Trialkylsilyl ethers

One of the more common methods of alcohol protection is by reaction with a chlorotrialkylsilane, CI-S1R3, to yield a trialkylsilyl ether, R -O-SilTj. Chlorotrimethylsilane is often used, and the reaction is carried out in the presence of a base, such as tciethylamine, to help form the alkoxide anion from the alcohol and to remove the HC1 by-product from the reaction. 

They react with a wide range of aliphatic and aromatic aldehydes in the presence of catalytic amounts of tetrabutylammonium fluoride (TBAF) to give the trialkylsilyl ethers of P-nitro alcohols with high anti-selectivity (98%). The diastereoselective Henry reaction is summarized in Table 3.2. The products are reduced to P-amino alcohols using Raney Ni-H2 with retention of the configuration of P-nitro alcohols (Scheme 3.12). 

Some illustrative examples from the field of polyquinanes are the synthesis of some derivatives of bicyclo[3.3.0]octane 6 (Scheme 6.7) [12] [15] -which have been used in the total syntheses of coriolin, hirsutic acid and quadrone- and the synthesis of triquinacene 7 and some of its derivatives. The retrosynthetic analysis of perhydrotriquinacene-l,4,7-trione (7a) is shown in Scheme 6.7bis. In the actual synthesis the hydroxy groups must be protected either as trialkylsilyl ethers or more conveniently as benzyl ethers [16] [17]. 

Acid Hydrolysis303 300 of Some Trialkylsilyl Ethers of Thymidine... 

The stability sequence for the O-trialkysilyl groups appears to be tert-butyl(tetramethylene)silyl > triisopropylsilyl > tert-butyldi-methylsilyl > isopropyl(tetramethylene)silyl > diisopropylmethyl-silyl. In all cases, the 3 -isomer (secondary position) is considerably more stable than the 5 -isomer (primary position), and this difference in reactivity permits303,304 the synthesis of a 3 -(trialkylsilyl) ether of the nucleoside from the corresponding 3, 5 -bis(trialkylsilyl) ether, in yields of 50%. 

Benzyl and alky] trialkylsilyl ethers undergo clean fluorination to give good yields of benzyl and alkyl fluorides, respectively, when reacted with a combination of a quaternary ammonium fluoride and methanesulfonyl o r p- toluenesulfonyl fluoride. The reactions are applicable strictly to a primary carbon-oxygen bond, secondary and tertiary alkyl silyl ethers remain intact or, under forcing conditions, are dehydrated to olefins [29] (equation 22)... 

Selective deprotection of trialkylsilyl ethers can also be accomplished by Nafion-H. Trimethylsilyl ethers are cleaved to the corresponding alcohols under mild conditions680 [Eq. (5.241)]. Nafion-H with Nal (1 equiv.) in methanol was shown to readily cleave ferf-butyldimethylsilyl ethers (room temperature, 4—25 h,... 

Sakaguchi, K. Fujita, M. Suzuki, H. Higa-shino, M. Ohfune, Y. Reverse Brook rearrangement of 2-alkynyl trialkylsilyl ether. Synthesis of optically active (l-hydroxy-2-alkynyl)-trialkylsilanes. Tetrahedron Lett. 2000, 43, 6589-6592. 

There have been several reports of catalytic methods for alcoholysis of trialkylsilanes,10-17 however only a few of these papers have included reactions with dialkyl(dihydrido)silanes.9a,d 15 Among the more reactive catalysts for the preparation of trialkylsilyl ethers from silyl hydrides... 

Allenyl trialkylsilyl ethers 771 can be a-deprotonated with f-BuLi in THF at — 78 °C to give the allenyllithiums 77210901091. They underwent reverse Brook rearrangement to afford the silaacrolein enolates 773, which react with aldehydes and ketones to yield the a,/9-unsaturated acyl silanes 774 (Scheme 200). For enolizable aldehydes transmetallation with ZnCl2-TMEDA, and MgBr2 for ketones, provided better yields. 

Alkylation of allylic ethers. PdCljCdppf) is the most effective catalyst for alkylation of allyl trialkylsilyl ethers with Grignard reagents to give an internal alkene. NiChfdppf) also catalyzes this reaction, but with the opposite cgioselectivity, thus forming a terminal alkene. 

Numerous methods can be used for the synthesis of trialkylsilyl ethers (Scheme 1.27). Alcohols react rapidly with trialkylsilyl chloride (R sSiCl) to give trialkylsilyl ethers (ROSiR 3) in the presence of an amine base like triethylamine, pyridine, imidazole or 2,6-lutidine (Table 1.2). 

Trialkylsilyl ethers such as ROSiMe3 are converted to the corresponding iodide with Si02-Cl/Nal. i ... 

Relative stabilities of trialkylsilyl ethers towards acid-catalyzed solvolysis... 

---