Abstract
Reaction of a 1,4-diaryl- 1-butene (7) with paraformaldehyde and the appropriate alkylaluminum halide generates the cation 8, via addition of formaldehyde to the double bond, which cyclizes to give the aryltetralin 9. Reaction of 1,4-diphenyl-2-butene (6a) with paraformaldehyde and methylaluminum sesquichloride gives the ene adduct 5a, which reacts further, analogously to 7, to give 4a which possesses the aryltetralin lignan skeleton.