Silyl cyclohexane

Tsuji has reported the palladium-catalyzed cyclization/disilylation of bis( 1,3-dienes) with disilanes to form disilylated divinylcycloalkanes. For example, reaction of ( , )-6,6-dicyano-l,3,8,10-undecatetraene 89a and diphenyltetra-methyldisilane (1.2equiv.) catalyzed by Pd(DBA)2 gave 90a in 74% yield with exclusive formation of the trans-E,Z-diastereomer (Equation (58)). The stereoselectivity of the palladium-catalyzed cyclization/disilylation of bis(dienes) was substrate dependent, and the Pd-catalyzed reaction of 89b gave the bis(silylated) cyclopentane 90b in 82% yield with 70% selectivity for the /ra //j - ,Z-diastereomer (Equation (58)). In comparison, the reaction of ( , )-6,6-bis(ethoxycarbonyl)-l,3,9,ll-dodecatetraene gave the bis(silylated)cyclohexane 91 in 49% yield with exclusive formation of the /ra //i - , -diastereomer (Equation (59)). 

In this section primarily reductions of aldehydes, ketones, and esters with sodium, lithium, and potassium in the presence of TCS 14 are discussed closely related reductions with metals such as Zn, Mg, Mn, Sm, Ti, etc., in the presence of TCS 14 are described in Section 13.2. Treatment of ethyl isobutyrate with sodium in the presence of TCS 14 in toluene affords the O-silylated Riihlmann-acyloin-condensation product 1915, which can be readily desilylated to the free acyloin 1916 [119]. Further reactions of methyl or ethyl 1,2- or 1,4-dicarboxylates are discussed elsewhere [120-122]. The same reaction with trimethylsilyl isobutyrate affords the C,0-silylated alcohol 1917, in 72% yield, which is desilylated to 1918 [123] (Scheme 12.34). Likewise, reduction of the diesters 1919 affords the cyclized O-silylated acyloin products 1920 in high yields, which give on saponification the acyloins 1921 [119]. Whereas electroreduction on a Mg-electrode in the presence of MesSiCl 14 converts esters such as ethyl cyclohexane-carboxylate via 1922 and subsequent saponification into acyloins such as 1923 [124], electroreduction of esters such as ethyl cyclohexylcarboxylate using a Mg-electrode without Me3SiCl 14 yields 1,2-ketones such as 1924 [125] (Scheme 12.34). 

Organic synthesis 74 [OS 74] Reaction between 4-bromobenzaldehyde and the silyl enol ether of cyclohexane [15]... 

A procedure developed by Prof. Olah based on the use of lithium sulfide as a base is well suitable for silylation of nitro derivatives of the cyclohexane series (180, 181) (Scheme 3.53). 

Rate constants for the reaction of thiyl radicals with the t-BuMePhSiH were also extracted from the kinetic analysis of the thiol-catalysed radical-chain racemization of enantiomerically pure (S)-isomer [34]. Scheme 3.2 shows the reaction mechanism that involves the rapid inversion of silyl radicals together with reactions of interest. The values in cyclohexane solvent at 60 °C are collected in the last column of Table 3.5. 

Trans-1 -allyl-2-(trimethylsilyl)cyclopentane and trans-1 -allyl-2-(trimethylsilyl)-cyclohexane are formed from the reaction of la with cyclopentene and cyclohexene, respectively. A second allylsilylation reaction of these compounds with la also gives unusual allylsilylation products, 7-cyclopent-l-enyl-2,2-dimethyl-4-(trimethylsilyl-methyl)-2-silaheptane (30%) and 4-((cyclohex-l-enyl)methyl)-2,2,8,8-tetramethyl-2,8-disilanonane (39%). As observed in the allylsilylation of 4-(trimethylsilyl-methyl)-l-alkenes, these products are likely formed via intramolecular silyl rearrangements. In this case, the results strongly suggest that a 1,5-silyl shift and... 

Group transfer polymerization allows the synthesis of block copolymers of different methacrylate or acrylate monomers, such as methyl methacrylate and allyl methacrylate [Hertler, 1996 Webster and Sogah, 1989]. The synthesis of mixed methacrylate-acrylate block copolymers requires that the less reactive monomer (methacrylate) be polymerized first. The silyl dialkylketene acetal propagating center from methacrylate polymerization is more reactive for initiation of acrylate polymerization than the silyl monoalkylketene acetal propagating center from acrylate polymerization is for initiation of methacrylate polymerization. Bifunctional initiators such as l,4-bis(methoxytri methyl si loxymethylene)cyclohexane (XXXIII) are useful for synthesizing ABA block copolymers where the middle block is methacrylate [Steinbrecht and Bandermann, 1989 Yu et al., 1988]. 

Tamao and Ito have reported a nickel-catalyzed protocol for the cyclization/hydrosilylation of 1,7-diynes to form (Z)-silylated dialkylidene cyclohexane derivatives.For example, reaction of 1,7-octadiyne with triethoxysilane catalyzed by a mixture of Ni(acac)2 (lmol%) and DIBAL-H (2mol%) in benzene at 50°G for 6h gave the corresponding silylated dialkylidene cyclohexane in 70% yield as a single isomer (Table 1). The reaction of 1,7-octadiyne was also realized with mono- and dialkoxysilanes, trialkylsilanes, and dialkylaminosilanes (Table 1). Diynes that possessed an internal alkyne also underwent nickel-catalyzed reaction, albeit with diminished efficiency (Table 1), while 1,6- and 1,8-diynes failed to undergo nickel-catalyzed cyclization/hydrosilylation. 

Tamao and Ito proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of 1,7-diynes initiated by oxidative addition of the silane to an Ni(0) species to form an Ni(ii) silyl hydride complex. Gomplexation of the diyne could then form the nickel(ii) diyne complex la (Scheme 1). Silylmetallation of the less-substituted G=C bond of la, followed by intramolecular / -migratory insertion of the coordinated G=G bond into the Ni-G bond of alkenyl alkyne intermediate Ila, could form dienylnickel hydride intermediate Ilia. Sequential G-H reductive elimination and Si-H oxidative addition would release the silylated dialkylidene cyclohexane and regenerate the silylnickel hydride catalyst (Scheme 1). 

Molander has developed effective protocols for the cyclization/hydrosilylation of 1,6-enynes catalyzed by lanthanide metallocene complexes/ For example, reaction of cyclohexyl-substituted 1,6-enyne 15a with phenylsilane catalyzed by Cp 2YMe(THF) in cyclohexane at room temperature for 2h gave silylated alkylidene cyclopentane 16a as a 6.5 1 mixture of trans. cis isomers (Table 5, entry 1). The diastereoselectivity of the reaction depended strongly on the nature of the allylic substituent. For example, yttrium-catalyzed cyclization/ hydrosilylation of the ethyl-substituted enyne 15b gave silylated cyclopentane 16b in 88% yield as a single diastereomer (Table 5, entry 2). 

Lanthanide-catalyzed enyne cyclization/hydrosilylation was also applied to the synthesis of silylated alkylidene cyclohexane derivatives. For example, reaction of the 3-silyloxy-l,7-enyne 17 with methylphenylsilane catalyzed by Gp 2YMe(THF) at 50°G for 8h gave 18 in quantitative yield as a 4 1 mixture of trans cis isomers (Equation (11)). Employment of methylphenylsilane in place of phenylsilane was required to inhibit silylation of the initially formed yttrium alkenyl complex, prior to intramolecular carbometallation (see Scheme 8). 

A related approach directed toward cyclohexane derivatives affords products without carbon substituents on the rings. Ozonolysis of the 6-deoxyhex-5-enopyranoside derivative 14, followed by silylation, gives the unusual pseudolactone 15 in high yield, and this reacts with lithio dimethyl methylphosphonate to yield the cyclohexenone 18 (Scheme 3),... 

Furthermore unsaturated aldehydes can be obtained by the reaction of 12 with e. g. cyclohexane carboxylic acid chloride, subsequent alkaline cleavage of the remaining silyl grouping and reduction with sodium borohydride give 3-hydroxy-3-cyclohexyl-1,1-dimethoxypropane (54) which yields 3-cyclohexyl-acrolein (JJ)51 via acid treatment under dehydratation. 

Through the NN-GA optimisation process, an important improvement in the activity and selectivity of the starting materials has been achieved (Fig. 5.5). The figure shows the cyclohexane epoxide yields for the eight evolved generations (8x21 samples). The best materials have low titanium contents, and were extracted and silylated. These materials have a Ti-MCM-41 structure and a very hydrophobic surface. 

Dihydrooxadiazines can be made in related fashion and they too offer novel access to important products. For example, the (9-silylated D-glucal 70, irradiated at 350 nm in cyclohexane with dibenzyl azodicarboxylate, affords adduct 74 in 71% yield,74 and this with an acid catalyst can be used as a glycosylating agent to make /J-linked 2-amino-2-deoxy-D-glucosides.75 This chemistry also is applicable to furanoid glycals.74 Scheme 6 outlines the regio- and stereoselectivities of these cycloaddition reactions and their applications in synthetically useful processes. 

The photochemistry of poly(di-n-hexylsilane) (PDHS) has been investigated by excimer laser flash photolysis20. Transient absorptions were found to be strongly dependent on the solvent employed and the near-UV absorptions at 385 and 360 run observed in cyclohexane and tetrahydrofuran, respectively, were ascribed to polysilylated silyl radicals, while that at 345 nm observed in dichloromethane was attributed to the radical cations of PDHS formed during the electron photoejection process. 

To a stirred solution of DIB (3.2 g, 10 mmol) in dichloromethane (40 ml) the silyl ether (1.7 g, 10 mmol) in dichloromethane (20 ml) was added at room temperature, under argon. After 6 h, the reaction mixture was concentrated and the residue extracted with pentane the extract was concentrated and then distilled to give 1-trimethylsilyloxy-2-acetoxy-cyclohexene (1.78 g, 78%), b.p. 55°C (0.2 mmHg). A by-product (7%) was 1,2-diacetoxy-l-trimethylsilyloxy-cyclohexane. 

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