CYCLOADDITIONS OF 6H-1,3,4-OXADIAZIN-6-ON ES (4,5-DIAZA-ALPHA-PYRONES) .14. REACTIONS OF 6H-1,3,4-OXADIAZIN-6-ONES WITH NORBORNENE - NONCATALYZED AND CATALYZED BY TRIFLUOROACETIC-ACID

In 11 out of 13 non-catalysed reactions of oxadiazinones 1 with norbor nene, gamma-oxoketenes 4 were observed and could be isolated in three cases (4b,d,m). Except for 4m, all gamma-oxoketenes isomerised to enol lactones of type 5 on thermolysis. However, 4b furnished the cyclobute ne derivative 10 as the major product. No gamma-oxoketenes were detect ed in the reactions of Ik and 11, which gave rise to the formation of 5k and the enollactone 19, respectively. The latter was converted into 51 on treatment with trifluoroacetic acid (TFA). Four oxadiazinones 1 were allowed to react with norbornene in the presence of TFA. Three o f them (1a,b,l) afforded mixtures of enollactones of type 5 and their diastereomers 12. Heating of 4 in the presence of norbornene led to th e formation of the symmetrical delta-lactones 6. This process was obse rved to be efficient only where the conversion 4 --> 5 is slow (4b) or inoperative (4m). In five cases, the treatment of the components with boron trifluoride etherate proved to be a useful preparative alternat ive (6a,d,g,h,m). On treatment of 4a with methanol, the pseudoester 7a was formed, whereas 4b gave mixtures of 7b and the esters 8b and 15. Hydrogen chloride converted 4b into the pseudochloride 14, which furni shed pseudoester 7b on methanolysis. Reaction of 4b,m with formic acid gave rise to pseudoanhydrides of type 13. From 4b and TFA a mixture o f the enollactones 5b and 12b was obtained. Boron trifluoride etherate transformed 4i to enollactone 12i; analogously, 12m resulted on treat ment of 4m with trifluoromethanesulfonic acid.