Indirect reduction

Quinoxaline gave l,4-diethyl-l,2,3,4-tetrahydroquinoxaline by indirect reductive alkylation (AcOH, KBHai, <15°C, 1 h, then reflux, 6h 87% presumably by nuclear reduction, A-acylation, and further reduction of the acetyl groups ). ... 

Alcohols can also be reduced indirectly by conversion to a sulfonate and reduction of that compound (10-80). The two reactions can be carried out without isolation of the sulfonate if the alcohol is treated with pyiidine-S03 in THF, and then LiAlH4 added. Another indirect reduction that can be done in one step involves treatment of the alcohol (primary, secondary, orbenzylic) with Nal, Zn, and Me3SiCl. In this case the alcohol is first converted to the iodide, which is reduced. For other indirect reductions of OH, see 10-86. 

Tetranuclear iron-sulfur clusters of the type [Fe4S4(SR)4]2, where R = CH2C6H5 and C6H5, were found138 to catalyze the reduction of C02 in DMF solutions. Controlled-potential electrolyses were carried out in a C02-saturated 0.1 M tetrabutylammonium tetrafluoroborate (TBAT)-DMF solution at a mercury pool cathode. In the absence of a catalyst, C02 was substantially reduced only at potentials more negative than -2.4 V versus SCE, while in the presence of a cluster, the reduction took place at around -1.7 V thus, potential shift of ca. 0.7 V was achieved. The products were analyzed by means of gas chromatography and isotachophoresis. Without a catalyst, oxalate was the main product, and addition of small amounts of water to the DMF solution favored formate production, whereas in the presence of the catalyst, formate was produced predominantly even in a dry DMF solution. This result was interpreted in terms of indirect reduction of C02, proceeding by electron transfer from the reduced cluster to C02 in the bulk... 

As discussed earlier, Azo biological decolorization are mainly reduced in a direct reduction or mediated/indirect reduction with nonspecial azo reductase or reduced enzyme cofactors (Figs. 1 and 3). According to the direct enzymatic reduction mechanism, nonspecial azo reductase can catalyze the transfer of reducing equivalents originating from the oxidation of original electron donor in the azo dyes. In... 

In contrast to the direct reduction as described above, the indirect electrochemical reduction of perfluoroalkyl halides is a versatile and novel method for generating perfluoroalkyl radicals selectively. Saveant et al. have demonstrated many successful examples. Using terephthalonitrile as a mediator, the indirect reduction of CF3Br in the presence of styrene leads to the dimer of the radical adduct obtained by the attack of CF on styrene. On the other hand, in the presence of butyl vinyl ether, the mediator reacts with the radical adduct obtained by the attack of CF3. on the olefin (Scheme 3.4) [14]. 

Indirect reduction, 14 501 Indirect sequence heuristic, for simple distillation, 22 299... 

Asymmetric electroreduction of ketones to the corresponding chiral alcohols has recently been reported. Typical examples are the reduction of ketones bearing chiral auxiliaries [68, 69], and the indirect reduction of ketones with alcohol dehydrogenase (ADH), as a mediator (Scheme 32) [70]. 

Structures such as (26) were demonstrated [103] to he fairly easily reduced at a Pt electrode. Thus, when R = Ph, an anion radical (E° = —1.26 V vs Ag/Agl/I 0.1 M) of high stahihty is formed. However, macroelectrolyses of the compounds (26) could not he achieved at all since whatever the amount of electricity passed through the cell, the starting material was totally recovered. The compounds (26) are expected to react slowly with the tetraalky-lammonium salt R4N+ and the reaction would correspond to an indirect reduction of the electrolyte. Compounds (26), with R = primary alkyl groups, led - even in DMF-to strong self-inhibition explained by the adsorption of produced... 

The allylic sulfonyl group is regioselectively cleaved in the presence of the alkyl-sulfonyl group by indirect reduction with anthracene as a mediator (Fig. 24) [125]. 

Indirect Reduction with Mediators Containing Nickel, Cobalt, and Iron 533... 

Indirect Reduction with Mediators Containing Titanium, Tin, and... 

Indirect Reduction with Mediators Containing Zinc (Zn), Mercury... 

Indirect Reduction with Mediators Containing Selenides (Se) or... 

Indirect Reduction with Mediators Containing Palladium, Rhodium, Iridium, and Platinum... 

Indirect Reduction with Mediators Containing Chromium, Molybdenum, and Tungsten... 

ET rate constants can also be determined using solution donors. Indirect reduction of peroxides and endoperoxides was accomplished by homogeneous... 

Several research groups ha ve been involved in the study of ET reactions from an electrochemically generated aromatic radical anion to alkyl halides in order to describe the dichotomy between ET and polar substitution (SN2). The mechanism for indirect reduction of alkyl halides by aromatic mediators has been described in several papers. For all aliphatic alkyl halides and most benzylic halides the cleavage of the carbon-halogen bond takes place concertedly with the... 

Abdel-Magid, A. F. Carson, K. G. Harris, B. D. Maryanoff, C. A. Shah, R. D. Reductive Amination of Aldehydes and Ketones with Sodium Triace-toxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures, J. Org. Chem. 1996, 67, 3849. 

Some examples of indirect reduction by means of inorganic and organic mediators in different types of reactions will be discussed briefly indirect oxidations may also be performed. 

Some direct elimination reactions may end up as indirect reductions thus if RCHXCHXR (8) is reduced to RCH=CHR (10), and 10 is more easily reducible than 8, then 10T will be formed and may then be the electrontransferring species.38... 

The double bond shift is explained in terms of a kinetically controlled protonation of the anion formed in an ECE process the anion would have the highest negative charge a to the ester group. Such a double bond shift seems to be rather general also for the indirect reduction of allyl alcohols.388... 

Here we consider carbon monoxide as a chemical reducing agent, with the oxidation product being C02 in all cases. Carbon monoxide may act as a reductant in three different ways (1) as a direct oxygen atom acceptor (2) as a two-electron reductant with water as the source of oxygen and (3) as an indirect reductant in which the reducing power of CO is used to make H2 which then carries out the desired reduction. The three ways are shown schematically as (24)-(26) (in (24) [O] represents an oxide source). Equation... 

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