Carbon deoxygenation

Atomic carbon deoxygenates oxiranes (Scheme 37) (B-71MI50501, 76JA3820). Silylenes can also deoxygenate oxiranes (Scheme 38) (80JA1451). 

In a study of the deoxygenation of carbonyl compounds by atomic carbon, Dewar and coworkers (8UA2802) presented experimental and theoretical evidence that the carbonyl group can react with carbon atoms to form a carbenaoxirane. 

Hydrogenation of epoxides lends itself well to both synthetic applications and mechanistic studies. The reaction is complex, for either carbon-oxygen bond may break with or without inversion of configuration, and the product may contain deoxygenated products (92,93) as well as ketones derived by isomerization (26). The reaction is especially sensitive to both catalyst and environment (74). 

Unexpectedly, neither direct complexation nor the deoxygenated complexes 95 or 96136,137 were observed in the reaction of diphenylthiirene oxide (18a) with iron nonacarbonyl. Instead, the red organosulfur-iron complex 97138 was isolated12, which required the cleavage of three carbon-sulfur bonds in the thiirene oxide system (see equation 33). The mechanism of the formation of 97 from 18a is as yet a matter of speculation. 

In an interesting contrast to the photochemical behavior of the simpler sulfine system, the photolysis of thioketene S-oxides such as 25 in carbon tetrachloride leads to the corresponding thioketenes in excellent yield36. This photochemical deoxygenation is... 

The deoxygenation of peroxycarbonates (53) with phosphines and phosphites has been examined. Reaction with phosphites favours pyrocarbonate formation (Path A) whilst phosphines favour carbonate formation (Path B). Secondary phosphine oxides are oxidized to phosphinic acids by perbenzoic acid. The kinetics of the deoxygenation of hydroperoxides by triphenylphosphine have been examined and the reaction shown to be catalysed by strong acids. ... 

Scheme 5.9 illustrates some of the conditions that have been developed for the reductive deoxygenation of alcohols. Entries 1 to 4 illustrate the most commonly used methods for generation of thiono esters and their reduction by tri-M-butylstannane. These include formation of thiono carbonates (Entry 1), xanthates (Entry 2), and thiono imidazolides (Entries 3 and 4). Entry 5 is an example of use of dimethyl phosphite as the hydrogen donor. Entry 6 uses r .s-(trimethylsilyl)silane as the hydrogen atom donor. 

As vicinal dibromides are usually made by bromination of alkenes, their utility for synthesis is limited, except for temporary masking of a double bond. Much more frequently it is desirable to convert a diol to an alkene, and several useful procedures have been developed. The reductive deoxygenation of diols via thiono carbonates was... 

Attempted deoxygenation of several fT-aryl thiono carbonates gave the unexpected product shown. In contrast, the corresponding a-isomers gave the desired deoxygenation product. Account for the formation of the observed products, and indicate why these products are not formed from the a-stereoisomers. 

S. Cenini, M. Pizzotti, and C. Crotti, Metal Catalyzed Deoxygenation Reactions by Carbon Monoxide of Nitroso and Nitro Compounds (D. Reidel Publishing), 6, (Aspects of Homogeneous Catalysis A Series of Advances), 97-198 (1988). 

Deoxygenation from nitroalkanes is possible by other various reagents, including TiCl3,119 Me3SiI,63 carbon disulfide in the presence of base,120 Me3SiSiMe3,121 and Sn(SPh)2-PhSH-Et3N (Eq. 6.62).122... 

The metal carbonyls Fe(CO)5, Ru3(CO)i2, and Rh6(Co) 16 are catalysts for the deoxygenation of o-nitrostyrenes under carbon monoxide pressure to give indole derivatives (Eq. 10.59).82... 

In a related approach from the same laboratory, the perfluorooctylsulfonyl tag was employed in a traceless strategy for the deoxygenation of phenols (Scheme 7.82) [94], These reactions were carried out in a toluene/acetone/water (4 4 1) solvent mixture, utilizing 5 equivalents of formic acid and potassium carbonate/[l,T-bis(diphe-nylphosphino)ferrocene]dichloropalladium(II) [Pd(dppf)Cl2] as the catalytic system. After 20 min of irradiation, the reaction mixture was subjected to fluorous solid-phase extraction (F-S PE) to afford the desired products in high yields. This new traceless fluorous tag has also been employed in the synthesis of pyrimidines and hydantoins. 

Several studies have shown that the direct electron transfer between cat and graphite or carbon soot electrodes in deoxygenated solutions was sluggish, with large peak separations [157-159], Based on the consideration that CNTs might be the best candidate among the various carbonaceous substrates for promoting the electron transfer... 

Although this classic picture evolved from "soft, mononuclear transition metal complexes suffices to explain a great deal of carbon monoxide chemistry, it is not clear that it is complete or accurate for understanding processes whereby CO is reduced, deoxygenated, and/or polymerized to form methane, long-chain hydrocarbons, alcohols, and other oxocarbons, especially in cases where heterogeneous catalysts or "hard" metals are involved (6, 7, ,9,J 0). This deficiency of information has led to the search for new modes of carbon monoxide reactivity and to attempts to understand carbon monoxide chemistry in nontraditional environments ... 

The potential of combining a lower need for deoxygenation and a higher product value is illustrated in Fig. 2.15. It shows that the selective incorporation of oxygen into a hydrocarbon, as done in the petrochemical industry, is very expensive. In contrast, the bio-based alternative enjoys two advantages. Firstly, the feedstock is cheaper than crude oil, even on an energy and carbon base, as discussed above. Secondly, its selective deoxygenation has been proven to cheaper than the petrochemical route in a few cases, e.g., for ethanol and furfural. The same can be expected for other biomass derivates in the future. 

Tertiary amine TV-oxides are rapidly deoxygenated by carbon disulphide1112. Oximes are reduced to primary amines by titanium(III) chloride in the presence of sodium cyanoborohydride, NaBTpCN1. The combined action of sodium borohydride and a chiral... 

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