Monosilyl

The chemoselective desilylation of one of the two different silyi enoi ethers in 10 to give the monosilyl enol ether II is realized by the Pd-catalyzed reaction of Bu3SnF. The chemoselectivity is controlled by steric congestion and the relative amount of the reagent[7,8]. An interesting transformation of the 6-alkoxy-2,3-dihydro-6//-pyran-3-one 12 into the cyclopentenone derivative 13 proceeds smoothly with catalysis by Pd(OAc)2 (10 mol%)[9]. 

Derivatives of 1,3- and 1,4-diols are stable to pH 4-10 at 22° for several hours, but derivatives of 1,2-diols undergo rapid hydrolysis under basic conditions (5 1 THF-pH 10 buffer, 22°, 5 min) to form monosilyl ethers of the parent diol. 

Similarly, in another example, alkylation of 111 with diepoxide (—)-115 (1 equiv.) in the presence of HMPA (1.3 equiv.) furnished diol (+)-117. Protection of (+)-117 to form the acetonide, removal of the silyl protecting groups (TBAF), and hydrolysis of the dithiane with Hg(Cl04)2 provided the diketone (+)-118. Hydroxy-directed syn-reduction of both carbonyl groups with NaBI U in the presence of Et2BOMe, and triacetonide formation, followed by hydrogenolysis and monosilylation, afforded the desired Schreiber subtarget (+)-119, which was employed in the synthesis of (+)-mycoticins A and B (Scheme 8.31) [56b]. 

Weiss et al. (1984) showed that A V-bis-silylated anilines react in aprotic dichloro-methane with generation of diazonium salts and formation of the non-nucleophilic hexamethyldisiloxane (Scheme 2-28). The authors indicate that the monosilylated aniline C6H5NHSi(CH3)3 reacts in many cases in an analogous way. This seems surprising, since the hydroxytrimethylsilane HOSi(CH3)3 that is formed is a potential proton donor, as it will rapidly condense to give (CH3)3SiOSi(CH3)3 + H20. 

In platinum chemistry, cleavage of bis(silyl) compounds by HCl may be used [Eqs. (58), (59)] to generate monosilyl complexes 63). 

But, as already mentioned, on working at ambient or lower temperatures and normal pressure, and at higher temperatures under pressure, the trimethylsilyl esters 30 react slowly with the liberated ammonia (or trimethylsilylamine 15) to form the primary amides 31 (Scheme 2.5) or their N-monosilylated analogs (cf Section 4.2.1). 

Nickel complexes formed in situ by the reaction of NiCl.S-COD) with the iini-dazolium salts IMesHCl or IPrHCl in the presence KO Bu catalyse the hydrosilylation of internal or terminal alkynes with EtjSiH. Interestingly, Ni tri-butylphosphine complexes are inactive in this hydrosilylation reaction. The monosilylated addition products were obtained with slow addition rates of the alkyne in the reaction mixture and were formed with variable degree of stereoselectivity, depending on the type of the alkyne, the silane and the ligand on Ni [50],... 

In a nice review of the preparative methods for silaaromatics, Maier221 suggested that the flash vacuum pyrolytic techniques that had been so useful for the monosilyl compound could be utilized to prepare 1,4-disila-benzene. Thermolysis of 1,4-disila-2,5-cyclohexadiene led to formation of... 

A-pyrrolyM-tri methyl si lyloxy)cyclobutenones and DMAD according to the following sequence (Scheme 93). The monosilylated indolizine-5,8-diols, 353, are the presumed key intermediates <1992TL7811>. 

Main problems of monosilylation of AN were considered in detail in Section 3.2.1.3. Transformations of SENAs were described in Section 3.4. Hence, the present section deals only with some aspects of the chemistry of these compounds and derivatives which were not covered in previous sections and which are associated with the process shown in Scheme 3.184. 

Intramolecular Trapping of Bis-N,N-Oxyiminium Cations Special y-functionalized nitro compounds (372) were constmcted with the aim of performing intramolecular trapping of bis-7V,7V-siloxyiminium cations prepared in process of double silylation of (372). Monosilylation of the latter compounds can afford different silyl derivatives (373a-c) (Scheme 3.212) (486, 487). 

Selective silylation of polychloromethanes using reactive metal electrodes such as zinc and magnesium has also been reported as shown in Scheme 37 [76, 77]. The electroreduction of carbon tetrachloride and chloroform in the presence of chlorotrimethylsilane affords the monosilylated and disilylated products. The product selectivity seems to depend upon the electrode material. 

Recently, Schaumann et al. 153,154 an(j Bienz et tf/.155,156 have developed dependable routes for the resolution of racemic functionalized organosilanes with Si-centered chirality using chiral auxiliaries, such as binaphthol (BINOL), 2-aminobutanol, and phenylethane-l,2-diol (Scheme 2). For instance, the successive reaction of BINOL with butyllithium and the chiral triorganochlorosilanes RPhMeSiCl (R = /-Pr, -Bu, /-Bu) affords the BINOL monosilyl ethers 9-11, which can be resolved into the pure enantiomers (A)-9-ll and (7 )-9-11, respectively. Reduction with LiAlFF produces the enantiomerically pure triorgano-H-silanes (A)- and (R)-RPhMeSiH (12, R = /-Pr 13, -Bu 14, /-Bu), respectively (Scheme 2). Tamao et al. have used chiral amines to prepare optically active organosilanes.157... 

The authors indicate that the monosilylated aniline CgHsNHSiMes reacts in many cases in an analogous way. This seems surprising, since the hydroxytrimethylsilane HOSiMe3 that is formed is a potential proton donor, as it will rapidly condense to give Me3SiOSiMe3 + H2O. 

Subsequent monosilylation and Wittig reaction furnished unsymmetrical double diene 170. The synthesis of the other Diels-Alder partner started from bromophenol 173 (prepared in three steps from dimethoxytoluene), which was doubly metalated and reacted with (S,S)-menthylp-toluenesulfinate 173. CAN oxidation delivered quinone 171, which underwent a Diels-Alder reaction with double diene 170 to give compound 175 possessing the correct regio- and stereochemistry. Upon heating in toluene the desired elimination occurred followed by IMDA reaction to adduct 176, which was obtained in an excellent yield and enantioselectivity. Both Diels-Alder reactions proceeded through an endo transition state the enantioselectivity of the first cyclization is due to the chiral auxiliary, which favors an endo approach of 170 to the sterically less congested face (top face) (Scheme 27). 

When the monosilylated precursor 26 was reacted in a similar manner with LiBH4 according to Scheme 11, the resulting product was the solvent-free lithium borate salt 27 (74% yield). This compound could be recrystallized from -hexane. 

The cyclohexyl-substituted analog of 40, [Et3NH] [ (c-CeHi 1)781701 i(OSi-Me3) 2Al] (44), was synthesized independently in our laboratory by dehydrochlorination of the monosilylated precursor 12 with anhydrous AICI3 in the presence of triethylamine (Scheme 13). A comparison of the X-ray crystal structures of... 

The fulvene route was also successfully employed in the preparation of a compound, which can be regarded as one of the most advanced molecular models for a catalytically active titanium center on a silica surface. When Cp Ti(C5Me4CH2) was reacted with the monosilylated silsesquioxane precursor 12 in refluxing toluene a color change from deep purple to amber was observed. Crystallization afforded a bright-yellow material, which was subsequently shown to be the novel mo o(pentamethyleyclopentadienyl) titanium(IV) silsesquioxane complex 126 (69% yield). Its formation is illustrated schematically in Scheme 42. 

A series of ferrasilsesquioxanes stabilized by phosphine ligands has been prepared and characterized by Baker et al Reactions of the iron(II) precursor FeCl2(dcpe) (dcpe = bis(dicyclohexylphosphino)ethane) with 2 or the monosilylated precursor (c-C5H9)7Si70g(0SiMe3)(0FI)2 (38) afforded the (dcpe)iron(II)-silsesquioxane... 

The first silsesquioxane derivative of copper was made in our laboratory according to Scheme 65. The reaction of the monosilylated disilanol precursor 12 with tetrameric copper(I)-r-butoxide in a molar ratio of 2 1 afforded the colorless copper(I) silsesquioxane complex 187, in which the CU4O4 core of copper(I)-t-but-oxide is retained. 

Thus, only few reports were disclosed for the [1,3] Brook isomerization Utimoto, Oshima and coworkers have reported that the treatment of tert-butyldimethyl(dibromomethyl)silane 64 with LDA followed by the addition of an excess of benzaldehyde lead to the 1,3-diol monosilyl ether 66 via the intermediacy of lithium carbenoid 65 (equation 24) . The rate of isomerization was dependent on the solvent used and HMPA was found to be the best solvent. ... 

---