Organoaluminum compounds addition

The regiochemistry of Al-H addition to unsymmetrically substituted alkynes can be significantly altered by the presence of a catalyst. This was first shown by Eisch and Foxton in the nickel-catalyzed hydroalumination of several disubstituted acetylenes [26, 32]. For example, the product of the uncatalyzed reaction of 1-phenyl-propyne (75) with BujAlH was exclusively ds-[3-methylstyrene (76). Quenching the intermediate organoaluminum compounds with DjO revealed a regioselectivity of 82 18. In the nickel-catalyzed reaction, cis-P-methylstyrene was also the major product (66%), but it was accompanied by 22% of n-propylbenzene (78) and 6% of (E,E)-2,3-dimethyl-l,4-diphenyl-l,3-butadiene (77). The selectivity of Al-H addition was again studied by deuterolytic workup a ratio of 76a 76b = 56 44 was found in this case. Hydroalumination of other unsymmetrical alkynes also showed a decrease in the regioselectivity in the presence of a nickel catalyst (Scheme 2-22). 

Organoaluminum compounds are also good nucleophiles for 1,4-addition to nitroalkenes as shown in Eq. 4.89.111... 

Organoaluminum compounds are widely used in the production of polyolefines and stereoregular elastomers (as components of catalyst complex), as raw stock in the production of higher alcohols and carboxylic acids, as additives for reactive fuels, etc. 

A highly convenient and versatile cyclopropanation method has been devised which involves treatment of olefins with different organoaluminum compounds and alkylidene iodide under mild conditions [93]. Although Miller found that cyclopropane formation by use of EtsAl-methylene iodide in cyclohexene proceeds in quite disappointing yields [94], Yamamoto and Maruoka reached the conclusion that the intermediate dialkyl(iodomethyl)aluminum species 97 is responsible for the cyclopropanation of olefins and that it readily decomposes in the absence of olefins or in the presence of excess trialkylaluminum. Hence the use of equimolar amounts of trialkyl-aluminum and methylene iodide in the presence of olefins is essential for the achievement of reproducible results in the cyclopropanation process. In addition, because di-alkylaluminum halide can also be used as a cyclopropanation agent, the use of half an equivalent of trialkylaluminum is not detrimental (Sch. 61). 

SCHEME 10.59 Bicyclic oxazolidinones derived fiom carbohydrates are efficient chiral auxiliaries in conjugate addition reactions of organoaluminum compounds. 

To the solution of the organoaluminum compounds, 549.3 g (4 mol) of phosphorus trichloride, diluted with 0.8 L of dichloromethane, is added dropwise over a period of 3 hr at a rate that keeps the reaction mixture at reflux. Thereafter, 613.3 g (4 mol) of phosphoryl chloride and 298.2 g (4 mol) of potassium chloride (ground and dried at 100°) are added within 1 hr. The reaction mixture is heated at reflux for an additional hour. Most of the dichloromethane is removed by distillation at normal pressure, and the waxy residue is extracted with four 500-mL volumes dry petroleum (bp 40/60). The petroleum is removed by distillation at normal pressure. Fractional distillation of the oily residue at 1.0 mbar, using a 20-cm Vigreux column affords methylenebis[dichlorophosphine]. Yield 134-160 g (32-38%), bp 54°/l mbar. 

Addition of Grignard reagents to ketones to form alcohols is a class of the most fundamental reactions in organic synthesis. Much data on selectivities of this reaction are available. Yamamoto et al. utilized a highly bulky organoaluminum compounds as a... 

This type of reaction attracted broad interest when it was discovered that high regioselectivity can also be effected with organoaluminum compounds and other nucleophiles in the presence of Lewis acids and that by employing chiral cyclic acetals (from optically active 1,2- or 1,3-diols) diastereoselective transformations can be realized. - Such reactions are synthetically very valuable when considering that the overall process represents an enantioselective Michael addition, where the chiral auxiliary can be recycled (Scheme 39). ... 

Since organoaluminum compounds have been known to add to a,) -unsaturated ketones, it is feasible that cyclopropyl ketones can react in a similar fashion. The nickel-catalyzed addition of trimethylaluminum to aryl cyclopropyl ketones 1 yielded the corresponding 1-arylpentanones 2 in moderate yields. It has been postulated that the first step of this reaction involves the nickel(0)-promoted electrophilic attack of alumimun at the carbonyl oxygen. 

Nd(OCOR)3/Al(i-Bu)3/AlEt2Cl, and Nd(OCOR)3/Al2Et3Cl3/AlH(i-Bu)2, polymerize 1,3-butadiene to produce the polymer with czs-1,4 structure [33]. The chlorinated organoaluminum compounds are indispensable for smooth polymerization. Addition of water and carboxylic acid improves the reactivity and selectivity. 

Tanaka (8) reported polymerization experiments with benzoyl peroxide. He observed the formation of insoluble polymers in addition to dimer. Wei (9) carried out polymerizations with butyllithium and organoaluminum compounds and obtained amorphous and partly crystalline products with thermoplastic properties the materials melted at 157°C and decomposed at 336°C. IR spectroscopy showed, a 1,4-trans structure. 

---