Silaboration isocyanides

Silaboration of bicyclopropylidene proceeds via proximal G-G bond cleavage at 130 °C in the presence of the palladium// r/-alkyl isocyanide catalyst (Equation (88)). In contrast to the aforementioned silaboration of methylene cyclopropanes, vinylsilane products are obtained with high regioselectivity.102... 

The reaction of silylborane with 1-halo-l-lithio-l-alkenes yields 1-boryl-l-silyl-l-alkenes via borate formation followed by 1,2-migration of silyl group (Equation (90)).76,240 The mechanism seems to be closely related to that proposed for the silaboration of isocyanide (Figure 2). Vinyl-substituted carbenoids, l-chloro-l-lithio-2-alkenes, react with silylpinacolborane to give l-boryl-l-silyl-2-alkanes in good yield (Equation (91)).241 This methodology is applied to the synthesis of l-boryl-l-silyl-2-cyclobutene.2 2 Similar reactions are carried out with other carbenoid... 

Silaboration of 3-substituted 1,2-dienes takes place smoothly at the internal double bond in the presence of the catalytic Pd(acac)2-2,6-xylyl isocyanide complex and the boryl group is regioselectively introduced to the central carbon atom of an allene (Scheme 16.55) [59, 60]. The same regioselectivity is observed with the catalytic system Pd2(dba)3-P(OCH2)3CEt [59]. 

In spite of the fact that compounds having Si—bonds (silylboranes) were already prepared in the early 1960s,somewhat surprisingly, transition-metal-catalyzed reaction of the silylboration had not been reported until 1996. Suginome, Nakamura, and Ito have found that silaboration of acetylenes proceeds smoothly in the presence of a catalyst Pd(OAc)2/t-octyl NC. Under reflux in toluene, addition of the Si—bonds across the carbon-carbon triple bond of 1-octyne took place in the presence of the catalyst prepared from 2 mol % of Pd(OAc)2 and 30 mol % of 1,1,3,3-tetramethylbutyl isocyanide (Scheme 21). 

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