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Acylation of Alkenes Generated in situ by Hydride Transfer from Isoalkanes. Synthesis of Pentalenones, Hydrindenones, and Cyclopentenones. -In the presence of AlCl3 and a hydride acceptor the acylation of methylcyclopentane (I), methylcyclohexane (IV) or 2-methylbutane (VI) by acyl chlorides such as (II) affords the pentalenones (III), contaminated by ca. 10-15% of 1-acetyl-2-methylcyclopentene, the hydrindenones (V) or the cyclopentenones (VII). Their formation from the alkanes proceeds probably via acylation of the in situ generated alkene, followed by conrotatory Nazarov cyclization of the resulting divinyl ketone intermediate. The condensations of isoalkanes such as ( VI) with sorboyl chloride (VIII) afford various products depending on the temperature. Thus, at room temperature the cyclopentanone (IX) is formed probably as the result of a methyl 1,4-migration. -(MOREL-FOURRIER, C.; DULCERE, J.-P.; SANTELLI, M.; J. Am. Chem. Soc. 113 (1991) 21, 8062-8069; CNRS, Cent. Saint-Jerome, 13397 Marseille, Fr.; EN)