Trimethylaluminum reaction with esters

The one-step conversion of diaminoethane into 2-imidazolines (89-%%) uses reaction with esters in the presence of trimethylaluminum <8UOC2824>. When 1,2-diamines are treated with glyoxal biimidazolidine (216) and azadecalin products are both formed <85JOC2365>. Other carbon sources which have proved useful include diphenyl A-sulfamoylcarbonimidate <918753), A-dichloro-methylenesulfonamides and arylcarbonimidates (Scheme 150) <828984,87864). 

This procedure, which is based on the work of Ishii and co-workers, affords a mild and general method for converting a wide variety of esters to primary, secondary, and tertiary amides (Table 1). While the preparation of the tertiary amide, N,N-dimethylcyclohexanecarboxamide, described here is carried out in benzene, aluminum amides derived from ammonia and a variety of primary amines have been prepared by reaction with trimethylaluminum in dichloromethane and utilized for aminolysis in this solvent. Although 1 equivalent of the dimethylaluminum amides from amines was generally sufficient for high conversion within 5-48 hours, best results were obtained when 2 equivalents of the aluminum reagent from ammonia was used. Diethyl-aluminum amides can also effect aminolysis, but with considerably slower rates. 

Hubbard and Miller87 used a Lewis acid catalyzed Diels-Alder reaction between y.y-disubstituted o. /i-unsaluralcd esters and cyclopentadiene in their approach toward oligomeric cyclopentanoids. In order for the reaction to proceed, they needed to add trimethylaluminum as a desiccant prior to addition of the Lewis acid catalyst aluminum trichloride. The endo/exo selectivity of the reaction with 97, depicted in equation 29, increased from 98/99 = 75/25 to 88/12 when the reaction temperature was dropped from room temperature to —20 °C. 

Stereoselective routes to the lactone precursors of the 1-hydroxyethylene isosteres using a titanium-mediated condensation has been reported by both Shibuya and co-workers1 and DeCamp et al. 19 The former method (Scheme 9) features the reaction between (2S)-2-dibenzylamino aldehydes and optically active dichloroisopropoxytitanium ester homo-enolates to provide the desired lactone with high erythro selectivity. Then, the lactone is opened by treatment with an amine and trimethylaluminum to give the 1-hydroxyethylene isostere. The experimental details of DeCamp et al. s high yielding and stereoselective synthesis 19 of lactone 8 (Scheme 10) is discussed in Section 10.6.2.2. 

Finally, fluorinated carboxylic acids react with epoxides (trimethylaluminum-catalyzed).- and conveniently with diazo conipounds. Cycloaddition is observed with diazo-methane. Reaction of compound 7 with trifluoroacetic acid alone is relatively slow (Freon 113, reflux, 12 h, for completion of reaction) however, catalytic amounts of copper(ll) perchlorate increase the rate of formation of ester 8 (rt, 5 min). ... 

Dimethylaluminum methylselenolate (38) is prepared in situ by the reaction of trimethylaluminum with elemental selenium in refluxing toluene [66]. The yellow-colored solution can be used in various reactions, such as the conversion of esters to the corresponding selenol esters, the ring opening of epoxides, and Michael addition to cyclohexenone (Scheme 36) [66]. 

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... 

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