Lewis Acid Catalyzed Cascade Reactions of 1,6‐Diynes and 1,6‐Enynes with Vinylidenecyclopropanes

Cascade reactions : Lewis acid catalyzed cascade reactions of 1,6‐diynes and 1,6‐enynes with arylvinylidenecyclopropanes produce polycyclic compounds and isopropylidene‐3,3‐diarylcyclobut‐1‐enylmethyl derivatives (see scheme) in good to high yields along with a PtCl 2 ‐catalyzed cyclization and a Cu(OAc) 2 ⋅ H 2 O‐catalyzed Eglinton coupling reaction.Lewis acid catalyzed reactions of N ‐(4‐hydroxy‐4,4‐diarylbut‐2‐ynyl)‐4‐methyl‐ N ‐prop‐2‐ynylbenzenesulfonamides or 1,1‐diphenyl‐4‐prop‐2‐ynyloxybut‐2‐yn‐1‐ol (1,6‐diynes) 1 and N ‐allyl‐ N ‐(4‐hydroxy‐4,4‐diarylbut‐2‐ynyl)‐4‐methylbenzenesulfonamides (1,6‐enynes) 2 with vinylidenecyclopropanes 3 selectively produce polycyclic compounds 4 , 5 and 10 as well as isopropylidene‐3,3‐diarylcyclobut‐1‐enylmethyl derivatives 6 or 7 in good to high yields depending on the substituents on the benzene ring of 3 under mild conditions. An interesting PtCl 2 ‐catalyzed cyclization of 6 and a Cu(OAc) 2 ⋅ H 2 O catalyzed Eglinton coupling reaction of 5 and 10 to produce the corresponding 5‐isopropylidene‐6‐methyl‐1‐(toluene‐4‐sulfonyl)‐7‐vinyl‐1,2,3,4,5,8‐hexahydroazocine derivatives 8 and the coupling products 9 and 11 in good yields have been disclosed, respectively. Plausible mechanisms of these processes have been proposed that belong to a cascade rearrangement followed by the Friedel–Crafts reaction, an intramolecular proton transferring and a cyclization reaction.