Ethylene derivatives decarbonylation

The photochemistry of cyclobutanones differs from that of less strained larger cycloalkanones. Fragmentation to ethylene and ketene (derivatives), decarbonylation and rearrangement to oxacarbenes predominate here. The oxacarbene formation, which occurs with retention of the configuration of the... 

Ghlorotris(triphenylphosphine) rhodium causes the decarbonylation of aroyl to aryl chlorides in excellent yields at relatively low temp. At higher temp., only catalytic amounts of the reagent are required. — E A mixture of henzoyl chloride, the above Rh-compound, and benzene heated 15 min. at 80° chlorobenzene. Y almost 100%. F. e. s. J. Blum, Tetrah. Let. 1966, 1605 chlorides from sulfonic acid chlorides s. Tetrah. Let. 1966, 3041 also ethylene derivatives from carboxylic acid chlorides s. J. Tsuji and K. Ohno, Am. Soc. 88, 3452 (1966) Tetrah. Let. 1966, 4713. 

Klemm (16) and Lee and coworkers (17) have examined the effect of various solvents on the photochemistry of cyclobutanone. By monitoring the quantum yields for formation of ethylene (B-cleavage product) and cyclopropane (decarbonylation product) in different solvents, they were able to demonstrate a significant reduction in the quantum yields for product formation in methanol as compared to other hydrocarbon solvents. Whereas the quantum yield of ethylene formation was found to be essentially solvent insensitive, that for cyclopropane formation was found to be somewhat solvent sensitive. This suggested that B-cleavage and decarbonylation do not result from the same immediate precursor. Since ring-expansion derivatives have not been isolated from photolyses carried out in saturated hydrocarbon solvents, the importance of this process under these conditions remains to be determined. Irradiation of cyclobutanone in the presence of 1,3-penta-diene (17,59) or 1,3-cyclohexadiene (16) did not appear to affect the quantum yields for ketone disappearance or product appearance. 

This reaction occurs readily under pressure at room temperature and has been successfully accomplished for tetrafluoroethylene, chlorotrifluoro-ethylene, and l,l-dichloro-2,2-difluoroethylene. HCF2CF2Mn(CO)s has also been synthesized by the decarbonylation of the acyl derivative HCF2 CF2COMn(CO)s 15J) Reaction of HMn(CO)5 with hexafluorobutyne-2 gives CF3CH=C(CF3)Mn(CO)s. 

The chemical selectivity in the photocycloaddition of ethylene (78) to benzene (77) was discussed. Diels-Alder cycloadducts of 1,2-benzo-quinones (82) with benzynes generated from (83) were converted to naphthalene derivatives (85) by photoinduced double decarbonylation of (84) (Scheme 22). ... 

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