Synthesis of Benzo[b]fluorenone Nuclei of Stealthins

Introduction Stealthins A (1a) and B (1b), isolated from Streptomyces viridochromogenes as potent radical scavengers, are the rst known members of natural benzo[b]uorenones [1]. Interest in this group of compounds grew considerably due to the identication of structurally allied natural products, stealthin C (1c) [2], kinauorenone (2) [3], prekinamycin (3) [4], and kinamycin antibiotics (e.g., kinamycin D, 4) [5] (Figure 1). eir synthesis became an active area of research since 1996 [6-19]. In line with the Ishikawa approach [19], we intended to explore the chemistry of benz[f ]indenones (e.g., 5b) to establish new synthetic routes to functionalized benzo[b]uorenones [20]. Herein, we report regiospecic construction of the D-ring of benzo[b]uorenones (e.g., 6) from the corresponding benz[f ] indenones.