Cyclopropanones decarbonylation reactions

Neither 1,3-shifts nor 1,5-shifts have been observed for these compounds although such products could conceivably be undetected intermediates in the decarbonylation reaction." The cyclopentenones or cyclopropanones which would arise from these shifts are, of course, photo-chemically labile and are potential intermediates prior to decarbonylation or they could be blind alley , thermally reversible, intermediates. However, no evidence for their formation has been found. 

Studies on the photochemistry of tetramethylcyclopropanone 17 have revealed efficient a-cleavage and decarbonylation reactions to give 2,3-dimethyl-2-butene 19 as the only product (Scheme 7). Interestingly, cyclopropanone 17 is prepared by an efficient decarbonylation of 2,2,4,4-tetramethylcyclobu-tanedione 16. Cyclopropanones, in general, are highly reactive compounds that can thermally equilibrate with oxyallyl, the open-shell 1,3-diyl 18. While cyclopropanones are highly susceptible to nucleophilic attack to form hydrates and hemiketals, oxyallyl was shown to react rapidly with oxygen and furan. 

Carbon monoxide may be eliminated from cyclopropanones either by thermal or photochemical processes (Table 12). In fact, decarbonylation is sometimes an undesirable side reaction in the synthesis of cyclopropanones. For example, the reaction of dimethylketene and ethyl diazoacetate affords carbon monoxide and ethyl acrylate 115 rather than the desired ketone. 2°)... 

Although 1-methylcyclopropene reacted with bis(trifluoromethyI)ketene in nonpolar solvents by an ene-type reaction, in polar solvents, such as acetonitrile, a fluorinated diene 2 was produced, apparently by electrophilic ring opening followed by decarbonylation of an intermediate cyclopropanone. ... 

Of the theoretical studies that have appeared, the MINDO/3 semiempirical MO treatment, developed by Dewar, has been expanded to unrestricted open-shell treatment by Bischof and applied to a series of radicals including the cyclopropyl species. A MINDO/3 study of the thermal decarbonylation of cyclopropanone by Shevlin and co-workers predicts the non-linear cheletropic mode of the reaction (A/f 41 kcalmol" ) to be favoured by ca. 45kcalmol over the linear mode, in... 

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