Acylsilane, hydrolysis

Acyclic cationic systems, chalcogen-halogen compounds, 35 299-301 Acylarsonic acids, 44 217 Acyldiazenido complexes, mechanisms of formation, 27 223-225 Acylium cation, 9 231, 241-243 Acylphosphonic acids, 44 217 Acylsilane, hydrolysis, 42 173 Adamantane... 

Triphenylsilanol is one of several products obtained in the thermally induced decarbonylation of Ph3SiC02H (129). Acylsilanes react readily with aqueous base for example, Ph3SiC(0)Ph affords Ph3SiOH and PhC(0)H when treated with aqueous sodium hydroxide solution (130). Similarly, hydrolysis of the allenyl silane 22 leads to the formation of 23 via the acylsilane 24 [Eq. (24)] (131). (For further examples of acylsilane chemistry, see Refs. 132-134.)... 

The unusual l-sila-l,2-diol (CH2=CH)CH(OH)SiPh2OH, prepared by hydrolysis of the acylsilane (CH2=CH)C(0)SiHPh2, has a structure comprising hydrogen-bonded double chains as shown in Fig. 9. Only COH - HOSi hydrogen bonds are present, with the bonds between the chains being shorter than those that build up the chain, 2.666 and 2.739 A, respectively (131, 210). 

Whereas deprotonation and halogen-lithium exchange represent the most common methods to access allenic and propargylic lithium intermediates, several less direct routes to more functionalized analogues have also been reported. Additions of various lithium acetylides to acylsilanes followed by Mel or EtI afforded alkylated allenyl silyl ethers (Table 9.4) [10]. The adducts were analyzed after hydrolysis to the related enones. 

Hydrosilane HSiR.3 behaves similar to H2 toward transition metal complexes in some cases. When HSiR.3 is used instead of hydrogen in hydroformylation, two reactions are expected. One is a hydrocarbonylation-type reaction, by which formation of the silyl enol ethers 62 via the acylmetal intermediate 61, and the acylsilanes 64 via the acyl complex 63, are expected in practice both reactions are observed. The other possibility is silylformylation to form 65, which is unknown, even though silylformylation of alkynes is known. When Co2(CO)8 is used, the silyl enol ether of aldehyde 66 is obtained [36], However, the silyl enol ether 67 of acylsilane 68 is obtained when an Ir complex is used, and converted to the acylsilane 68 by hydrolysis [37],... 

Acylsilanes react with alkylmetals to give a-silylated alcohols, which can be readily desilylated by fluoride ion-induced hydrolysis with stereochemical retention. For this reason, they have been used as aldehyde equivalents for highly stereo- and regioselective synthesis of alcohols.227-228b When acylsilanes or alkylmetals have a leaving group at... 

S-Substituted a-lithiated silyl enol ether 557 has been prepared by reductive lithia-tion of vinyl tellurides834 and sulfides835,836 with lithium 1 -(dimethylamino)naphthalenide (LDMAN). This intermediate 557 gave, after inverse Brook rearrangement, the enolate 558 and after hydrolysis the corresponding acylsilane (Scheme 151). 

There are several procedures available for the preparation of acylsilanes. A general synthesis of acyl silanes is via the dithiane route.Hydrolysis of 2-silyl-l,3-dithianes which leads to acyl silanes can be accomplished with mercury(II) salts. To repress formation of aldehyde by-products, various modifications for the deprotection of silyl dithi-anes have been reported, including the use of HgO-F3B OEt2 or chloramine-T. ... 

AcylsilanesJ The lithiated species formed by using LDA undergoes alkylation. Hydrolysis of the products afford the acylsilanes. A key intermediate for dammarenediol-II has been prepared by this method. 

Acylsilanes. 2-Silyl-l,3-dithianes undergo oxidative hydrolysis on exposure to NBS in aqueous acetone. Addition of a base (triethylamine or barium hydroxide) prevents further conversion of the products to carboxylic acids. 

Acylsilanes have been known since 1957 when Brook described the synthesis of benzoyltriphenylsHane. Their unique reactivity has made them very useful reagents for organic syntheses. The simplest known member of this class of compounds, acetyltrimethylsilane, has been prepared from the oxidation of 1-trimethylsilylethanol, the hydrolysis of 2-methyl-2-tr1methyl silyl-1,3-... 

The displacement of primary iodides in some carbohydrate derivatives by lithiated 2-trimethylsilyl-l,3-dithiane followed by hydrolysis of the dithioacetal has allowed the synthesis of some acylsilanes (e.g. 21 from 20), and a review on the oxidation of the carbon-silicon bond has included a number of carbohydrate examples. ... 

Versatile preparation of conjugated acylsilanes involves hydrolysis of a-silylated allenyl ethers that can be derived from lithiated allenyl ethers.The method is applicable to the synthesis of not only a variety of substituted a,(3-unsaturated acylsilanes but also acetylenic acylsilanes (Scheme 6.6T... 

Ozonization of vinylmetalloids does not appear to yield acylsilanes readily. The formation of trimethylsilylformaldehyde (McaSiCHO) during hydrolysis of the ozonide of vinyltrimethylsilane was postulated but only decomposition products were isolated (40). 

Another general approach to acyl(methyldiphenyl)silanes starts from 1,3-dithiane (30), which, on lithiation with n-BuLi and subsequent treatment with methyldiphenylchlorosilane forms 2-methyldiphenylsilyl-1,3-dithiane (31a). This may be alkylated following a second deprotonation to yield the corresponding substituted 1,3-dithianes (31b). Hydrolysis of the thioacetals to afford the corresponding acylsilanes (32) was conducted with... 

The instability of aldehydo-acylsilane (46) required a different approach for its preparation (eq 22). Thus l-(methyldiphenylsilyl) propan-1-one (44) was converted into the corresponding NJSI-dimethylhydrazone that was alkylated with 3-bromo-1,1-dimetho-xypropane to give compound (45). Hydrolysis with Amber-lyst-15 as catalyst afforded the target aldehyde (46). 

The synthesis of symmetrical and unsymmetrical bis-(acylsilanes) has also been reported.The former category of compounds are easily prepared from the symmetrical bis-(dithianes) by lithiation, methyldiphenylsilylation, and hydrolysis. The synthesis of uns3mimetrical analogs has been effected by the stepwise treatment of dihaloalkanes with different lithi-ated 2-silyl-l,3-dithianes (eq 23). Deprotection of the products (e.g. compound (47)) with Hg(C104)2/CaC03 or l2/CaC03... 

Synthesis of Acylsilanes. The title reagent (1) and other related derivatives undergo sequential isomerization to a-silylalkeny 1 ethers upon treatment with palladium on carbon which subsequently give acylsilanes by hydrolysis (eq 4). ... 

Two alternative routes to (+)-swainsonine (ent-37S) developed by Chen and Tsai, Hke that used in their synthesis of lentiginosine (c Scheme 47 Section 3.3.2), created the bond to C-8a by means of free radical cycUzations onto an acylsilane. The first approach entailed the creation of the C-l/C-8a bond (Scheme 86). Amide formation between the amine 638 and the acid chloride prepared in situ from the chiral lactone-acid 639 yielded (—)-640, which was cyclized with base to the imide (—)-641 in 91% yield. Chemoselective reduction of the C-2 carbonyl group, acid-catalyzed reaction with thiophenol, and protection of the hydroxyl substituent as the benzoate gave 642 as a mixture of isomers. After hydrolysis of the dithiane to the acylsilane 643 with iodobenzene bis(trifluoroacetate), treatment with tri-butyltin hydride and l,lCazobis(cyclohexane-l-carbonitrile) (ACCN) as radical initiator produced the indohzidin-5-one 644 in 86% yield as a... 

As described for the hydrozirconation of alkynyl derivatives containing a tritsopro-pylsilyl acylsilane moiety (see Schemes 12.9and 12.10), the hydrozirconation of alkene 20 and subsequent hydrolysis led to the alkane 21 in 94% yield (Scheme 12.16) [13]. 

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