Asymmetric palladium-catalyzed annulation of benzene-1,2-diol and racemic secondary propargylic carbonates bearing two different substituents
作者:Norbert Dominczak、Céline Damez、Bouchra Rhers、Jean-Robert Labrosse、Paul Lhoste、Boguslaw Kryczka、Denis Sinou
DOI:10.1016/j.tet.2005.01.084
日期:2005.3
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.