Multicomponent Reactions of Arylglyoxal, 4‐Hydroxycoumarin, and Cyclic 1,3‐C,N‐Binucleophiles: Binucleophile‐Directed Synthesis of Fused Five‐ and Six‐Membered N‐Heterocycles

Abstract

The multicomponent reaction (MCR) of arylglyoxal, 4‐hydroxycoumarin, and various cyclic 1,3‐C,N‐binucleophiles in acetic acid under microwave conditions provides fused five‐ or six‐ membered N‐heterocycles depending on the ring size of the binucleophiles. 1,3‐C,N‐binucleophiles, such as amino‐pyrazole/oxazole, that have a five‐membered ring provide fused six‐membered dihydropyridines or pyridine derivatives, whereas aminouracil, cytosine, and 4/3‐aminocoumarines that have a six‐membered ring provide the corresponding five‐membered fused pyrroles. By using DFT calculations, the mechanism of the ring‐size‐dependent multicomponent cyclization reaction is explained. Cyclic 1,3‐C,N‐binucleophiles, such as aminopyrazole, aminooxazole, aminocoumarin, aminouracil, and cytosine, were explored in this MCR, and the corresponding fused pyrroles/dihydropyridines or pyridines were obtained in very good yields. The structures of the fused molecules were unambiguously confirmed by spectroscopic techniques and single‐crystal X‐ray analysis.