ACYLATION OF ALKENES GENERATED INSITU BY HYDRIDE TRANSFER FROM ISOALKANES - SYNTHESIS OF PENTALENONES, HYDRINDENONES, AND CYCLOPENTENONES

Acylation, in the presence of AlCl3 and hydride acceptor, of methylcyclopentane, methylcyclohexane, and 2-methylbutane by ethylenic acyl chlorides, in CH2Cl2 solution, respectively, leads to tetrahydropentalenones, tetrahydroindenones, and cyclopentenones in good yields. Hydride acceptor may be either acetyl chloride or the alkenoyl chloride itself. Better results are performed in the presence of nitromethane and CuSO4. Overall yields are better than those obtained by the two-step process involving acylation of alkenes by alkenoyl chlorides and subsequent Nazarov cyclization of the resulting divinylketones. Methyl 1,4-migration is observed during the acylation of 2-methylbutane by sorboyl chloride. The mechanism of these conversions is discussed on the basis of results observed with cyclohexane-d12 and methylbutane-d6 as well as stereochemical studies of the cyclization process.