Cyclopropanones allene oxide/cyclopropanone rearrangement

An unusual example of the allene oxide-cyclopropanone isomerization is found in the results of singlet oxygen oxygenation of 6,6-disubstituted fulvenes (18) The production of 3,3-disubstituted 2(3//)-oxepinones (20) in this process can be rationalized by the sequence of transformations outlined in equation 8. The initially formed endoperoxide (19) undergoes a well-precedented rearrangement to the epoxy ketone (19a) which contains the allene oxide residue. Rearrangement to the cyclopropanone form is... 

The rearrangements of 3-methylbut-l-ene oxides" and l,2-epoxybut-3-ene on lithium phosphate have been studied, and a detailed theoretical study of the rearrangement of allene oxide (342) to cyclopropanone (344), which shows that the transformation proceeds via an intermediate oxyallyl (343), has been presented. It has been shown that aldehydes, ketones, and cyclic ethers are all produced... 

In connection with the above discussion, formation of 3,3-disubsti-tuted 2 (3 H)-oxepinones (73) in the dye-sensitized photooxygenation of 6,6-disubstituted fulvenes is of special interest. 57>58> The reaction may be pictured in terms of an allene oxide intermediate which, as shown in Scheme 11, isomerizes to a cyclopropanone, followed by intramolecular rearrangement. 

An interesting route to the cyclopropanone system involves the rearrangement of allene oxides, usually generated by the epoxidation of allenes. Thus, 1,3-di-t-butylallene oxide (11) may be prepared by the reaction of 1,3-di-t-butylallene with m-chloroperbenzoic acid. Heating 11 to 100 °C leads to isomerization, forming truns-2,3-di-t-butylcyclopropanone (10) (Scheme 4) Similarly, 1,1-di-t-butylallene (15) yields 2,2-di-t-butylcyclopropanone with peracetic acid (equation 7) ... 

Cyclopropanones are involved in the Favorski rearrangement, and there has been considerable interest in the allene oxide-cyclopropanone system. Estimation of the relative energies of the various structures involved (Scheme 62) is notoriously... 

The details of the Favorskii rearrangement continue to attract attention and cyclopropanone intermediates in the peracid epoxidation of allenes have been noted. The fluoride-ion-promoted elimination of chlorotrimethylsilane from (375) leads to the allene oxide (376) which undergoes regiospecific ring-opening with nucleophiles. However, rearrangement of (376) to cyclopropanone (377) only occurs prior to nucleophilic capture when C-1 carries an aryl substituent (Scheme 45). ... 

Cyclic allenes have also been subjected to DMD oxidations (Scheme 25). Treatment of 1,2-cyclononadiene (126) with DMD affords the corresponding stable dioxide (127) exclusively <9lJOCH53> on the other hand, MCPBA oxidation of (128) leads to an unstable monooxide (129) which gives (130) via rearrangement to the corresponding cyclopropanone and CO loss <9iJOC6372>. 

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