Silyl ethers siloxy

A proposed mechanism for silyl ether displacement is shown in Scheme 6.14. In the first step, the fluoride anion converts the trimethyl siloxy group into a phe-nolate salt. In the following step, the phenolate anion attacks the activated fluoro monomer to generate an ether bond. The amount of catalyst required is about 0.1-0.3 mol%. Catalyst type and concentration are crucial for this reaction. 

Scheme 9). Although cyanohydrin acetonide 64 could conceivably have been used, the silyl ether 75 was chosen. This compound is readily available from (l)-malic acid, and can undergo electrophilic activation under far more mild conditions than compound 64. Alkylation of the 1,3-diol synthon 75 with bromide 76 created the C11-C26 framework of roflamycoin, in 85% yield. A two-step conversion of the terminal siloxy group to the primary iodide (78) proceeded in 80% overall yield. 

Silyl ethers of vinyl allyl alcohols can also be used in oxy-Cope rearrangements.215 Known as the siloxy-Cope rearrangement, this methodology has been used in... 

Several classes of silyl ethers have been shown to be excellent substrates for the C-H insertion chemistry of donor/ acceptor-substituted carbenoids.81 Effective C-H insertions predominantly occur at methylene sites. Primary sites are not sufficiently activated electronically while tertiary sites are sterically too crowded. Rl -DOSP -catalyzed functionalization of the allyl silyl ether 3 resulted in a highly diastereoselective transformation, leading to the formation of the /3-hydroxyester 4 in 94% yield and 82% ee (Equation (17)).81 This example illustrates the regioselectivity of this chemistry, because 3 contains two allylic sites but only the methylene site adjacent to the siloxy group was functionalized. Even better substrates are the commercially available tetraalkoxysilanes such as 5, because with these substrates, the high diastereoselectivity was retained while the enantioselectivity was increased (Equation (18)).81... 

Epoxy Silyl Ether MABR P-Siloxy Aldehyde Yield (%)... 

When iridium complexes, [IrCl(CO)3]n and Ir4(CO)12, are used to catalyze the reaction of terminal alkenes with HSiR3 and CO, good yields of enol silyl ethers of acylsilanes are obtained. One molecule of CO and two molecules of silane are incorporated regioselectively at the terminal carbon atom of the alkene to form a siloxy(silyl)methylene unit [Eq. (38)].107... 

Siloxy-l-vinylcyclopropanes rearrange thermally to give 1-siloxycyclopentene derivatives or may be hydrolyzed to cyclobutanones by acids (J.M. Conia, 1975 B.M. Trost, 1973 G.C. Girard, 1974). The cyclopropane ring may also be opened by base-catalyzed hydrolysis of the silyl ethers to form ethyl ketones. 

Intramolecular hydrosilylation of siloxy acetone 55 catalyzed by a cationic Rh complex with DuPHOS-i-Pr (56), [Rh(COD)(DuPHOS-i-Pr)]OTf, to give the corresponding cyclic silyl ether with 93% ee (5) [42]. The product was converted to 1,2-diol 57, which can also be prepared by asymmetric dihydroxylation of propene. In the same reaction, the use of BINAP 58 gave only... 

Since Hassner s initial report in 1975,7 oxidation of an enol silyl ether with peracid has been a reliable method for the preparation of a-siloxy and ot-hydroxy ketones. However, the submitters have found that, if the enol silyl ether possesses certain structural features, the reaction, with more than two equivalents of the oxidant, affords oc.a -dihydroxylated ketones (i.e., introduction of two oxygen atoms in a single-step) instead of the expected monohydroxylated compounds.8... 

These side reactions can be minimized by adding trimethylsilyl chloride to the reaction mixture as an alkoxide scavenger. This traps the enediolate dianion as a bis-silyl enol ether, and traps the sodium or potassium alkoxides, which are catalysts for the Dieckmann ring closure, as neutral silyl ethers." The resultant bis-siloxy cycloalkenes are either isolated or converted in situ to a-hydroxy ketones by alcoholysis or by acid hydrolysis. ... 

Siloxycyclopropanes are also opened by platinum(II) complexes such as Zeise s dimer. - While 1-aryl-1-siloxycyclopropanes are transformed into P-platinum ketone complexes, 2-alkyl-substituted siloxycyclopropanes are isomerized cleanly to allyl silyl ethers in good yields. The reaction is quite general and proceeds with catalytic amounts of Zeise s dimer (2-10mol%) in many different suitable solvents (chloroform, dichloromethane, ethyl acetate, ethers, benzene) at ambient temperature with 100% inversion of configuration at the siloxy carbon and provides only silyl ethers of 2-methylene alkanols without contamination of doublebond isomers. ... 

In previous work using Pd catalysts, cycloisomerizations involving substrates bearing siloxy groups at the allylic position generated 1,3-dienes preferentially (Equation 1.49, path a), in contrast to their normal behavior [47]. In the Ru-catalyzed version, the normal 1,4-diene is obtained (Equation 1.49, path b), which generates a very useful enol silyl ether with excellent chemo-, regio-, and diastereoselectivity [48]. 

In the dienol silyl ether (63), where the 7-selectivity of the siloxy diene is enhanced by the second sil-oxy substituent, reactions with electrophiles occur exclusively in the 7-position as illustrated in Scheme... 

Best results with tetrafluorophcny -/.5-phosphane in fluorinations of silyl ethers are achieved with substrates stabilized by electron-withdrawing substituents in the a- or -position relative to the siloxy group,11 15 e.g. formation of 3,13 and with steroids, e.g. formation of 4.16... 

Hydrosilylation and silylformylation of carbonyls. Condensation of RR SiHj with arbonyl compounds provides chiral silyl ethers in the presence of [RhCl(cod)]2 and a hiral ligand. In the presence of CO, a-siloxy carbonyl compounds are obtained. ... 

The equilibrium between a-silyl alkoxides and silojq carbanions can be shifted toward the carbanion side by introduction of a conjugating group into either or both the acylsilane and the nucleophile. In 1980, Reich et al. reported that treatment of all l-substituted acylsilanes with vinyllithium followed by a variety of electrophiles affords a-substituted enol silyl ethers 22 via a siloxy allyllithium intermediate 21 fScheme 8.1Similar reactions using phenyllithium give products in which electrophilic quenching occurred at the benzylic position. 

To probe further the relevance of the above Newman projections, silyl ether 71 was examined under identical reaction conditions. The well-established [190, 191] preference for 4-siloxy and ahcoxy groups to occupy the axial position in chair... 

Quinazoline-2,4-dione Quinazolinone Dihydro Quinoline Quinolone Quinone Selenide Selenoxide Silane Tetraalkyl Siloxy Ether Silyl Chloride Silyl Enol Ether Silyl Ether... 

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