Photocyclizations Mannich reactions

A number of years ago Armesto and his colleagues reported the photochemical Mannich reactions of the dienes (92) in the presence of perchloric acid. This reaction brought about conversion into the isoquinolinones (93) efficiently via the photocyclization of the protonated species (94). The mechanism for the transformation was proposed to involve an intramolecular SET process as a key event in the reaction. The present report gives details of quantum yield measurements on a series of derivatives that support this mechanistic postulate. Kojima and coworkers have studied the dicyanobenzene-sensitized reactions of the dienes (95) and (96) in acetonitrile/water/ammonia systems. Products (97) and (98) are... 

Furthermore, the following compounds were synthetically prepared racemic cheilanthifoline (58c) (47), kikemanine (58d) (129), canadine (58e), berberine (59a) (590, 614), tetrahydropalmatine (58g) (475), sinac-tine (58h), cavidine (68d) (616,617), nandinine (58i) (590, 614, 615), capaurine (58p) (618), capaurimine (58o) (128, 618a), xylopinine (60c) (610, 615, 619), O-methylcaseanadine (62b) (70, 620), thalictricavine (68b), and corydaline (68h) (615). Xylopinine (60c) and some other alkaloids were synthesized by benzoylation of 1-alkyl-3,4-dihydroisoquinolines followed by photocyclization. This method provides a useful route to the synthesis of other protoberberine alkaloids (619). It is also applicable to the synthesis of cularine (51) and spirobenzyltetrahydroisoquinoline alkaloids (188). Xylopinine was also synthesized from the corresponding enamide under benzyne reaction conditions (615). Kametani etal. summarized their findings on the synthesis of these alkaloids and described the formation of protoberberines by debenzylation and photolysis of tetrahydroisoquinolines (622, 623). The total stereospecific synthesis of racemic ophiocarpine (70a) from the 3,4-dihydroisoquinoline derivative by Mannich cyclization was also described (624). 

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