Dyotropic Rearrangements Research Articles

Dyotropic Rearrangements of Fused Tricyclic β-Lactones: Application to the Synthesis of (−)-Curcumanolide A and (−)-Curcumalactone

Dyotropic rearrangements of fused, tricyclic β-lactones are described that proceed via unprecedented stereospecific, 1,2-acyl migrations delivering bridged, spiro-γ-butyrolactones. A unique example of this dyotropic process involves a fused bis-lactone possessing both β- and δ-lactone moieties which enabled rapid access to the core structures of curcumanolide A and curcumalactone. Our current mechanistic understanding of the latter dyotropic process, based on computational studies, is also described. Other key transformations in the described divergent syntheses of (-)-curcumanolide A and (-)-curcumalactone from a common intermediate (11 and 12 steps from 2-methyl-1,3-cyclopentanedione, respectively), include a catalytic, asymmetric nucleophile (Lewis base)-catalyzed aldol-lactonization (NCAL) leading to a tricyclic β-lactone, a Baeyer-Villiger oxidation in the presence of a β-lactone, and highly facial-selective and stereocomplementary reductions of an intermediate spirocyclic enoate. The described dyotropic rearrangements significantly alter the topology of the starting tricyclic β-lactone, providing access to complex spirocyclic cyclopentyl-γ-lactones and bis-γ-lactones in a single synthetic operation.

Switching between Concerted and Stepwise Mechanisms for Dyotropic Rearrangements of β-Lactones Leading to Spirocyclic, Bridged γ-Butyrolactones

Quantum chemical computations (B3LYP/6-31+G(d,p)) were applied to examine the mechanisms of dyotropic rearrangements of spirolactones in order to assess whether these reactions are concerted. Mechanistic experiments, designed on the basis of the results of these calculations, support the conclusions derived from theory. In particular, Zn(II) salts or Brønsted acids induce stepwise dyotropic processes, whereas dyotropic rearrangements mediated by silyltriflates are concerted processes. Additional products isolated with Zn(II) salts support a stepwise process with a carbocationic intermediate. Furthermore, a facile Grob-type fragmentation emanating from both a tricyclic-β-lactone and a spiro-γ-lactone was identified.

Reaction mechanisms: pericyclic reactions

This report surveys the 2010 literature on mechanisms of pericyclic reactions. Among the newer concepts highlighted in this year's studies are the distortion-interaction model of reactivity, the importance of CH-π interactions in controlling selectivity, and the catalysis of pericyclic reactions by transition metals and organocatalysts. This year, a substantial number of (4+3) cycloadditions and dyotropic rearrangements were examined; these reactions have received limited attention in the past.

ChemInform Abstract: Concise Synthesis of Spirocyclic, Bridged γ‐Butyrolactones via Stereospecific, Dyotropic Rearrangements of β‐Lactones Involving 1,2‐Acyl and δ‐Lactone Migrations.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Concise Synthesis of Spirocyclic, Bridged γ-Butyrolactones via Stereospecific, Dyotropic Rearrangements of β-Lactones Involving 1,2-Acyl and δ-Lactone Migrations

Dyotropic processes involving unprecedented 1,2-acyl migrations provide access to novel spirocyclic, bridged keto-gamma-lactones from a series of fused, tricyclic-beta-lactones, available via biscyclization of ketoacids including a new asymmetric variant. In addition, a spirocyclic bis-gamma-lactone was generated via a dyotropic process involving a 1,2-beta-lactone/sigma-lactone interchange. Overall, this sequence provides a simple, two-step process for conversion of diketoacids to complex spiro[5.n]alkanes bearing a contiguous tertiary carbon center, a quaternary carbon center, and a tertiary alcohol in the form of a bridging gamma-lactone.

Dyotropic Rearrangements of Tetraazafulvalenes - A New Approach to ­Aminosubstituted 1,4,5,8-Tetraazanaphthalenes

Tetraazafulvalenes 1 rearrange in the presence of Montmorillonite-clay to give strongly fluorescent 1,4,5,8-tetraazanaphthalenes of type 2. This observation agrees with that reported for the cross-conjugated systeme of indigo, thus indicating a dyotropic rearrangement has taken place. Inclusion of the extended π-electron-systeme of 1 should facilitate this symmetry forbidden [σ2+σ2]-process. Based on these results, some reactions of heterofulvalenes and -fulvenes reported in the literature can now be explained by dyotropic rearrangements. The easy rearrangement of 1 in the presence of K10 and DMF opens the way for the synthesis of hard to obtain ring-fused pyrazines of type 2.

Dyotropic Rearrangements of Dihalogenated Hydrocarbons: A Density Functional Theory Study

A series of dyotropic rearrangements for dihalogenated hydrocarbons have been investigated by using the B3LYP/6-311++G(d,p) method. In all cases, an ethylenic transition state has been located. The activation energy of the basic dyotropic rearrangement of chlorine migration is calculated to be 41.9 kcal/mol. Both conjugation and hyperconjugation effects lead to a delocalization of the newly formed π electrons in the transition state and therefore facilitate the rearrangement. For the dichlorinated cycloalkane series, it has been shown that the variation of the activation energy simply depends on the ring strain. In contrast, the dyotropic rearrangements of dichloro-cycloalkenes possess some complexity. In particular, the dyotropic reaction of 5,6-dichlorocyclohexa-1,3-diene is predicted to have an anomalous lower barrier, which can be attributed, to a great extent, to the aromaticity of the transition state. Similarly, due to the involvement of antiaromaticity in the transition states, the dyotropic migration barriers of 3,4-dichlorocyclobutene are found to be significantly higher than those of the corresponding dichlorinated cycloalkanes. Two possibly competitive processes, thermal elimination and sigmatropic migration, have been examined for some systems. The results suggest that the sigmatropic migration often possesses a lower barrier and therefore needs to be scrutinized to predict the observable dyotropic process. In addition, the dyotropic bromine migrations have also been investigated and predicted to have a much lower activation energy, indicating that the dyotropic rearrangement is more likely to occur in the dibrominated compounds. A mixed dyotropic rearrangement in which the chlorine and the bromine interchange their positions has proven to be feasible with the activation energy lying between that of the dyotropic chlorine migration and that of the dyotropic bromine migration.

Mono- and bis(hydroxylamino)silanes – synthesis, isomerisation and quantum chemical calculations

Silylhydroxylamines can undergo anionic, neutral and thermal rearrangements. Lithium derivatives of silylhydroxylamines have been used for more than 30 years in such synthesis. They are formed by the reaction of N,O-bis(silyl)hydroxylamines with n-butyl-lithium and crystallize as O-lithium-N,N-bis(silyl)hydroxylamides under silyl group migration from the oxygen to the nitrogen atom. Depending on the reaction conditions and the bulkiness of the substituents, dimeric, trimeric and tetrameric oligomers are isolated. Lithium is bonded end on to the oxygen atom in the dimeric and trimeric silylhydroxylamides and side on to the N-O bond in the tetrameric oligomer.Fluorofunctional bis(silyl)hydroxylamines are excellent precursors for ring systems. In the reactions of dihalosilanes and hydroxylamine the first bis(hydroxylamino)silanes, R2Si(O-NH2)2, areobtained.O-Fluorosilyl- and O-stannyl-N,N-bis(trialkylsilyl)hydroxylamines undergo irreversible dyotropic rearrangements to N-fluorosilyl-N,O-bis(trialkylsilyl)hydroxylamines and N-stannyl-N,O-bis(trialkylsilyl)hydroxylamines, respectively. Thermal rearrangement of tris(silyl)hydroxylamines leads to the formation of silylaminodisiloxanes.Quantum chemical calculations for model compounds demonstrate the course of the dyotropic and thermal rearrangements. The results of these calculations allow the prediction of the resulting isomeric silylaminodisiloxane.

Highly stereocontrolled synthesis of substituted propiolactones and butyrolactones from achiral lithium enolates and homociral aldehydes

Lithium enolates derived from achiral thiol esters react in a highly stereoselective fashion with homochiral aldehydes to yield the corresponding 2-oxetanones. The stereochemical outcome of the reaction corresponds to a non-chelation control. except when O-silylated mandelaldehyde is used. The propiolactones thus formed are efficiently transformed into δ-lactones via Lewis acid promoted dyotropic rearrangements.

ChemInform Abstract: Diallylic and Diallenic Dyotropic Rearrangements.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Dyotropic rearrangements of Cp 2Zr ligand complexes; a theoretical study

The dyotropic rearrangements in Cp 2Zr ligand complexes such as Cp 2Zr(X) (CH 2SR) ( 3) have been studied by molecular orbital theory. The higher reactivity for the compound with X = Ph in comparison to that with X = Me, Cl, or CH 2Ph is related to the energy match of MO's of the migrating fragment with those of the remaining fragment along an assumed reaction coordinate. The ease of conversion of Cp 2Zr(C 4H 3O) 2 ( 5) into a zircona-cyclic species 6 can be similarly accounted for. Other substituents that should make the above reactions faster are suggested on the basis of the studies. A general discussion is presented on the migratory aptitudes and the difficulties involved in assigning migratory aptitudes that are independent of the specific reaction.

Intramolecular 2H Group-Transfer (Dyotropic Rearrangements) in Alicyclic and Heterocyclic Bridged-Ring Systems

Examples of alicyclic frameworks containing a cyclohexa-1,3-diene ring as 2H donor held proximate to a variously-substituted acceptor Π-bond are compared for their reactivity in thermal 2H group-transfer reactions. Kinetic analysis reveals marked effects on rearrangement-rate as the acceptor Π-bond substieuents are varied. Attempted synthesis of exact structural analogues of these compounds but with a 2,3-diazacyclohexadiene component replacing the cyclohexadiene element [by (4 + 2)Π cycloadditions of 3,6-diaryl-1,2:4,5-tetrazines to dienophiles of the isodrin type] usually gives instead products of concomitant 2H group-transfer. These results are compared with the similar but generally slower 2H group-transfer rearrangement of pentacyclic 2-pyrazoline derivatives having relevant critical stereochemical features which result from 1,3-diarylnitrilioine (4 + 2)Π adductions with dipolarophiles of the isodrin type. Alkoxy and chlorine substitution of the acceptor Π-bond is rate-retarding for 2H group-transfer in both the alicyclic and heterocyclic representative systems examined, indicating truly pericyclic behaviour.

Basische metalle: XLIX. Halbsandwichverbindungen des typs C 5H 5RhL 2 und C 5H 5RhLL′ als synthesebausteine für carbenoid- und ylidrhodium(III)-komplexe

Half-sandwich type compounds C 5H 5RhLL′ (L= PMe 3, L′= PR 3, P(OR′) 3; L = PR 3, L′ = P(OMe) 3; L = C 2H 4, L′ = P(OMe) 3, SMe 2; L = L′ = CNR) are prepared starting from [(C 8H 14) 2RhCl] 2 and [(C 2H 4) 2RhCl] 2 by stepwise displacement of the olefinic ligands and final cleavage of the chloride bridges with NaC 5H 5. The compounds C 5H 5RhL 2 and C 5H 5RhLL′ react with CH 2I 2 form the carbenoid-rhodium(III) complexes C 5H 5RhCH 2I(L)I and [C 5H 5RhCH 2I(L)L′] +, the latter being isolated as the BF 4 or PF 6 salts. For L′ = P(OR) 3 (R = Me, Et), successive reaction with NaI gives the dialkylphosphonate compounds C 5H 5RhCH 2I(L)P(O)(OR) 2. The carbenoid complexes [C 5H 3RhCH 2I(PMe 3) 2]X and [C 5H 5RhCH 2I(PR 3)L]PF 6 isomerize thermally or on addition of NEt 3 to produce the yliderhodium(III) compounds [C 5H 5Rh(CH 2PMe 3)(PMe 3)I]PF 6 and [C 5H 5Rh(CH 2PR 3)(L)I]PF 6, respectively. In all cases, the ligand with the strongest donor properties migrates from the metal to the carbon. Kinetic studies of the reaction of [C 5H 5RhCH 2I(PMe 3)P(OMe) 3]PF 6 to give [C 5H 5Rh(CH 2PMe 3)(P(OMe) 3)I]PF 6 show a distinct dependence of the isomerization rate on the NEt 3 concentration and suggest an intramolecular exchange mechanism similar to that of dyotropic rearrangements. Substitution of the carbon-bonded iodide in [C 5H 5RhCH 2I(PMe 3) 2]I and C 5H 5RhCH 2I(PMe 3)P(O)(OMe) 2 leads to the formation of the ylide complexes [C 5H 5Rh(CH 2PMe 3)(PMe 3) 2]I 2 and [C 5H 5Rh(CH 2L)(PMe 3)P(O)(OMe) 2]I. The syntheses of the compounds [C 5H 5RhCH 2X(PMe 3) 2]PF 6 (X = Cl, CN), [C 5H 5RhCH 2X(PMe 3)P(OMe) 3]PF 6 (X = Cl, Br), [C 5H 5Rh(CH 2PMe 3)(PMe 3)Br]PF 6, C 5H 5RhCH 3(PMe 3)P(O)(OMe) 2 and C 5H 5RhCH 3(PMe 3)P(O)(OMe) 2 · NaI are also described.

Formal dyotropic rearrangements of N-chloroamines catalysed by alumina

Rearrangement of N-chloro-2-azabicyclo[2.2.1]heptanes, [2.2.1]hept-5-enes, and [2.1.1]hexanes involving 1,2-migration of an sp3 or an sp2 carbon to nitrogen accompanied by 2,1-migration of chlorine occurs cleanly and efficiently on chromatographic alumina.

Primary and secondary orbital effects in dyotropic rearrangements

A new class of orbital symmetry controlled reactions which involve the simultaneous migration of two σ-bonds is discussed. Analysis of the stereochemical fate of the migrating groups in thermal and photochemical shifts, based on the Woodward-Hoffmann roles and supported by MINDO/2 calculations, is presented.

Dyotropic Rearrangements, a New Class of Orbital‐Symmetry Controlled Reactions. Type I

Dyotropic Rearrangements, a New Class of Orbital‐Symmetry Controlled Reactions. Type I

Dyotropic Rearrangements, a New Class of Orbital‐Symmetry Controlled Reactions. Type II

Angewandte Chemie International Edition in EnglishVolume 11, Issue 2 p. 130-131 Communication Dyotropic Rearrangements, a New Class of Orbital-Symmetry Controlled Reactions. Type II Dr. Manfred T. Reetz, Corresponding Author Dr. Manfred T. Reetz Fachbereich Chemie der Universität 355 Marburg, Lahnberge (Germany)Fachbereich Chemie der Universität 355 Marburg, Lahnberge (Germany)Search for more papers by this author Dr. Manfred T. Reetz, Corresponding Author Dr. Manfred T. Reetz Fachbereich Chemie der Universität 355 Marburg, Lahnberge (Germany)Fachbereich Chemie der Universität 355 Marburg, Lahnberge (Germany)Search for more papers by this author First published: February 1972 https://doi.org/10.1002/anie.197201301Citations: 83AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume11, Issue2February 1972Pages 130-131 RelatedInformation