Palladium‐katalysierte Ringschlußreaktionen zu Benzofuranen: ein neuer und effektiver Zugang zu Azacumöstrolderivaten

Abstract
Palladium‐Catalyzed Ring Closure Reactions to Benzofuranes: A New and Effective Approach to AzacoumestrolsAzacoumestans (benzofuro[3,2‐c]quinolinones) 4 have been synthesized using the following three methods: ring closure of 3‐aryl‐4‐hydroxy‐2‐quinolones 3a–e by Pd‐catalyzed cyclodehydrogenation, ring closure of 3‐hydroxy‐3‐aryl‐2,4‐quinolinediones 5 by acid‐catalyzed cyclodehydratation, or ring closure of 4‐aryloxy‐3‐iodo‐quinolones 8, which are obtained by rearrangement of iodonium ylides 7, by palladium‐mediated cyclodehydrohalogenation. Only the latter reaction yielded the coumestrol analog dimethoxy derivatives 4c, d, which have been transformed into the hydroxy and acetoxy derivatives 9, 10.