Trimethylaluminum reaction with ketones

Stereoselective reaction with ketones. The reaction of ketone 1 with methyl-lithium, trimethylaluminum, and lithium letramethylaluminate shows no stcrco-specificity. The reaction with mcthylmagncsium bromide gives the two possible adducts in the ratio 2.4 1. The best stereospccificity is observed with dimethylsulf-oxonium methylide, which converts 1 into 2 and 3 in a ratio about 5 1. Reduction of the epoxides with lithium triethylborohydride gives the desired tertiary alcohols. This reaction was used in a synthesis of ( ) stemodin (4).2... 

Another route to aluminum enolates is through the reaction of ketones with a trialkylaluminum, usually trimethylaluminum (Scheme 30). ... 

Hydrazones. The reagent is prepared from A(,Af-dimethylhydrazine and trimethylaluminum in hot toluene (97% yield). It is useful for derivatization of unre-active ketones (e.g., ferrocenyl ketones) in refluxing toluene. The fully substituted hydrazones can undergo exchange on reaction with N2H4 in ethanol. Tropone hydra-zone, which has previously been unavailable, can be prepared by this method. 

Conjugate addition to a,p-unsaturated ketones. Nickel(II) acetylacetonate catalyzes the reaction of ketones with trimethylaluminum to give methyl-carbinols however, other unexpected products are formed, sometimes extensively. This organonickel compound also catalyzes the conjugate addition of trimethylaluminum to a, 3-unsaturated ketones (equation I). The yields of... 

Methyl ketones. Nitriles (aliphatic and aromatic) are converted into methyl ketones by reaction with trimethylaluminum in the presence of various catalysts,... 

An early reference teaches us that even trimethylaluminum can cause deprotonation of a specialized ketone to generate the aluminum enolate under rather drastic conditions (toluene, reflux) [42]. As expected, the reaction proceeded under thermodynamic control, in which aldol and retro-aldol reactions occurred reversibly, to give a high level of anti diastereoselectivity, with concomitant removal of chelation complex 46 from the solvent (Scheme 6.22). 

Ertas and Seebach " have studied the synr-anti isomerization of aldol adducts chelated to aluminum for the reaction of ethyl trityl ketone with aldehydes in the presence of trimethylaluminum (Scheme 52). 

The CIO methyl was installed using a sequence of steps, which included an asymmetric hydroboration reaction. This approach was developed by Tatsuda for the synthesis of herbimycin and later followed by Panek for macbecin. Other unsuccessful approaches to this difficult region of the molecule are outlined below. To ready the material for this event, the ester 6 was reduced to the aldehyde and trimethylaluminum was added to generate alcohol 24 (Scheme 8). Oxidation to the ketone, Wittig reaction, and TBS removal with HF provided allyl alcohol 25 in... 

Tetrazoles. Aryl nitriles and alkyl nitriles are converted into the corresponding tetrazoles in the presence of dibutyltin oxide or trimethylaluminum in moderate to good yields. Amides or thioamides also react with TMSA to form tetrazoles. Reaction of a,/3-unsaturated ketones with TMSA can be catalyzed by TMSOTf in dichloromethane. A tandem strategy for fused tetra-zole formation has also been reported a [3-1-2] cycloaddition between a nitrile and TMSA in presence of dibutyltin oxide is followed by an intramolecular allylation to form a fused tetrazole in 60-82% yields. 

Deprotonation has only rarely been applied for the formation of aluminum enolates, for example, by treatment of trityl-ethyl or mesityl-ethyl ketones with trimethylaluminum [124]. In general, however, this reaction is plagued by side reactions, in particular addition to the carbonyl group. Concerning zinc enolates, in situ deprotonation of aryl-alkyl ketones occurs when they are... 

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