FORMATION AND REARRANGEMENT OF A 2,2-DIMETHOXYOXIRANE FROM DIMETHOXYCARBENE AND FLUORENONE

Thermolysis of dimethoxy-5,5-dimethyl-Delta(3)-1,3,4-oxadiazoline (1) at 110 degrees C in the presence of 9-fluorenone (3) yielded 9-(dimeth oxymethylene)fluorene oxide (4) and methyl 9-methoxyfluorene-9-carboxy late (5), which are the result of the addition of dimethoxycarbene (2) to the carbonyl group of 9-fluorenone. While the epoxide 4 is most li kely generated from direct [2 + 1] cycloaddition, the ester 5 is the r esult of subsequent rearrangement of the oxirane. Thermolysis of the t rideuterio-methoxy oxadiazoline 1-d(3) in the presence of fluorenone s howed that 5 is not formed by an intermolecular process because eviden ce for crossover of the label in the product 5 was not found. The rear rangement of 4 to 5 does not proceed by ring opening and intramolecula r methyl transfer either but, instead, by ring opening and intramolecu lar methoxy transfer. Thus, as predicted by the Baldwin rules, the str ained intramolecular 5-endo-tet methyl transfer is avoided in favor of another process.