Hydrosilylation of cyclic dienes

Hydrosilylation of cyclic dienes also worked well to give allylic silanes. Thus, palladium-catalyzed hydrosilylation of cyclopenta-1,3-diene and cyclohexa-1,3-diene afforded the corresponding allylsilanes in good yield [13,14]. 

ASYMMETRIC HYDROSILYLATION OF CYCLIC DIENES WITH HSiCI, CATALYZED BY CHIRAL PHOSPHINE-PALLADIUM(II) COMPLEXES [22]... 

The Pd/MOP combination has proved active for the asymmetric hydrosilylation of cyclic alkenes and dienes. Thus treatment of norbornene with HSiCl3 at 0 °C for 24 h in the presence of 0.01 mol.% of M eO-MOIV[Pd(// -C3H5)Cl]2 gave quantitative yield of evo-2-(trichlorosilyl)norbornane oxidation produced the corresponding alcohol in 93% ee (Equation (12)). Lowering the temperature (to — 20 °C) increased this to a 96% ee. Both mono- and difunctionalization of nbd has proved possible, depending upon the quantity of trichlorosilane used (Scheme 22). In both reactions, extremely good enantioselectivities are observed 113... 

The most active and stereoselective catalysts for hydrosilylation of cyclic and acyclic dienes are analogs of [PPFA]PdCl2 C containing fluoroalkyl groups in the R side chain15. 

For asymmetric hydrosilylation of cyclic 1,3-dienes, PPF-OAc ligand was appropriate for achieving relatively high ee, and thus we could obtain 2-... 

Early studies on the palladium-catalyzed asymmetric hydrosilylation of cyclic conjugated dienes employing menthyl- and neomenthyldiphenylphosphine and ferrocenylamino-phosphine ligands gave low enantiomeric excesses of the corresponding allylsilane [13]. 

In a recent study, a significant improvement was accomplished in the asymmetric palladium-catalyzed 1,4-hydrosilylation of cyclic 1,3-dienes with the use of chiral ligand (/ )-MOP-phen (Scheme 8-2) [18]. Thus hydrosilylation of cyclopentadiene gave 5 in 99% yield with an enantiomeric excess of 80%, which is the highest reported ee value for Pd-catalyzed hydrosilylations of 1,3-dienes. With 1,3-cyclohexadiene, the yield of the... 

Asymmetric hydrosilylation of 1,3-dienes provides convenient access to optically active a-chiral allylsilanes.107 1073 1071 The combination of 7r-allylpalladium chloride dimer with axially chiral monophosphine ligand 17 realizes high catalytic activity and enantioselectivity in the reaction of cyclic 1,3-dienes with HSiCl3.108,108a The allyltrichlorosilanes obtained react with aldehydes in a syn-Se mode to give homoallyl alcohols with high diastereo-and enantioselectivity (Scheme 9). 

The asymmetric hydrosilylation of a-methylstyrene with methyldi-chlorosilane has been catalyzed by (/ )-benzylmethylphenylphosphine complexes of platinum(II) 302) or nickel(II) 304) to give a 5 or 17.6% excess of one enantiomer in the addition product, 2-phenylpropyl-methyldichlorosilane. The corresponding palladium(II) complexes were, however, only slightly useful for asymmetric synthesis in hydrosilylation of olefins. Nevertheless, palladium(II) complexes of methyldiphenyl-phosphine or epimeric neomethyldiphenylphosphine, where the dissymmetry is remote from the phosphorus, are especially useful for the induction of asymmetry in the hydrosilylation of styrene and some cyclic conjugated dienes 199). A similar procedure has been used for... 

The hydrosilylation of fully conjugated diene esters followed by hydrolysis on silica gives the corresponding 0,y-unsaturated esters through 1,6-addition (equation 73)193. When a y,<5-double bond is a part of a cyclic structure, viz., the double bond is... 

Silylpalladium complexes have attracted attention due to their relevance in the mechanism of Pd complex catalyzed reactions such as hydrosilylation of alkenes and dienes, bis-silylation of dienes and alkynes, carbosilylation of alkynes, cross-coupling of organic halides with disilanes, and ring-opening oligomerization and polymerization of cyclic disilanes and polysilanes. 

Both nickel(0)- and nickel(n)-phosphine complexes, e.g. [Ni(C2H4)(diphos)], [NiCl2(diphos)], can catalyse hydrosilylation of alkenes. An induction period is observed with the nickel(ii) system and it appears that an important step with these catalysts is reduction of nickel(ii) to nickel(0). The reduction does not occur below 100 °C. A possible mechanism for the reaction is given in Scheme 27. Asymmetric hydrosilylation of styrene and cyclic dienes with HSiCls can... 

This can be illustrated by the acylation of linear and cyclic vinylsilanes. It is quite simple to prepare methylvinylketone (59) or l-methyl-6-TMS-hexa-2,5-diene-4-one (70) In the latter case the starting material is bis(trimethylsilyl)-ethene (62) which can either be achieved via hydrosilylation (vide supra) or by the more classical approaches " Furthermore, because of the hi stereospecifi-ty, compounds like E- cinnamaldehyde (77) are obtainable in good yields and with superb optical purity ... 

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