CYCLOPROPANONES FROM THE OXIDATION OF HINDERED [4]-CUMULENES AND [5]-CUMULENES WITH EPOXIDATION REAGENTS

The oxidation of tert-butyl-substituted [51-cumulene 4 with epoxidizing agents was shown to give sequentially formed conjugated cyclopropanones 15 and 11. The more stable cyclopropanone 11 was isolated and shown to add carboxylic acids to give allenyl ketones of type 5 and to thermally and photochemically lose carbon monoxide to give the [4]-cumulene 6. The oxidation of 4 with peracids leads directly to allenyl ketones 5 as isolated products. Hydrolysis of 5a produced the novel furofuran 9. The oxidation of the hindered [4]-cumulene 6 gave conjugated cyclopropanone 19, which underwent chemical transformations similar to those of 11. These oxidations are rationalized in terms of hypothetical cumulene oxide intermediates that rapidly isomerize to the observed cyclopropanones.