Dialkylaluminum chloride

The hydroalumination of alkenes with BujAlCl catalyzed by Cp2ZrCl2 produces higher dialkylaluminum chlorides, which cannot be prepared by non-catalytic hydroalumination (Scheme 2-12) [63-65]. Terminal alkenes, internal linear alkenes and cycloalkenes can serve as substrates at reaction temperatures increasing in this order. 1,5-Dienes react to give cyclized products. 

During the catalyst activation reactions in Kealy s catalyst system discussed above [Eqs. (6)—(7) and (8)—(10)], a monoalkylaluminum chloride is formed. Because the initial dialkylaluminum chloride R2A1C1 is present in excess, the effective cocatalyst could be the original R2A1C1 or the RA1C12 formed during the reaction. To clarify the role of the aluminum component in the actual codimerization reaction the following catalyst combinations have been tested ... 

The above results indicate that the monoalkylaluminum chloride rather than the dialkylaluminum chloride is the more effective cocatalyst. The relatively high activity of Kealy s catalyst can be attributed to the in situ formation of RA1C12 as a result of reduction of Ni11 by the dialkylaluminum chloride. However, such reduction is not possible in the R2A1C1/Ni° catalyst system. Thus, the differences between RA1C12 and R2A1C1 can be readily compared with the Ni° catalyst systems. 

Monoalkyl- and dialkylaluminum chloride differ not only in their Lewis acidity but in their alkylation ability. However, in the above experiment,... 

Attempts to use the isobutyl group in the carbometalation of alkynes only give rise to hy-drometalated products, but ethyl and n-propyl groups can be successfully transferred from the corresponding dialkylaluminum chlorides. The regioselectivity in these reactions is lower than that for the methyl transfer. Indeed, the reaction mechanism may be different from that of methylalumination [62]. 

Asymmetric Diels-Alder reactions. Unlike methyl crotonate, which is a weak dienophile, chiral (E)-crotonyl oxazolidinones when activated by a dialkylaluminum chloride (1 equiv.) are highly reactive and diastereoselective dienophiles. For this purpose, the unsaturated imides formed from oxazolidinones (Xp) derived from (S)-phenylalanol show consistently higher diastereoselectivity than those derived from (S)-valinol or (IS, 2R)-norephedrine. The effect of the phenyl group is attributed in part at least to an electronic interaction of the aromatic ring. The reactions of the unsaturated imide 1 shown in equation (I) are typical of reactions of unsaturated N-acyloxazolidinones with cyclic and acyclic dienes. All the Diels-Alder reactions show almost complete endo-selectivity and high diastereoselectivity. Oxazolidinones are useful chiral auxiliaries for intramolecular Diels-Alder... 

However, Natta, Pasquon, Zambelli and Gatti (63) have shown that titanium trichloride-dialkylaluminum chloride or titanium trichloride and alkylaluminum dichloride with nucleophilic materials are good catalysts for the polymerization of propylene to the isotactic structure. The titanium trichloride could also be made in situ from titanium tetrachloride and triethyl aluminum. Vesely, Ambroz, Vilin and Hamrik (64) showed the addition of the nucleophilic materials to diethylaluminumchloride-titanium trichloride polymerizations decreased the rate of polymerization and changed the stereospecificity. The more nucleophilic materials such as sulfur compounds were more effective than the less nucleophilic oxygen materials. 

Syndiotactic polypropylene has been made by Zambelli, Natta and Pasquon (75). The anionic catalysts made from dialkylaluminum chloride, vanadium acetylacetonate and anisole reverse the addition to the propylene molecule so that control by an ultimate asymmetric carbon is no longer possible. The formation of syndiotactic polypropylene is shown in Fig. 8 close to the region of inverted reaction of the propylene molecule. 

Recently, Kunz reported that dialkylaluminum chlorides add in a 1,4-mode to N-(a,f3-unsaturated acyl)oxazolidones (9 Scheme 3),12 while high enantioselectivity is obtained with the chiral N-(a, 3-un-saturated acyl)oxazolinone (11). Typically, higher dialkylaluminum halides (R = ethyl, isobutyl) do not... 

The alkyrlaluminums were obtained from Texas Alkyls Inc. and purified by vacuum distillation in nitrogen atmosphere. B.P. °C/mm Hg MCaAl 60768.5 EtjAl 977100 Et AlCl 125-126750mm MejAlCl 847200. Prior to distillation the dialkylaluminum chlorides were stirred over dry sodium chloride at 80° C for 2 hrs. to remove alkyl-aluminum dichlorides. The distilled dialkylaluminum chlorides were stored over sodium chloride to prevent the accumulation of the dihalide. 

Among the four alkylaluminums, dialkylaluminum chlorides in conjunction with a suitable alkyl halide will yield highest molecular weight polyisobutylene. The Me2AlCl/t-BuX system should be the best in this respect. The dialkylaluminum chlorides should have higher coinitiator efficiencies than trialkylaluminums. 

Rueck-Braun, K, Stamm, A, Engel, S, Kunz, H, (i-branched a-halo carboxylic acid derivatives via stereoselective 1,4-addition of dialkylaluminum chlorides to a,p-unsaturated A-acyloxazolidinones, J. Org. Chem., 62, 967-975, 1997. 

The Kunz group further demonstrated the asymmetric s)uithesis of )3-alkylated a-halogenated (Cl or Br) carboxylic acid derivatives. Eor this purpose, the Al-functionalized D-galactosamine-derived oxazolidinone 52 was treated with dialkylaluminum chloride, which was followed by addition of NXS (X = Cl, Br) to trap the intermediary enolate. Consequently, a variety of j8-branched a-halo carboxylic acid derivatives were obtained with good diastereoselectivities [63]. 

OrChlorocarboxylic acids. Immediately following the conjugate addition of dialkylaluminum chloride to Al-alkenoyloxazolidin-2-ones, the addition of NCS converts the enolates to the a-chloro derivatives. 

Okauchi, T., Itonaga, M., Minami, T., Owa, T., Kitoh, K., and Yoshino, H. 2000. A general method for acylation of indoles at the 3-position with acyl chlorides in the presence of dialkylaluminum chloride. Org. Lett. 2 1485-1487. 

Dialkylaluminum chloride. 20,126-127 Addition to imines. The adducts fror the addition to M-sulfonylimines, which is ... 

Historically, Friedel-Crafts acylations of N-unsubstituted indoles were found to provide a mixture of 3-acyl- and 1,3-diacylindoles. Last year, Yoshino disclosed a novel method for the regioselective C-3 acylation of N-unsubstituted indoles with acyl chlorides in the presence of dialkylaluminum chlorides in a process that obviated the need for prior N-protection . Intriguingly, despite the known susceptibility of ind(jles towards acid-catalyzed dimerization processes, Yoshino nevertheless pretreated the indoles 166 with the Lewis acid prior to addition of the acid chlorides, an artifice that in some way may account for the observed selectivity for the desired 3-acyl derivatives J67. Ottoni confirms the effectiveness of this sequence and also notes the importance of added nitromethane as cosolvent <010L1005>. 

The first metallocene catalysts were biscyclopentadienyl titanium complexes and dialkylaluminum chloride. These catalysts were not stable and produced very low yields. However, they were the first catalyst systems to produce copolymers of polypropylene and 1-butene with very high comonomer uniformity, due to the fact that they had only one type of active site. 

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