Aluminum amide

A key step in the synthesis of the spiroketal subunit is the convergent union of intermediates 8 and 9 through an Evans asymmetric aldol reaction (see Scheme 2). Coupling of aldehyde 9 with the boron enolate derived from imide 8 through an asymmetric aldol condensation is followed by transamination with an excess of aluminum amide reagent to afford intermediate 38 in an overall yield of 85 % (see Scheme 7). During the course of the asymmetric aldol condensation... 

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. 

Another method for converting esters to amides involves aluminum amides, which can be prepared from trimethylaluminum and the amine. These reagents convert esters directly to amides at room temperature.142... 

The total syntheses of these pepper alkaloids are not those of pyrrolidines but rather syntheses of their acid parts. Thus dihydrowisanidine (137) has been prepared by a series of reactions, the key step of which is the formation of the carbon-carbon double bond by a Wittig-Homer reaction (217, 218). Schemes 41 and 42 summarize two syntheses of okolasine from sesamolmethyl ether (279) of course, routes to okolasine also yield the corresponding piperidine alkaloid wisanine. Molybdenum-catalyzed elimination of allylic acetate (149) yielded (E,E)-diene ester 150 en route to trichonine (220) worthy of note is the use of an aluminum amide in the preparation of amide 143 from ester 150 (Scheme 43). 

The aluminum amide is prepared by reaction of N-methylaniline with A1(CH,), in CH2C12 at 25 °. 

Liquid injection molding, for silicone rubbers, 3, 674—675 Liquid ligands, in metal vapor synthesis, 1, 229 Liquid-phase catalysis, supported, for green olefin hydroformylation, 12, 855 Lithiacarbaboranes, preparation, 3, 114 Lithiation, arene chromium tricarbonyls, 5, 236 Lithium aluminum amides, reactions, 3, 282 Lithium aluminum hydride, for alcohol reductions, 3, 279 Lithium borohydride, in hydroborations, 9, 158 Lithium gallium hydride, in reduction reactions, 9, 738 Lithium indium hydride, in carbonyl reductions, 9, 713—714... 

The use of a cationic aza-Cope rearrangement in concert with a Mannich cyclization has also been applied to the total synthesis of enantiomerically pure (—)-crinine (359) (205). In the event, nucleophilic opening of cyclopentenoxide with the aluminum amide that was formed on reaction of (/ )-a-methylbenzyl-amine and trimethylaluminum gave the amino alcohol 485 together with its (15,25) diastereomer. Although there was essentially no asymmetric induction in this process, the diastereomeric amino alcohols were readily separated by chromatography, and the overall procedure therefore constitutes an efficient means for the preparation of enantiomerically pure 2-amino alcohols from epoxides. When the hydrochloride salt derived from 485 was treated with paraformaldehyde and potassium cyanide, the amino nitrile 486 was formed. Subsequent Swem oxida-... 

Figure 2 Sketches and molecular structures of (a) aluminum amid-rnate complex Al HC(CMeNDipp)2 (H atoms removed for clarity) and (b) germanium aminotroponiminate cation [Ge(C7H5N2J-Pr2)]+...

Janot ef al. [48] prepared lithium aluminum amide (LiAl(NH2)4) and used it instead of LiNH2 in the Li-N-H system. The mixture of LiAl(NH2)4 and 4LiH released more than 5 mass % hydrogen at 130 °G. Ho vever, the experimental result of the hydrogenation indicated that this combination vould have a poor reversibility because of the existence of AlN after the dehydrogenation. 

Reagent (42) is readily prepared " by the treatment of primary and secondary amines and hydrazines (substituted or unsubstituted) or the corresponding hydrochlorides with trimethylaluminum. The aluminum amide reagents (42) readily react with a variety of ester substrates, such as conjugated esters (entries 2,5 and 11, Table 16 " ), N-blocked amino acid esters (entry 10, Table 16), as well as alkyl esters (en-... 

Table 16 The Addition of Aluminum Amide Reagents (42) to Esters (equation 19)...

As an extension of their chiral aldol and alkylation technology, Evans and cowotkers have reported a variety of methods for cleaving and replacing Ae chiral oxazolidinone auxiliary once chain construction has been completed. Included in this methodology was the direct transformation of a chiral imide to an lV-methoxy-/V-methylamide through the use of aluminum amides (prepared in situ). ° This reaction has been shown to be rather general for complex substrates (Scheme 2). ... 

Since it had been determined that ketone or aldehyde functionality was not directly accessible from chiral A/-acyloxazolidinones, the transamination-metal alkyl addition procedure provided a conveniently expeditious alternative. The first step, transamination, proceeded in high yield by introduction of the N-acyloxazolidinone into a solution of the aluminum amide in dichloromethane at -IS C. The reaction is favored by the presence of a-heteroatom substituents and by -alcohol functionality (aldol adducts). Acceleration of the transamination in the latter case is most likely due to formation of a chelated intermediate (5) which serves to activate only the exocyclic carbonyl towards attack (equation 4). Because of the indicated activation, these aldol adducts are often the best substrates for this permutation. The effectiveness of the transamination in the case of (4) is noteworthy, as retroaldol fragmentation of this substrate usually occurs under mild base catalysis. 

AMIDES FROM ESTERS WITH DIMETHYL ALUMINUM AMIDES... 

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