Aryl silyl ethers

Aryl and alkyl trimethylsilyl ethers can often be cleaved by refluxing in aqueous methanol, an advantage for acid- or base-sensitive substrates. The ethers are stable to Grignard and Wittig reactions and to reduction with lithium aluminum hydride at —15°. Aryl -butyldimethylsilyl ethers and other sterically more demanding silyl ethers require acid- or fluoride ion-catalyzed hydrolysis for removal. Increased steric bulk also improves their stability to a much harsher set of conditions. An excellent review of the selective deprotection of alkyl silyl ethers and aryl silyl ethers has been published. ... 

Aminosilanes, 87-9 Artemisia ketone, 33 Aryl silyl ethers, 41 Arylsilanes, 39-43 Arylsulphonylhydrazones, 12 Aryltrimethylsilanes, 39, 42,43 Azetidin-2-ones, 70 Azetidin-2-one 4-carboxylic acids, 92... 

Dienols with 2 equiv. of 1 gave the corresponding bimetallic alkoxide organozir-conocene complexes however, protolysis allowed recovery of the alcohol functionality (Scheme 8-29) [107]. Alcohols can also be easily converted to ethers. Alkyl, aryl, silyl [85,112,183, 210] and THP [17, 153, 211, 219] ethers are stable under hydrozirconation conditions side products were observed only with the trimethylsUyl group [220, 221]. 

The cleavage of benzyl ethers using hydrobromic acid is promoted by tetra-n-butylammonium bromide [38]. Selective cleavage of aryl silyl ethers can be effected in the presence of aliphatic silyl ethers using solid sodium hydroxide with tetra-n-butyl-ammonium hydrogen sulphate [39]. 

Aryl silyl ethers are cleaved by a variety of reagents. Treatment of alkoxysilanes with electrophilic reagents like the boron trifluoride-diethyl ether complex results in the cleavage of the Si-O bond to form mono-, di- and trifluorosilanes.22... 

Arylation of silyl enol ethers.1 Silyl enol ethers of methyl n- or sec-alkyl ketones undergo arylation when treated with an aryl bromide and tri-n-butyltin fluoride and a... 

Aryl insylates, methyl ethers, and silyl ethers do not undergo this coupling. 

The use of aryl-A3-iodanes for C-heteroatom bond formation at the a-carbon atoms of ketones and / -dicarbonyl compounds, and related transformations of silyl enol ethers and silyl ketene acetals, has been exhaustively summarized in recent reviews (Scheme 27) [5,8]. Reactions of this type are especially useful for the introduction of oxygen ligands (e. g., L2 = OH, OR, OCOR, 0S02R, OPO(OR)2), and have been extensively utilized for the synthesis of a-sulfonyl-oxy ketones and a-hydroxy dimethyl ketals. 

The photo-SNl reaction with particular classes of alkenes - namely enamines, silyl enol ethers and silyl ketene acetals - affords a smooth synthesis of a-aryl ketones,... 

Rather more conventional means were used to remove an alkyl silyl ether in the presence of an ary silyl ether in a synthesis of Dynemicin Here the task was simply accomplished with HF in acetonitrile [Scheme 4.56].92 Acidic conditions also prevailed in a synthesis of Doliculide wherein an alkyl tert-butyl ether, a tert-butyl ester and an N-fert-butoxycarbonyl group were cleaved simultaneously without challenge to the remaining aryl silyl ether [Scheme 4.57] ... 

Tertiary halides, acetates and methyl ethers, aryl-activated secondary halides, prenyl halides and acetates, acetals, ketals, thioacetals, a-chloroalkyl ethers, and, particularly, a-chloroalkyl phenyl sulrides have been widely used as alkylating agents. Such reagents may contain a variety of functional groups including alkenes, esters, halides, ketones, nitro groups and silyl ethers. 

Cesium fluoride. 13,68 14,79 15,75-76 16,69-70 17,68 18,88-89 19,70-72 Ethers. A direct transformation of aryl silyl ethers to aryl alkyl ethers is by their reaction with alkyl halides in the presence of CsF-DMF. Monobenzylation of glycols such as methyl glycerate via dibutylstannylene acetals. ... 

Selective O-desilylation. PPTS in ethanol removes silyl groups (e.g., TBS) from aliphatic silyl ethers in preference to the aryl silyl ethers thus the chemoselec-tivity is opposite to the reaction with KaCOj-Kriptofix 222 (in MeCN). 

Reduction of aryl silyl ethers nonconjugated cycloenones, The isopropyldi-methyl and r-butyldimethyl silyl ethers 1 are reduced by lithium ammonia to dihydroaryl silyl ethers (2). These can be converted to lithium enolates (a). One... 

The introduction of a t-butyl group a - to a carbonyl group has been achieved by Friedel-Crafts alkylation of the appropriate trimethylsilyl enol ether. In the presence of a nickel(ii) catalyst, u/c-bromotrimethylsilyloxyalkenes couple with Grignard reagents to produce alkylated and arylated silyl enol ethers, which, after hydrolysis, furnish the corresponding a-alkylated or a-arylated ketones (Scheme 36). ... 

Substituted cyclohex-3-enones are conveniently prepared by metal-ammonia reduction of aryl silyl ethers followed by desilylation (Scheme 71). ... 

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