REACTIONS OF 2,7-DIMETHYLOXEPIN WITH DIMETHYLDIOXIRANE AND METHYL(TRIFLUOROMETHYL)DIOXIRANE - RING-OPENING AND PROBABLE OBSERVATION OF THE INTERMEDIATE 2,3-EPOXYOXEPIN

The reactions of dimethyldioxirane (7) and methyl(trifluoromethyl)diox irane (8) with 2,7-(4) both yielded Z,Z-3,5-octadiene 2,7-dione (Z,Z-6 ) as their initial stable products. This is the first published reacti on of a dioxirane with an isolable pure oxepin. Reaction of the diened ione Z,Z-6 with one mole equivalent of either 7 or 8 yielded the corre sponding monoepoxide. Treatment of this monoepoxide with another equiv alent of 8 yielded the corresponding di-epoxides (probably meso and R, S). The suggestion of Murray and co-workers that dioxiranes may model some of the reactivities of monooxygenases and their rapid epoxidation s of alkenes under neutral conditions at low temperatures suggested th eir use. Our initial attempts to directly observe the putative interme diate ,3-dimethyl-2,8-dioxabicyclo-[5.1.0]octa-3,5-diene [''2,7-dimeth yl-2,3-oxepin'' (2)] at low temperatures (ca. -60 degrees C) yielded p romising but inconclusive results when dimethyldioxirane (7) was emplo yed. The epoxidation reaction was sufficiently slow that it only occur red measurably above -30 degrees C, a temperature at which thermal rin g opening to the dienedione is competitive. Initial reactions with the much more reactive methyl trifluoromethyl dioxirane (8) led to immedi ate ring opening at temperatures as low as -80 degrees C. Since 8 is k nown to isomerize to methyl trifluoroacetate and since water is presen t, a trace of trifluoroacetic acid was suspected of catalyzing the rin g opening of 2, Thus, inclusion of either suspended Na2HPO4 or miscibl e 2,6-di-t-butylpyridine at -80 degrees C yielded an intermediate stab le up to ca. 0 degrees C, which is likely to be the 2,3-epoxyoxepin 2.