Alkene Hydro silylation

Palladium oxazoline compounds (e.g., (47)) have been used to catalyze the cyclization/hydro-silylation of functionalized 1,6-dienes (Scheme 31). With R = Pr1, >95% diastereomeric excess and 87% ee was achieved at low temperature. Changing the ligand bulk with R = Bu1 gave a higher ee value, but poorer diastereoselectivity. A range of functional groups can be tolerated at both the allylic and terminal alkene positions.135-137... 

A proposed mechanism and stereochemical course of the 1,4-reduction are described in Fig. 2. As in the case of hydrosilylation of alkenes described in Scheme 10, the phebox-Rh(l) intermediate 16 reacts with hydrosilane to give a hydro silyl Rh(lll) species 17. The hydride attacks to the Si face on the (3-carbon atom of the a,(3-unsaturated carbonyl compound to give the R-product. On the other hand, the stereochemistry with the Re face attack involves the steric repulsion between the oxazoline substituent and the carbonyl group. In the catalytic reaction. 

The silylcarbonylation of alkenes catalyzed by Co2(CO)s giving homologous silyl enol ethers was reported by Murai and coworkers in 1977 as a silicon version of hydro-formylation of alkenes, and developed as a unique synthetic method302-304. Although... 

Addition reactions of the Si-Si bonds across carbon-carbon triple bonds have been most extensively studied since the 1970s by means of palladium catalysts. In the early reports, palladium complexes bearing tertiary phosphine ligands, mostly PPh3, were exclusively employed as effective catalysts, enabling the alkyne bis-silylation with activated disilanes, i.e., disilanes with electronegative elements on the silicon atoms such as hydro [36], fluoro [37], chloro [38], and alkoxy-disilanes [39,40] and those with cyclic structure (Scheme 4) [41-44]. The bis-silylation reactions could be successfully applied to terminal alkynes and acetylenedicarboxylates to give (Z)-l,2-bis(silyl)alkenes, which are otherwise difficult to synthesize. 

Borabicyclo[3.3.1]nonane (9-BBN) has found use in the selective hydro-boration of alkenes in the presence of other reducible functional groups and its reaction with alkynylstannates has been studied. o-Stannyl- and a-silyl-substituted crotyl-9-BBN show promise as reagents for the stereo-regulated synthesis of acyclic systems. A series of papers covers the question of olefin-alkyl exchange in. 5-alkyl-9-BBN s, " the kinetics of reduction of substituted benzaldehydes with 9-BBN, and the kinetics and mechanism of hydroboration of alkynes with 9-BBN dimers. Selective dehalogenation of tertiary alkyl, benzyl, and allyl halides in the presence of secondary or primary alkyl or aryl halides is possible with (165). The... 

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