Synthesis of bicyclic tetrahydropyridine enamides and enecarbamates by hetero-Cope rearrangement of nitroso cycloadducts

The hetero-Cope rearrangement reactions of inverse carbamate and amide nitroso Diels–Alder cycloadducts with 1,2-dihydropyridines to give novel tetrahydropyridine enamides and enecarbamates have been studied in detail identifying optimal reaction conditions. The possibility to obtain tetrahydropyridine enamides and carbamates containing a free OH at the C-4 position is restricted to only particular substitution patterns when dealing with carbamate nitroso cycloadducts. On the other hand, starting from easily available amide nitroso cycloadducts and catalytic amounts of cuprous salts, it is now possible to obtain several substituted 4a,7,8a-tetrahydropyrido[4,3- e ]-[1,4,2]dioxazines in moderate to good yields.