Trimethylsilyl epoxides

Trimethylsilyl- and 2-trimethylsilylmethyl>aziridines result from Me SiR (B vinyl or allyl) and methyl N,N-dichlorocarbamate, while olf/ -trimethylsilyl epoxides are ring opened by N-silylated 2 carboxamides Me SiMMeCOR to give the acetamide... 

Homologation Reactions of Ketones. When generated in pentane/THF at — 100°C, diazo(trimethylsilyl)methyllithium reacts with ketones (three examples) and benzaldehyde to give the unstable l-diazo-l-trimethylsilyl-2-alkanols (eq 2) On gentle wanning, the diazo alcohols rapidly lose N2 to give trimethylsilyl epoxides. Since such epoxides readily give aldehydes on treatment... 

Me3SiI, CH2CI2, 25°, 15 min, 85-95% yield.Under these cleavage conditions i,3-dithiolanes, alkyl and trimethylsilyl enol ethers, and enol acetates are stable. 1,3-Dioxolanes give complex mixtures. Alcohols, epoxides, trityl, r-butyl, and benzyl ethers and esters are reactive. Most other ethers and esters, amines, amides, ketones, olefins, acetylenes, and halides are expected to be stable. 

Table 12.2 Epoxidation of olefins with bis(trimethylsilyl) peroxide (BTSP) catalyzed by high-valent oxorhenium deri-vatives> bl...

S-adenosylmethionine 406 biosynthesis of epoxide 349 bis(trimethylsilyl) peroxide (BTSP) 448, 450 bis(trimethylsilyl)urea 449 bis-oxepane ring 281... 

Metalated epoxides are a special class of a-alkoxy organometallic reagent. Unstabilized oxiranyl anions, however, tend to undergo a-elimination. On the other hand, attempts to metalate simple unfunctionalized epoxides may lead to nucleophilic ring opening. The anion-stabilizing capability of a trimethylsilyl substituent overcomes these problems. Epoxysilanes 22 were... 

A completely different way of preparing isocyanides involves the reaction of epoxides or oxetanes with trimethylsilyl cyanide and zinc iodide, for example, ... 

The analogous chromium complex was used in the asymmetric ring opening of meso epoxides with trimethylsilyl azide [15] (Scheme 4). In this case a strong dependence on the anion of the ionic hquid was observed. Anions leading to hydrophobic ionic hquids, such as PFe" and SbFe", led to high... 

Method B was also used in the preparation of occluded (salen)Cr complexes. ligands Ih and li were prepared within the pores of Cr -exchanged EMT and Y zeolites, respectively [25]. These complexes were tested as catalysts in the ring opening of meso-epoxides with trimethylsilyl azide (Scheme 4). The occluded complexes showed a dramatic decrease in catalytic... 

When epoxides such as tra s-3-hexene-epoxide 1885 are heated to 65 °C with hexamethyidisiiane 857 and potassium methoxide in anhydrous HMPA, trimethylsilyl potassium 1882 is generated in situ to open the epoxide rings and give 1886, which subsequently looses potassium trimethylsilanolate 97 to afford olefins with inverted stereochemistry, for example as cis-3-hexene 1887, in high yield [103]. The reaction also proceeds at 65 °C in THF, rather than HMPA, if 18-crown-6 is added [103a] (Scheme 12.29). 

Synthesis of 31 by Method I (107,108) and its conversion to the related anti and syn diol epoxide derivatives (32,33) has been reported (108). The isomeric trans-1,lOb-dihydrodiot 37) and the corresponding anti and syn diol epoxide isomers (38,39) have also been prepared (108) (Figure 19). Synthesis of 37 from 2,3-dihydro-fluoranthene (109) could not be accomplished by Prevost oxidation. An alternative route involving conversion of 2,3-dihydrofluoranthene to the i8-tetrahydrodiol (3-J) with OsO followed by dehydration, silylation, and oxidation with peracid gave the Ot-hydroxyketone 35. The trimethylsilyl ether derivative of the latter underwent stereoselective phenylselenylation to yield 36. Reduction of 3 with LiAlH, followed by oxidative elimination of the selenide function afforded 3J. Epoxidation of 37 with t-BuOOH/VO(acac) and de-silylation gave 38, while epoxidation of the acetate of JJ and deacetylation furnished 39. 

More traditional carbon nucleophiles can also be used for an alkylative ring-opening strategy, as exemplified by the titanium tetrachloride promoted reaction of trimethylsilyl enol ethers (82) with ethylene oxide, a protocol which provides aldol products (84) in moderate to good yields <00TL763>. While typical lithium enolates of esters and ketones do not react directly with epoxides, aluminum ester enolates (e.g., 86) can be used quite effectively. This methodology is the subject of a recent review <00T1149>. 

The electron-rich thiophene ring system can be elaborated into complex, fused thiophenes by acid-mediated intramolecular annelation reactions. For example, treatment of alcohol 96 with trimethylsilyl triflate promoted a Friedel-Crafts acylation and subsequent dehydration giving benzo[b]thiophene 97, a potential analgesic <00JMC765>. Treatment of ketone 98 with p-toluenesulfonic acid resulted in the formation of fused benzo[b]thiophene 99 <00T8153>. Another variant involved the cyclization of epoxide 100 to fused benzo[f>]thiophene 101 mediated by boron trifluoride-etherate . 

Insertion of phenyl, trimethylsilyl, and nitrile-stabilized metalated epoxides into zircona-cyclcs gives the product 160, generally in good yield (Scheme 3.37). With trimethylsilyl-substituted epoxides, the insertion/elimination has been shown to be stereospecific, whereas with nitrile-substituted epoxides it is not, presumably due to isomerization of the lithiated epoxide prior to insertion [86]. With lithiated trimethylsilyl-substituted epoxides, up to 25 % of a double insertion product, e. g. 161, is formed in the reaction with zirconacyclopentanes. Surprisingly, the ratio of mono- to bis-inserted products is little affected by the quantity of the carbenoid used. In the case of insertion of trimethylsilyl-substituted epoxides into zirconacydopentenes, no double insertion product is formed, but product 162, derived from elimination of Me3SiO , is formed to an extent of up to 26%. 

Phenylthio-l-trimethylsilylalkanes are easily prepared by the alkylation of (phenylthioXtrimethylsilyl)mcthane as shown in Scheme 10 [40], The treatment of (phenylthio)(trimethylsilyl)methane with butyllithium/tetramethylethylene-diamine (TMEDA) in hexane followed by the addition of alkyl halides or epoxides produces alkylation products which can be oxidized electrochemically to yield the acetals. Since acetals are readily hydrolyzed to aldehydes, (phenylthioXtrimethylsilyl)methane provides a synthon of the formyl anion. This is an alternative to the oxidative transformation of a-thiosilanes to aldehydes via Sila-Pummerer rearrangement under application of MCPBA as oxidant [40, 41]. 

C-Allyl glycosides can be prepared by the reaction of glycal epoxides with allyltributyltin in the presence of tributyltin triflate as a Lewis acid,281 and aldonitrones can be allylated with trimethylsilyl triflate as a catalyst (Equations (101) and (102)).282... 

Aminocarbonylation can also be carried out by use of CO and a silyl amide. Watanabe et al. reported the cobalt-catalyzed aminocarbonylation of epoxides [55]. Some silyl amides such as PhCH2NHSiMe3 and Et2NSiMe3 were applicable to the reaction to give the /i-siloxy amide in good yields, whereas high reaction temperature was required. The use of 4-(trimethylsilyl) morpholine was found to be crucial for a milder and more efficient carboami-nation here, the reaction proceeded at ambient temperature under 0.1 MPa of CO. However, N-(2-hydroxyalkyl)morpholines, a product without carbonyla-tion, were yielded as by-products (Scheme 18) [56]. 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

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