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■ Microwave-Irradiated Synthesis of 1,2-Dihydropyridines from N-Functionalized Enaminones and Enals through Domino Condensation and 6π-Azaelectrocyclization

Elkhabiry Shaban, Md. Imran Hossain, Ming-Yu Wu, Yoshihiko Takemasa, Sachie Nagae, Wei Peng, Hiroyuki Kawafuchi, and Tsutomu Inokuchi*

*Division of Chemsitry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan

Abstract

N-Amino-substituted 1,2-dihydropyridine motifs are constructed using cyclohexane-1,3-diones via the Knoevenagel condensation with enals followed by 6π-electrocyclization using ethylenediammonium diacetate as a catalyst under MW irradiation. A survey of substituents on the N atom indicated that the phenylamino and benzoylamino groups are favorable for the reaction, while phenyl, benzyl, and no-substituent are not. The substituent at C2 of enals is crucial for smooth formation of the corresponding adducts and slightly higher yields are obtained with enals bearing an electron-withdrawing aromatic at C3.