Hydroxylamine-Mediated Anthrapyranone Formation, Solving 5-exo/6-endo Issue toward Synthesis of Pluramycin-Class Antibiotics.

In our synthetic study on pluramycin-class antibiotics, an unexpected issue arose, i.e., unfavorable regioselectivity of 5-exo rather than 6-endo cyclization to form the pyranone ring. The issue was solved by an addition-elimination process of a phenol-ynone substrate. AZADOL was specifically effective, enabling the first synthesis of saptomycinone H.