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

摘要

The cycloaddition reaction of cyclic imidates, 2-benzyl-5,6-dihydro-4H-1,3- oxazines 1a-f, 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-f (71-79%), dimethyl 2-(6-oxo-3,4,6,7-tetrahydro-2H-pyrrolo[2,1-b]-1,3-oxazin-7-yl)malonates 5b-f (43-71%), or methyl 6-oxo-3,4-dihydro-2H,6H-pyrido[2,1-b]-1,3-oxazine-7- carboxylates 7a-f (32-59%), respectively. In these reactions, 1a-f (cyclic imidates, iminoethers) functioned as their N,C-tautomers (enaminoethers) 1′ to α,β-unsaturated esters 2, 4, and 6 to give annulation products 3, 5, and 7 following to the elimination of methanol, respectively.