2- cyclopentanone cyclobutanone Transformation

If the 3-position is a tertiary, rather than a quaternary, stereocenter, Rh(I)/Tol-BINAP effects an intriguing parallel kinetic resolution - thus, one enantiomer of the substrate selectively undergoes hydroacylation to generate a cyclobutanone, while the other enantiomer is transformed into a cyclopentanone (Eq. 22) [24]. This observation is quite interesting, given the limited number of examples of parallel kinetic resolutions, particularly catalytic processes that involve carbon-carbon bond formation, and catalytic methods for the construction of cyclobutanones. 

Further reaction of Aese species with carbonyl compounds and hydrolysis of the resulting alkoxide leads to p-oxidoalkyl selenoxides which have been transformed into allyl alcohols on thermal decomposition (Schemes 51, 52 and 54, entry a see Section 2.6.4.4) or reduced to p-hydroxyalkyl selenides or to alkenes (Scheme 53). P-Oxidoalkyl selenoxides derived from cyclobutanones react in a different way since Aey rearrange to cyclopentanones upon heating (Scheme 54, b. Schemes 120 and 121 and Section 2.6.4.5.3). 

It is well known that cyclobutanones can be transformed to cyclopentane derivatives directly with diazomethane or indirectly via the cyanohydrins218> 228), or with tris(phe-nylthio)methyllithium 219,220), but in many cases the reactions are not regioselective and lead to different regioisomers. Cyclobutyl ketones lead to substituted cyclopentanones in highly acidic media 226 and the synthesis of cyclopentanones from methylene-cyclobutanes requires a palladium catalyst 227). 

The Norrish Type I reaction usually leads to decarbonylation. This is the case with dicyclopropyl ketone on irradiation at 193 nm. Decarbonylation, however, is a second step and this is preceded by ring opening of the cyclopropyl moieties to diallyl ketone. Calculations have shown that decarbonylation of cyclobutanone occurs from the nji triplet state. The resultant triplet trimethylene biradical undergoes ISC to the ground state before formation of cyclopropane. On the other hand, the cycloelimination reaction to yield ketene and ethene arises from the singlet excited state.Irradiation of cyclopentanone in aqueous and frozen aqueous solutions has been examined and the influence of applied magnetic fields assessed. Photodecarbonylation in the crystalline phase of the ketone (3) at 310 nm takes place stereospecifically with the formation of the cyclopentane derivative (4). The latter can be readily transformed into racemic herbertenolide (5). ... 

A similar transformation has been developed for selenium. When cyclobutanone 32 is treated with a lithiated alkyl selenoxide, cyclopentanone 33 is produced. ... 

The rhodium-catalyzed successive C-C/C-O bond cleavage reaction of a cyclobutanone 77 containing a phenoxymethyl side chain was affected by the employed bidentate diphosphine ligand (Scheme 3.44) [53]. In the presence of [Rh(nbd)(dppe)]PF 5 (nbd, norborna-2,5-diene dppe, l,2-bis(diphenylphos-phino)ethane) (5 mol%) and diphenylacetylene (20 mol%), cyclobutanone 77 was transformed into the alkenoic ester 78 in 88% yield via C-C bond cleavage, P-oxygen elimination, and reductive elimination. In contrast, the [Rh(nbd)(dppp)]PFg-catalyzed (dppp, l,3-bis(diphenylphosphino)propane) reaction afforded cyclopentanone 79 in 81% yield through a rhodacyclohexanone species that was formed by 6-endo cyclization. The reaction of the cyclobutanone 77 catalyzed by [Rh(nbd)(dppb)]PFg (dppb, l,4-bis(diphenylphosphino)butane) led to exclusive formation of cyclopropane 80 via decarbonylation. 

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