Application of Furan as a Diene: Preparation of Condensed 1,3-Oxazines by Retro-Diels−Alder Reactions

(Di-exo-3-amino-7-oxabicyclo[2.2.1]hept-5-en-2-yl)methanol (3) was treated with oxo carboxylic acids [p-toluoylpropionic acid, cis- or trans-(p-toluoyl)cyclohexanecarboxylic acid, -benzoic acid or methanobenzocyclooctenecarboxylic acid] to furnish the oxanorbornene-fused pyrrolo[1,3]oxazine 4, the isoindolo[1,3]oxazines 5 and 6, and the methanobenzocyclooctenepyrrolo[1,3]oxazine 10, together with the retro-Diels−Alder products pyrrolooxazinone 7, oxazinoisoindolones 8 and 9, and oxazinopyrrolobenzocyclooctene 11. On reflux in chlorobenzene, furan was released from the oxanorbornene heterocycles 5 and 10 to give the retro-Diels−Alder products. The structures of the new compounds were establi…