Pyrazolo phenanthridines

Das cyclische Sulfon I wird bei —1,8 V zur Sulfinsaure II reduziert, die beim Erhitzen mit Schwefelsaurc unter Eliminierung von Schwefeldioxid 2-Methyl-(pyrazolo-[l,5-f]-phenanthridin) (60% d.Th.) ergibt7 ... 

Reaction of 2-bromoacetophenone 45 with dimethylfomiamide dimethylacetal (DMF-DMA) to the intermediate enaminoketones followed by reaction with various arylhydrazines afforded diarylpyrazoles 46, which underwent Mizoroki-Heck palladium-catalyzed intramolecular couplings to give pyrazolo[l,5-/ phenanthridines 47 <030L1095>. 

On reduction of aryl halides the initially formed ion radical decomposes to halide ion and aryl radical [13-16]. In appropriate substituted compounds the radical may in an intramolecular attack effect a ring closure. This is exemplified in the reductive cyclization of 5-(2-chlorophenyl)-l-phenylpyrazole to pyrazolo[l, 5-/]phenanthridine [13] and iV-allyl-... 

The Pd-catalyzed intramolecular coupling of aryl halides or triflates with aromatic rings to give biaryl compounds offers useful synthetic methods. Intramolecular aryla-tion of benzene derivatives was reported first by Ames. Cyclization of 102, catalyzed by Pd(OAc)2 in the presence of DBU, is an example [23]. Pyrimido[4,5-fe]indole was prepared by intramolecular arylation of 4-anilino-5-iodopyrimidine 103 in 86 % yield in the presence of Pd(OAc>2, PPh3 and AcONa in DMF [24]. Cyclization of the monobrominated diarylpyrazole 104 afforded pyrazolo[l,5-/]phenanthridine in 65 % yield in the presence of phosphine-free Pd(OAc>2, Bu NBr, LiCl and K2CO3 in DMF at 110°C [25]. 

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