Hydroxy trimethylsiloxy

When the reaction was performed with an excess of dihydroxy tellurium tetrafluoride, hydroxy trimethylsiloxy tellurium tetrafluoride was detected in the reaction mixture by I9F-NMR spectroscopy2. 

Perfect stereochemical control in the synthesis of sy -a-methyl-/ -hydroxy thioesters has been achieved by asymmetric aldol reaction between the silyl enol ether of. S -ethyl propanethioate (1-trimethylsiloxy-l-ethylthiopropene) and aldehydes using a stoichiometric amount of chiral diamine-coordinated tin(II)... 

Turner et al. [71, 72] also report on hyperbranched polyesters derived from 3,5-bis(trimethylsiloxy)benzoyl chloride and from 3,5-diacetoxybenzoic acid, which both yield phenolic polyesters after hydrolysis of the end groups. The same group investigated the hyperbranched polyesters obtained in the melt condensation of 5-acetoxyisophthalic acid and 5-(2-hydroxy)-ethoxyisophthalic acid respectively. The latter yields a soluble product while the former results in an insoluble polymer due to formation of anhydride bridges. 

Eine niitzliche, breit anwendbare Variante der in Bd. XI/1, S.571, beschriebenen Reduk-tion von a-Hydroxy-carbonsaure-nitrilen (Cyanhydrinen) als Teil der Umwandlung von Aldehyden Oder Ketonen in Amino-alkohole unter Verlangerung der C-Kette um ein C-Atom (eine CH2-Gruppe) besteht in der Reduktion von a-Trimethylsiloxy-carbonsaure-nitrilen (aus O-Silyl-enolen und Cyanwasserstoff Oder besser aus Aldehyden oder Ketonen und Cyan-trimethyl-silan) mit Lithiumalanat5-7 die a-Siloxy-carbonsaure-nitrile brau-chen dabei nicht in reiner Form isoliert zu werden. 

Das ziemlich einfach herstellbare 1 -Hydroxy- 1-piperidino-cyclopropan kann in Gegen-wart von Titan(IV)-chlorid in einer Variante der Mannich-Reaktion als Aquivalent von Cyclopropanon/Piperidin dienen nach der anzunehmenden in-situ-Umwandlung in 1-Cyclopropyliden-piperidinium-chlorid erfolgen Reaktionen z.B. mit 1-Trimethylsiloxy-cyclohexen zu 2-Oxo-l-(l-piperidino-cyclopropyl)-cyclohexan (63%) und mit 1-Methyl-pyrrol bzw. Indol zu l-Methyl-2-( 1-piperidino-cyclopropyl)-pyrrol (65%) bzw. 3-(l-Pipe-ridino-cyclopropyl)-indol (84%)2 ... 

TABLE 8. Synthesis of trimethylsiloxy and hydroxy compounds from magnesium enolates and bis(trimethylsilyl)peroxide... 

Since the double bond placement in enol silyl ethers is predictable and controllable,18 the method allows the regiospecific introduction of a-hydroxy groups. Omission of the fluoride treatment permits isolation of a-trimethylsiloxy carbonyl compounds,17 while treatment of enol silyl ethers, first with HCPBA, then with triethyl ammonium fluorlde/acetic anhydride gives... 

The reactions of 1-TMS-cyclohexene oxide are similar (112). Treatment78,82 with sulfuric acid/water (in acetone), concentrated hydrobromic acid, sulfuric acid/ methanol, lithium aluminum hydride afford the corresponding compounds 1,2-di-hydroxy- (113)-, l-bromo-2-hydroxy- (114)-, l-methoxy-2-hydroxy- (115)-, 1-hydroxy-2-TMS-cyclohexane (117). Application of base to 115 yields 1-methoxy-l-cyclohexene (116). Pyrolysis of 112 gives a mixture of 1-trimethylsiloxy-l-cyclo-hexene (118) and 3-trimethylsiloxy-1-cyclohexene (ii9)77 (Scheme 13). 

If 1-trimethylsiloxy-l-cyclohexene (193) is treated with borane/THF, hydrogen peroxide/alkali and then hydrolyzed, trans-l,2-cyclohexanediol (203) is obtained137 but trans-1 -hydroxy-2-trimethylsiloxycyclohexane (202) can be isolated without subsequent acid-catalyzed hydrolysis138 whereas the direct hydrolysis of the borane adduct 204 leads directly to cyclohexene (205)139K Very interesting is the use of TiCLt as catalyst. 193 plus benzaldehyde and TCI4 gives after hydrolysis 2-[hydroxy-(phenylmethyl)] cyclohexane-1-one (206)l40 ... 

Refluxing cis- or trans-hydroxy methoxy tellurium tetrafluoride with an excess of chlorotrimethylsilane for 12 hours and distilling the reaction mixture, quantitatively produced cis- and trans-methoxy trimethylsiloxy tellurium tetrafluoride3. 

BTMSPO has been mainly employed as a reagent for the transformation of carbanions into the corresponding trimethylsiloxy or hydroxy derivatives,6 and in the hydroxylation of neutral aromatic systems7 (in the presence of TfOH). 

Stereoselective aldol condensation. Heathcock and Buse have previously employed 2-methyl-2-trimethylsiloxy-3-pentanone (1) in a highly stereoselective route to 3-hydroxy-2-methylcarboxylic acids (8, 295). Aldol condensation of the lithium enolate derived from 1 with a chiral aldehyde yields ery//iro-aldols, which are cleaved with periodic acid to -hydroxy carboxylic acids. However, when 1 is condensed with a chiral aldehyde such as 2, two eryt/iro-products (3 and 4) are produced. Heathcock and co-workers now report that the 1,2-diastereoselectivity of these aldol condensations can be enhanced by use of the ketone 5. Reaction of racemic 5 with racemic aldehyde 2 furnishes a single (racemic) adduct 6. 

Trimethylsiloxy)allyl cations (5 Y = OSiMea) are obtained by the reaction of 2-(trimethylsi-loxy)allyl chlorides (4 X = Cl, Y = OSiMea) with silver perchlorate in nitromethane (Scheme 2). lliese intermediates are also obtained with the aid of a Lewis acid. It has been reported that 2-siloxyacrolein (12a R = H), but not the less electrophilic (12b R = Me), when activated by an equimolar amount of SnCl4 serves as a l-hydroxy-2-oxidoallyl synthon (13) (Scheme 5). ... 

Cis- and ranj-hydroxy methoxy tellurium tetrafluoride reacted stereospecifically with chlorotrimethylsilane tetramethylstannane, and boron trichloride with elimination of hydrogen chloride or methane. The compounds obtained are trimethylsiloxy methoxy tellurium tetrafluoride trimethylstannoxy methoxy tellurium tetrafluoride, and boron tris[methoxo(oxo)tetrafluorotellurate (VI)]... 

The most systematically investigated acyl anion equivalents have been the IMS ethers of aromatic and heteroaromatic aldehyde cyanohydrins, TBDMS-protected cyanohydrins, - benzoyl-protected cyanohydrins, alkoxycaibonyl-protected cyanohydrins, THP-protected cyanohydrins, ethoxyethyl-protect cyanohydrins, a-(dialkylamino)nitriles, cyanophosphates, diethyl l-(trimethylsiloxy)-phenyimethyl phosphonate and dithioacetals. Deprotonation di these masked acyl anions under the action of strong basie, usually LDA, followed by treatment with a wide varies of electrophiles is of great synthetic value. If the electrophUe is another aldehyde, a-hydroxy ketones or benzoins are formed. More recently, the acyl caibanion equivalents formed by electroreduction of oxazolium salts were found to be useful for the formation of ketones, aldehydes or a-hydroxy ketones (Scheme 4). a-Methoxyvinyl-lithium also can act as an acyl anion equivalent and can be used for the formation of a-hydroxy ketones, a-diketones, ketones, y-diketones and silyl ketones. - - ... 

C-Glycosides. 2-(Trimethylsiloxy)alkenyl glycosides undergo rearrangement on exposure to SnCl to afford 2-(l-hydroxy-2-oxoalkyl)tetrahydropyrans. 

Effectively, addition of bromine (1 equivalent) to 3-methyl-l,2-bis(trimethylsiloxy)cy-clobutene, prepared by sodium induced acyloin cyclization of methyl 2-methylbutanoate in the presence of chlorotrimethylsilane, followed by treatment with sodium hydroxide and acidification, gave cfs-l-hydroxy-2-methylcyclopropanecarboxylic acid (9) quantitatively (dia-stereoselectivity > 96%). ... 

Cyclization of dimethyl (.R)-2-methylbutanedioate by sodium in the presence of chloro-trimethylsilane gave the (/ )-3-methyl-l,2-bis(trimethylsiloxy)cyclobutene [(7 )-14] in 78% yield. Then, successive addition of one equivalent of bromine in pentane at — 50 "C and of 2 M sodium hydroxide solution at 0 yielded, after acidification with 2 M hydrochloric acid, directly the (1 5,27 )-1 -hydroxy-2-methylcyclopropanecarboxylic acid (95%). Esterification with methanol (acidified by thionyl chloride) at reflux for 18 hours gave methyl (1 S,2R )-l -hydroxy-2-methylcyclopropanecarboxylate [(15,2i )-15] containing 5% of the (l/ ,2/ )-diastereomer. By heating (15, 2/ )-15 in methanol (acidified by thionyl chloride) at reflux for five days it was shown that the hydroxy ester (IR,2R) was not a product of isomerization of the major stereoisomer (15,27 ). 

Aminocyclopropanecarbonitriles represent important intermediate products en route to aminocyclopropanecarboxylic acid derivatives. Introduction of the cyano group by nucleophilic substitution into a suitable aminocyclopropane precursor, therefore, is of interest. Thus, the hydroxy- or trimethylsiloxy group of monocyclic A,0-acetals or hemiaminals is readily displaced by the cyanide anion as nucleophile to give products 1. Weak acids catalyze these displacements. ... 

As described in the sections above, it is well established that reactions of Lewis acid-activated aldehydes and ketones with silyl enolates afford -hydroxy or /7-sil-oxy carbonyl compounds (Mukaiyama aldol reactions). Occasionally, however, ene-type adducts, that is /-siloxy homoallyl alcohols, are the main products. The first example of the carbonyl-ene reaction of silyl enolates was reported by Snider et al. in 1983 [176]. They found that the formaldehyde-MesAl complex reacted smoothly with ketone TMS enolates to give y-trimethylsiloxy homoallyl alcohols in good yield. Yamamoto et al. reported a similar reaction of formaldehyde complexed with methylaluminum bis(2,6-diphenylphenoxide) [177]. After these early reports, Kuwajima et al. have demonstrated that the aluminum Lewis acid-promoted system is valuable for the ene reactions of several aldehydes [178] and for-maldimine [179] with silyl enolates bearing a bulky silyl group. A stepwise mechanism including nucleophihc addition via an acyclic transition structure has been proposed for the Lewis acid-promoted ene reactions. 

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