Amides from esters with dimethylaluminum

AMIDES FROM ESTERS WITH DIMETHYLALUMINUM AMIDES... 

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. 

A simultaneous reduction-oxidation sequence of hydroxy carbonyl substrates in the Meerwein-Ponndorf-Verley reduction can be accomplished by use of a catalytic amount of (2,7-dimethyl-l,8-biphenylenedioxy)bis(dimethylaluminum) (8) [33], This is an efficient hydride transfer from the sec-alcohol moiety to the remote carbonyl group and, because of its insensitivity to other functionalities, should find vast potential in the synthesis of complex polyfunctional molecules, including natural and unnatural products. Thus, treatment of hydroxy aldehyde 18 with 8 (5 mol%) in CH2CI2 at 21 °C for 12 h resulted in formation of hydroxy ketone 19 in 78 % yield. As expected, the use of 25 mol% 8 enhanced the rate and the chemical yield was increased to 92 %. A similar tendency was observed with the cyclohexanone derivative. It should be noted that the present reduction-oxidation sequence is highly chemoselective, and can be utilized in the presence of other functionalities such as esters, amides, rert-alco-hols, nitriles and nitro compounds, as depicted in Sch. 10. 

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