Titanocene-catalyzed carbosilylation of alkenes and dienes using alkyl halides and chlorosilanes

A new method for regioselective carbosilylation of alkenes and dienes has b een developed by the use of a titanocene catalyst. This reaction proceeds e fficiently at 0 degrees C in THF in the presence of Grignard reagents by th e combined use of alkyl halides (R'-X, X = Br or Cl) and chlorotrialkylsila nes (R-3"Si-Cl) as the alkylating and silylating reagents, respectively. Te rminal 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 int roduced at the 1- and 3-positions giving rise to allylsilanes in high yield s under similar conditions. The present reaction involves (i) addition of a lkyl radicals toward alkenes or dienes, and (ii) electrophilic trapping of benzyl- or allylmagnesium halides with chlorosilanes. The titanocene cataly st plays important roles in generation of these active species, i.e., alkyl radicals and benzyl- or allylmagnesium halides.