Pd-Catalyzed Regio- and Stereoselective Addition of Boronic Acids to Silylacetylenes: A Stereodivergent Assembly of β,β-Disubstituted Alkenylsilanes and Alkenyl Halides
Pd-catalyzed addition of boronicacids to silylacetylenes is described, providing β,β-disubstituted (E)- or (Z)-alkenylsilanes in satisfactory yields with excellent regio- and stereoselectivity under mild reaction conditions. It represents the first highly regio- and stereoselective addition of boronicacids to aryl and alkenyl silylacetylenes. Moreover, the sequential Pd-catalyzed boron addition/N-halosuccinimide-mediated
The reaction of terminal acetylenes with Me(3)SiI (1) and organozinc reagents in the presence of Pd(PPh(3))(4) results in addition of the trimethylsilyl group of 1 and an alkyl group of the organozinc reagent to the acetylenes. In all cases the trimethylsilyl group adds to the terminal carbon of the acetylenes. Both aromatic and aliphatic terminal acetylenes undergo the coupling reaction with high regio- and stereoselectivities. The yield and stereoselectivity are relatively sensitive to the nature of the organozinc reagent used. The reaction of phenylacetylene (2) using Bu(2)Zn gives the corresponding coupling product in high yield with high stereoselectivity (>98%). In contrast, the use of BuZnI results in 92% stereoselectivity. The stereoselectivity for the reaction using (Me(3)-SiCH2)(2)Zn is lower than those for Me(2)Zn, Et(2)Zn, and Bu(2)Zn. For organozinc reagents, alkylzinc works well while phenyl-, ethynyl-, and allylzinc do not. The reaction using Me(3)SiCl, Me(3)SiBr, Me(3)SiSPh, Me(3)SiSePh, and Me(3)SiOTf in place of 1 does not proceed. The reaction with Me(3)SiMe(2)-SiI and Me(3)SiMe(2)SiMe(2)SiI in place of 1 gives the corresponding vinyldisilane and -trisilane, respectively.
Efficient synthesis of trisubstituted alkenes in an aqueous–organic system using a versatile and recyclable Rh/ m -TPPTC catalyst
We have found that the use of [Rh(cod)OH](2) associated with the water-soluble ligand m-TPPTC was highly efficient for the Rh-catalyzed arylation of alkynes. Aryl and alkyl alkynes were transformed to alkenes using 3 mol% rhodium catalyst and 2.5 equiv of boronic acid Lit 100degreesC in a biphasic water/toluene system in 80-99% yield. The reaction was found to be totally regioselective for alkyl arylalkynes and alkyl silylated alkynes. The Rh/m-TPPTC system was for the first tune recycled with no loss of the activity and with excellent Purity of the desired alkene. (C) 2004 Elsevier Ltd. All rights reserved.
Regiospecific and stereospecific synthesis of E- and Z-trisubstituted alkenes via 2,2-disubstituted vinylsilanes
作者:Shang Shing P. Chou、Hwei Lon Kuo、Chung Jen Wang、Chung Ying Tsai、Chung Ming Sun
DOI:10.1021/jo00265a028
日期:1989.2
Synthesis of vinyl silanes from vinyl silane phosphates
作者:Frederick L. Koerwitz、Gerald B. Hammond、David F. Wiemer