Selective transition metal-free aroylation of diarylmethanes with 2-acyl-imidazolium salts via acyl C–C bond cleavage
A highly chemoselective method is reported for the aroylation of simple diarylmethane derivatives via direct acyl C–C cleavage with 2-acyl-imidazolium salts under transition metal-free conditions. This represents a straightforward way to access a variety of sterically and electronically diverse 1,2,2-triarylethanones, a class of compounds with biological activities and various applications.
Base-Promoted Amidation and Esterification of Imidazolium Salts via Acyl C-C bond Cleavage: Access to Aromatic Amides and Esters
Imidazolium salts have been effectively employed as suitable acyl transfer agents in amidation and esterification in organic synthesis. The weak acyl C(O)-C imidazolium bond was exploited to generate acyl electrophiles, which further react with amines and alcohols to afford amides and esters. The broad substrate scope of anilines and benzylic amines and base-promoted conditions are the benefits of this route. Interestingly, phenol, benzylic alcohols, and a biologically active alcohol can also be subjected to esterification under the optimized conditions.
Synthesis and Application of Imidazole Derivatives. Synthesis and Acyl Activation of 2-Acyl-1-methyl-1H-imidazoles
2-Acyl-1-methyl-1H-imidazoles (3) were prepared in good yields by treating 1-acylpyrrolidines (5) with 2-lithio-1-methyl-1H-imidazole (2) at -78 deg C.The acyl group of 3 was very stable under various severe conditions, but 2-benzoylimidazole (3a) was gradually hydrolyzed by heating with 1.3 N NaOH to produce benzoic acid and 1-methyl-1H-imidazole.Acyl activation of 3 was performed by direct quaternization of 3 with iodomethane or dimethyl sulfate or more successfully by quaternization of the corresponding O-trimethylsilylated gem-cyanohydrin (11) with dimethyl sulfate.Keywords- acylimidazole; 2-acylimidazole; imidazolium salt; acyl group activation; acylation; C-C bond fission; protecting group; latent functionality
GENERATION OF AN ACTIVE ACYL SPECIES FROM STABLE 1-METHYL-2-ACYL-1H-IMIDAZOLES
1-Methyl-2-(1'-cyano-1'-trimethylsilyloxy)alkyl-1H-imidazoles (2) were easily prepared from the corresponding stable carbonyl compounds, 1-methyl-2-acyl-1H-imidazoles (1).When the quarternary salts of 2 were treated with various nucleophiles, reactive acyl species, which was presumed to be acylcyanide (12), was generated in situ under C-C bond fission to result in producing the corresponding acylated compounds (5-10) in good yields.
Ohta, Shunsaku,Hayakawa, Satoshi,Okamoto, Masao
p. 5681 - 5684
(2007/10/02)
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