Cyclobutanone, radical cation

The base peak in the mass spectrum of cyclohexanone is, however, miz 55, which arises by the loss of a propyl radical following the six-center H-transfer reaction in the initially formed distonic ion. Loss of both CO and C2H4 is observed in fragmentation of the cyclobutanone radical cation [30]. Similar fragmentation pathways are exhibited by ionized cycloalkylamines. 

Cycloreversion Reactions A cycloreversion reaction is the reverse of a cycloaddition reaction and leads to the formation of the starting reactants through the cleavage of two bonds in the ring [18], A typical example is the formation of C2H4+ and neutral C2H4 from the cyclobutane radical cation. As shown in reaction (6.37), this reaction proceeds through the intermediacy of a distonic ion. The radical cations of a variety of other four-membered cyclic compounds, such as cyclobutanones (3), diketene (4), oxetane (5), cyclobutylamine (6), and thiocyclobutane (7), are known to participate in cycloreversion reactions [27]. 

Addition of alkyllithium to cyclobutanones and transmetallation with VO(OEt)Cl2 is considered to give a similar alkoxide intermediates, which are converted to either the y-chloroketones 239 or the olefinic ketone 240 depending on the substituent of cyclobutanones. Deprotonation of the cationic species, formed by further oxidation of the radical intermediate, leads to 240. The oxovanadium compound also induces tandem nucleophilic addition of silyl enol ethers and oxidative ring-opening transformation to produce 6-chloro-l,3-diketones and 2-tetrahydrofurylidene ketones. (Scheme 95)... 

Cyclopropanes adjacent to an electron-deficient centre X (carbon or heteroatom) undergo C3 - C4 ring enlargement into four-membered ring derivatives via routes involving cations, radicals or car bene intermediates. Furthermore, when the cyclopropanes also bear on the same carbon an electron-donor substituent Y they undergo a specific C3 - C4 ring expansion, important from the synthetic point of view, into cyclobutanone (or related) derivatives (equation 67). 

The treatment of cyclobutanone with alkylhthium followed by VO(OEt)Cl2 leads to the alkoxide intermediate, which undergo oxidative ring opening to the y-chloro ketone 61 or the olefinic ketone 62. Additional one-electron oxidation of the radical intermediate affords a cationic species, which is then deprotonated to give 62 (Scheme 2.48). 

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