Triethylaluminum, addition

Woodward s total synthesis of cephalosporin C begins with L-cysteine (48) which establishes the chiral center at C-7. The cis geometry at C-6,7 is achieved in intermediate (49) which is cyclized to (50) by treatment with triethylaluminum. The dihydrothiazine ring is constructed by Michael addition to the condensation product of trichloroethyl glyoxylate... 

The lithium 2-butenyl(triethyl)aluminate complex, prepared in situ from 2-butenyllithium and triethylaluminum, displayed poor diastereoselectivity in a reaction with benzaldehyde (anti/syn 56 44)7. (Z)-3-Alkoxy-substituted aluminate complexes such as A-C, however, give good diastereoselectivity in aldehyde addition reactions8. The reactions of A with aldehydes at —100 °C give the jyw-diol monoether with >95% diastereoselectivity and >80-95% regiose-... 

In the two-step Alfen process stoichiometric amounts of triethylaluminum are used, which have to be recovered in an additional process step before being reintroduced. 

The titanium reagent also dimethylates aromatic aldehydes." Triethylaluminum reacts with aldehydes, however, to give the mono-ethyl alcohol, and in the presence of a chiral additive the reaction proceeds with good asymmetric induction." A complex of Me3Ti-MeLi has been shown to be selective for 1,2 addition with conjugated ketones, in the presence of nonconjugated ketones." ... 

Remember from Chapter 6 that energy is released when a bond forms. Consequently, atoms that form covalent bonds tend to use all their valence s and p orbitals to make as many bonds as possible. We might expect the S p -hybridized aluminum atom to form a fourth bond with its unused 3 p orbital. A fourth bond does not form in A1 (C2 115)3 because the carbon atoms bonded to aluminum have neither orbitals nor electrons available for additional bond formation. The potential to form a fourth bond makes triethylaluminum a very reactive molecule. 

Cyanide addition has also been done under Lewis acid catalysis. Triethylaluminum-hydrogen cyanide and diethylaluminum cyanide are useful reagents for conjugate... 

In addition to the obvious uses of solubility parameters in predicting physical properties, it is also possible in some cases to study other types of intermolecular interactions. For example, the solubility parameter for triethylboron, (C2H5)3B, is 15.4h, whereas that for triethylaluminum (C2H5)3A1 is 23.7h. Triethylboron is known from other studies not to associate, whereas triethylaluminum exists as dimers. 

High polymers are generally obtained on treatment with Lewis acids at low temperatures in an inert solvent. Boron trifluoride and boron trifluoride etherate are the most widely used catalysts, but a small amount of water must be present, which is termed a promoter triethylaluminum and triisobutylaluminum are also useful initiators and are generally used with addition of water. Alkylating agents, such as ethyl triflate, triethyloxonium tetrafluoro-borate and hexafluorophosphite, and 2-methyl-l,3-dioxolenium perchlorate, are also effective initiators (76MI51301,72MI51304). 

Neat tripropylaluminum of 96% purity was supplied in a metal cylinder from Toyo Stauffer Chemical Company, Ltd. (Japan). This reagent is contaminated by 1.2% of triethylaluminum, 2.2% of triisobutylaluminum, and other compounds. Neat tripropylaluminum is also available from Aldrich Chemical Company, Inc. Since neat tripropylaluminum is pyrophoric and reacts violently with oxygen and water, the syringe should be washed with hexane immediately after addition. 

Conjugate addition. In the presence of 1 equivalent of triethylaluminum, cyanotrimethylsilane undergoes conjugate addition to a,/ -enones in high yield. The products arc converted into /J-cyano ketones by acid hydrolysis. The addition is kinetically controlled in toluene at room temperature, but thermodynamically controlled in refluxing THF (equation I). 

Except for the well-documented conjugate additions of diethylaluminum cyanide,92 triethylaluminum-hydrogen cyanide and Lewis acid-tertiary alkyl isonitriles,93 examples of Lewis acid catalyzed conjugate additions of acyl anion equivalents are scant Notable examples are additions of copper aldimines (233),94, 94b prepared from (232), and silyl ketene acetals (234)940 to a,(3-enones which afford 1,4-ketoal-dehydes (235) and 2,5-diketo esters (236), respectively (Scheme 37). The acetal (234) is considered a glyoxylate ester anion equivalent. 

Addition of traces of chloride in the form of bis(cyclopentadienyl)-titanium dichloride lowered the yield of polyethylene and initiated the known reduction reaction (129). Finally, it was found that polyethylene formation was caused by traces of water ( 10-8 mol%). Consequently, the yield increased to 500,000 g polyethylene per gram of titanium when two equivalents of trimethyl- or triethylaluminum previously treated with one equivalent of water was added to dimethylbis(cyclopentadienyl)ti-tanium (Table VII). 

Addition of ethylene to triethylaluminum is first-order in monomeric triethylaluminum and ethylene (7) Since triethyl-aluminum is largely dimeric in the liquid phase, kinetics of the growth reaction take the following form ... 

The triethylaluminum reaction product is divided into two streams. One stream, 70-75 percent of, the total, is recycled directly to the hydrogenation unit to form additional diethylaluminum hydride. The other stream, 25-30 percent of the total, is the actual product stream. It is first centrifuged to remove the bulk of unreacted aluminum which is recycled to the hydrogenation reactor along with recycle triethylaluminum. Product... 

The chemical activation of aluminum. The reactor is loaded with a suspension of aluminum in petrol and activating additive (triethylaluminum or triethylaluminum mixed with aluminum chloride). The mixture is agitated and heated in hydrogen to 160-200 °C and held at this temperature for 10 hours. After the activation the reactor is cooled, the excess hydrogen is withdrawn and the synthesis is started. 

In all the following examples, the targeted double bonds were activated by suitable substituents to increase the efficacy of the desired cyclization mode. For the total synthesis of acutumine (26), an activated a,p-unsaturated ketone 27 was chosen as precursor (Scheme 10) [74, 75], Aryl radical additions to this type of alkenes are known to proceed about ten times faster than to comparable allylic alcohols. In a radical-polar crossover reaction, the spirocyclic product 28 was obtained in the presence of triethylaluminum as promoter and an oxaziridine as hydroxylating agent. The fact that even the efficient hydrogen donor tetrahydrofuran could be used as solvent nicely demonstrates the high efficacy of the cyclization step. 

The color change and the sensitivity of conversion to order of addition of monomers and peroxide indicate that in order to obtain an AFR polymer the polar monomers must first be complexed or allowed to react with the active or living end of the anionic polymer chain, or otherwise solvate it before the polymer chain is attacked by the peroxide. Success or failure of the subsequent free radical block polymerization depends on the nature of the complex or reaction product formed. The resultant species are no longer active for propylene polymerization. The necessity of complex formation has also been observed by Milovskaya and coworkers (4). They have shown that vinyl chloride, a weak complexing agent, can be polymerized effectively with triethylaluminum peroxide only when it is present with a more active complexing compound such as an ester or an ether. 

Modification of Solids. Our next step was to investigate the behavior of washed solids when recombined with various alkylaluminum compounds. A 0.9 1-BU3AI solid with relatively little residual activity was chosen for this purpose. Figure 9 illustrates a typical polymerization curve for the solid upon activation with triethylaluminum. The addition of only minute amounts, in the range of 0.025-0.075 mole per mole Ti in the solid, was needed to regain or surpass the original activity of the unseparated catalyst. The same procedures were used to study the activation of the above brown TiCh solid with other organo-... 

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