Catalytic system trimethylsilyl

Whereas the Prins-type cyclizations reported in this and the preceeding chapter were performed using stoichiometric amounts of Fe salts as Lewis acids, a breakthrough in the field of catalysis was reported in 2009 when the first iron-catalyzed Prins- and aza-Prins cyclization was reported. The catalytic system, which is obtained by combining catalytic amounts of an iron salt with trimethylsilyl halides as a halide source, is widely applicable and promotes the construction of substituted six-membered oxa- and aza-cycles (Scheme 33) [44]. 

Optically pure cyanohydrins serve as highly versatile synthetic building blocks [24], Much effort has, therefore, been devoted to the development of efficient catalytic systems for the enantioselective cyanation of aldehydes and ketones using HCN or trimethylsilyl cyanide (TMSCN) as a cyanide source [24], More recently, cyanoformic esters (ROC(O)CN), acetyl cyanide (CH3C(0)CN), and diethyl cyanophosphonate have also been successfully employed as cyanide sources to afford the corresponding functionalized cyanohydrins. It should be noted here that, as mentioned in Chapter 1, the cinchona alkaloid catalyzed asymmetric hydrocyanation of aldehydes discovered... 

In the synthesis of analogs of the antibiotic spectinomycin, Danishefsky and coworkers used the hetero Diels-Alder reaction to construct a precursor to install the stereochemistry on the tricyclic ring system. " Trimethylsilyl diene (145) reacts with acetaldehyde and a catalytic amount of Eu(fod)3 to give a 5.7 1... 

Work continued albeit at a lower pace after the above discoveries. For example the formation of N-Si bonds was established in the laboratory of Hidai and in this case a catalytic system was developed for formation of trimethylsilyl species from MejSiCl, using trans-[Mo(N2)2(dppe)2] and other dinitrogen complexes as catalysts (21)." ... 

Addition to C=0. Several protocols have been developed for the preparation of chiral cyanohydrins or their trimethylsilyl ethers. Catalytic systems including vanadyl-salen... 

The cross-coupling of aryl bromides and alkynes was found to be catalyzed by Pd(0Ac)2/IMes-HCl/Cs2C03 in DMAc at 80 °C (Scheme 17). Undesired dimerization products were obtained when phenylacetylene was employed as the alkyne source. This side reaction was suppressed by using a more reactive substrate, l-phenyl-2-(trimethylsilyl)acetylene [65]. Worthy of note is that high yields of coupled products were achieved under Cu-free conditions. Addition of 2 mol% Cul increased the reaction rates, most notably with deactivated or sterically encumbered aryl bromides. The catalytic system has a limited... 

Okamoto et reported a catalytic system based on an aminetris(aiyl-oxide) titanium complex, which gives a low-valent titanium species in the presence of trimethylsilyl chloride and magnesium powder. This system was studied in radieal ring opening of epoxides and oxetanes to generate the corresponding aleohols. 

In 2007, Feng et al. reported an efficient self-assembled catalytic system for the addition of trimethylsilyl cyanide to imines. The combined use of cinchonine (27), achiral 3,3 -(2-naphthyl)-2,2 -biphenol (28), and titanium tetra-isopropoxide gave an efficient catalyst for aldimines and ketimines (Scheme 7.19). Cinchonine induces a chiral environment around the titanium atom by fixing a stable chiral configuration to the biphenol ligand, and also activates hydrogen cyanide, generated in situ. In addition to trimethylsilyl cyanide, safer ethyl cyanoformate can be used with similar results. 

Miura. ° Reaction of allg nes with benzamides in dioxane at 100 °C proceeded under total regio- and stereoselective control to provide the ort/zo-alkenylated product (Scheme 9). It was essential to add stoichiometric amounts of AcOH to obtain optimal yield. Reaction of benzamide with various alkynes proceeded smoothly to produce the desired products in moderate to good yields. The reaction of 1-phenyl-2-(trimethylsilyl)acetylene proceeded efficiently but it underwent desilylation to afford the 1,1-diarylethene in 63% yield. In addition, the catalytic system was found to be suitable to the coupling of phenylazoles and phenylimidazoles with several alkyne derivatives giving dialkenylated products. In contrast, the sterically more hindered l-methyl-2-phenylimidazole provided the mono-alkenylated product selectively as the sole product. ... 

We studied a behavior of 5-trimethylsilyl-2-norbomene under the conditions of addition polymerization initiated by some Ni- and Pd-containing catalytic systems. The catalysts of this type have already demonstrated high activity in addition polymerization of norbomene and its alkyl derivatives [25,26]. The known Pd-containing catalytic systems (Ti -allyl)Pd(SbF6) [27] and a,7t-bicyclic complex [NB(OMe)PdCl]2 [28] turned out to be practically inactive in polymerization of 5-trimethylsilyl-2-norbomene. On the contrary, Ni-based complexes displayed a real activity in respect to this monomer. As a result saturated cyclolinear polymers were formed according to Scheme 6 of addition polymerization. The absence of any unsaturation in these polymers was confirmed by both infrared (IR) (no bands in 1620-1680 cm region) and H NMR spectroscopy (no signals at 5-6 ppm). 

Some details of polymerization process are represented in Table 6. Addition poly(5-trimethylsilyl-2-norbomenes) were obtained with tiie yields up to 80%. All of them were completely soluble in aromatic solvents. Among the Ni-based catalytic systems presented in Table 6. 

Table 6, Ni(II)naphtenate-inethylaluminoxane (MAO) and (7t-C5H9NiCl)2-MAO were more aetive. Polymers prepared in the presence of Ni(II)naphtenate-MAO catalyst had the highest molecular weights and demonstrated better fihn-forming properties. They did not show any glass transition up to 340°C (DSC). Gas-Uquid chromatography (GLC) analysis of the final polymerization mixtures indicated that in the course of the reaction exo-conformer was consumed much faster than endo-form independently of the type of catalytic system employed. It should be noted that polymerization of 5-trimethylsilyl-2-norbomene proceeded substantially slower than that of unsubstituted norbomene.

In 2011, Enders et al. reported a sequential organocatalytic cascade reaction between a,p-unsaturated aldehydes and p-oxosulfones, using a combination of a chiral diaiylprolinol trimethylsilyl ether and an achiral N-heterocyclic carbene as a catalytic system. This sequential... 

A unique system for catalytic silaboration of allenes, in which a catalytic amount of organic halide is used as a crucial additive, has been reported (Equation (86)).232 In the presence of Pd2(dba)3 (5 mol%) with 3-iodo-2-methyl-2-cyclohexen-l-one (10mol%), reactions of terminal allenes with a silylborane afford /3-silylallylboranes in good yields with excellent regioselectivity. It is worth noting that the addition takes place at the terminal C=C bond in contrast to the above-mentioned palladium-catalyzed silaboration. The alkenyl iodide can be replaced with iodine or trimethylsilyl iodide. The key reaction intermediate seems to be silylpalladium(n) iodide, which promotes the insertion of allenes with Si-C bond formation at the central -carbon. 

The chiral nonracemic bis-benzothiazine ligand 75 has been screened for activity in asymmetric Pd-catalyzed allylic alkylation reactions (Scheme 42) <20010L3321>. The test system chosen for this ligand was the reaction of 1,3-diphenylallyl acetate 301 with dimethyl malonate 302. A stochiometric amount of bis(trimethylsilyl)acetamide (BSA) and a catalytic amount of KOAc were added to the reaction mixture. A catalytic amount of chiral ligand 75 along with a variety of Pd-sources afforded up to 90% yield and 82% ee s of diester 303. Since both enantiomers of the chiral ligand are available, both R- and -configurations of the alkylation product 303 can be obtained. The best results in terms of yield and stereoselectivity were obtained in nonpolar solvents, such as benzene. The allylic alkylation of racemic cyclohexenyl acetate with dimethyl malonate was performed but with lower yields (up to 53%) and only modest enantioselectivity (60% ee). 

Information of the Gif system has been summarized,1055 1123 and new results, including new oxidants such as bis(trimethylsilyl) peroxide,1124 the synergistic oxidation of saturated hydrocarbons and H2S,1125 studies with the Fe3+-picolinate complex encapsulated within zeolites,1126 and the use of Udenfriend s system under Gif conditions1127 were disclosed. Gif-type oxidations were found to be moderately stereoselective.1128 Iron/zinc-containing species involved in Gif-type chemistry were synthesized, and their reactivity and catalytic behavior were studied.1129... 

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