Complications in the reductive

In striking contrast to the above observations is the finding that both reduction and reductive methylation of the tetrahydropyranyl ether of 17a-ace-toxypregnenolone (71) afford the expected products (72a, b) in 85-88 % yields by direct crystallization of the crude reaction products. Clearly, the complications in the reduction of the 16-en-20-one system are attributable primarily to reactions of the carbon-carbon double bond rather than to the a-carbanion (73), which is the final intermediate in both the reduction of the 16-dehydro compounds and the 17-acetoxy ketones. 

A further complication in the reduction of aryl Group IV derivatives is the formation of biphenyl radical anion (135, 100, 97, 20) or its derivatives (32). However, this reaction is not peculiar to organometallic radical anions but appears to be quite general for alkali metal reduction of phenylated compounds (135). 

A complicated situation arises when ox or red is insoluble, for instance in the reductive chronopotentiometry of an ion of a non-amalgamating metal then the metal precipitates on the stationary Hg electrode surface without further diffusion, so that... 

However, it should be noted that caution should be exercised when Prelog s rule is applied to such complicated systems as intact cells (baker s yeast), which may contain oxidoreductases of different stereoselectivity230 231. For example, in the reduction of 39 to alcohol 40, Prelog s rule fails232. 

However, the important consequences of this analysis are that the complications of the reduction in the density of B between A reactants only develops during the decay of the non-steady-state density of B towards the steady state. The average concentration of B after reaction has begun is less than the initial (or bulk) value [B]0 usually used in the Smoluchowski theory. The diffusion of B towards A is driven by the larger concentration of B at considerable distances from A than the concentration of B nearer to A. The concentration or density gradient of B at A is decreased slightly by this competition between different A reactants for B. Hence, the current B towards one A remains almost as it was in the Smoluchowski theory [eqn. (18)], viz. 

The further reduction of Tx is more complicated, In the first place... 

The conversion of oxime 71 to imide 72 is a related but more complicated reaction104). The reduction of the oxime concurrent with migration finds analogy in the conversion of steroid ketoximes 74 to enimides 75 under identical conditions 105). The imide 72 may be hydrolyzed to arsaniline 73. It might also be noted that in the case of benzyl substituents 69 b and 71b the reactions take place with partial loss of substituent (to 70 c and 72 c). Thus, these procedures may be used to prepare the unsubstituted 4-arsaniline and 4-arsaphenol. 

Although all agents reduce ischemic risk in the setting of PCI, there is some heterogeneity in the magnitude and durability of treatment effect (6). Indirect comparison suggests that the reduction in ischemic complications in the setting of PCI... 

The results described above illustrate the problem of separating effects due to catalysis provided by pyrrhotite from those due to the chemistry of the reduction of pyrite. It must also be borne in mind that reduction of pyrite produces a nearly equivalent amount of l S, which remains available to enter subsequent reactions by mechanisms now only poorly understood. In order to remove these complications, pyrrhotite was prepared by the reduction of pyrite with tetralin, isolated from the reaction residue, and then heated with fresh tetralin. Figures 4 and 5 contain the yields of naphthalene and 1-methylindan, and the ratios of trans- to cis-decalin as a function of concentration. In this case, the pyrite was a hand-picked sample of micro-crystals taken from a coal nodule. As may be seen, the yields of naphthalene and 1-methylindan, and the ratio of trans- to cis-decalin all increase with pyrite concentration. The slope of the line for naphthalene yield is 0.91. A slope of 0.53 is calculated for stoichiometric reduction of FeS to FeS by tetralin to yield naphthalene. Thus, roughly half of the naphthalene produced can be accounted for by the demand for hydrogen in the reduction of pyrite. 

Sometimes the polarographic behavior of heteroaromatic compounds is complicated by adsorption of depolarizer and/or products the adsorbability generally increases with the number of aromatic nuclei in the molecule. In the reduction of benzoyl pyiidines270 it was found that the adsorption of both depolarizer and products was important in acid solution, whereas only the former was adsorbed at high pH. 

To complete the alkene hydrogenation reaction sequence, the first hydrogen transfer must be followed by a second, which results in the reductive elimination of the alkane product. This proceeds through a three-centered transition state. The catalytic cycle is shown in Fig. 22-1 but the process is actually more complicated since the equilibria are dependent on phosphine, alkene, rhodium concentrations, temperature, and pressure. 

A few electrochemical studies have been also addressed to the structurally characterized (XRD ) VO(acac)2 ". It undergoes oxidation to [VO(acac)2]+ by a process which seems to be reversible in the short times of cyclic voltammetry, but coupled to chemical complications in the longer times of exhaustive electrolysis. One of its salts has been spectroscopically identified as [VO(acac)2](l5). VO(acac)2 also undergoes irreversible or partially reversible reduction processes, particularly in the presence of uncomplexed acac, which ultimately afford [V(acac)3] . The pertinent electrode potentials are listed in Table 8. 

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