Asymmetric Friedel-Crafts Alkylation of Indoles with Nitrodienes and 2-Propargyloxy-β-nitrostyrenes Catalyzed by Diphenylamine-Linked Bis(oxazoline)-Zn-(OTf)2 Complexes

The catalytic asymmetric FriedelCrafts reaction of indoles with nitrodienes and 2-propargyloxy-beta-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 beta-nitrostyrene derivatives). Further transformation of the corresponding FriedelCrafts alkylation product of indole with 2-propargyloxy-beta-nitrostyrene was carried out to give the chiral isoxazolobenzoxepane derivative, which is of medicinal chemistry interest, with retained enantiomeric purity.