Internal Lewis acid catalyzed ring-expansion reactions of cyclopropylalkanoyl chlorides

Lewis acid promoted reactions of n-(1-phenylcyclopropyl)alkanoyl chlorides. Ring-size effects in competitive intramolecular acylation of phenyl and cyclopropyl substituents

“…We have recently reported that cyclopropylalkanoyl chlorides undergo Lewis acid catalyzed intramolecular acylation reactions to form five-, six-, and seven-membered ring ketones. 2 The facility of these intramolecular rearrangements, which are analogous to Lewis acid catalyzed cyclizations of alkenoyl and arylalkanoyl chlorides,3•4 has led us to investigate the reactivity of the cyclopropane ring relative to the benzene ring in Lewis acid promoted intramolecular cyclizations of n-(l-phenylcyclopropyl)alkanoyl chlorides (1). Although O (CH2)n-,COCl 1 intermolecular acylation of phenylcyclopropane with acetyl chloride-aluminum chloride occurs exclusively at the para position of the benzene ring,5 ring-size effects in intramolecular acylation of 1, due to the positioning of the electrophilic acyl group relative to the phenyl and cyclopropyl rings, may be expected to have a dominant influence on acylation selectivity.3d•6 Intramolecular acylation of the cyclopropane ring of 1 is expected to occur through an intermediate state that connects + 2 carbon atoms, whereas intramolecular acylation of the benzene ring should occur through an intermediate state that joins + 3 carbon atoms.…”