Regiospecific thermal rearrangements of 2-allyloxypyridine N-oxides

Alker, David; Mageswaran, S.; Ollis, W. D.; Shahriari-Zavareh, Hooshang

doi:10.1039/p19900001631

Cited by 6 publications

(18 citation statements)

References 22 publications

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“…Schöllkopf and Hoppe [5] found no skeletal isomerization in the rearrangement of 1, R cyclopropylcarbinyl, and the a-methallyl compound (1, R CHCH 3 -CH CH 2 ) gave only the Claisen rearrangement product, with skeletal isomerization of the alkenyl substituent, and not the reported 2, R CHCH 3 -CHCH 2 . Ollis and co-workers [2,6] have made similar observations concerning the competition between the O 3O (Tieckelmann) and O 3C (Claisen) rearrangement pathways. These workers also observed that heating the cis-cinnamyl ether 6 for 60 h at 53 8C yielded the cis-cinnamyl ether pyridone 7 exclusively.…”

Section: Introductionsupporting

confidence: 58%

“…The reaction of 2-chloropyridine-1-oxide with a-deuteriobenzyl alcohol, [a] The combination of first-order kinetics, a low enthalpy of activation, a high negative entropy of activation, and, most importantly, rearrangement of the benzyl substituent with retention of configuration led Schöllkopf and Hoppe to the conclusion [5,8] ªsomit scheint für die 2-Alkoxypyridinoxide ein (symmetrie-erlaubt [10] ) sigmatroper Umlagerungsverlauf als gesichertº (translation: herewith it would appear that for the 2-alkoxypyridine a sigmatropic reaarangement mechanism (symmetry allowed [10] ) is certain; Figure 1). A concerted [1s,4s] sigmatropic rearrangement mechanism is also advocated by Ollis and co-workers [2,6] and is consistent with the stereospecific rearrangement 6 37.…”

supporting

confidence: 59%

“…These include the crossover studies of Litster and Tieckelmann [4a] and of Ballesteros et al, [11] the rearrangement of 6 to 7, [6] the p-substituent effect in the rearrangement of 2-benzyloxypyridine-1-oxides, [7] the negative volume of activation, [12] and the disputed skeletal isomerization in the rearrangement of the cyclopropylcarbinyl substituent. [4a, 5] Experimental Section General: Solvents were dried by standard procedures and redistilled prior to use.…”

Section: Discussionmentioning

confidence: 99%

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Alkyl Transfer with Retention and Inversion of Configuration: Reexamination of a Putative [1s,4s] Sigmatropic Rearrangement

et al. 1998

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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 À1 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.

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Section: Introductionsupporting

confidence: 58%

supporting

confidence: 59%

Section: Discussionmentioning

confidence: 99%

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Alkyl Transfer with Retention and Inversion of Configuration: Reexamination of a Putative [1s,4s] Sigmatropic Rearrangement

et al. 1998

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“…Our general interest in the mechanism of sigmatropic rearrangements involving anionic or dipolar precursors has promoted a detailed examination1m2 of the thermal transformation of 2alkoxypyridine N-oxides into N-alkoxy-Zpyridones (Scheme 1; reaction a). This reaction is a [ 1,4] sigmatropic rearrangement and was first described by Dinan and Tieckelmann in 1964. 3 At first sight, the occurrence of this reaction apparently conflicts with the generalisation put forward by Eschenmoser in 19704 that endocyclic intramolecular nucleophilic substitutions would be inhibited.…”

mentioning

confidence: 92%

[1,4] and [5,5] thermal sigmatropic rearrangements of 2-pentadienyloxypyridine N-oxides

Alker¹,

Ollis²,

Shahriari-Zavareh³

1990

J. Chem. Soc., Perkin Trans. 1

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“…[70][71][72] These transformation are shown to be regiospecific and the reactions involve concerted [1,4] and [3,3] sigmatropic rearrangements.…”

Section: Rearrangement Of Allyloxypyridine N-oxidementioning

confidence: 99%

Recent trends in the chemistry of pyridine N-oxide

Youssif¹

2001

Arkivoc

112

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This review describes the synthesis and reactions of pyridine N-oxides within the last ten years. The first part surveys the different synthetic methods which include ring transformation, classical oxidations using peracids, the use of metalloorganic oxidizing agents and cycloaddition reactions. The second part surveys the reactions of pyridine N-oxides including the deoxygenation, nucleophilic reaction and cycloaddition to N-O bond.

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Regiospecific thermal rearrangements of 2-allyloxypyridine N-oxides

Cited by 6 publications

References 22 publications

Alkyl Transfer with Retention and Inversion of Configuration: Reexamination of a Putative [1s,4s] Sigmatropic Rearrangement

Alkyl Transfer with Retention and Inversion of Configuration: Reexamination of a Putative [1s,4s] Sigmatropic Rearrangement

[1,4] and [5,5] thermal sigmatropic rearrangements of 2-pentadienyloxypyridine N-oxides

Recent trends in the chemistry of pyridine N-oxide

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