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

Palladium‐Catalyzed Ring Closure Reactions to Benzofuranes: A New and Effective Approach to Azacoumestrols Azacoumestans (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 .