Oxydation d'esters de Hantzsch, par le nouveau système HNO3/bentonite, et irradiation aux micro-ondes

Eco‐Mn Ecocatalysts: Toolbox for Sustainable and Green Lewis Acid Catalysis and Oxidation Reactions

“…The preparation of 1,4‐dihydropyridine is based on Hantzsch reaction between aldehydes, β ‐keto esters, and amines. The synthesis of pyridines can be performed by aromatization of dihydropyridines with various reagents such as HNO 3 , (NH 4 ) 2 Ce(NO 3 ) 6 , Cu(NO 3 ) 2 , Bi(NO 3 ) ⋅ 5H 2 O, Mn(OAc) 3 , Zr(NO 3 ) 4 , Fe(NO 3 ) 3 , PCC, Pd/C, I 2 /MeOH, o ‐iodoxybenzoic acid (IBX), SeO 2 , KBrO 3 /SnCl 4 ⋅ 5H 2 O, KMnO 4 , MnO 2 under microwave irradiation or sonication and DDQ (2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone) . Despite these numerous works, the development of effective and green methods are still required.…”

Synthesis and Aromatization of Hantzsch 1,4-Dihydropyridines under Microwave Irradiation. An Overview

“…Indeed those reactions afforded, unexpectedly, mixtures of 4-alkylpyridines ( 10 ) and 4-unsubstituted pyridine ( 11 ). In contrast, the same group related [ 25 ], two years later, that those 4-alkyl 1,4-DHP (0.25 g) do not undergo the dealkylation process when they are treated for 1 minute in a domestic microwave oven in the presence of a HNO 3 /Mexican bentonite clay system (2.5 g; prepared from a 1:1 mixture of the components). Aromatization of 1,4-DHP has also been studied by Varma [ 26 ].…”

Mild oxidative aromatization of 1,4-dihydropyridines with trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane promoted by ammonium bromide/HOAc in water/MeCN

“…Mashraqui & Karnik, 1998;Nakamichi et al, 2002;Pfister, 1990;Sabitha et al, 2003;Sausins & Duburs, 1988;Vanden Eynde et al, 1995;Vanden Eynde et al, 1992;Varma & Kumar, 1999); however, unfortunately, most of these methods use strong oxidants accomplished by the transition metals such as ferric nitrate (Khadilkar & Borkar, 1998), CrO 3 (Sausins & Duburs, 1988), MnO 2 (Vanden Eynde et al, 1995), PCC (Vanden Eynde et al, 1992), Zr(NO 3 ) 4 (Sabitha et al, 2003), Bi(NO 3 ) 3 (Mashraqui & Karnik, 1998), claysupported cupric nitrate (Maquestiau et al, 1991), H 2 O 2 /Co(OAc) 2 (Hashemi et al, 2003), Pb(OAc) 4 (Litvić et al, 2005), RuCl 3 /O 2 (Sausins & Duburs, 1988), ceric ammonium nitrate (CAN) (Pfister, 1990), Pd/C (Nakamichi et al, 2002), KMnO 4 (Eynde, D'Orazio, & Haverbeke, 1994) and Mn(OAc) 3 (Varma & Kumar, 1999). Also, some other oxidants such as DDQ (Vanden Eynde et al, 1995), heteropolyacid/NaNO 2 /SiO 2 (Niknam, Zolfigol, Razavian, & Mohammadpoor, 2005), I 2 /MeOH (Yadav, Subba Reddy, Sabitha, & Kiran Kumar Reddy, 2000), nitric oxide (Itoh, Nagata, Okada, & Ohsawa, 1995), HNO 3 (García, Delgado, Cano, & Alvarez, 1993) and SeO 2 (Cai, Yang, & Zhang, 2005) have been used for aromatization of 1,4-dihyroptridines. But, many of these methodologies suffer from drawbacks such as requiring intensive reaction conditions or needing excess oxidants or long times and afford only poor to moderate yields of products with difficult work-up procedure (Cai et al, 2005;Garcia et al, 1993;Hashemi et al, 2003;Itoh et al, 1995;…”