Nitriles silyl esters

Figure 11.11 Pyrogram of a paint sample collected from a decorative frame of the Universal Judgement by Bonamico Buffalmacco (fourteenth century, Monumental Cemetery of Pisa, Italy). Pyrolysis was performed with a microfurnace pyrolyser, at 600°C, in the presence of HMDS. 1, Benzene 2, ethyl acrylate 3, methyl methacrylate 4, acetic acid, trimethyl silyl ester 5, pyrrole 6, toluene 7, 2 methylpyrrole 8, 3 methylpyrrole 9, crotonic acid 10, ben zaldehyde 11, phenol 12, 2 methylphenol 13, 4 methylphenol 14, 2,4 dimethyl phenol 15, benzyl nitrile 16, 3 phenylpropionitrile 17, indole 18, phthalate 19, phthalate 20, ben zyl benzoate HMDS pyrolysis products [27]...

Silyl esters of trivalent phosphorus acids have been used successfully in conjugate addition reactions using acrylates,393 395 nitriles,394 amides,396 397 ketones and aldehydes,398-404 and nitro compounds.387... 

The formation of the latter compounds can be attributed to the result of the direct attack of the nucleophile R on the a- or p-carbon atoms of SENAs after elimination of the corresponding protons. However, it is most likely that the reaction proceeds through nitrile oxides or conjugated nitrosoalkenes (see Scheme 3.93). This interpretation is evidenced by generation of silyl esters of hydroxamic acids R CONHOSi as by-products. The reactions with more saturated solutions give the latter compounds as the major products. 

Even the addition of silyl radicals derived from silanes 411 to a,p-unsaturated carbonyl compounds 401 leading to fl-silyl esters or nitriles 412 can be promoted under similar conditions in 42-74% yield (Fig. 96) [439]. 

Transition metal carbonyls such as Co2(CO)8 and CoH(CO)4, formed in the reaction of R3SiH with dimer (but also Fe(CO)5 and M3(CO)i2 (M = Fe, Ru, Os)) have been found to be active catalysts for the hydrosilylation of olefins, dienes, unsaturated nitriles, and esters as well as for hydrosilylation C=0 and C=N bonds [56]. Hydrosilylation of phenylthioacetylenes in the presence of this catalyst is extremely regioselective [57]. Cobalt(I) complexes, e. g., CoH(X)2L3 (X = H, N), could be prospective candidates for investigation of the effectiveness of alkene hydrosilylation by trialkoxysilanes as well as dehydro-genative silylation [58]. Direct evidence for the silyl migration mechanism operative in a catalytic hydrosilylation pathway was presented by Brookhart and Grant [59] using the electrophilic Co cationic complex. 

Both diethyl trimethylsilyl phosphite and tris(trimethylsilyl) phosphite participate in conjugate addition reactions with a,p-unsaturated nitriles.With acrylonitrile, addition occurs readily at 120°C at the P position, with transfer of the silyl ester linkage to the a position of the nitrile, to give 2-silylated 2-cyanoethylphosphonates in 46-72% yields. Protodesilylation with a proton donor leads to the simple 2-cyanoethylphosphonates (Scheme 6.28). ... 

A simple Pt-catalyzed protocol has been developed by Widenhoefer and coworkers [230] that uses 2.5 mol% [PtCl2(H2C=CH2)]2 and 5 mol% PPhj for the intramolecular hydroamination of secondary amines (Scheme 15.49). This robust catalyst system can accommodate some functionality (e.g., silyl ethers, hahdes, nitriles, and esters) and unactivated terminal alkenes show good reactivity to give five- and... 

Ketosilanes result frcMnoC-silyl esters and are used to prepare homoallyl alcohols and aldols, while cyclic 5-silyl ketones form olefinic nitriles from the silicon-directed Beckmann fragmenta-... 

The reaLUons of phenyltetrafluorophosphorane with numerous silylated secondary or tertiary a- or (1-hydroxy esters, ketones, nitriles, ethers, nitro, and trichloromethyl derivatives have been investigated, the corresponding a or p fluoro derivatives are obtained in yields varying from reasonable to nearly quantitative [24, 25, 26, 27 The application of phenyltetrafluorophosphorane for fliiorination of silyloxy steroids has also been reported [28]... 

Silyl enol ethers and ketene acetals derived from ketones, aldehydes, esters and lactones are converted into the corresponding o/i-unsaturated derivatives on treatment with allyl carbonates in high yields in the catalytic presence of the palladium-bis(diphenylphosphino)ethane complex (32). A phosphinc-free catalyst gives higher selectivity in certain cases, such as those involving ketene acetals. Nitrile solvents, such as acetonitrile, are essential for success. 

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

Ketones and carboxylic esters can be a hydroxylated by treatment of their enolate forms (prepared by adding the ketone or ester to LDA) with a molybdenum peroxide reagent (MoOs-pyridine-HMPA) in THF-hexane at -70°C. The enolate forms of amides and estersand the enamine derivatives of ketones can similarly be converted to their a hydroxy derivatives by reaction with molecular oxygen. The M0O5 method can also be applied to certain nitriles. Ketones have also been Qc hydroxylated by treating the corresponding silyl enol ethers with /n-chloroperoxy-... 

The hydroxyl group was usually protected, because cyanohydrins have tendency to racemization or even decomposition. Vinyl ethers or acetal and acid catalysts furnish acetals [62]. Trialkylsilyl chlorides and imidazole are used to give silyl ethers [63]. Commonly used protective groups are silyl ether, ester, methoxy isopropyl (MIP) ether, and tetrahydro-pyranyl ether. ( -Protected cyanohydrins are tolerant to a wider range of cyanide/nitrile transformations and are utilized widely in the synthesis of compounds of synthetic relevance in organic chemistry. 

Palladium-catalyzed bis-silylation of a,/ -unsaturated ketones using bis(disilanyl)dithiane affords seven-membered ring silyl enol ethers in high yields via 1,4-addition (Equation (48)).8,97 Application of this reaction to a,/ -unsaturated esters and nitriles gives five-membered ring 1,2-addition products in good yields (Equation (49)). 

In the cathodic reduction of activated olefins, chlorosilanes also act as trapping agents of anionic intermediates. Nishiguchi and coworkers described the electrochemical reduction of a,/ -unsaturated esters, nitriles, and ketones in the presence of Me3SiCl using a reactive metal anode (Mg, Zn, Al) in an undivided cell to afford the silylated compounds [78]. This reaction provides a valuable method for the introduction of a silyl group into activated olefins. 

Kobayashi et al. developed the polymeric scandium(lll)-catalyst (42) (PA-Sc-TAD) which promotes the three-component couphng reactions of aldehydes and aromatic amines with either alkenes to generate quinohnes or silylated nucleophiles to form y9-amino ketones, esters and nitriles. This methodology turned out to be highly efficient with regard to automated high throughput synthesis (Scheme 4.27) [119]. 

Group-transfer polymerizations make use of a silicon-mediated Michael addition reaction. They allow the synthesis of isolatable, well-characterized living polymers whose reactive end groups can be converted into other functional groups. It allows the polymerization of alpha, beta-unsaturated esters, ketones, amides, or nitriles through the use of silyl ketenes in the presence of suitable nucleophilic catalysts such as soluble Lewis acids, fluorides, cyanides, azides, and bifluorides, HF. ... 

CsF in the presence ol tetraalkoxysilanes also effects Michael addition of ketones lo a,/ -unsaturaied ketones, esters, and nitriles. Presumably the enolate is generated and is converted by Si(OR)a into the silyl enol ether, which reacts in situ.2 Examples ... 

Typically, oc,0-unsaturated esters, a,0-unsaturated aldehydes and a,0-unsaturated nitriles are poor acceptors for the Lewis acid catalyzed silylallylation procedure, but they are excellent acceptors for the complementary fluoride ion mediated allylation procedure (cf. Volume 4, Chapter 1.2, Section 1.2.2.1.7). Other suitable acceptors include 1,4-quinones,70 a,0-unsaturated acyl cyanides (162),718 silyl ot,0-enoates (163)71b and nitroalkenes (Scheme 26) 72 reduction (titanium(III) trichloride) of the intermediate nitronates arising from nitroalkene allylation affords y,8-enones (166). 

Moreover, the formation of enoxy-silanes via silylation of ketones127 by means of N-methyl-N-TMS-acetamide (1 72) in presence of sodium trimethylsilanolate (173) was reported in 1969 and since then, the use of silylating reagents in presence of a catalyst has found wide appreciation and growing utilization as shown in recent papers128-132 (Scheme 27). Diacetyl (181) can be converted by trifluoromethylsul-fonic acid-TMS-ester (182) into 2,3-bis(trimethylsiloxy)-l, 3-butadiene (7treatment with ethyl TMS acetate (7 5)/tetrakis(n-butyl)amine fluoride l-trimethylsiloxy-2-methyl-styrene (i<56)130. Cyclohexanone reacts with the combination dimethyl-TMS-amine (18 7)/p-toluenesulfonic acid to 1-trimethylsiloxy-l-cyclohexene (iSS)131. Similarly, acetylacetone plus phenyl-triethylsilyl-sulfide (189) afford 2-triethylsiloxy-2-pentene-4-one (790)132. ... 

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