Reduction routes

Synthesis Since we can make both compounds from the same intermediate 395A, we ll use the Birch reduction route ... 

Some reductive route (via amide or imine) will give (15) and the rest of the synthesis is simple. The final... 

The mechanism of formation of Pt particles by the or-ganometallic reduction route, however, was found to proceed differently, for example in the reductive stabilization of Pt nanoparticles produced by reacting Pt-acetylacetonate with excess trimethylaluminium. Here, derivates of aluminium alkyls act as both reducing agents and colloidal stabilizers. As was shown by a combination... 

Apart from playing an important role in reducing many metal oxides (in some cases its use has been incorporated in commercial practice), hydrogen has also been exploited as a reductant for metal sulfides. However, the hydrogen reduction route for metal sulfides has not yet passed the laboratory development stage as the process involves interesting phyiscochemical principles. 

Benzoxathiin Reduction Route to the cis-Diaryl Dihydrobenzoxathiin Intermediate 12... 

Initially, two plausible mechanisms were considered, as depicted in Scheme 5.16. The first was a hydroboration route (a), where the B-H bond was added across the olefin from the same face of S-0 and upon aqueous work-up, the resulting C-B bond was replaced with a C-H bond. The tis B-H addition to the olefin led to the cis-stereochemistry of the two adjacent aryl substituents. The reduction of the sulfoxide oxygen occurs in the next step. The alternative mechanism was the borane reduction route (h), which was similar to 1,4-addition of hydride,... 

There is but one major set of reductive routes from non-metals to small organic molecules in the metabolome including molecules for energy distribution. They gave rise to the biopolymers also by one basic set of pathways. 

As was suggested by Aylmer-Kelly et at. (1973) Gressin and co-workers (1979) also postulated that the formation of oxalate could occur via two possible routes the dimerisation of CO (route 2 in Figure 3.47) or the attack of the CO 2 on a second molecule of C02 followed by reduction (route 3). Both of these routes involve coupling via C-C bond formation. Coupling can also occur to give the C-O-C linkage (route 3 ), the route responsible for the formation of CO and CO - (steps 5,5 and 6). 

Syntheses of the 1,2- and the 3,4-dihydrodiols of MBA via Methods II and IV have been described (74). The 1,2- and 3,4-diol dibenzoates of 1,2,3,4-tetrahydro-MBA prepared from MBA via the Li/-NH reduction route were readily separable by crystallization. Introduction of the olefinic bond into the 1,2-position of the 3,4-diol dibenzoate by the usual bromination-dehydrobromination procedure was complicated by the greater facility of bromination by NBS on the methyl group than the 1-position. This problem was solved (Figure 14) by allowing bromination to proceed to the dibromo stage, followed by selective reduction of the bromomethyl group with NaBH in diglyme. The monobromo derivative underwent dehydrobromination... 

All this shows the complicated array of reduction routes, ET processes and surface reactions of absorbed intermediates which must be taken into account. 

Another low temperature reduction route has been described by Xie et al. (1999). It corresponds to the reaction ... 

For further contributions on the dia-stereoselectivity in electropinacolizations, see Ref. [286-295]. Reduction in DMF at a Fig cathode can lead to improved yield and selectivity upon addition of catalytic amounts of tetraalkylammonium salts to the electrolyte. On the basis of preparative scale electrolyses and cyclic voltammetry for that behavior, a mechanism is proposed that involves an initial reduction of the tetraalkylammonium cation with the participation of the electrode material to form a catalyst that favors le reduction routes [296, 297]. Stoichiometric amounts of ytterbium(II), generated by reduction of Yb(III), support the stereospecific coupling of 1,3-dibenzoylpropane to cis-cyclopentane-l,2-diol. However, Yb(III) remains bounded to the pinacol and cannot be released to act as a catalyst. This leads to a loss of stereoselectivity in the course of the reaction [298]. Also, with the addition of a Ce( IV)-complex the stereochemical course of the reduction can be altered [299]. In a weakly acidic solution, the meso/rac ratio in the EHD (electrohy-drodimerization) of acetophenone could be influenced by ultrasonication [300]. Besides phenyl ketone compounds, examples with other aromatic groups have also been published [294, 295, 301, 302]. 

The original procedure for the bromination-oxidation-reduction route used bromine in aqueous potassium hydroxide, followed by oxidation with nitric acid-hydrogen peroxide and reduction with alkaline ethanol. This procedure was improved by using NBS in aqueous sodium bicarbonate for the initial oxime bromination, followed by oxidation with nitric acid and final reduction of the Q -bromonitroalkane with sodium borohydride in methanol. It is possible to convert oximes to nitroalkanes via this procedure without isolating or purifying any of the intermediates. This procedure is reported to give yields of between 10 and 55 % for a range of oxime to nitroalkane conversions. ... 

The bromination-oxidation-reduction route has been used in the syntheses of many energetic polynitropolycycloalkanes. Some of these reactions are illustrated in Table 1.6 (see also Chapter 2). A common strategy in these reactions is to use the oxime functionality to incorporate the nitro group, followed by oxidative nitration to gem-dinitro functionality via the Kaplan-Shechter reaction. This has been used in the case of 2,5-dinitronorbornane to synthesize 2,2,5,5-tetranitronorbornane. ... 

Research has focused on improving the efficiency of the halogenation-oxidation-reduction route by using reagents that perform the halogenation-oxidation in one step. Hypochlorous acid-hypochlorite and hypobromous acid-hypobromite " systems have also been explored for the direct conversion of oximes to a-bromonitroalkanes and a-chloronitroalkanes respectively. Some A-haloheterocycles have been reported to affect direct oxime to a-halonitroalkane conversion, and on some occasions, the use of NBS or the free halogens also leads to a-halonitroalkanes. A mixture of oxone and sodium chloride as a suspension in chloroform is reported as a one-pot method for the direct conversion of oximes to a-chloronitroalkanes. ... 

The reductive route used to prepare heterocyclic enamines has the advantage of avoiding the hydroxylation reaction sometimes found in the mercuric acetate oxidation of saturated heterocyclic amines [126]. The lithium-n-propyl-amine reducing system has been used by Leonard to reduce julodine to A5-tetrahydrojulolidine (66% yield) and l-methyl-l,2,3,4-tetrahydroquinoline to a mixture of enamines (87% yield), consisting of l-methyl-A8-octahydro-quinoline and 1-methyl-A9-octahydroquinoline [135] (Eqs. 51, 52). 

The only route to dibenzenetitanium so far described is the reaction of titanium atoms with benzene the reductive routes that give access to arene complexes of Group V and VI metals fail for titanium. Although yields of about 30% are reported for the preparation of dibenzene-, ditoluene-, and dimesitylenetitanium, the reactions are more sensitive than most to the effect of excess metal. Unless the ligand-to-titanium ratio is high and the rate of deposition of titanium vapor kept low, the products seem to be catalytically decomposed by finely divided Ti metal 4a, 7). 

Pyrimidotriazole (241) is reported378 to be reduced in aqueous solution in a two-electron reduction to the 4,5-dihydro derivative 242. In view of the reduction route of purine (Part I), it seems more likely that the product is the 6,7-dihydro derivative 243 [Eq. (130)]. 

The oxidation-reduction route was also used to prepare copolymers 53 of bis[bis(tri-methylsilyl)amido]germanium and acetylene derivatives130 (Scheme 27). Rhodium compounds such as [Rh(norbornadiene)Cl]2 were used as catalysts. In contrast to other polymers prepared from germylenes, the monomer-to-monomer ratio was not regular. Relatively low molecular weight polymers 53 (Mn = 1 x 103-104) were isolated. 

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