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Rearrangements of N-Ylide Generated from 1-Ethoxycarbonylmethyl-1-methyl-4-phenyl-1,2,3,6-tetrahydropyridinium Chloride

“…While continuing our systematic investigations of the chemistry of tetrahydropyridines [7][8][9], we studied the question of how the ratio of the expected products is affected by the presence of an aryl substituent at C(4) in the anhydro base (the N-ylide A) generated from 1-ethoxycarbonylmethyl-1-methyl-4-phenyl-1,2,3,6-tetrahydropyridinium chloride (1) when it is heated in the presence of sodium hydride. We found that the presence of a phenyl substituent has a substantial effect on the direction of the reaction: we isolated two compounds from the reaction mixture in 1.5:1 ratio with overall yield 64%, where the first compound had the structure of the expected 4-phenylpyrrolidine 2 while the other compound, to our surprise, proved to be the tetrahydroazepine 3.…”

Oxidation of heterocyclic compounds by manganese dioxide (Review)*

“…With trimethylsilyl azide the product from oxidation of 2,3-dihydro-1H-imidazo- [4,5-c]pyridine 108 forms the 4-azido derivative 109, which is quickly transformed into the tetrazole 110 (yield 46%) [105]. When a mixture of tetrahydropyridine 111 with MnO 2 (a fivefold excess) and malononitrile was kept without heat the hydroxymethylation product 112 was obtained (yield 36.5%) [106,107]. It is assumed that formaldehyde or its imine can be formed from the dinitrile under the reaction conditions and then adds at the multiple bond of the heterocycle.…”

Advances in the synthesis of 4-aryl- and 4-hetarylpyridines

“…102 4-Aryltetrahydropyridines 100a,b were oxidised under more drastic conditions, namely, on boiling in toluene with tenfold excess of MnO 2 . 103,104 Ar = Ph (a, 45%), 4-MeC6H4 (b, 42%).…”