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Triethylborane/oxygen

TABLE 12.2 Summary of Two Comparative Sets of VDF/TrFEyCTFE Terpolymers Prepared by Triethylborane/Oxygen Radical Initiator... [Pg.299]

Trialkylboranes, especially triethylborane, are used in conjunction with 02 to generate radicals.297 The alkyl radicals are generated by breakdown of a borane-oxygen adduct. An advantage this method has over many other radical initiation systems is that it proceeds at low temperature, e.g., -78°C. [Pg.958]

An alternative system for initiating radical cyclization uses triethylborane and oxygen. Under these conditions, fm-(trimethylsilyl)silane is an effective hydrogen donor.330... [Pg.971]

Triethylborane in combination with oxygen provides an efficient and useful system for iodine atom abstraction from alkyl iodide, and thus is a good initiator for iodine atom transfer reactions [13,33,34]. Indeed, the ethyl radical, issued from the reaction of triethylborane with molecular oxygen, can abstract an iodine atom from the radical precursor to produce a radical R that enters into the chain process (Scheme 13). The iodine exchange is fast and efficient when R is more stable than the ethyl radical. [Pg.89]

Triethylborane in the presence of very small amounts of oxygen is an excellent initiator for radical chain reactions. For a long time it has been known that trialkylboranes R3B react spontaneously with molecular oxygen to give alkyl radicals (Reaction 4.7), but only recently has this approach successfully been applied as the initiation [22]. The reactions can be run at temperatures as low as — 78 °C, which allow for a better control of stereoselectivity (see below). [Pg.53]

There remains an area where progress is still to be made. This is in the invention of new, inexpensive, and temperature-variable initiators. The present reliance on azoiso-butyronitrile (AlBN) and dibenzoyl peroxide limits the temperature range, and there is always some danger with peroxides. The use of triethylborane and oxygen, originally introduced by Brown some decades ago, has recently been appreciated better because it permits radical initiation at low temperatures. [Pg.157]

An intermolecular homoallylation of glutaraldehyde with isoprene occurs regioselectively at C-l when promoted by [Ni(acac)2]/triethylborane to afford the tetrahydropyran 383 as a single isomer, the methyl group being 1,3-anti with respect to the tetrahydropyranyl oxygen (Equation 159) <2001AGE3600>. [Pg.504]

Treatment of a-iodo lactone (45) with triethylborane under oxygen atmosphere gives the corresponding a-hydroxy lactone (46), via a-lactone radical species. This reaction comprises of SH2 reaction by Ef on the iodine atom of a-iodo lactones, reaction of the formed a-lactone radical with molecular oxygen, and subsequent hydrogen-atom abstraction from the solvent to form alkyl hydroperoxide (ROOH). Finally, by the addition of dimethyl sulfide for the reduction of the peroxide, the corresponding a-hydroxy lactone is obtained (eq. 2.24) [58]. [Pg.49]

Triethylborane generates Et via the reaction with molecular oxygen under air, and its reacts with RfI to generate Rf and EtI via SH2 reaction pathway. So, Et3B/RfI/electron-rich olefin system can be used for the carbon-carbon bond forming reaction. [Pg.129]

This reaction comprises firstly of SH2 reaction on the iodine atom of ethyl iodoacetate by an ethyl radical, formed from triethylborane and molecular oxygen, to form a more stable Chester radical and ethyl iodide. Electrophilic addition of the a-ester radical to electron-rich aromatics (36) forms an adduct radical, and finally abstraction of a hydrogen atom from the adduct by the ethyl radical or oxidation by molecular oxygen generates ethyl arylacetate (37), as shown in eq. 5.20. Here, a nucleophilic ethyl radical does not react with electron-rich aromatics (36), while only an electrophilic a-ester radical reacts with electron-rich aromatics via SOMO-HOMO interaction. [Pg.169]

One-pot synthesis of ( )-alkenes has been directly performed from nitromethane by a radical process (Liu and Yao, 2001). In fact, the strategy is to react P-nitrostirene (3) as shown in Figure 2.1, in situ prepared from aromatic aldehydes (1) with nitromethane (2) in the acetic acid solution with a catalytic amount of ammonium acetate at 70-100°C, with triethylborane in the biphase of diethyl ether and aqueous solution in the presence of oxygen in air as radical initiator, to generate (4). [Pg.55]

Carbon-boron bonds are generally rather easily oxidized and indeed volatile trialkylboranes such as trimethylborane and triethylborane are spontaneously inflammable when exposed to air. Less volatile or-ganylboranes do not spontaneously inflame but are nevertheless readily oxidized by oxygen and a variety of other reagents. Consequently, it is normally necessary to carry out organoborane reactions in an inert atmosphere. [Pg.593]

Although peroxides are usually the preferred initiators for triggering the chain reaction, other initiators such as diazo derivatives, a combination of triethylborane and oxygen etc., can also be used in some cases. Initiation may equally be performed photochemically. [Pg.204]

The reactions sometimes occur without imposed initiation, but most commonly initiation is brought about by AIBN at 75-85 °C in a solvent such as benzene or toluene, or by triethylborane in the presence of a trace of oxygen,109-110 or by irradiation with a sunlamp. Methods for removing organotin residues during the workup of the products of these reactions are discussed in Section 22.3. [Pg.256]


See other pages where Triethylborane/oxygen is mentioned: [Pg.217]    [Pg.88]    [Pg.88]    [Pg.90]    [Pg.86]    [Pg.1050]    [Pg.86]    [Pg.62]    [Pg.63]    [Pg.217]    [Pg.88]    [Pg.88]    [Pg.90]    [Pg.86]    [Pg.1050]    [Pg.86]    [Pg.62]    [Pg.63]    [Pg.197]    [Pg.244]    [Pg.84]    [Pg.109]    [Pg.38]    [Pg.155]    [Pg.19]    [Pg.171]    [Pg.2224]    [Pg.187]    [Pg.73]    [Pg.98]    [Pg.378]    [Pg.383]    [Pg.193]    [Pg.469]    [Pg.244]    [Pg.481]    [Pg.481]    [Pg.421]    [Pg.520]    [Pg.40]   
See also in sourсe #XX -- [ Pg.11 , Pg.66 , Pg.73 , Pg.77 , Pg.79 , Pg.92 , Pg.323 ]

See also in sourсe #XX -- [ Pg.257 ]




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