DIELS-ALDER CYCLOADDITIONS USING NUCLEOPHILIC 2-PYRIDONES - REGIOCONTROLLED AND STEREOCONTROLLED SYNTHESIS OF UNSATURATED, BRIDGED, BICYCLIC LACTAMS

Captodative 3-oxy-and 3-(tolylthio)-1-tosyl-2-pyridones 1a-1d are shown to be reactive as nucleophilic dienes undergoing 2 + 4-cycloadditions with various electrophilic alkenes under sufficiently mild thermal conditions (90-100-degrees-C) that the initial bicylic lactam adducts can be isolated on gram scale in fair to very good yields (23-83%) without loss of an isocyanate from the heteroatom bridge. These bicyclic adducts are formed with complete regiocontrol and stereocontrol. For pyridone sulfide 1d, these Diels-Alder cycloadditions are the first examples of a captodative unsaturated sulfide acting as an enophile. NMR data (C-13) are presented correlating the electron density in the pyridone diene systems with their Diels-Alder reactivity, and some transformations of the bicyclic lactam adducts are shown to illustrate the value and versatility of these richly functionalized synthetic intermediates.