Allylic alcohols intramolecular hydrosilations

Intramolecular hydrosilation. Tamao et al. have extended their hydrosily-lation-oxidation sequence (12,243-245) to allyl and homoallyl alcohols as an approach to 1,3-diols. When applied to cyclic homoallylic alcohols, only a cis-1,3-diol is obtained, presumably by way of a cyclic intermediate (equation I). Acyclic homoallylic alcohols can be converted by this approach to either syn- or anti-1,3-... 

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. 

Asymmetric Intramolecular Hydrosilation. Intramolecular hydrosilation of allylic alcohols followed by oxidation is a convenient method for the stereoselective preparation of 1,3-diols. An enantioselective version is achieved by use of diene-free BINAP-Rh+ (eq 6). Both silyl ethers derived from cinnamyl alcohol and its cis isomer give (iJ)-l-phenylpropane-l,3-diol in high ee regardless of alkene geometry. 

Intramolecular Hydrosilation of Allyl and Homoallyl Alcohols. For a detailed description of the intramolecular hydro-silation-oxidation sequence, see 1,1,3,3-tetramethyldisilazane. 1,1,3,3-Tetramethyldisilazane and AA -diethylaminodimethyl-silane are frequently employed for preparation of hydrodimethyl-silyl ethers for the intramolecular hydrosilation of allyl and homoallyl alcohols. Chlorodimethylsilane in combination with a tertiary amine such as triethylamine is another useful reagent for the synthesis of hydrodimethylsilyl ethers, especially for large scale preparations. ... 

Intramolecular Hydrosilation of Allyl Amines. The amino group of an allyl amine is silylated with chlorodimethylsilane, and then the resulting silazane is subjected to standard platinum-catalyzed cyclization and oxidation steps to form a syn-2-amino alcohol (eq 1). Exclusive formation of the four-membered cyclic product and the high stereoselectivity should be noted. ... 

Hydrosilation Agent. Another application of this difunctional hydrosilane is in the nickel-catalyzed hydrosilation of 1,7-octadiyne, which affords a 1,2-dialkylidenecyclohexane with a (Z)-vinylsilane moiety. This exocyclic silyl diene is treated with an allyl alcohol to give a silicon-tethered triene that undergoes intramolecular Diels-Alder reaction and subsequent oxidative cleavage of the silicon-carbon bond to afford a bicyclic diol (eq 2) ... 

Intramolecular Hydrosilation Agent. For a detailed description of the intramolecular hydrosilation procedure, see 1,1,3,3-tetramethyldisilazane. lV,lV-Diethylaminodimethylsilane is a useful reagent for the conversion of hydroxy groups of allyl or homoallyl alcohols into hydrodimethylsilyl ethers for use in intramolecular hydrosilation reactions. In some cases, lV,lV-dieth-ylaminodimethylsilane gives superior results compared to the more commonly employed 1,1,3,3-tetramethyldisilazane (eq 1). ... 

Intramolecular Hydrosilation. Allyl and homoallyl alcohols are transformed into 1,3-diols in a highly regio- and stereoselective fashion via intramolecular hydrosilation followed by oxidative cleavage of the silicon-carbon bonds by hydrogen peroxide, which proceeds with complete retention of configuration at carbon (eqs 1 and 2). ... 

This methodology has been applied to the construction of a variety of stereoisomers of polypropionate skeletons, as exemplified by the formation of a tetraol from a symmetrical bis-allyl alcohol by a sequence involving three intramolecular hydrosilation-oxidation steps (eq 3). ... 

The intramolecular hydrosilation of allyl alcohols containing an ester group at the terminal carbon proceeds in a 5-endo fashion to form the five-membered cyclic products with modest stereoselectivity. The silyl group a to the carbonyl group is readily cleaved by a fluoride ion in protic solvents (eq 8). ... 

Catalytic asymmetric intramolecular hydrosilation of allyl alcohols has been achieved by using chlorodiphenylsilane or 1-chloro-l-silacyclohexane as the silylating agent. 

---