Triethylsilane reductive cleavage with

Fig. 4.42. Reductive depolymerization of a permethylated galactomannan (according to Kiwitt-Haschemie et al., 1996) 1. Reductive cleavage with triethylsilane and trimethylsilylmethanesulfonate/boron trifluoride 2. Acetylation with acetic anhydride and N-methylimidazole...

Olah, G.A., Yamato, T., Iyer, P.S. and Prakash, G.K.S., Catalysis by solid superacids. 20. Nafion-H catalyzed reductive cleavage of acetals and ketals to ethers with triethylsilane, /. Org. Chem., 1986, 51, 2826. 

Conversion to the Aldehyde. This transformation is accomplished through a two-step procedure. One such variant requires reduction to the alcohol (e.g. LiAllTt, H2O) and subsequent oxidation (e.g. Swem conditions). Alternatively, Wein-reb transamination " followed by Diisobutylaluminum Hydride or conversion to the thioester (see below) and subsequent Triethylsilane reduction, afford the desired aldehyde in excellent yields. Weinreb transamination proceeds with minimal endocyclic cleavage when there is a p-hydroxy moiety free for internal direction of the aluminum species. 

Hydrodesulfnrisation of benzothiophenes is conveniently achieved using Raney nickel. Reduction of the hetero-rings of both benzofuran and benzothiophene giving 2,3-dihydro derivatives, notably with retention of the snlfur in the latter case, can be achieved using triethylsilane in acidic solution, or with hydrogen over colloidal rhodium. Reductive cleavage of benzofuran to 2-hydroxystyrene is caused by lithium with 4,4 -di-f-butylbiphenyl (DTBB). ... 

In a useful variant of the classical methylation procedure for linkage analysis in the structural determination of oligo- and poly-sacccharides, the fully methylated oligomer is treated with triethylsilane and boron trifluoride etherate or triethylsilane and trimethylsilyl trifluoromethanesulfonate. This procedure produces partially methylated anhydroalditols. These are acetylated and analyzed by GLC-MS.222 223 This reductive-cleavage method makes possible simultaneous determination of identity, ratio, linkage position, and especially the ring size for each monosaccharide component. 

With strong protic acids, the regiochemistry of the reductive cleavage reverses to give the benzyl ether of the less hindered alcohol. One of the few metal hydrides that can withstand the harshly acidic conditions of the reaction is sodium cyanoborohydride. When used in large excess, it will reduce benzylidene acetals in the presence of anhydrous HG [Scheme 3.61] -or trifluoro-methanesulfonic acid. The excess is required because the sodium cyanoborohydride is consumed under the reaction conditions at an appreciable rate. More convenient reaction conditions were described by DeNinno and co-workers in which the benzylidene acetal is reductively cleaved using triethylsilane in the presence of trifluoroacetic acid [Scheme 3.62]. ... 

Table 8.7 Rates of formation of 1,5-anhydroalditol by reductive cleavage of permethylated methyl D-glycopyranosides with triethylsilane and Me3Si0S02CF3 (1 5 5 by molar equiv.) at 25 °C...

A new method of D-glucan analysis involves reductive cleavage of permethylated compounds with triethylsilane and trimethylsilyl triflate or boron trifluoride-etherate as catalyst, followed by acetylation, which yields a series of acetylated, methylated 1,5-anhydro-glucitols. A number of isomeric substituted 1,5-anhydro-glucitols were synthesized as references. /3-Glycosyl-... 

Reductive cleavage (triethylsilane-trimethylsilyl triilate) of the isopropylidene derivatives 17 gives anhydro-sugars 18. The OH-2 groups in 18 have been further converted to mediates and displaced with purine bases or azide (further converted into a pyrimidine ring) to lead to nucleoside analogues. ... 

The regioselective reductive-cleavage of the galactose-glucose link in die sialic acid containing trisaccharide derivative 7 with borane-dimethylsulfide complex in the presence of boron trifluoride or by triethylsilane afforded anhydro derivative 8."... 

McMurray [151] has described the acid-assisted cleavage of the N]-C4 bond in trans 4-hydroxyphenyl p-lactams. The ring opening reaction may proceed with concomitant reduction or formation of carbon-carbon coupling products, as a function of the reagent employed. For instance, Scheme 60, treatment of 196 with 4 equivalents of triethylsilane in neat trifluoroacetic acid led to compound 197. On the contrary, treatment with anisole in trifluoroacetic acid led to compound 198. Unfortunately, no data are provided by authors regarding process yield or final diastereomeric ratio. 

Reduction of Acetals. Reductions of acetals of 2,4-pentanediol can provide (after removal of the chiral auxiliary by oxidation and 3 elimination) secondary alcohols with good enan-tioselectivity. The choice of reagents dictates the configuration of the final product. Use of Dibromoalane gives products from selective syn cleavage of the acetal while Triethylsilane/Titanium(IV) Chloride gives the more usual anti cleavage products (eq 2). ... 

Reduction of 2 with triethylsilane catalyzed by TiCU effects only cleavage of the C-O bond to give 5 in >94% de. This product is reduced to the lactam 6 by Li/NH. Unfortunately the chiral auxiliary is not recovered. 

The reactions of rranj-(+)-[PtCl(SiMePh l-naphthyl )(PPhMea)2] and of its PPhg analogue with lithium aluminium hydride, triethylsilane, or thiophenol involve silicon-platinum bond cleavage. There is predominant retention of configuration at the silicon centre. A mechanism involving successive oxidative addition and reductive elimination steps, with platinum(iv) intermediates, is thought to operate for these reactions. ... 

Derivative 61 was synthesized in 71% yield by reductive bond cleavage of the corresponding 4,6-0-o-nitrobenzylidene acetal of methyl 3,4-acetyl- 5-glucoside with triethylsilane and boron trifluoride ether-ate, followed by deacetylation of the 3,4-diacetates with sodium methoxide in methanol. 

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