Dimethylphenylsilane

Heptyl 3-Phenylpropyl Ether [Electrogenerated Acid-Promoted Reduction of an Aldehyde to an Unsymmetrical Ether].333 A mixture of 1-heptanal (1.0 mmol), 3-phenylpropoxytrimethylsilane (1.2 mmol), tetra-n-butylammonium perchlorate (0.1 mmol), and lithium perchlorate (0.1 mmol) was dissolved in CH2CI2 (3 mL) in an undivided cell. The mixture was electrolyzed under constant current (1.67 mA cm-2) with platinum electrodes at ambient temperature. After 5 minutes, dimethylphenylsilane (1.2 mmol) was added drop-wise and the electrolysis was continued (0.06 Faraday/mol). After completion of the reaction, one drop of Et3N was added and the solution was concentrated. The residue was chromatographed on Si02 to give 1-heptyl 3-phenylpropyl... 

Example of use with dimethylphenylsilane (11). A mixture of the a/3-unsaturated ketone (1.05 mmol), dimethylphenylsilane (1.1 mmol) and tris(triphenylphosphine)rhodium(i) chloride (0.002 mmol) was heated at 55 °C for 1 h. The silyl enol ether was distilled directly from the reaction. 

C-Alkylation. (Chloromethyl)dimethylphenylsilane (1) can be utilized to install a silylmethyl group on carbon via base promoted C-alkylation of terminal alkynes, dihydropyrazines, mal-onic esters, phenylacetonitriles, sulfoxides, and imines. Although 1 has been used directly in the alkylation, conversion to the corresponding iodide 2 via Finkelstein displacement (eq 1) prior to alkylation is sometimes warranted. Except for the malonic esters (eq 2), strongly basic conditions and low temperatures (with slow warming) are generally employed in the transformation (eqs 3 and 4). 

V-Alkylation. (Chloromethyl)dimethylphenylsilane (1) has been utilized for the alkylation of nitrogen nucleophiles including amines, a-aminoesters (eq 5), anilides and anilines (eq 6), 4 benzimidazole, potassium cyanate (with in situ treatment with ammonia to afford a nitrosourea), and sodium azide (eq 1)P Although 1 has been utilized for IV-alkylation of a variety of nitrogen nucleophiles, the reaction conditions tend to be similar and usually involve employing an exogenous base, elevated temperatures, and polar aprotic solvents (e.g., DMF, DMSO, DMPU) to effect the M-alkylation. In some cases, for instance, alkylation of Q -aminoester 9, potassium iodide is incorporated to facilitate the reaction. 

The reduction of tributyltin methoxide with optically active methyl-phenyl-1-naphthylsilane involves retention of configuration at the silicon atom and follows second-order kinetics (2 72). The reaction between tributyltin methoxide and ring-substituted dimethylphenylsilanes shows a Hammett p-value of -t-0.903, and that between dimethyl-phenylsilane and ring-substituted tributyltin phenoxides shows a p-value of -1.319 this is compatible with the reactions proceeding through a 4-centered (SNi-Si) transition state (272, 173). 

In a similar way as described for the hydroformylation, the rhodium-catalyzed silaformylation can also be used in a domino process. The elementary step is the formation of an alkenyl-rhodium species by insertion of an alkyne into a Rh-Si bond (silylrhodation), which provides the trigger for a carbocyclization, followed by an insertion of CO. Thus, when Matsuda and coworkers [216] treated a solution of the 1,6-enyne 6/2-87 in benzene with the dimethylphenylsilane under CO pressure (36 kg cm"2) in the presence of catalytic amounts of Rh4(CO)12, the cyclopentane derivative 6/2-88 was obtained in 85 % yield. The procedure is not restricted to the formation of carbocycles rather, heterocycles can also be synthesized using 1,6-enynes as 6/2-89 and 6/2-90 with a heteroatom in the tether (Scheme 6/2.19). Interestingly, 6/2-91 did not lead to the domino product neither could 1,7-enynes be used as substrates, while the Thorpe-Ingold effect (geminal substitution) seems important in achieving good yields. 

Itoh and coworkers [223] have shown that fullerene derivatives as 6/2-113, which to date have been prepared in a stepwise procedure, can be obtained in a three-component domino process by treatment of diynes 6/2-109, dimethylphenylsilane 6/2-110 and fullerene (C60) in the presence of a Rh-catalyst [223]. Interestingly, using maleic anhydride as dienophile failed to give the desired cycloadduct, whereas Cso -in spite of its strong tendency to form complexes with various transition metals [224] - never suppressed the catalytic silylative cyclization step to give the diene 6/2-112 (Scheme 6/2.24). 

Wilkinson s catalyst brings about the hydrosilylation of a range of terminal alkenes (1-octene, trimethylvinylsilane) by 2-dimethylsilylpyridine with good regioselectivity for the anti-Markovnikoff product. Both 3-dimethylsilylpyridine and dimethylphenylsilane are less reactive sources of Si-H. In contrast, these two substrates are far more reactive than 2-dimethylsilylpyridine for the hydrosilylation of alkynes by [Pt(CH2 = CHSiMe2)20]/PR3 (R = Ph, Bu ). This difference was explained to be due to the operation of the two different pathways for Si-H addition—the standard Chalk-Harrod pathway with platinum and the modified Chalk-Harrod pathway with rhodium.108... 

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... 

Benzaldehyde itself forms no toluene only dibenzyl ether and benzyl trifluo-roacetate are formed. Triethylsilane (2.2 equivalents) causes the transformation of /7-anisaldehyde into /7-methylanisole in 76% yield after only 30 minutes. Use of a three-fold excess of dimethylphenylsilane in place of the triethylsilane results in a slight improvement in yield to 83% after 45 minutes.69... 

Similar treatment of a trifluoroacetic acid solution of p-tolualdehyde with triethylsilane gives only a 20% yield of /7-xylene after 11 hours reaction time followed by basic workup. Use of 2.5 equivalents of dimethylphenylsilane enhances the yield to 52% after only 15 minutes. This reaction proceeds stepwise through the formation of a mixture of the trifluoroacetate and the symmetrical ether. These intermediates slowly form the desired /7-xylene product along with Friedel-Crafts side products under the reaction conditions (Eq. 192).73 Addition of co-solvents such as carbon tetrachloride or nitromethane helps reduce the amount of the Friedel-Crafts side products.73... 

The diastereoselectivity of the reduction of a-substiluted ketones has been the subject of much investigation. The reagent combination of trifluoroacetic acid and dimethylphenylsilane is an effective method for the synthesis of erythro isomers of 2-amino alcohols, 1,2-diols, and 3-hydroxyalkanoic acid derivatives.86,87,276,375 Quite often the selectivity for formation of the erythro isomer over the threo isomer of a given pair is >99 1. Examples where high erythro preference is found in the products are shown below (Eqs. 218-220).276 Similar but complementary results are obtained with R3SiH/TBAF, where the threo isomer product... 

A. ( )-1-(Dimethylphenylsilyl)-1-buten-3-ol (2a). A solution of 10.0 g (0.143 mol) of racemic 3-butyn-2-ol (Note 1) dissolved in 255 mL of tetrahydrofuran (THF, Note 2) in a 1-L, round-bottomed flask equipped with a reflux condenser and nitrogen atmosphere is prepared. Dimethylphenylsilane (21.4 g, 0.157 mol) (Note 3) and a small piece of sodium metal (ca. 5 mg) (Note 4) are placed in the reaction mixture. The solution is stirred for 15 min and 12 mg (2.05 x 10 5 mol) of bis(q-divinyltetramethyldisiloxane)tri-tert-butylphosphineplatinum(O) (Note 5) is added. The reaction mixture is then heated under reflux for 12 hr. The orange solution is cooled to ambient temperature, and the solvent is removed under reduced pressure to yield a crude orange residue containing 2a. The oil is subjected to column chromatography on silica gel (Note 6) (gradient elution 5, 10, 20, 35% EtOAc/hexanes) providing 25.4 g (123.23 mmol, 86%) of pure 2a as a yellow oil (Note 7). 

Dimethylphenylsilane is purchased from United Chemical Technologies, Inc (formerly Hiils Petrarch Inc.). 

Iridium siloxide complexes show a similar activity. Catalytic tests performed in the presence of [ Ir( 4-OSiMe3)(cod) 2], with the use of trimethylvinylsilane and dimethylphenylsilane as reactants [59], gave the same type of silicon derivatives as those obtained by Murai and coworkers [58], but the siloxide iridium precursor used appeared to be more efficient under milder conditions. When the [Ir(cod)(PCy3)(OSiMe3)] was used rather than the binuclear iridium siloxide complex, Z-Me3SiCH2CH=CHOSiMe2Ph was obtained exclusively [59],... 

The consecutive reduction and cyclization of O-benzoyl protected 5-0-methylhexose 0-(terf-butyldiphenylsilyl)oxime (104) with dimethylphenylsilane in trifluoroacetic acid afforded a iV-hydroxypyrrolidine (105) ring system in good yield (equation 44). The mechanism involves a cascade of neighboring group participation steps involving the 0-benzoyl protecting groups " ". ... 

Matsuda reported a protocol for the cyclization/hydrosilylation of diynes to form silylated ( )-I,2-dialkylidene cyclopentanes catalyzed by neutral Rh(i) and Rh(iii) complexes.For example, reaction of dimethyl dipropargylmalonate with dimethylphenylsilane catalyzed by Rh(H)(SiMe2Ph)Gl(PPh3)2 7 in dichloromethane at room temperature gave... 

Shibata and co-workers have reported an effective protocol for the cyclization/hydrosilylation of functionalized eneallenes catalyzed by mononuclear rhodium carbonyl complexes.For example, reaction of tosylamide 13 (X = NTs, R = Me) with triethoxysilane catalyzed by Rh(acac)(GO)2 in toluene at 60 °G gave protected pyrrolidine 14 in 82% yield with >20 1 diastereoselectivity and with exclusive delivery of the silane to the G=G bond of the eneallene (Equation (10)). Whereas trimethoxysilane gave results comparable to those obtained with triethoxysilane, employment of dimethylphenylsilane or a trialkylsilane led to significantly diminished yields of 14. Although effective rhodium-catalyzed cyclization/hydrosilylation was restricted to eneallenes that possessed terminal disubstitution of the allene moiety, the protocol tolerated both alkyl and aryl substitution on the terminal alkyne carbon atom and was applicable to the synthesis of cyclopentanes, pyrrolidines, and tetrahydrofurans (Equation (10)). 

Palladium-catalyzed diene cyclization/hydrosilylation was compatible with a number of functionalized silanes, including dimethylphenylsilane, dimethylbenzylsilane, dimethylbenzhydrylsilane, and pentamethyldisiloxane... 

Matsuda independently developed an alternative procedure for the cyclization/silylformylation of enynes that did not require the use of phosphite ligand, and which was effective with low catalyst loading. As an example, reaction of a benzene solution of acetal 65 (0.1 M) and dimethylphenylsilane catalyzed by Rh(acac)(GO)2 (0.005 mol%) under GO (20 bar) at 90 °G for 14 h formed silylated alkylidene carboxaldehyde 66 in 89% yield (Equation (44)). 

Rhodium carbonyl complexes also catalyze the cascade cyclization/hydrosilylation of 6-dodecene-l,l 1-diynes to form silylated tethered 2,2 -dimethylenebicyclopentanes. For example, reaction of ( )-85 with dimethylphenylsilane catalyzed by Rh(acac)(CO)2 in toluene at 50 °G under GO (1 atm) gave 86a in 55% yield as a single diastereomer (Equation (56)). Rhodium-catalyzed caseade cyclization/hydrosilylation of enediynes was stereospecific, and reaction of (Z)-85 under the conditions noted above gave 86b in 50% yield as a single diastereomer (Equation (57)). Rhodium(i)-catalyzed cascade cyclization/hydrosilylation of 6-dodecene-1,11-diynes was proposed to occur via silyl-metallation of one of the terminal G=G bonds of the enediyne with a silyl-Rh(iii) hydride complex, followed by two sequential intramolecular carbometallations and G-H reductive elimination. ... 

In contrast to the reactivity of 6-dodecene-1,11-diynes, rhodium-catalyzed reaction of l-dodecene-6,11-diynes with silane led not to cascade cyclization/hydrosilylation but rather to carbonylative tricyclization. For example, reaction of 87 [X = G(G02Me)2] and dimethylphenylsilane catalyzed by Rh(acac)(GO)2 in THE at room temperature under GO gave the cyclopenta[e]azulene 88 in 92% yield as the exclusive product (Scheme 22). Although the protocol was... 

This reaction is also a transfer dehydrogenative reaction, as two reactant hydrogen atoms are not incorporated into the enol silyl ether product but instead serve to hydrogenate another molecule of starting alkene. For example, in the reaction of vinylcyclohexane, ethylcyclohexane is obtained in equal amounts to the silylated product. Both iridium complexes effectively catalyze the reaction. Various silanes can be used, including di-ethylmethyl-, triethyl-, and dimethylphenylsilane. The reaction is successful for a range of terminal alkenes, even those bearing cyano, acetal, and epoxide functionalities. The E isomer of the product is predominantly formed. 

Reaction with dimethylphenylsilane is catalyzed at room temperature under 250 psi of carbon monoxide. Other silanes tested, triethyl- and triphenylsi-lane, are not effective reagents in this system. A variety of aldehydes are good substrates for the reaction, including benzaldehyde, substituted benzaldehydes, and heterocyclic aldehydes. Aliphatic aldehydes also yield a-siloxy aldehyde products, but the reaction must be run at higher CO pressure (1000 psi) to avoid hydrosilylation. The reaction does not tolerate substrates bearing strong electron-withdrawing substituents, such as p-nitrobenzaldehyde. 

Dimethylphenylsilane, 123 2-Oxazolidones, chiral, 225 Potassium triethylborohydride, 260 Hydroxy esters and lactones a-Hydroxy esters and lactones By hydroxylation a to the carbonyl group... 

Hydroxylamines and derivatives Borane-Tetrahydrofuran, 42 Dimethylphenylsilane, 123 Hydroxy nitriles (see also Cyanohydrins) Nickel, 197 Hydroxy selenides... 

Dichlorodiphenylsilane, 74 1,2-Diethoxy-1,2-bis(trimethylsilyloxy)-ethylene, 108 Diethoxymethylsilane, 76 Dimethoxy[ 1-trimethylsilyl-l, 2-buta-dienyljborane, 218 Dimethylphenylsilane, 123 Dimethylphenylsilane-Tris(diethyl-amino)sulfonium difluorotrimethyl-silicate, 123... 

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