The natural tendency of 1,4-dihydropyridines to undergo ªbiomimeticº oxidation to afford pyridinium salts can be switched off and, through the use of reagents that interact electrophilically with the enamine moiety present in the heterocyclic system, it is possible to promote alternative oxidations. In this way, efficient regio-and stereocontrolled synthetic methods have been developed that lead to diversely substituted di-and tetrahydropyridines. These include iodoazida-

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A general route to the eburnamine-vincamine and tacamine indole alkaloid groups has been developed. The key features of the synthetic strategy are the halocyclization of a dihydropyridine (a non-biomimetic oxidation of these compounds) and the radical addition of the resulting halo derivative to activated alkenes. The latter process shows an un-

Electrophilic interaction of iodine with N-alkyl-1,4-dihydropyridines 1 in the presence of secondary amines stereoselectively leads to the corresponding trans-2,3-diamino-1,2,3,4-tetrahydropyridines 2 in satisfactory yields (79-94%); the method allows the synthesis of piperidine, pyrrolidine, morpholine and piperazine derivatives.

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