Trialkylaluminum compounds/reagents

Zirconocene dichlondc and related complexes catalyze the addition of trialkylaluminum compounds to tenninal acetylenes7 and olefins8 as well as the addition of ethyl, propyl, and butyl Grignard reagents to alkenes.9-12 These transformations occur with a high degree of regiosclectivity (cf. hydroboration), such that the metal atom always adds to the end position of a terminal multiple bond like that in 25. If addition is to a triple bond, M and R in the product are cis to each other... 

Trialkylaluminum compounds and trialkylboranes seem to reduce carbonyls in the same fashion as Grignard reagents and diaikylzincs. The reactivity towards carbonyl groups is greater than that of diaikylzincs, despite the third substituent, which does provide, however, additional opportunities for recognition. The compounds are well defined and can encompass a fairly wide range of alkyl substituents. This is especially true of the trialkylboranes. 

Organomagnesium-halide, organolithium and organoaluminum reagents are preferred to other organometaiiics. Commercially available trialkylaluminum compounds are convenient starting materials for the lower trialkylboranes. Solvents are not required, and trialkylborane can be isolated by distillation directly from the mixture ... 

Another modification with trialkylaluminum compounds as the metalating agent (see Table 1) is reported to occur stereospecifically but without any diastereoselectivity7 (for a procedure see Vol. E 19b. p 209). Interestingly, this carbenoid source exhibits a rather different chemoselectivity compared to the diiodomethane/diethylzinc combination the preference for allylic alcohols with the latter reagent to react with.yyn stereoselectivity (see Section 1.6.1.5.1.2.) is not observed with the aluminum-based reagent. 

For alkylation reagents, trialkylaluminum compounds are more interesting than other organometallic reagents because they are economically obtained on an industrial scale from aluminum hydride and alkenes. Despite this... 

Trialkylaluminum compounds are available in bulk quantities and would therefore be valuable alkylating reagents for the enantioselective addition to aldehydes. Several successful attempts along these lines have been reported [52]. In most cases, an excessive amount of Ti(O Pr)4 and use of tetrahydrofuran (THF) as the solvent are necessary in order to get satisfactory results of the catalysis. Similar... 

With the development of the cross coupling methodology, many 6-C-substituted purines have been prepared in the past decade. Thus, 6 halopurine derivatives react with arylmagnesium halides,25 alkyl(aryl)zinc or tin reagents,26 trialkylaluminum,27 or alkylcuprates28 to give the 6-alkylpurine derivatives. Also a reverse approach based on the reaction of purine-6-zinc iodide with aryl or vinyl halides has recently been described.29 For the synthesis of 6-arylpurines, an alternative approach makes use of radical photochemical reactions of adenine derivatives with aromatic compounds,30 but this method is very unselective and for substituted benzenes, mixtures of ortho-, meta-, and para substituted derivatives were obtained. 

Scheme 5 Synthesis of (//6-arcnc)l,nfAlCl4j3 (Ln = Y, Pr, Nd, Sm, Gd) subsequent reaction with trialkylaluminum reagents Me3Al or Et3Al gives alkylated ( 6-arene) Ln(AlCl3R)3 (R = Me, Et) compounds in good yields [105]...

When sterically more demanding trialkylaluminum reagents (R = i-butyl or 2-phenyl-propyl) are allowed to react with 9 a in diethyl ether or n-hexane, the cyclooligomerization process ends at the 1 3 compounds 82 (Scheme 6-21) [65J. The compounds have the structure of a triphosphametallahomobenzvalene, as has been confirmed for the case of R = CH2—CHPh —CH3 by X-ray crystallography. A plausible mechanistic rationale for the product formation involves a two-fold 1,2-addition of the triorganoaluminum to two equivalents of phosphaalkyne 9a (- 84). This is followed by a crossed [2 + 2]-cycloaddition... 

Trialkylaluminum agents should be handled in the laboratory using the "basic prudent practices" described in Chapter 5.C, supplemented by the additional precautions for work with highly flammable (Chapter 5.F) and reactive (Chapter 5.G) substances. Safety glasses, impermeable gloves, and a fire-retardant laboratory coat should be worn at all times when working with these compounds. Trialkylaluminum reagents should be handled only under an inert atmosphere. 

Polymers Derived from Trialkylaluminum. The most widely studied approach to alazane polymers utilizes ammonia or amine derivatives of trialkylaluminum reagents. The method following the steps of equation 1, which was first described over fifty years ago (75), was recently reinvestigated (J4-J7). Trialkyl and triarylaluminum compounds form 1 1 adducts with Lewis bases such as ammonia or amines. These adducts readily undergo intermolecular condensation with elimination of a... 

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