Intramolecular alkene Friedel–Crafts cyclization of 1-allyl-1-N-(ortho-alkylphenylamino)cyclohexanes. A useful route to alkyl substituted dihydrospiro[(1H)quinoline-2,1′-cyclohexanes]. Unprecedented ipso-substitution of alkyl groups

An unprecedented intramolecular Friedel–Crafts ipso-alkylation at the ortho-alkyl group of the N-arylamino moiety of 1-allyl-1-N-arylaminocycloalkanes to give alkyl substituted dihydrospiro[(1H) quinoline-2,1′-cycloalkanes] is reported. Unexpected results were explained in the context of intramolecular ipso-substitution of alkyl groups and their 1,2-rearrangement. A plausible mechanism for this type of Friedel–Crafts alkylation by an alkene moiety promoted by a Brönsted acid (H2SO4) is proposed.