Dihydropyridine-chromium tricarbonyl complexes

The 1,2-dihydropyridine chromium tricarbonyl complex (85) has been converted into the tetrahydropyridine (86) as shown in Scheme 32. The endo peroxides of l-alkoxycarbonyl-l,2-dihydropyridines, e.g. (87) react with carbon nucleophiles such as enamines, in the presence of stannous chloride, to give substitution products, e.g. (88) (Scheme 33). ... 

The reaction of iminium ions with dihydropyridines is a method, suggested from biosynthetic studies, for the formation of carbon-carbon bonds to these six-membered heterocycles. The 1,4-dihydropyridine (8), a presumed intermediate from the reaction of ammonia with glutaraldehyde, reacts with the cyclic iminium ion (159) to give, after oxidation, nicotine (160) (72CC1091). Another example of this reaction has provided a total synthesis of olivacine (163). The 1,2-dihydropyridine ring system in (161), generated from its chromium tricarbonyl complex, was observed to undergo an intramolecular cyclization... 

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