366 Acta Chim. Slov. 2007, 54, 366–369 Zeynizadeh et al.: Mild and Convenient Method for Aromatization of Hantzsch Esters ... 1. Introduction Hantzsch esters of 1,4-dihydropyridine based drugs such as Nifedipine, Amoldipine and Nitrendipine are the calcium channel blockers and have been widely used in the treatment of various cardiovascular diseases. 1 In hu- man body and during the first pass metabolism in the liv- er, it has been observed that 1,4-dihydropyridines undergo an oxidation reaction to produce pyridine compounds. 2 Because of the relevance of this oxidative conversion to biologically significant NADH redox processes and to the metabolic studies, 3 this transformation has attracted a great deal of attentions for the discovery of mild and gen- eral protocols applicable to a wide range of 1,4-dihy- dropyridines. In this context, a number of methods and reagents have been reported. 4–20 However; some of these methods have some disadvantages such as long reaction times, low yields of products, the requirement for severe conditions and the use of strong or toxic oxidants. Therefore, the introduction and development of a conven- ient, mild and efficient method for the oxidation of 1,4-di- hydropyridines to pyridine compounds is practically im- portant and is still demanded. 2. Results and Discussion The literature review shows that silver (I) oxide, Ag 2 O, has been found useful applications in organic syn- thesis as a mild oxidizing agent. 21 However, as far as we know, the aromatization of 1,4-dihydropyridines with Ag 2 O has not been reported yet. Our continuous efforts toward the development of this synthetic protocol 22 prompted us to report a new and practical method for the aromatization of substituted 4-aryl and 4-alkyl 1,4-dihy- dropyridines to the corresponding pyridines with Ag 2 O under mild conditions (Scheme 1). The optimization experiments on the aromatization of 1,4-dihydropyridine (2) showed that CH 3 CN was the solvent of choice for the excellent yield of product. The reaction in various other solvents such as CH 2 Cl 2 , C 6 H 6 , MeOH and THF was slow and had low efficiency (Table Short communication Mild and Convenient Method for Aromatization of Hantzsch Esters of 1,4-Dihydropyridines with Ag 2 O Behzad Zeynizadeh,* Karim Akbari Dilmaghani and Mansoor Mirzaei * Corresponding author: Department of Chemistry, Faculty of Sciences, Urmia University, Urmia 57159-165, Iran E-mail: bzeynizadeh@gmail.com Received: 17-07-2006 Abstract Hantzsch esters of 1,4-dihydropyridines were readily aromatized to their corresponding pyridine compounds by Ag 2 O in quantitative yields. The reactions were carried out in refluxing CH 3 CN within 0.9–4.5 h. Keywords: Aromatization, hantzsch esters of 1,4-dihydropyridines, Ag 2 O. Schema 1