Reduction of N -(alkoxy(aryl)methyl)benzamide Compounds by a Hantzsch Ester 1,4-Dihydropyridine Using Pd/C as a Catalyst
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Reduction of N-(alkoxy(aryl)methyl)benzamide Compounds by a Hantzsch Ester 1,4-Dihydropyridine Using Pd/C as a Catalyst Xiao-Xia Shen Æ Qiang Liu Æ Rui-Guang Xing Æ Bo Zhou
Received: 18 July 2008 / Accepted: 27 August 2008 / Published online: 15 October 2008 Springer Science+Business Media, LLC 2008
Abstract Pd/C-catalyzed transfer hydrogenation with Hantzsch ester1,4-dihydropyridine was found to be very effective for the selective reduction of N-(alkoxy(aryl) methyl) benzamide compounds to the corresponding benzamides. The reaction conditions, solvent effects, and reaction mechanism were discussed in the present work. Keywords N-(alkoxy(aryl)methyl)benzamide compounds Palladium on carbon Reduction Hantzsch ester 1,4-dihydropyridine
1 Introduction The development of new reduction procedures using safe and practically useful reducing agents is of great importance. Existing reducing agents such as H2 (gas), NaBH4, LiAlH4 and DIBAL-H, although efficient in producing good yields of the desired products, require precautions in handling. The title reagent, namely, Hantzsch ester. 1,4dihydropyridine (HEH) is being investigated as a safe, easy-to-handle, cheap and environmentally benign reagent for the reduction of organic functional groups. Hantzsch ester 1,4-dihydropyrindine, a well-known model compound of co-enzyme nicotinamide adenine dinucleotide (NADH), has been found to be an attractive biomemetic reducing agent for a variety of useful organic transformations. Many studies have been conducted concerning the mechanism of X.-X. Shen (&) Q. Liu R.-G. Xing B. Zhou State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, People’s Republic of China e-mail: [email protected] Q. Liu e-mail: [email protected]
its reduction of various electron-deficient functional groups [1–5]. Recently, there has been much interest in finding an application for HEH as a biomimetic reducing agent in synthetically useful organic transformations [6], such as organocatalytic and enantioselective reduction of a,b-unsaturated aldehydes [7–10], a,b-unsaturated ketones [11, 12], nitroolefins [13], conjugated olefins [14], a-Ketoesters [15] and Imines [16, 17], reduction of tertiary amides [18], reductive amination of carbonyl compounds [19–25], reductive cyclization of electron-deficient double bonds [26], and cascade asymmetric synthesis of Wieland– Miescher ketone analogs [27]. Actually, we also expended some useful HEH-based synthetic methods [28–30]. It is well-known that Pd/C is a cost-efficiency heterogeneous catalyst and is used extensively in organic chemistry [31–34]. Hayashi and his co-workers have reported an efficient dehydrogenative method using a catalytic amount of Pd/C under an ethylene atmosphere [35–38]. The dramatic catalytic ability of Pd/C was shown vividly in oxidative aromatization of HEH and it is analogs [39]. The facile and effective catalyst activity of Pd/C intrigued our interest in developing it is further application for HEH-bas
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