Phenanthridine dihydropyridine

Dihydropyridines have also been starting points for stereospecific syntheses of hydro-phenanthridines and isoquinolines. Interest exists in these compounds because of the occurrence of this structural feature in alkaloids. For example, isoquinuclidine (263), derived from JV-alkoxycarbonyl-l,2-dihydropyridine, undergoes a Cope rearrangement to give the isoquinoline derivative (264) (80JA6157). Further chemical transformations of (264) provided a formal total synthesis of reserpine (Scheme 50). 

Heteroaromatic cations undergo reduction when treated with 1,4-dihydronicotinamide. An early study showed that the 10-methylacridinium ion (87) was rapidly reduced in a redox reaction to the 9,10-dihydro adduct by 1,4-dihydronicotinamides (M Scheme 18). A variety of systems including py-ridines, isoquinolines, quinolines and phenanthridines have been studied using this and related procedures. The selective reduction of pyridinium and quinolinium salts with 1-benzyl-1,2-dihydro-isonicotinamide (89) has been achieved. The selective conversion to the thermodynamically more stable 1,4-dihydro species (90 Scheme 18) is rationalized by the reversibility in the formation of the kinetic products (i.e. the 1,2-adducts) in the presence of pyridinium ions. In the pyridinium case 1,6-di-hydro adducts were also observed in some cases. Reactivity in such systems is sometimes hindered due to hydration of the dihydropyridine system. This is particularly so in aqueous systems designed to replicate biological activity. Dihydroazines derived from isoquinolines and 3,5-disubstituted pyridines have been reported to overcome some of these difficulties. ... 

In 2012, a palladium-catalyzed ring opening of aminocyclopropyl Ugi adducts was presented. Dihydropyridine and benzoazepinone derivatives were produced in moderate yields (Scheme 3.35a). Catellani and co-workers reported a palladium-catalyzed synthesis of substituted phenanthridine derivatives in 2008. Selectively substituted phenanthridine derivatives were obtained by a facile reaction of o-allqrlated aiyl iodides, o-bromoar-enesulfonylanilines and activated olefins in the presence of palladium and norbornene as catalysts. The reaction takes place under mild conditions to give the products in satisfactory yields using readily available starting materials (Scheme 3.35b). 

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