Reaction of cyclic imidates with α,β‐unsaturated esters: Synthesis of new pyrrolo[2,1‐b]‐1,3‐oxazine and pyrido[2,1‐b]‐1,3‐oxazine derivatives

Abstract

AbstractThe cycloaddition reaction of cyclic imidates, 2‐benzyl‐5,6‐dihydro‐4H‐1,3‐oxazines 1a, 1b, 1c, 1d, 1e, 1f, with dimethyl acetylenedicarboxylate 2, trimethyl ethylenetricarboxylate 4, or dimethyl 2‐(methoxymethylene)malonate 6 afforded new fused heterocyclic compounds, such as methyl (6‐oxo‐3,4‐dihydro‐2H‐pyrrolo[2,1‐b]‐1,3‐oxazin‐7‐ylidene)acetates 3a, 3b, 3c, 3d, 3e, 3f (71–79%), dimethyl 2‐(6‐oxo‐3,4,6,7‐tetrahydro‐2H‐pyrrolo[2,1‐b]‐1,3‐oxazin‐7‐yl)malonates 5b, 5c, 5d, 5e, 5f (43–71%), or methyl 6‐oxo‐3,4‐dihydro‐2H,6H‐pyrido[2,1‐b]‐1,3‐oxazine‐7‐carboxylates 7a, 7b, 7c, 7d, 7e, 7f (32–59%), respectively. In these reactions, 1a, 1b, 1c, 1d, 1e, 1f (cyclic imidates, iminoethers) functioned as their N,C‐tautomers (enaminoethers) 2 to α,β‐unsaturated esters 2, 4, and 6 to give annulation products 3, 5, and 7 following to the elimination of methanol, respectively. J. Heterocyclic Chem., (2011).