Lewis-Acid-Catalyzed Rearrangement of Arylvinylidenecyclopropanes: Significant Influence of Substituents and Electronic Nature of Aryl Groups

Lewis-acid-catalyzed reactions of arylvinylidenecyclopropanes having three substituents at the corresponding cyclopropyl rings have been investigated thoroughly. The reaction products are highly dependent
on the substituents at the corresponding cyclopropyl rings and the electronic nature of the aryl groups.
For arylvinylidenecyclopropanes bearing two alkyl groups at the C-1 position (R1, R2, R3 = aryl; R4 =
H; R5, R6 = alkyl), naphthalene derivatives were formed in the presence of Lewis-acid Eu(OTf)3 in DCE
at 40 °C. For arylvinylidenecyclopropanes in which R1, R2, R3 = aryl and R4, R5 = alkyl (syn/anti
isomeric mixtures), the corresponding 6aH-benzo[c]fluorine derivatives were formed in the syn-configuration via a double intramolecular Friedel−Crafts reaction when all of the aryl groups do not
have electron-withdrawing groups or the corresponding indene derivatives were obtained via an
intramolecular Friedel−Crafts reaction as long as one electron-deficient aryl group was attached. For
arylvinylidenecyclopropanes in which R1, R2, R3, R4 = aryl and R5 = alkyl or H, the corresponding
indene derivatives were obtained exclusively via a sterically demanding intramolecular Friedel−Crafts
reaction. Lewis-acid effects and mechanistic insights have been discussed on the basis of experimental
investigations.