). In contra st, the methyl oxophenyloxadiazinecarboxylate 1 a gave a low yield of the cyclopentenone derivative 8 and 7 a in the ratio 2.3: 1.0. A third type of product, i.e. the cyclobutanone derivative 9, resulted on exp osure of the anisyl(isopropyl)oxadiazinone 1 f to 6. The oxadiazinones 1 d, e, f have been prepared for the first time. X-ray structure anal yses established the identity of the compounds 7 d and 9.