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. ... 

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). ... 

Thus, an alcohol is converted into a hydrodimethylsilyl ether by treatment with 1,1,3,3-tetramethyldisilazane in the absence or presence of a catalytic amount of ammonium chloride as a promoter. The ammonia produced in this reaction and the excess disilazane must be removed prior to the hydrosilation step. The intramolecular hydrosilation can be achieved by using a platinum or rhodium catalyst (<1 mol%) such as acidic H2PtCl6-6H20 in /-PrOH (Speier s catalyst) or THF,... 

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 homopropargyl alcohols also proceeds in a 5-exo manner to form five-membered cyclic vinylsilanes exclusively. Subsequent oxidation affords a p hydroxy ketone (eq 6). The vinylsilane also undergoes a Pd-catalyzed cross-coupling reaction with aryl or alkenyl halides stereoselectively (eq 6). The intramolecular hydrosilation thus provides an efficient methodology for the regio- and/or stereoselective functionalization and carbon-carbon bond formation of the alkyne moiety in homopropargyl alcohol. 

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. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

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) ... 

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