A chiral bicyclic skeleton-tethered bipyridine-Zn(OTf)2 complex as a Lewis acid: enantioselective Friedel-Crafts alkylation of indoles with nitroalkenes

A conformationally rigid chiral bicyclic skeleton tethered bipyridine-Zn(OTf)(2) complex facilitated the enantioselective Friedel-Crafts alkylation of indoles with trans-beta-nitroarylalkenes in an enantioselective manner at elevated temperature. Indoles reacted smoothly with beta-nitroarylalkenes to generate the corresponding 3-(2-nitroalkyl) indoles in good to excellent yields (up to 94%) with moderate to excellent enantioselectivities (up to 91%). The stereochemical outcome of the product from indole and trans-beta-nitrostyrene in the presence of the CRCB tethered bipyridine-Zn(OTf)(2) complex and the DFT calculation of the CRCB tethered bipyridine-Zn: trans-beta-nitrostyrene complex support the si-face attack of indole on trans-beta-nitrostyrene.