Titanocene-Catalyzed Carbosilylation of Alkenes and Dienes Using Alkyl Halides and Chlorosilanes

A new method for regioselective carbosilylation of alkenes and dienes has been developed by the use of a titanocene catalyst. This reaction proceeds efficiently at 0 °C in THF in the presence of Grignard reagents by the combined use of alkyl halides (R‘−X, X = Br or Cl) and chlorotrialkylsilanes (R3‘ ‘Si−Cl) as the alkylating and silylating reagents, respectively. Terminal alkenes having aryl or silyl substituents (YRCCH2, Y = Ar or Me3Si, R = H or Me) afford addition products YRC(SiR‘ ‘3)−CH2R‘ in good yields, whereas 1-octene and internal alkenes were sluggish. When 2,3-disubstituted 1,3-butadienes were used instead of alkenes, alkyl and silyl units are introduced at the 1- and 4-positions giving rise to allylsilanes in high yields under similar conditions. The present reaction involves (i) addition of alkyl radicals toward alkenes or dienes, and (ii) electrophilic trapping of benzyl- or allylmagnesium halides with chlorosilanes. The titanocene catalyst plays important roles in generation of these active species, i.e., alkyl radicals and benzyl- or allylmagnesium halides.