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

• Published in: Journal of heterocyclic chemistry 2011-05, Vol.48 (3), p.577-581
• Main Authors: Ihara, Shogo, Soma, Takashi, Yano, Daigo, Aikawa, Shunichi, Yoshida, Yasuhiko
• Format: Article
• Language: English
• ISSN: 0022-152X; 1943-5193
• DOI: 10.1002/jhet.539

The 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).