Borane-induced ring closure reaction of oligomethylene-linked bis-allenes.

摘要: The trimethylene-linked bis-allene 3a reacts with Piers' borane [HB(C6F5)2] by a hydroboration/allylboration sequence to generate the cyclization product 5a. Its pyridine adduct was isolated and characterized X-ray diffraction. Compound 5a undergoes typical frustrated Lewis pair 1,2-P/B alkene addition reaction PPh3 give heterobicyclic bridged olefinic zwitterionic 9a. tetramethylene-linked 3b its phenylene annulated analogue 3c react HB(C6F5)2 analogous seven-membered ring products 5b,c under mild conditions. series of sequential allylboration reactions two equivalents allene followed ring-closure four-component coupling 12a. It FLP an exo-methylene group upon treatment PPh3. 12a is oxidatively converted boron-free alcohol.