Palladium-Catalyzed Allylic C−OH Functionalization for Efficient Synthesis of Functionalized Allylsilanes
作者:Nicklas Selander、Jennifer R. Paasch、Kálmán J. Szabó
DOI:10.1021/ja1096732
日期:2011.1.26
A new method is described for palladium-catalyzed allylic silylation using allylic alcohols and disilanes as precursors. The reactions proceed smoothly under mild and neutralconditions, and this method is suitable for synthesis of regio- and stereodefined allylsilanes. The presented silylation reaction can be easily extended to include synthesis of allylboronates by change of the dimetallic reagent
Silylation of allylic acetates (1) using organodisilanes (2) was carried out in the presence of a catalytic amount of Pd(DBA)2-LiCl at 100 degrees C. The silylation proceeded smoothly without beta-hydrogen elimination of. resulting (pi-allyl)palladium intermediate. The added chloride salt such as LiCl or NaCl was indispensable for the catalytic activity. On the other hand, remarkable improvement of the silylation was realized by employing allylic trifluoroacetates (4) in place of the acetates (1) as the substrates. The silylation proceeded even at room temperature, and the added chloride salts was not necessary as the catalyst component. In the silylation, transmetalation of the disilanes (2) with (eta(3)-allyl)palladium intermediate (7) might be a critical step in the catalytic cycle. Model reactions for the transmetalation were carried out.
Tris(trimethylsilyl)aluminum and transition-metal catalysts. Silylation of allyl acetates