Trapping reductive

The imines formed in the cyclization reactions may be trapped reductively (vide supra), Reaction of the intermediate formed by ring-closure with trimethylaluminum to give a gem-dimethyl group as in equation (29) further increases the scope of this transformation. 

The dependence of trap B on the sample structure is similar to that of trap A. Our results therefore suggest that, for electron trap reduction, increasing the SiN coverage (e.g. from 5 to 6 min deposition) in a single layer is a more effective approach than adding a second nanonetwork layer with the same SiN coverage (double 5 min SiN nanonetworks). 

In short, the sequence enantioselective lithiation-electrophilic trapping-reductive elimination represents an enantioselective demethylation of 4 to produce optically pure 9. As seen through this book, secondary phosphine boranes are versatile synthons in P-stereogenic chemistry. In this case, they were alkylated with 2-(chloromethyl)benzothiophene providing phosphine boranes 10 in good yields, which were used in HPLC analysis to evaluate the optical purity of 9. 

No clear picture of the primary radical intermediate(s) in the HO2 photooxidation of water has appeared. The nature of the observed radical species depends on the origin and pretreatment of the HO2 sample, on the conditions and extent of its reduction, on the extent of surface hydroxylation, and on the presence of adventitious electron acceptors such as molecular oxygen (41). The hole is trapped on the terminal OH group (54). 

For the production of lamp-filament wire, aluminum, potassium, and siHcon dopants are added to the blue oxide. Some dopants are trapped in the tungsten particles upon reduction. Excess dopants are then removed by washing the powder in hydroflouric acid. Eor welding electrodes and some other appHcations, thorium nitrate is added to the blue oxide. After reduction, the thorium is present as a finely dispersed thorium oxide. 

The sampling system consists of a condensate trap, flow-control system, and sample tank (Fig. 25-38). The analytical system consists of two major subsystems an oxidation system for the recovery and conditioning of the condensate-trap contents and an NMO analyzer. The NMO analyzer is a gas chromatograph with backflush capabihty for NMO analysis and is equipped with an oxidation catalyst, a reduction catalyst, and an FID. The system for the recovery and conditioning of the organics captured in the condensate trap consists of a heat source, an oxidation catalyst, a nondispersive infrared (NDIR) analyzer, and an intermediate collec tion vessel. 

This procedure is representative of a new general method for the preparation of noncyclic acyloins by thiazol ium-catalyzed dimerization of aldehydes in the presence of weak bases (Table I). The advantages of this method over the classical reductive coupling of esters or the modern variation in which the intermediate enediolate is trapped by silylation, are the simplicity of the procedure, the inexpensive materials used, and the purity of the products obtained. For volatile aldehydes such as acetaldehyde and propionaldehyde the reaction Is conducted without solvent in a small, heated autoclave. With the exception of furoin the preparation of benzoins from aromatic aldehydes is best carried out with a different thiazolium catalyst bearing an N-methyl or N-ethyl substituent, instead of the N-benzyl group. Benzoins have usually been prepared by cyanide-catalyzed condensation of aromatic and heterocyclic aldehydes.Unsymnetrical acyloins may be obtained by thiazol1um-catalyzed cross-condensation of two different aldehydes. -1 The thiazolium ion-catalyzed cyclization of 1,5-dialdehydes to cyclic acyloins has been reported. 

Use of the trapping agent is recommended as the most efficient method for running acyloin condensations for many reasons. Among them are (a) the work-up is very simple filter and distil (b) the bis-(silyloxy)olefin is usually easier to store than the free acyloin and is readily purified by redistillation (c) unwanted base-catalyzed side reactions during reduction are completely avoided and (d) the bis-(silyloxy)olefin can be easily converted directly into the diketone by treatment with 1 mole of bromine in carbon tetrachloride.Other reactions are described in Riihlmann s review and in Organic Reactions ... 

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