<i>Descriptive General Chemistry</i>
            . By S. E. Tillman, Professor in the U. S. Military Academy. New York, John Wiley &amp; Sons. 1899. 2d Ed,, p. 429.

Smith, Edgar F.

doi:10.1126/science.10.249.496.a

Cited by 8 publications

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“…The effect of substituent size probably reflects differences in nonbonded interactions in the spirocyclic N -diazonium intermediates (Figure ). In general, the preferential migration of a bond antiperiplanar to the leaving group has been presumed in the classical Schmidt and Beckmann reactions . This supposition is also consistent with high stereoselectivity observed in the asymmetric ring-expansion reactions of hydroxy azides as reported elsewhere. 3a,d The hydroxy azide can attack the intermediate oxonium ion from either an equatorial or an axial direction; again, previous work has indicated that the former is likely preferred 3a,d although this point has not been rigorously proven.…”

Section: Resultssupporting

confidence: 56%

“…Nitrogen ring expansion reactions are capable of converting an unsymmetrically substituted ketone to one of two regioisomeric lactams (eq 1). In general, the Schmidt and Beckmann reactions preferentially lead to products of the type a (R 2 = H), in which the most highly substituted carbon has undergone migration to an electron-deficient nitrogen atom . On the other hand, the only ring-expansion technique that reliably affords products of the type b (where R 2 = alkyl) utilizes the photochemical rearrangement of an intermediate oxaziridine …”

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Regiochemical Studies of the Ring Expansion Reactions of Hydroxy Azides with Cyclic Ketones

2000

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The regiochemistry of ring expansions of 2-substituted cyclic ketones using 1,2-azidoethanol and 1,3-azidopropanol was examined. It was determined that the reactions of ketones with an adjacent methyl or ethyl group are generally unselective, but that bulkier substituents lead to preferential migration of the more highly substituted carbon. In addition, it was found that ketones bearing inductively electron-withdrawing substituents (OMe, Ph, Br) undergo selective migration of the less highly substituted carbon. For some substrates, alternative reaction pathways were also identified.

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Section: Resultssupporting

confidence: 56%

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confidence: 99%

Regiochemical Studies of the Ring Expansion Reactions of Hydroxy Azides with Cyclic Ketones

2000

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“…1 kcal/mol) to stereochemical inversion including the Beckmann and classical Schmidt rearrangements. Additionally, Pearson has invoked antiperiplanar migration in studies in the closely analogous reactions of alkyl azides with unstabilized carbocations 12b,h and Hoffman has also proposed this relationship in rearrangements of N -(arylsulfonoxy)amines .…”

Section: Discussionmentioning

confidence: 99%

Asymmetric Schmidt Reaction of Hydroxyalkyl Azides with Ketones

et al. 2003

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An asymmetric equivalent of the Schmidt reaction permits stereocontrol in ring expansions of symmetrical cyclohexanones. The procedure involves the reaction of chiral 1,2- and 1,3-hydroxyalkyl azides with ketones under acid catalysis; the initial reaction affords an iminium ether that can be subsequently opened with base. A systematic study of this reaction is reported, in which ketone substrates, chiral hydroxyalkyl azides, and reaction conditions are varied. Selectivities as high as ca. 98:2 are possible for the synthesis of substituted caprolactams, with up to 1,7-stereoselection involved in the overall process. The fact that either possible migrating carbon is electronically identical provides an unusual opportunity to study a ring-expansion reaction controlled entirely by stereoelectronic factors. The mechanism of the reaction and the source of its stereoselectivity are also discussed.

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“…However, as stated above, such a stereoelectronic rationale is only one factor to consider; the ability of the migrating group and the migration origin to stabilize a positive charge are also important factors. For example, neglecting stereoelectronic issues, aryl groups have a higher migratory aptitude than alkyl groups in 1,2-rearrangements from C to N, , presumably due to their ability to bear positive charge in the rearrangement in the form of phenonium ion intermediates. Ideally, modeling of transition states and other intermediates encountered on the rearrangement pathway (e.g., phenonium ions) would be required for a more useful prediction.…”

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confidence: 99%

Synthesis of Benzo-Fused 1-Azabicyclo[m.n.0]alkanes via the Schmidt Reaction: A Formal Synthesis of Gephyrotoxin

2000

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The intramolecular capture of benzocyclobutyl, benzocyclopentyl, and benzocyclohexyl carbocations 7 by azides produces spirocyclic aminodiazonium ions 8, which undergo 1,2-C-to-N rearrangement with loss of dinitrogen to produce benzo-fused iminium ions resulting from either aryl (9) or alkyl (10) migration to the electron-deficient nitrogen atom. Reduction of the iminium ions affords regioisomeric benzo-fused 1-azabicyclo[m.n.0]alkanes, e.g., benzopyrrolizidines, benzoindolizidines, benzoquinolizidines, or perhydrobenzo[f]pyrrolo[1,2-a]azepines in two regioisomeric versions, anilines (e.g., 11-14) and benzylic amines (e.g., 15-18), the result of aryl and alkyl migrations, respectively. Generally, aryl migration is preferred, despite modeling that shows that the lowest energy aminodiazonium ions are those where the departing dinitrogen is preferentially antiperiplanar to the migrating alkyl group rather than the aryl group. The utility of this methodology was illustrated by a formal synthesis of the alkaloid gephyrotoxin 4. A dependence on the efficiency and regioselectivity of the Schmidt reaction upon subtle changes in the structure of the cation precursor was observed, necessitating the exploration of a variety of substrates. Fortunately, these materials were easily made. Ultimately, the azido-alkene 81 bearing a 2-bromoethyl side-chain was useful for the Schmidt reaction, producing the known benzo-fused indolizidine 49, which had been transformed by Ito et al. into gephyrotoxin 4. The synthesis of 49 required nine steps (five purifications) from commercially available 4-methoxy-1-indanone 60 and proceeded in 22% overall yield.

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Descriptive General Chemistry . By S. E. Tillman, Professor in the U. S. Military Academy. New York, John Wiley & Sons. 1899. 2d Ed,, p. 429.

Cited by 8 publications

References 0 publications

Regiochemical Studies of the Ring Expansion Reactions of Hydroxy Azides with Cyclic Ketones

Regiochemical Studies of the Ring Expansion Reactions of Hydroxy Azides with Cyclic Ketones

Asymmetric Schmidt Reaction of Hydroxyalkyl Azides with Ketones

Synthesis of Benzo-Fused 1-Azabicyclo[m.n.0]alkanes via the Schmidt Reaction: A Formal Synthesis of Gephyrotoxin

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