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.
Palladium-catalyzed silylation of allylic acetates with hexamethyldisilane or (trimethylsilyl)tributylstannane
Various allylic acetates (1a-j) are silylated with hexamethyldisilane (Me3SiSiMe3, 2) in the presence of a catalytic amount of Pd(DBA)2 and LiCl at 100-degrees-C to afford the corresponding allylic silanes in high yields. In addition, (trimethylsilyl)tributylstannane (Me3SiSnBu3, 3) can be used for the silylation of aromatic allylic acetates 1g-j at room temperature.
Tsuji Yasushi, Kajita Satoshi, Isobe Shinya, Funato Masahiro, J. Org. Chem., 58 (1993) N 14, S 3607-3608