FIRST TOTAL SYNTHESIS OF THE 2,7-NAPHTHYRIDINE ALKALOID NEOZEYLANICINE AND UNEXPECTED FORMATION OF ISOQUINOLINES FROM ETHOXYVINYL PYRIDINES

The 2,7-naphthyridine alkaloid neozeylanicine (6) was prepared startin g from 3-bromo-4-picoline (1) by side-chain methoxycarbonylation, Pd-c atalyzed ring acetylation and one-pot ring anellation in 32% overall y ield. Condensation of the intermediate pyridyl enol ether 3 with dimet hylformamide diethyl acetal to the examine 7 was followed by spontaneo us electrocyclization to give the isoquinoline 8. On treatment with ac id or base 3 was cyclized to the 6(2H)-isoquinolinone 10.