SYNTHESIS OF SUBSTITUTED PYRIDINES VIA REGIOCONTROLLED [4-CYCLOADDITIONS OF OXIMINOSULFONATES(2])

Diels-Alder cycloadditions of oximinosulfonate 8 with a variety of 1,3 -dienes proceed with regiochemistry opposite to that observed with con ventional imino dienophiles, providing expeditious synthetic routes to substituted pyridines, tetrahydropyridines, and pyrrolines. The oximi nosulfonate 8 is prepared in one convenient synthetic operation from M eldrum's acid and reacts with conjugated dienes at -78 degrees C in th e presence of 2 equiv of dimethylaluminum chloride to afford [4 + 2] c ycloadducts in good to excellent yield. Exposure of these cycloadducts to the action of NaOMe and N-chlorosuccinimide in methanol-THF at roo m temperature then produces substituted pyridines. The utility of this new two-step annulation protocol is demonstrated in total syntheses o f the pyridine alkaloids fusaric acid and (S)-(+)-fusarinolic acid. He ating the [4 + 2] cycloadducts derived from 8 in a mixture of acetonit rile and pH 7 phosphate buffer induces an unusual Stieglitz-type rearr angement leading to the formation of interesting spirobicyclic pyrroli nes.