Asymmetric Friedel-Crafts alkylation of indoles with nitrodienes and 2-propargyloxy-β-nitrostyrenes catalyzed by diphenylamine-linked bis(oxazoline)-Zn(OTf) _2 complexes

摘要

The catalytic asymmetric Friedel-Crafts reaction of indoles with nitrodienes and 2-propargyloxy-β-nitrostyrenes was systematically investigated with diphenylamine-linked bis(oxazoline)-Zn(OTf) _2 complexes. Moderate to good enantioselectivities were obtained with both kinds of substrates (up to 89 % ee for nitrodienes and up to 93 % ee for β-nitrostyrene derivatives). Further transformation of the corresponding Friedel-Crafts alkylation product of indole with 2-propargyloxy-β- nitrostyrene was carried out to give the chiral isoxazolobenzoxepane derivative, which is of medicinal chemistry interest, with retained enantiomeric purity.