Homoallyl alcohols intramolecular hydrosilylation

Intramolecular hydrosilylation.1 Hydrosilylation of internal double bonds requires drastic conditions and results in concomitant isomerization to the terminal position. However, an intramolecular hydrosilylation is possible with allylic or homoallylic alcohols under mild conditions by reaction with 1 at 25° to give a hydrosilyl ether (a), which then forms a cyclic ether (2) in the presence of H2PtCl6-6H20 at 60°. Oxidative cleavage of the C—Si bond results in a 1,3-diol (3). 

The C—Si bond formed by the hydrosilation of alkene is a stable bond. Although it is difficult to convert the C—Si bond to other functional groups, it can be converted to alcohols by oxidation with MCPBA or H2O2. This reaction enhances the usefulness of hydrosilylation of alkenes [219], Combination of intramolecular hydrosilylation of allylic or homoallylic alcohols and the oxidation offers regio- and stereoselective preparation of diols [220], Internal alkenes are difficult to hydrosilylate without isomerization to terminal alkenes. However, intramolecular hydrosilation of internal alkenes can be carried out without isomerization. Intramolecular hydrosilylation of the silyl ether 572 of the homoallylic alcohol 571 afforded 573 regio- and stereoselectively, and the Prelog-Djerassi lactone 574 was prepared by applying this method. 

Finally, the regio- and stereoselectivities of the intramolecular hydrosilylation of allyl alcohols, homoallyl alcohols, and allylamlnes are summarized in Scheme 1. While these results have been obtained with the dimethylsilyl (HMe2Si) group in the presence of a platinum catalyst, stereoselectivity, but not regioselectivity, can be controlled by other silyl groups such as the diphenyl (HPh2Si) or di(isopropyl)silyl [H(i-Pr)2Si] groups. 

Intramolecular hydrosilylation of allyl and homoallyl alcohols, with subsequent oxidative cleavage of the resultant C—Si bond, has provided a new approach to the regiocontrolled synthesis of 1,2-and/or... 

Ito et al. have reported that a sequence of intramolecular hydrosilylation or cya-nosilylation and the Pd-catalyzed coupling reaction is useful for regio- and stereo-defined synthesis of tri- or tetrasubstituted homoallyl alcohols from homopropargyl alcohols (Scheme 10.212) [551, 552]. More recently Denmark et al. have used ring-closing metathesis for the alkene synthesis via vinylsilanes [553]. 

The intramolecular hydrosilylation of allylic and homoallylic alcohols and the subsequent oxidative cleavage of the initially formed... 

Both exo-dig and endo-dig silacycloadducts formed by intramolecular hy-drosilylation, are crucial intermediates for a number of organic syntheses. For example, alkylidenesilacyclopentanes produced by intramolecular hydrosilylation of homopropagyl alcohols are coupled with aryl or alkenyl halides in the presence of TBAF and palladium(O) catalyst to give highly stereoselective trisubstitued homoallylic alcohols (113,120). 

The synthetic potential of this strategy based on consecutive Pt- or Ru-catalyzed intramolecular hydrosilylation of propargyl and homopropargyl alcohols Pd-catalyzed cross-coupling reactions have been proved in the stereoselective synthesis of a wide variety of aryl-substituted (E)- and (Z)-allyl and homoallyl alcohols (Scheme 25) (178-180) ... 

Bis(allyl)homoallyloxysilanes 56a and 56b are designed for a tandem intramolecular silylformylation-allylsUylation reaction, which has turned out to be an efficient approach to construct polyol and polyketide frameworks [21], For example, heating a solution of 56 in benzene at 60 °C in the presence of Rh(acac)(CO)2 under CO atmosphere followed by the Tamao oxidation gives syn,syn-triols 59 stereoselectively via oxasilacyclopentanes 57 and 58 (Scheme 5.14). Bis(ds-cro-tyl)silane 56b is readily prepared by double Pd-catalyzed 1,4-hydrosilylation of 1,3-butadiene with dichlorosilane followed by reduction with UAIH4 and alcoholysis with the corresponding homoallylic alcohol. 

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