Reduction of S

The reduction of (S)-4 to (S)-3,6-dihydro-2fi-pyran-2-yl methanol 5 was carried out readily by adding the ester slowly to solutions of lithium aluminum hydride (LAH) in THF or adding LAH solution to the ester. The reaction was carried out at 0-10 °C to reduce racemization. The ee of the alcohol 5 obtained was generally close to that of the starting ester. The yield of the product in this step was 85-90%. 

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Problems sulfur and nitrogen transferred to the products (and coke) Solutions feed hydrotreating, reduction of S, N, Conradson carbon, metals Results higher quality products reduction in pollution better yields of valuable products reduced post-treatment... 

SO2 absorbed with buffered citric acid solution. SO2 reduced with H2S to S. H2S produced on site by reduction of S with steam and methane. 

The reduction of ,/S-unsaturated y-diketones can conveniently be done with zinc in acetic acid. The following procedure is applicable to the reduction of the Diels-Alder adduct of quinone and butadiene (Chapter 8, Section II). 

This is known as an autoredox reaction. S(1V) is thus not thermodynamically stable at all and need not be considered further in this problem. Instead of considering reactions 1 and 2, we consider the direction reduction of S(V1) to S(0),... 

For example, precursor (S)-57 may be prepared by reaction of R)-56 with methyllithium or by reduction of (S)-56 with lithium naphthalenide and subsequent methylation with iodomethane, making the overall transformation of the diastereomeric mixture 56 nearly quantitatively (Scheme 6) [87]. 

The result obtained from a Hj (5%)/Ar (95%) - TPR/MS in a soak-ramp mode test is shown in Figure 3 for a sample of DESOX. The onset temperature found for H S release in this case, approximately 580°C, is substantially higher than 450°C, the typical onset temperature found in the propane-TPR/MS test. The result was essentially identical in terms of the onset temperature for H S release even when undiluted was used as the reactant. Unlike the propane-TPR/MS tests, where the reaction products are essentially HjS only with virtually negligible amounts of SOj, Hj-TPR/MS tests always showed both SOj and HjS. These data, notably the pattern of change in the rates of SOj and H2S released with temperature in Figure 3, clearly demonstrate, as expected, that the reduction of S to S in step 3 is a consecutive reaction. 

Proof Let S be either a two dimensional abelian variety or a geometrically ruled surface over an elliptic curve over C. Let S be a good reduction of S modulo q, where gcd(q, n) = 1 such that the assumptions of lemma 2.4.7 hold. Then A 5n iis a good reduction of KSn- modulo q. (3) now follows by lemma 2.4.10 and remark 1.2.2. (1) and (2) follow from this by the formula of Macdonald for p(S n z) (see the proof of theorem 2.3.10). ... 

W Beck, G Jung. Convenient reduction of S-oxides in synthetic peptides, lipopeptides and peptide libraries, (trimethylsilyl bromide) Lett Pept Sci 1,31, 1994. 

Carbon-sulfur hybrid materials, i.e., porous carbons [58,59] or CNTs having nanosized S in the pores or channels, are the most promising solution for the Li-S battery to increase the electronic and ionic conductivity of sulfur or sulfide, and prevent, to a great extent, the solubility of the polysulfide ions formed on reduction of S or upon oxidation of insoluble sulfides [60]. An intimate contact between carbon and sulfur is essential [61]. 

Reduction of (S)-pinanediol [phenyl(chloro)methyl]boronate with commercially available lithium triethylborodeuteride yields a chirally deuterated benzylboronic ester. Deboronation of the deuterated benzylboronic ester with hydrogen peroxide yields chirally deuterated benzyl alcohol in 96-98% ee70. The conversion of the deuterated benzylboronic ester to chirally deuterated phenylalanine has also been accomplished (Section 1.1.2.1.4.2.). 

Radical-anion complexes Scope of this review 91 Thermodynamic and kinetic methodologies Voltammetric methods 92 Homogeneous redox catalysis 94 Convolution analysis 98 Laser flash photolysis 102 Photoacoustic calorimetry 103 Thermochemical estimates 105 Fleduction of C—O and O O bonds 106 Reduction of ethers 107 Reduction of peroxides and endoperoxides Reduction of S—S and C—S bonds 136 Reduction of disulfides 137 Reduction of sulfides 150 Concluding remarks 157 Fleferences 160... 

Table 1. Reduction of (S)-2-[(Ethoxycarbonyl)amino]propiophenone (74) to Ephedrine (75a) and Pseudoephedrine (76 b)...

These intermediates were used to synthesize optically pure ephedrines and amphetamines without recourse to resolution, since the chirality of the amino acid educt was entirely conserved throughout the process. The reduction of (S)-2-(ethoxycarbo-nyl)amino-propiophenone (74) first produced a mixture of alcohols (75a, b) Lithium aluminium hydride reduction then produced the desired secondary amino alcohols (76a, b). Table 1 illustrates the reduction scheme and the diastereomer ratios obtained "K... 

Two types of electron transfer sensitization can be identified. In one the excited sensitizer S functions as an electron acceptor. In the presence of a suitable electron donor D, reduction of S produces the donor cation radical D+, which... 

If Af particles are hydrophobic enough, they can penetrate through the membrane and transfer the electron to the ultimate acceptor k2 in the water phase outside the vesicle. The electron transport in the systems like those is schematically shown in Fig. 4c (in this figure MB stands for the methylene blue and ZnTMPyP4+ — for tetramethylpyridiniumporphyrinatozinc(II)). Note that owing to the efficient suppression of S+ and Ajf recombination because of fast irreversible reduction of S+ (under experimental conditions of Refs. [80,81] ks[D]in > kr[Af]in), the quantum yield of PET across the membrane is equal to that of Af generation ... 

The synthesis of merucathinone described above followed a procedure that was also utilized for the synthesis of two other khat constituents, merucathine and pseudomerucathine (408). The ethyl carbamate of L-alanine l(S)-15] was de-protonated with 2 equiv butyllithium and subsequently reacted with 1 equiv styryllithium to yield the ester (5)-16. Reduction of (S)-16 with diisobutylalumi-num hydride gave a 1 1 diastereomeric mixture of (1S,2S)-17 and (1S,2R)-17. Treatment of this diasteromeric mixture with 1 M potassium hydroxide in methanol at room temperature for 4 hr resulted in the formation of the epimeric oxazolidines (4S,5/ )-18 and (4S,5S)-18 in high yield. These epimers could easily be separated quantitatively by flash chromatography. Ring opening of epimers 18 was accomplished by treatment with potassium hydroxide in methanol-water under reflux. 

S- Acyl-o-aminothiophenols (537), generally formed by the reduction of S-acyl-o-nitrothiophenols (536) readily undergo cyclization to 2-hydroxybenzothiazoles (538 Scheme 289). 

Keck recently applied the diastereoselective reduction of ( S-hydroxy ketones in an approach to the anti-tumour natural products epothilone A and B. Sml2-mediated reduction of p-hydroxy ketone 15 in THF-MeOH gave anti- 1,3-diol 16 in 94% yield and as a 96 4 mixture of diastereoisomers.18 Attempts to carry out the reduction using common hydride reducing agents gave 16 with poor levels of diastereoselectivity (Scheme 4.10).18... 

Elemental S (crystalline or colloidal form) can accumulate as a residue in must as the result of its use as a vineyard agrochemical, where it is used to control grape vine powdery mildew Erysiphe necator and various pests. Direct reduction of S to H2S is induced by the highly reductive conditions that exist at the yeast cell surface during fermentation. This mechanism is of little practical importance except when the application of elemental S is not used according to manufacturers recommendations, such as application within the recommended with-holding period before grape harvest (Rankine 1963 Rauhut and Kiirbel 1994 Thomas et al. 1993). 

This reaction type has also been used for the diastereoselective reduction of a variety of structurally related o -amino-/3-keto esters (equations 9 and 10). Treatment of rac-73 with a substoichiometric amount of chiral mediator 72, using formic acid and triethylamine as the hydrogen source, gave the enantiomerically pure a-amino-/ -hydroxy ester (R,S)-syn-74 in 100% yield with 95 5 dr and 99% ee (equation 9), via the diastereoselective reduction of (S)-73. The unreacted R)-73 efficiently racemizes through tautomerization under these reaction conditions. 

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