Tris silane with aldehyde

The trimethylsilylated ylides (1), easily generated from trimethyl chlorosilane and ylides, react with aldehydes 2 to form vi-nylsilanes 3 (2,3). The vinylphosphonium silanolates 4 are also formed. Compounds 3 are versatile reagents for further reactions (4). The ylide J (with R1 =H) reacts with aldehydes 2 to give the dienes j). The oxidation of with the adduct 6, from triphenyl-phosphite and ozone, gives access to a generaT synthesis of acyl-silanes (trimethylsilylketones) (2). The silylated ylides react to form phosphonium salts 7 with halogen compounds. The salts 7.can be desilylated by fluorine ions. The disubstituted ylides JO Tormed can be converted in statu nascendi with aldehydes V[ into the tris-substituted olefin J2 (2,3). In the case of R3-I, vinyl... 

In a limited number of cases, arylsilanes react with aldehydes as if they were aryl Grignard or aryllithium reagents. Both trimethyl(perchlorophenyl)silane and trimethyl(perfluoro-phenyl)silane react with benzaldehyde to give the corresponding 7.-(pcrhalophenyl)bcnzyl tri-methylsilyl ethers.163 Benzaldehyde reacts completely with trimethyl(perfluorophenyl)silane in diethyl ether in the presence of either a catalytic amount of the potassium cyanide/18-crown-6 complex in less than 5 hours at room temperature or potassium fluoride in dimethylform-umide.164 In the case of aryltrimcthylsilanes containing electron-withdrawing substituents in the ortho position, the reaction is observed only under the conditions of nucleophilic catalysis by potassium fluoride or cesium fluoride. 

Treatment of trifluoromethyl(trimethyl)silane with fhe fused salt gives the tri-fluoromefhyl anion-equivalent species. This adds to the aldehyde in good yield to form fhe alcohol wifh a trifluoromethyl group (Scheme 2.11). 

The Cossy " and Marden groups independently demonstrated that the RCM reactions of allylsiloxanes 60 and the subsequent Sakurai reaction of the resulting cyclic allyl-silane 61 with aldehydes or ketones afforded the tri- or tet-rasubstituted cyclic ethers (Scheme 24.17). Marsden and Akindele applied this protocol to a concise synthesis of the lignan (+)-virgatusin (64, Scheme 24.17). ... 

This method can be applied to a variety of diazoesters in the presence of differently substituted silanes. Steric hindrance aroimd the silicon group does not interfere with the process. The allylsi-lanes obtained through this method were functionalized, for instance, through reduction of the ester function into an alcohol followed by an electrophilic 5-endo-tng cyclization, giving rise to a variety of tri- and tetrasubstituted tetrahydrofurans with high diastereocontrol (9). Panek et al. used these allylsilanes in Lewis acid—catalyzed crotylation processes with aldehydes to prepare highly functionalized vinylogous aldol products (10). 

Fluoride ion catalyzes the hydrosilylation of both alkyl and aryl aldehydes to silyl ethers that can be easily hydrolyzed to the free alcohols by treatment with 1 M hydrogen chloride in methanol.320 The most effective sources of fluoride are TBAF and tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF). Somewhat less effective are CsF and KF. Solvent effects are marked. The reactions are facilitated in polar, aprotic solvents such as hexamethylphosphortriamide (HMPA) or 1,3-dimethyl-3,4,5,6-tetrahydro-2(l //)-pyrirnidinone (DMPU), go moderately well in dimethylformamide, but do not proceed well in either tetrahydrofuran or dichloromethane. The solvent effects are dramatically illustrated in the reaction of undecanal and dimethylphenylsilane to produce undecyloxyphenyldimethylsi-lane. After one hour at room temperature with TBAF as the source of fluoride and a 10 mol% excess of silane, yields of 91% in HMPA, 89% in DMPU, 56% in dimethylformamide, 9% in tetrahydrofuran, and only 1% in dichloromethane are obtained (Eq. 164).320... 

The ruthenium carbene catalysts 1 developed by Grubbs are distinguished by an exceptional tolerance towards polar functional groups [3]. Although generalizations are difficult and further experimental data are necessary in order to obtain a fully comprehensive picture, some trends may be deduced from the literature reports. Thus, many examples indicate that ethers, silyl ethers, acetals, esters, amides, carbamates, sulfonamides, silanes and various heterocyclic entities do not disturb. Moreover, ketones and even aldehyde functions are compatible, in contrast to reactions catalyzed by the molybdenum alkylidene complex 24 which is known to react with these groups under certain conditions [26]. Even unprotected alcohols and free carboxylic acids seem to be tolerated by 1. It should also be emphasized that the sensitivity of 1 toward the substitution pattern of alkenes outlined above usually leaves pre-existing di-, tri- and tetrasubstituted double bonds in the substrates unaffected. A nice example that illustrates many of these features is the clean dimerization of FK-506 45 to compound 46 reported by Schreiber et al. (Scheme 12) [27]. 

The radical-initiated allylation of alkyl halides with allyltris(trimethylsilyl)silanes proceeds via an SH2 process mediated by a tris(trimethylsilyl)silyl radical.225 The radical-allylating agents react with alkenes, alkynes, and aldehydes via a radical chain process to give the corresponding allylsilylation products.226... 

The hydrolysis of thiazolidines to aldehydes is conveniently carried out under neutral conditions by the assistance of metal ions such as Hg" or Cu" <93JOC275>. Unlike the above hydrolysis under acid or base conditions, the synthetic value of this important transformation has been demonstrated (see Section 3.06.12). Open-chain compounds are obtained when thiazolidines are treated with tris(trimethylsilyl)silane in a reaction in which the thiazolidine derivatives act as a source of a-aminoalkyl radicals <91TL2857,91TL6265>. 

The magnesium-mediated reductive trifluoromethylation also works for other structurally diverse chlorosilanes. Chlorotriethyl-silane, f-hutyldimethylsilyl chloride, and tris(trimethylsilyl)silyl chloride have been applied to prepare corresponding trifluoro-methyl-containing silanes. However, the reductive trifluoromethylation did not take place with other electrophiles such as aldehydes, ketones, allyl bromide, benzyl chloride, or tributyltin chloride. Even tributyltin hydride and allyltrimethylsilane showed no reactivity The reason for such behavior is not clear. Probably, chlorosilanes play an important role during the reductive trifluoromethylation both as a silylating agent and a single-electron transfer promoter. 

Similarly, through the use of [difluoro(phenylthio)methyl]tri-methylsilane or [difluoro(phenylseleno)methyl]trimethyl-silane treated with TBAT, in the presence of amides, imines, or aldehydes, the respective difluoromethylene phenylsulfide or difluoromethylene phenylselenide is produced (eq 19). 

An unselective synthesis by RajanBabu and coworkers is of interest in that it appears to be the only route to date in which additional diastereomers of indolizidine 223A (1556) were produced (Scheme 264). The racemic aUene-aldehyde precursor 2097, used as a mixture of four diastereomers, cychzed rapidly when treated with trimethyl(tri-tt-butylstannyl)silane and aUylpaUadium chloride dimer to give a mixture of four indoUzidin-3-ones 2098 in 82% combined yield. The isomers could be separated and individually characterized with the aid of NMR spectroscopy. After protodesilyla-tion to isomers of 2099, various reductive transformations eventually led to the isolation of two different racemic diastereomers of the alkaloid, viz. ( )-5,8-di- (-indohzidine 223A 2100 and ( )-6,8-di-epi-indolizidine 223A 2101. Also obtained in this work was the lactam 2102, which could presumably be reduced to give ( )-8- (-indolizidine 223A. 

The reduction of alkyl hahdes has been important in many syntheses. Sodium cyanoborohydride in HMPA will reduce alkyl iodides, bromides, and tosylates selectively in the presence of ester, amide, nitro, chloro, cyano, alkene, epoxide, and aldehyde groups [118]. Tri-n-butyltin hydride will replace chloro, bromo, or iodo groups with hydrogen via a free radical chain reaction initiated by thermal decomposition of AIBN [119]. Other functionality such as ketones, esters, amides, ethers, and alcohols survive unchanged. The less toxic tris(trimethylsilyl) silane can be used similarly [120]. 

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