Boronation reaction

N.N. Greenwood We have not yet undertaken detailed mechanistic studies of the ortho-cyclo boronation reactions but the sequence you envisage has also seemed quite plausible to us. 

In the reaction of (R,R)-tartrate allyl-boronate with aldehydes, Si attack of the nucleophile on the carbonyl group has been observed, while Re attack occurs in (S, S )-tartrate allyl-boronate reactions. Thus, an (S )-alcohol is produced preferentially when an (R,R)-allyl reagent is used, and the (R)-product can be obtained from an (S.Sj-reagent. assuming that the R substituent in the aldehyde substrate takes priority over the allyl group to be transferred. In fact, no exceptions to this generalization have yet been found in over 40 well-characterized cases where the tartrate auxiliary controls the stereochemical outcome of the allyl or crotyl transfer.72... 

MB6, M = Y, Gd, Tb, and Dy, which dissociate into MB4 and boron. Reaction of H2B12H12,6H20 with lanthanide, scandium or yttrium hydroxides or carbonates afforded40 M2(B12H12)3,xH20 (x = 15, 18, 20, or 21 depending on M) the compounds are ionic. 

This process is sometimes abbreviated to S f2 at silicon to save space. The intermediate is a trigonal bipyramid with negatively charged pentacovalent silicon. It is often omitted in drawings because it is formed slowly and decomposes quickly. This mechanism is similar to nucleophilic substitution at boron except that the intermediate is pentacovalent (Si) rather than tetrahedral (B). The hydrolysis of a boron ester at the end of a hydroboration-oxidation sequence would be an example of an analogous boron reaction. 

Boronation reaction of borane (BH3) with OH groups Carboniogenic production of carbon cations from hydrocarbons... 

A C2-nonsymmetric FeNx3(BC6H5)(BF) complex was obtained via a "re-boronating" reaction from the initial FeNx3(BC6H5)2 clathrochelate attacked by triethyloxonium boron fluoride, and the complex obtained was chromatographically isolated (Scheme 10). 

The study in 1993 of a pulsed laser evaporated boron reaction with ethyne in argon matrix discovered the formation of the borirene radical BC2H2 (48) among other cyclic and linear products (Equation (1)) (93JA2510, 93JPC5839). The reaction was monitored by matrix IR spectra, and the radical (49) is photosensitive and forms spontaneously on annealing above 18 K. The excellent... 

Each material has a characteristic stopping power and therefore the resolution and the depth of profiling will vary in different materials. The lithium particle from the boron reaction is heavier than its alpha counterpart and usually loses energy more rapidly allowing greater depth resolution however, the alpha particles have the greater range and consequently allow deeper profiles to be obtained. 

Tandem Aza-Diels-Alder and Allyl Boronate Reactions... 

The first step is of course the aza-Diels-Alder reaction 218 with no regioselectivity but lots of stereochemistry. The cis ring junction in 217 comes from the cis alkene in maleimide and the endo transition state gives the remaining centre. The next step is an allyl boronate reaction 219 with the aldehyde. Coordination of the aldehyde oxygen with the boron ensures that the aldehyde is delivered to the top face and the aldol stereochemistry comes from the six-membered cyclic transition state. Snieckus comments that the reaction works well as a tandem process because the 4 + 2 cycloaddition is slower than the allyl boronate reaction so the unstable intermediate does not accumulate. This comment has more general application. 

In Chapter 5, the cis addition inherent to hydroboration is the result of a four-center transition state (sec. 5.2.A.ii), which delivered boron and hydrogen from the same face. Subsequent transformations that involve boron lead to a new group on the same face as boron. Reaction of methylcyclopentene with 9-BBN, for example, gave exclusively the trans borane (96), and that was converted to aldehyde 97 by carbonylation. The addition of the boron dictated the stereochemical relationship of the methyl group and the 9-BBN moiety. The carbonylation and oxidation reactions proceeded with net retention of configuration, maintaining the trans geometry in the isolated product. 

There are a number of limitations, however, which must be taken into account in evaluating the boron content of soils and waters in terms of food and fiber production. Boron reactions in soil-water systems, forms readily available to plants, and diagnostic criteria for soil and water analysis are examined in the following discussion. 

The complexity of both alpha particle and gamma ray spectra and the great width of the upper resonances probably account for the fact that neither experimental nor theoretical information on the boron reactions is yet satisfactory. Christy 27 concludes that neither the L S nor the jj coupling model is satisfactory for this reaction and implies that intermediate coupling may produce a better result. 

Conditions A temperature/time (°C/h) for the boronation reaction. Conditions B temperature/time (°C/h) for the allylation reaction. 

Second, although only a small amount of tritium is produced from the pure water, there are two other sources of tritium that will produce substantial amounts in a PWR. When boron is used as a chemical shim, fast neutron reactions with boron will produce tritium. Also, tritium is produced as a fission product, and it can escape through clad leaks into the water. Finally, use of Li OH for pH control can contribute tritium. The boron reactions are responsible for most of the tritium, however. 

Boron.—Reactions of boron trichloride with aromatic amines may proceed by formation of the Cl3B,NH2R adduct and then by hydrogen chloride elimination to give ClaB=NHR en route to the ultimate product (CIB—NR),. The mechanism of these reactions has been probed by isolation and characterization of intermediates, and stoicheiometric and kinetic studies -the kinetics can be followed by monitoring the evolution of hydrogen chloride. Photochemical reaction of triethylboron with iodine in cyclohexane takes place by a free-radical mechanism, indicated by the determined rate law. ... 

The new boronation reaction is not confined to haUde-starting materials Aryl triflates also react with pinacol diboron and related diboron reagents. These developments have changed the face of organic synthesis by making a wide variety of boronic acids and esters readily available in the... 

Boron Reaction with curcumin, forming red rosocyanine... 

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