The reactions of 1-unsubstituted 2-pyridones with benzyne afforded the Diels-Alder adduct, 5, 6-benzo-2-azabarrelen-3 (2H)-ones, together with a large amount of the Michael-type adduct, 2-phenoxypyridines.
The reactions of 2-pyridones with benzyne were investigated in order to gain some insight into the structure–reactivity–chemoselectivity relationship involved in the tautomeric systems. All reactions examined have resulted in the formation of Diels-Alder and Michael-type adducts. It has been shown that the Diels-Alder reactivities were well correlated with the HOMO energy levels of the 2-pyridone form and the yields of the Michael-type adduct were closely associated with the tautomeric equilibria. In summary, the chemoselectivities of 2-pyridones in the reaction with benzyne were largely affected by the tautomeric properties.
DIELS–ALDER ADDUCTS FROM N-UNSUBSTITUTED TAUTOMERIC 2(1<i>H</i>)-PYRIDONE-2-HYDROXYPYRIDINES; 5,6-BENZO-2-AZABARRELENONES AND 5,6-BENZO-2-AZABARRELENES
Diels–Alder reactions of several N-unsubstituted tautomeric 2(1H)-pyridone-2-hydroxypyridines with benzyne were examined and found to afford 5,6-benzo-2-azabarrelenones, which were converted to hitherto unknown 5,6-benzo-2-azabarrelenes.