SYNTHESIS OF PREVIOUSLY UNKNOWN BRIDGED AZABICYCLES BY CATALYTIC CYCLOPADDITION OF ALKYNES TO METHYL 1H-AZEPINE-1-CARBOXYLATE

Cobalt(I)-catalyzed [6π+2π] cycloaddition of terminal alkynes (hexyne-1, 4-pentyn-1-ol, 5-hexynenitrile) to methyl 1H-azepine-1-carboxylate was reported for the first time to afford previously undescribed 9-azabicyclo[4.2.1]nona-2,4,7-trienes in high yields (71–91%). A three-component system consisting of a cobalt(II) salt bound to a 1,2-bis(diphenylphosphino)ethane ligand (Co(acac)2(dppe), CoBr2(dppe), CoI2(dppe), CoCl2(dppe)), a Zn reducing agent, and a Lewis acid ZnI2 was used as a catalyst. The highest yield of 9-azabicyclo[4.2.1]nona-2,4,7-trienes is observed when using Co(acac)2(dppe) (88–91%), CoBr2(dppe) (79–89%) and CoI2(dppe) (86–91%) salts as catalysts. In the case of using CoCl2(dppe) the yield of azabicycles decreases (71–77%). According to the analysis of one- and two-dimensional NMR spectra, 9-azabicyclo[4.2.1]nona-2,4,7 trienes are formed as two rotamers in a 1:1 ratio.