Gold(III) chloride-catalyzed diastereoselective alkylation reactions with chiral benzylic acetates

Abstract

Gold(III) chloride was shown to be an efficient catalyst for the diastereoselective C-C bond formation of various chiral para-methoxybenzylic acetates and different nucleophiles. All electrophilic acetates carried next to the reacting center a stereogenic carbon center bound to a functional group (FG), a methyl substituent and a proton. Selectivities were good (dr > 80/20) in favor of the anti-product for FG = COOMe, NO2, CN and in favor of the syn-product for FG = SO2Et, PO(OEt)2. The reactions proceed most likely via a free carbocation, in which a face differentation is facilitated by a preferred conformation. Several arene nucleophiles were shown to be compatible with the catalysis conditions providing the corresponding substitution products in high yields (13 examples, 62-98%). Moreover, other nucleophiles (allyltrimethylsilane, trimethylsilyl cyanide, 2,2-dimethyl-3- (trimethylsilyloxy)butane, p-toluenesulfonamide, and acetylacetone) reacted with a representative chiral electrophile in a high yielding and diastereoselective fashion. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.