Annulated 1,4-dihydropyridines

The reaction proceeds via ANRORC-recyclization induced by alkoxide ion, and subsequent oxidative aromatization. Authors believe that aroma-tization occurs at the expense of disproportionation of the intermediate dihydropyridine because yields never exceed 50%. These results were reproduced and expanded (00PHA269), and used in a synthesis of 4,6-diaryl-2-methoxy-3-cyanopyridines and annulated methoxypyridines (88TL2703) (with low yields). 

Amuilations of pyridinium- and quinolinium-salts however have not been reported so far. From the addition reactions of C-nucIeophiles like Grignard, organozinc and organotin reagents to pyridinium- and quinolinium-salts have been reported to be valuable methods for the construction of substituted dihydropyridine [4a-4d] and dihydroquinoline-derivatives [4d-4e] results of our studies in the field of benzothiopyrylium-salts [5] we concluded that the sequential intermolecular 1,2-addition/intramolecular 1,4-addition of 4-silyloxyquinolinium-salts 1 with 2-silyloxy-l,3-butadienes 2 might be useful for the diastereoselective preparation of annulated quinolones 3. 

Rhodium-catalyzed chelation-assisted C—H bond functionalization reactions (enantioselective annulation of aryl imines, dihydropyridine synthesis from imines and ahcynes, one-pot synthesis of pyridines from imines and alkynes, 2-arylpyridine alkylation with imines) 12ACR814. Synthesis of pyridine and dihydropyridine derivatives by regjo- and stereoselective addition to N-activated pyridines 12CRV2642. 

Heteroatom Wittig chemistry also includes reactions of N-sulfonyl imines. It was demostrated that these compounds underwent olefination reactions with nonstabilized phosphonium ylides under mild conditions to afford an array of both Z- and E-isomers of 1,2-disubstituted alkenes, allylic alcohols, and allylic amines.Additionally, studies of the reactions of 5-bromo-4,6-dimethyl-2-thioxo-l,2-dihydropyridine-3-carboni-trile and thiazolidinone with phosphorus ylides have proved the formation of new phosphonium ylides. Annulations via P-ylides are a common occurrence in the literature. For example, on photochemical irradiation, phosphonium-iodonium ylides were shown to undergo 1,3-dipolar cycloaddition reactions with triple bonds, via a carbene intermediate, to yield furans. " Even more common are the reactions of Morita-Baylis-Hillman (MBH) acetates and carbonates. Zhou et al. demostrated that these substrates were able to generate very reactive 1,3-dipoles in the presence of tertiary phosphines the dipoles then underwent cycloaddition reactions to yield annulation products (Scheme 16). ... 

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