Diverse Alkyl–Silyl Cross-Coupling via Homolysis of Unactivated C(sp<sup>3</sup>)–O Bonds with the Cooperation of Gold Nanoparticles and Amphoteric Zirconium Oxides
the degradation of polyesters and the synthesis of organosilanes were realized concurrently by the unique catalysis of supported gold nanoparticles. Mechanistic studies corroborated the notion that the generation of alkyl radicals is involved in C(sp3)–Si coupling and the cooperation of gold and an acid–base pair on ZrO2 is responsible for the homolysis of stable C(sp3)–O bonds. The high reusability and
The palladium-catalyzed cyclization of benzene-1,2-diol with various racemic secondary propargyl carbonates having no acetylenic hydrogen in the presence of (R)-Binap as the chiral ligand afforded the two regioisomers of the corresponding 2,3-dihydro-1,4-dioxin derivatives in quite good yields, and also in enantioselectivities going from 40 to 97%. The cyclization of benzene-1,2-diol with methyl (R)-1-methyl-3-phenylpro-2-yn-1-yl carbonate in the presence of dppb as the achiral ligand afforded 2-benzylidene-3-methyl-2,3-dihydro-1,4-benzodioxine as the major product with 15% ee. The use of (R)-Binap as the chiral ligand afforded the (+) cyclized compound in 45% ee, when the (-) enantiomer was obtained with 77% ee in the presence of (S)-Binap. All the results suggest that in this case the enantioselective step is the diastereoselective protonation of the palladium-carbene intermediates. (C) 2005 Elsevier Ltd. All rights reserved.
Gold-Catalyzed Oxidative Reactions of Propargylic Carbonates Involving 1,2-Carbonate Migration: Stereoselective Synthesis of Functionalized Alkenes
作者:Ning Sun、Ming Chen、Yuanhong Liu
DOI:10.1021/jo500573s
日期:2014.5.2
A gold-catalyzed oxidative reaction of propargylic carbonates or acetates using 3,5-dichloropyridine as the oxidant has been developed. The reaction provides efficient access to α-functionalized-α,β-unsaturated ketones with excellent regio- and diastereocontrol via a regioselective attack of the N-oxide to the gold-activated alkyne followed by a 1,2-carbonate migration. In addition, the alkene products