Benzene elimination

This simple, convenient procedure eliminates the use of strong acids which sometimes cause unwanted molecular rearrangements and the isolation and handling of toxic organomercuric halides. It also allows you to apply the borohydride reduction directly to the adduct, without precipitating it as the chloride. The main precursor is any allyl benzene eliminating the need for conversion to a propenyl benzene. 

T. Agapie, P. L. Diaconescu, and C. C Cummins, Methine (CH) Transfer via a Chlorine Atom Abstraction/Benzene-Elimination Strategy Molybdenum Methylidyne Synthesis and Elaboration to a Phosphaisocyanide Complex, Angew. Chem. Int. Ed. 45, 862-870 (2006). 

It was found that after the curing time, three-dimensional crosslinking of the system has been increased due to a benzene elimination mechanism, as shown in Eq. 1. 

The energy of the 1236 A light is greater than the ionization potential of benzene, and hence additional reaction paths are available. All the above products were observed for the photolysis of benzene at 1236 A, with all except hydrogen having somewhat lower quantum yields. No pressure effect was observed in the photolysis at 1236 A. For the photolysis with either lamp, the addition of 3 torr NO to 1 torr of benzene eliminated allene, cyclohexadienes, biphenyl and dihydrobiphenyl as products, while the other products remained unaffected. Hentz and Rzad conclude that the former are formed by free-radical reactions, while the latter are formed by molecular elimination. In view of the curious pressure effects observed by Shindo and Lipsky at 1849 A, conclusions regarding the effect of added gases must be made with caution. 

The reaction of [Os(Ph)Cl(CO)(PPh3)2] with Tm results in benzene elimination and formation of the first osmaboratrane [Os B(mt)3 -(CO)(PPh3)](Os - B), showing a somewhat long trans-annular dative bond between osmium(O) and boron(III) (Fig. 5.23).95... 

Scheme 20. Thermally induced intramolecular alkane (benzene) elimination...

When isoxazolidine 25 (the 2 2 adduct of phenylhydroxylamine and dimethyl acetylenedicarboxylate) is heated in refluxing benzene, elimination of phenylhydroxylamine takes place.44... 

D-Ribonic acid, esters D-psicosides from, 272 Ribonucleic acid. See RNA Ring cleavage electrocyclic (cycloreversion) [l+l-i- 2]- double CO elimination, 78, 339 [1 + 4]- CO elimination, 337 S02 elimination, 80,153 [2 + 2]- benzene elimination, 331, 332-333 prismane opening, 330-331 rhodium( 1 + )-catalysed, 332 thermal, 79-80... 

Certain triarylbismuthine dibromides when boiled in dry benzene eliminate aryl bromide ... 

The high reactivity of bis-arylactinide complexes can be observed by the benzene elimination that takes place to form actinide benzyne-type complexes, which further undergo reverse reaction of benzene to form o-diphenylene (Scheme 25) [249]. 

While all of the substrates discussed above are not shown in Fig. 2, the same analysis can be performed with all of them (alkynes, substituted methanes). One caveat that we encountered was that many of these substituted derivatives proved to be very stable. Loss of alkane from the n-pentyl hydride complex has a half-hfe of about an hour at 25°C. Methane loss from 3 has a half-life of about 5 h. Loss of benzene from 2, however, is extremely slow (months), and therefore, the rate of benzene reductive elimination at 25°C was determined by extrapolation from the rate at higher temperatures. The Eyring plot of hi( /T) vs. 1/T gave activation parameters for reductive elimination of benzene A// = 37.8 (1.1) kcal/mol and = 23 (3) e.u., which can be used to calculate the rate at other temperatures. As mentioned above, the substituted derivatives are much more stable. Reductive elimination of the alkynyl hydrides was examined at lOO C, as was the elimination of many of the substituted methyl derivatives. In these cases, the rate of benzene elimination was calculated from the Eyring parameters at the same temperature as that where the rate of reductive elimination was measured, so that the barriers could be directly compared as in Fig. 2. The determinatimi of AG° for all substrates allows Eq. 7 to be used to determine relative metal-carbon bond strengths for these compounds. Table 1 summarizes these data, giving A AG, AG°, and Drei(Rh-C) for all substrates. 

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