- Alkyl transfer with retention and inversion of configuration: Reexamination of a putative [1s,4s] sigmatropic rearrangement
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The thermal rearrangement of 2-alkoxypyridine-1-oxides to 1-alkoxy-2-pyridones, which has been reported to proceed by an intramolecular [1s,4s] sigmatropic migration of the alkyl group with retention of configuration and first-order kinetics, has been reexamined. The intramolecular barriers have been computed to be at least 20 kcal mol-1 higher than the reported experimental barriers. An alternative bimolecular mechanism, discovered computationally, has been confirmed by a variety of experiments including crossover studies, determination of solvent effects and secondary H/D isotope effects, and new kinetic and stereochemical studies. In the new mechanism there is an initial intermolecular transfer of the alkyl group, with inversion of configuration, to the N-oxide. Depending on the nature of the alkyl group and the solvent, this is followed by a second transfer, also with inversion of configuration, of one of the alkyl groups of the cationic intermediate to one of the oxygens of the anionic intermediate. The product is then formed either without crossover, by a double inversion of one alkyl group, or with crossover by two single inversions of different alkyl groups. The proposed intermediates of this mechanism can be synthesized; they react to form a 1-alkoxy-2-pyridone at room temperature.
- Wolfe, Saul,Yang, Kiyull,Weinberg, Noham,Shi, Zheng,Hsieh, Yih-Huang,Sharma, Rajendra Dev,Ro, Stephen,Kim, Chan-Kyung
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p. 886 - 902
(2007/10/03)
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- STUDY OF THE CATALYTIC PROPERTIES OF TRIS (3,6-DIOXAHEPTYL)AMINE (TDA-1) IN HETEROAROMATIC NUCLEOPHILIC SUBSTITUTION OF CHLOROPYRIDINES AND THEIR N-OXIDES
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Catalytic properties of tris(3,6-dioxaheptyl)amine (TDA-1) have been analyzed in reactions of alkoxydehalogenation of 2- and 4-chloropyridine and their N-oxides under solid-liquid phase transfer catalysis conditions.Alkoxypyridines were obtained in excellent yields but with N-oxides a competitive alkaline cleavage of the performed ether was observed.
- Ballesteros, P.,Claramunt, R.M.
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p. 2557 - 2564
(2007/10/02)
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