Triethylsilane deoxygenation with

Reduction of the keto group in naphtho derivative 115 with sodium borohydride results in 69% of the alcohol 116 (Scheme 23, Section 2.1.3.3 (1999PHA645)). Further triethylsilane reduction gives 117 in 67% yield. Synthesis of a series of pyrrolo-benzazepine and pyrrolo-benzothiazepine acetic acids (Scheme 77, Section 5.1.1 (1994MI385)) includes reduction of ketoesters 380 into corresponding hydroxyl esters, subsequent deoxygenation with iodine/PPhs and hydrolysis. 

Deoxygenation via iodohydrin intermediates using chlorosilane/sodium iodideand p-toluenesul-fonic acid/sodium iodidehas also been reported. In a natural product synthesis, an epoxide has been deoxygenated with a large excess of triethylsilane at 300 C for 30 h (equation 51). 

However, this sequence can be reversed. - Thus, the activated cyclopropane can be de-protonated by lithium diisopropylamide, reacted with an appropriate ketone and opened by various methods such as treatment with acid or desilylation with fluoride. Using this reaction sequence, y-lactones 52 with various substituents can be obtained by the intramolecular attack of the ketone oxygen on the siloxy-substituted carbon followed by oxidation with pyridinium chlorochromate. The cyclic hemiacetal intermediates 53 can be converted to the tetrahyd-rofuran derivatives 55 by deoxygenation with triethylsilane/boron trifluoride. 

The low reactivity of alkyl and/or phenyl substituted organosilanes in reduction processes can be ameliorated in the presence of a catalytic amount of alkanethiols. The reaction mechanism is reported in Scheme 5 and shows that alkyl radicals abstract hydrogen from thiols and the resulting thiyl radical abstracts hydrogen from the silane. This procedure, which was coined polarity-reversal catalysis, has been applied to dehalogenation, deoxygenation, and desulfurization reactions.For example, 1-bromoadamantane is quantitatively reduced with 2 equiv of triethylsilane in the presence of a catalytic amount of ferf-dodecanethiol. 

J. Nicholas Kirwan, B. P. Roberts, and C. R. Willis, Deoxygenation of alcohols by the reactions of their xanthate esters with triethylsilane An alternative to tributyltin hydride in the Barton-McCombie reaction, Tetrahedron Lett., 31 (1990) 5093-5096. 

Lactones -> ethers, y- and (5-Lactones can be converted into tetrahydrofuranes and tetrahydropyranes, respectively, by a two-step procedure. The first step is the well-known reduction of lactones to lactols with DIBAH (1, 261 2, 140). The second step is deoxygenation of the alcohol with triethylsilane and BF3 etherate.1 This reaction is compatible with several other functional groups, even including hydroxyl groups. 

The chemistry of )9-(thiocarbonyloxy)alkyl radicals stands in complete contrast to that of the (acyloxy)alkyl radicals, with elimination, while not the rule, being the norm [I]. The difference between the acyloxy and thiocarbonyloxy series is likely a consequence of the much weaker thiocarbonyl bond and the related higher stability of sulfur-centered radicals. The method has been developed in combination with the Barton deoxygenation method (Volume 1, Chapter 1.6) as a means of converting a vicinal diol, via the dixanthate, into an alkene (Scheme 33) [60-62]. Tributyltin hydride has been the reagent of choice for this reaction but it may also be conducted with the triethylsilane/benzoyl peroxide couple [63] and, doubtless, tris(trimethylsilyl)silane. 

As with the similarly polarized boron and aluminium hydrides, hydrido-silanes can transfer formal hydride ions to electropositive carbon centres. Unlike the first two reducing agents, hydridosilanes require additional activation of the carbon centre by Lewis or protic acids before such hydride transfer can take place. This overall process is known as ionic hydrogenation (4). The reagent system of triethylsilane and boron trifluoride etherate has provided an extremely selective method for the reductive deoxygenation of lactols (5), derived in turn from DIBAL reduction (6) of the corresponding y- or 6-lactones ... 

The second approach to the synthesis of CNT 31 [81] involves opening of the 2, 3 -anhydro-P-D-lyxonucleoside 50 with lithium cyanide to give stereo-selectively 51 (R = Trityl). Attempts to deoxygenate the 2 -OH group by reaction with Ar,AT-thiocarbonyldiimidazole gave the a,P-unsaturated nitrile 48 (R = trityl). Reduction of the double bond of 48 (R = trityl) with triethylsilane and tris(triphenylphosphine)rhodium (I) chloride gave a mixture of the two... 

Barton s group have given full accounts of earlier Inief reports (see Vols. 25 and 26) on the use of phenylsilane, triphenylsilane and triethylsilane, and of diphenylsilane as hydrogen sources in free radical deoxygenations of thionocarbonates, with particular emphasis on the applications of these methods for the preparation of deoxysugars. 

A full account of a preliminary communication (Vol.2S, p. 144, and p. 158) on the deoxygenation of primary and secondary vicinal thionocarbonates or xanthates to give olefins on treatment with phenylsilane, triphenyl- or triethylsilane has appeared. ... 

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