- Aryl Radical Endo Cyclization of Enamidines. Selective Preparation of Trans and Cis Fused Octahydrobenzo[f]quinolines
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Aryl radicals from N-protected 6-[2-(2-halophenyl)ethyl]-1,2,3,4-tetrahydropyridines and 6-[3-(2-halophenyl)propyl]-1,2,3,4-tetrahydropyridines undergo intramolecular cyclization onto the enamide/ enamidine double bond by 6-endo and 7-endo closure, respectively. In the 6-endo cyclization the trans/cis ratio of the formed N-protected octahydrobenzo[f]quinoline can be controlled, and selective synthesis of either the trans or the cis isomer can be achieved with triphenyltin hydride and tris(trimethylsilyl)silicon hydride, respectively. In the 7-endo cyclization to N-protected octahydro-1H-benzo[3,4]cyclohepta[1,2-b]pyridine, the trans fused isomer predominates, although the selectivity is low. The oxidized cyclization products, with a restored enamide/enamidine double bond, are formed at low concentrations of tris(trimethylsilyl)silicon hydride.
- Ripa, Lena,Hallberg, Anders
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- α-Amino Carbanions. Preparation, Metalation, and Alkylation of Enamidines. Synthesis of Piperidine and Pyrrolidine Natural Products and Homologation of Carbonyl Compounds
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Saturated heterocycles, as their tert-butylformamidines, may be transformed into enamidines, by metalation-selenation-elimination.These enamidines are valuable precursors to 2-substituted, 2,4-disubstituted, and 2,4,6-trisubstituted pyrrolidines, piperidines, and perhydroazepines, prepared in a regiospecific manner.The method is demonstrated by the synthsesis of selenopsin A and the red fire ant venom.The use of acyclic enamidines is displayed as a homologation reagent which converts carbonyl compounds to higher alkyl derivatives.
- Meyers, A. I.,Edwards, Philip D.,Bailey, Thomas R.,Jagdmann, G. Erik
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p. 1019 - 1026
(2007/10/02)
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