CYCLOADDITIONS OF 6H-1,3,4-OXADIAZIN-6-ONES(4,5-DIAZA-ALPHA-PYRONES) .15. REACTIONS OF 6H-1,3,4-OXADIAZIN-6-ONES WITH NORBORNADIENE - A NEWROUTE TO 3,6-DISUBSTITUTED ALPHA-PYRONES

Upon reaction with norbornadiene, ten disubstituted 1,3,4-oxadiazin-6- ones 1 were converted into 3,6-disubstituted alpha-pyrones 6. For this purpose, solutions of the substrates were treated with boron trifluor ide-ether or trifluoroacetic acid. The smooth formation of 6 was also observed when a gamma-oxo ketene, initially generated by heating a sol ution of the substrates in the absence of boron trifluoride-ether, was allowed to react with the Lewis acid. Without use of an acid, only 6f could be obtained free from further compounds, whereas in the other c ases enol lactones and 1:2 products of the types 8 and 7 were formed a dditionally. Oxadiazinone 1j gave enol lactone 10 in the noncatalysed reaction.