Chemistry
2 3 Sigmatropic Rearrangement
The 2 3 Sigmatropic Rearrangement is a chemical reaction that involves the migration of a substituent from one carbon atom to an adjacent carbon atom. This rearrangement occurs through a concerted process, where the breaking and forming of bonds happen simultaneously. It is a useful tool in organic synthesis for creating complex molecules.
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11 Key excerpts on "2 3 Sigmatropic Rearrangement"
eBook - PDF- James Morrison(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
δ Chirality Transfer via Sigmatropic Rearrangements Richard K. Hill Department of Chemistry University of Georgia Athens, Georgia I. Introduction 503 II. 3,3-Sigmatropic Rearrangements 504 A. The Claisen and Related Rearrangements 504 B. The Cope Rearrangement 536 III. 2,3-Sigmatropic Rearrangements 545 A. Creation of an Additional Asymmetric Center 548 B. Configuration of the Double Bond 549 C. Transfer of Chirality 551 D. Erythro/Threo Ratio 560 E. Formation of Chiral Aliènes 561 IV. Summary 562 References 563 I. Introduction One of the most powerful methods developed during the past several decades for creating a new asymmetric center in a predictable configura-tion involves the use of sigmatropic rearrangements. Most of the useful examples take the form of internal transfer of an allyl group through concerted 3,3- or 2,3-rearrangements (Scheme 1). Because these rear-rangements take place through highly ordered cyclic transition states, chirality in the starting material can be transferred to a new site in the A S Y M M E T R I C S Y N T H E S I S V O L U M E 3 503 Copyright © 1984 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-507703-3 504 R. K. Hill 3, 3-Sigmatropic rearrangement :Y Χ Υ Χ: 2,3-Sigmatropic rearrangement Scheme 1 product. Moreover, because the most favorable transition-state geometry can ordinarily be predicted from principles of conformational analysis, the stereochemical outcome is subject to prediction and control. This chapter summarizes the stereochemical principles that govern these rear-rangements and describes some important applications. This category encompasses the Claisen, Cope, and related rearrange-ments that proceed via six-membered cyclic transition states. The first observation of chirality transfer in a sigmatropic rearrangement was that of Alexander and Kluiber (7) in 1951 in the Claisen rearrangement of a chiral aryl allyl ether.
eBook - ePubPericyclic Reactions
A Mechanistic and Problem-Solving Approach
- Sunil Kumar, Vinod Kumar, S.P. Singh(Authors)
- 2015(Publication Date)
- Academic Press(Publisher)
Figure 3.1 ).Figure 3.1 Different modes of hydrogen atom migration in [1,5] sigmatropic rearrangements.The shift may occur with retention or inversion at the migrating group R. For example, the four possible stereochemical outcomes of 1,3-sigmatropic shift are illustrated below. Carbon atom C-4 can migrate to the top (suprafacial) or bottom (antarafacial) of C-1 and in the process may undergo retention or inversion. The four possibilities give rise to distinct products (Figure 3.2 ).Figure 3.2 Different modes of carbon atom migration in [1,3] sigmatropic rearrangements.3.2. Analysis of Sigmatropic Rearrangements of Hydrogen
For the analysis of sigmatropic rearrangements, the correlation diagrams are not relevant since it is only the transition state and not the reactants or products that may possess molecular symmetry elements. However, these reactions can be analyzed satisfactorily by using frontier molecular orbital (FMO ) and perturbation molecular orbital (PMO ) methods.3.2.1. FMO Analysis of [1,3] Sigmatropic Rearrangements of Hydrogen
One of the ways to analyze sigmatropic rearrangements is to assume that the migrating bond undergoes homolytic cleavage resulting in the formation of a pair of radicals. As bonding characters are to be maintained throughout the course of the rearrangements, the most important bonding interaction will be between the highest occupied molecular orbitals (HOMOs) of the two species produced by this cleavage. This is to be expected, as it is these orbitals that contain the unpaired electrons. We shall illustrate this analysis by examining a [1,3] sigmatropic shift of hydrogen in which the homolytic cleavage results in the production of a hydrogen atom and allyl radical (Figure 3.3 ).The ground state electronic configuration of allyl radical is. HOMO (Ψ2 ) of this radical has opposite sign on the terminal lobes (C 2 symmetry). Suprafacial [1,3] hydrogen shift under thermal condition is forbidden because there is no question of inversion at this atom, which is bonded to the carbon atom through its spherically symmetrical 1sΨ 12Ψ 21
eBook - PDFOrbital Symmetry
A Problem - Solving Approach
- Roland Lehr(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
PROBLEM 111.12 The following reaction has been observed: Chapter IV THE STEREOCHEMISTRY OF SIGMATROPIC REACTIONS Extensive studies of the stereochemistry of concerted, sigmatropic carbon-carbon bond rearrangements of orders [1,3] and [1,5] have been carried out by Professor J. A. Berson at Yale University and by Professor Η. E. Zimmerman at the University of Wisconsin. In this chapter, we shall consider their work in this area to exemplify the constraints imposed on the stereochemical outcome of concerted sigmatropic rearrangements in cases where orbital symmetry is conserved. PROBLEM IV.1 By way of orientation, the reader should review the sections in Chapter I which deal with the applications of orbital symmetry relationships to sigmatropic rearrangements. (a) Consider first suprafacial sigmatropic rearrangements of order [ 1 , 3 ] : What is the stereochemical fate of the migrating group, R, if this reaction is to proceed thermally in accordance with the Woodward-Hoffmann rules? (I.e., does R retain its configuration or does it suffer inversion in the thermally allowed suprafacial [1,3] sigmatropic rearrangement?) (b) Repeat your analysis of part (a), above, for a thermal, suprafacial sigmatropic rearrangement of order [1,5]. 6 0 P R O B L E M IV.3 61 PROBLEM IV.2 (a) Suggest a mechanism for the following transformation: (b) Consider the following thermal [1.3] sigmatropic rearrangements: The rearrangement of eA7tfaexo -6-acetoxy-7-methylbicyclo[3.2.0] hept-2-ene (I) is seen to proceed with predominant inversion, whereas rearrangement of the corresponding endo, endo isomer proceeds with predominant retention of configuration of the migrating center. Furthermore, exo ^ endo epimeriza-tion of the methyl group does not compete with rearrangement during the pyrolysis of I, but this process is found to occur 60% as fast as the rearrange-ment of II to A and B. Offer a detailed explanation to account for these observations.
eBook - ePub- Werner Bonrath, Jonathan Medlock, Marc-André Müller, Jan Schütz(Authors)
- 2021(Publication Date)
- De Gruyter(Publisher)
7 Rearrangement reactions7.1 Introduction
Rearrangement reactions are a broad class of organic reactions in which the reactant undergoes a rearrangement to give a structural isomer of the original molecule via a migration of an H atom or a larger molecular fragment. From the view of atom economy and E-factor, rearrangement reactions fulfil the criteria of the modern type of chemistry and green chemistry, with all atoms of the starting material being present in the product structure.In many rearrangement reactions, the migration occurs directly to a neighbouring position. These rearrangements belong to the class of [1,2]-rearrangements or [1,2]-shifts. These reactions are often sigmatropic rearrangements meaning that a σ-bond migrates during the reaction. The nomenclature of rearrangement reactions is described by numbering the atoms directly attached to the bond that is broken with 1 and 1ʹ (Scheme 7.1 ). The following atoms in the direction of the rearrangement are labelled 2, 3 and so forth starting from 1 and 2ʹ, 3ʹ and so forth starting from 1ʹ. After the rearrangement the new σ-bond is connected to two atoms which characterise the rearrangement. The numbers are listed in square brackets and the prime is removed from the second number.Scheme 7.1: Naming and examples of sigmatropic rearrangements.Some of the most important industrial rearrangement reactions, such as [3,3]-sigmatropic rearrangements, are used in the synthesis of isoprenoid building blocks such as isophytol, β-ionone or aroma compounds such as methyl heptanone. These are the main focus of this chapter.7.2 Wagner–Meerwein rearrangements
The Wagner–Meerwein rearrangement is a predominately acid-catalysed [1,2]-rearrangement in which a hydrogen, alkyl or aryl group migrates from one carbon to a neighbouring carbon to generate a new carbocation. This carbocation reacts with a nucleophile or a proton from a neighbouring atom is eliminated. The driving force of the reaction is that the initially formed carbocation has the tendency to rearrange to a thermodynamically more stable structure. In the terpene chemistry, the Wagner–Meerwein rearrangement is of importance in the manufacture of camphene from isoborneol (Scheme 7.2
eBook - PDF- R. B. Woodward, R. Hoffmann(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
7. Theory of Sigmatropic Reactions We denned as a sigmatropic change of order [i,j] the migration of a a bond, flanked by one or more π electron systems, to a new position whose termini are ;-l and/-l atoms removed from the original bonded loci, in an uncatalyzed intramolec-ular process. Thus, the well-known Claisen and Cope rearrangements are sigma-tropic changes of order [3,3]. Suprafacial C Antarafacial C Figure 28. Suprafacial and antarafacial [1,5] shifts of a hydrogen atom. A priori, there are two topologically distinct ways of effecting a sigmatropic migra-tion. These are illustrated in Figure 28 for the [1,5] shifts of a hydrogen atom. In the first, suprafacial process, the transferred hydrogen atom is associated at all times with the same face of the π system. In the second, antarafacial process, the migrat-ing atom is passed from the top face of one carbon terminus to the bottom face of the other. For the analysis of these reactions correlation diagrams are not relevant since it is only the transition state and not the reactants or products which may possess molec-ular symmetry elements. We shall present several equivalent methods for ana-lyzing these reactions. 1. The use of the principle of conservationof orbital symmetry is here illustrated for the case of a suprafacial [1,3] hydrogen shift. The relevant correlations are shown in Figure 29. Clearly, two electrons can enter a bonding orbital, either a or π, of the product, but the other two must be placed either in a σ* or a π* orbital, if orbital symmetry is to be conserved. The reaction is symmetry-forbidden. 7. Theory of Sigmatropic Reactions 115 c=c f, ·:? a-b Isolated orbitale a+b Interacting orbitals before transfer of hydrogen Interacting orbitals after transfer of hydrogen Figure 29. Conservation of orbital symmetry in a suprafacial [1,3] hydrogen shift.
eBook - ePub- Michael Harmata(Author)
- 2011(Publication Date)
- Wiley(Publisher)
Chapter 3 Sigmatropic Rearrangements and Related Processes Promoted by Silver Jean-Marc Weibel, Aurélien Blanc, and Patrick Pale Laboratory for Organic Synthesis and Reactivity, Institute of Chemistry, University of Strasbourg, France 3.1 IntroductionSigmatropic shifts represent a large class of reactions involving the migration of at least one sigma bond. Therefore, such migrations lead to skeletal rearrangements of the carbon frame within the molecule undergoing this reaction.Sigmatropic rearrangements usually involve σ bonds adjacent to a π system or a σ bond included in a strained system. As other transition metals, but with specific properties due to its d 10 electronic configuration, f orbitals and a relativistic effect,1 silver easily interacts with such systems. Silver salts have thus been explored as catalysts to facilitate and promote sigmatropic rearrangements.3.2 Wolff and Arndt–Eistert Rearrangements and Related ReactionsThe Wolff and Arndt–Eistert rearrangements are probably among the earliest known reactions promoted by silver ions.2, 3 Discovered at the turn of the nineteenth/twentieth century, the Wolff rearrangement allows the transformation of α-diazoketones to carboxylic acids,4 while the Arndt–Eistert rearrangement is a similar sequence also leading to carboxylic acids, but including the preparation of α-diazoketones from a shorter acid chloride (Scheme 3.1 ).5Scheme 3.1Numerous conditions have been developed for this transformation, but reproducible yields have usually been obtained by mixing a silver salt with a coreagent, such as silver nitrate associated with wet ammonia, silver oxide with triethylamine or sodium thiosulfate, and silver benzoate with triethylamine. Nonbasic conditions have also been described by Koch and Podlech using silver trifluoroacetate deposited on silica.6
eBook - PDFOrbital Symmetry
A Problem-Solving Approach
- Roland E. Lehr, Alan P. Marchand(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
B. SIGMATROPIC REACTIONS 13 Though the rules for sigmatropic reactions appear complex at this time, we shall find in Section D that they can be summarized in one simple rule once we examine the involvement of the sigma-bond in more detail. It is worth noting here, though, that the dichotomy of behavior with respect to the influence of heat and light we noted for electrocyclic reactions persists in sigmatropic reactions. Furthermore, an examination of Tables 1.3 and 1.4 reveals that the stereo-Table 1.3 Rules for [i,j] Sigmatropic Shifts {i,j > 1 ) / + / Antara-antara or supra-supra Antara-supra or supra-antara An Thermally forbidden, photochemically allowed 4/7 + 2 Thermally allowed, photochemically forbidden Thermally allowed, photochemically forbidden Thermally forbidden, photochemically allowed chemistry of the preferred mode of migration is determined by the number of electrons involved in the process. For example, if we consider [1,/] sigmatropic shifts, the number of electrons involved in a [1,5] shift in a neutral system [a (1 + j) = 6 = (4/7 + 2) system] is 6 (2 sigma + 4 pi), which is equal to the number of electrons involved in a [1,6] shift in a cation [a(1 + / ) = 7 = (4/7 + 3) system]. The tables reveal that the stereochemical behavior of a neutral (4/7 + 2) system should be the same as a cationic (An + 3) system. Table 1.4 Rules for [ 1,/] Sigmatropic Shifts for Charged Species 3 1 +/ Mode of migration Cation Anion An + 1 Suprafacial Thermally forbidden, photochemically allowed Antarafacial Thermally allowed, photochemically forbidden 4/7 + 3 Suprafacial Thermally allowed, photochemically forbidden Antarafacial Thermally forbidden, photochemically allowed Thermally allowed, photochemically forbidden Thermally forbidden, photochemically allowed Thermally forbidden, photochemically allowed Thermally allowed, photochemically forbidden n = integer.
eBook - ePubOrganic Reaction Mechanisms 2010
An annual survey covering the literature dated January to December 2010
- A. C. Knipe(Author)
- 2012(Publication Date)
- Wiley(Publisher)
Chapter 13 Molecular Rearrangements: Part 1. Pericyclic Reactions J. M. CoxonDepartment of Chemistry, University of Canterbury, Christchurch, New Zealand[3,3]-Sigmatropic, Claisen, and Cope Rearrangements [2,3]-Reactions Vinyl Cyclobutane and Vinyl Cyclopropane Rearrangement 1,2-Migration Ene Reaction Bergman Reaction Electrocyclic Reactions Cyclization 4 + 2-Cycloadditions 3 + 2-Cycloadditions Metathesis Metal-catalysed Reactions Miscellaneous References[3,3]-Sigmatropic, Claisen, and Cope Rearrangements
The diastereoselectivity of the [3,3]-rearrangement of 1,1-disubstituted allyl carboxylates (Scheme 1 ) has been reported to be a consequence of the transition state having a boat-like transition structure because of the participation of the lone pairs and the secondary orbital interaction.1 Although the transition structure for the [1,3]-rearrangement has a higher barrier, it is said not to proceed in the usual antarafacial manner due to the cyclic orbital interaction among two lone pairs of the carboxylate and the allylic lumo. The geminal bond participation controls the stereoselectivity in the [3,3]-rearrangement. The bond model analysis showed that electron-withdrawing σ-bond substituents prefer to occupy the Z
eBook - PDFOrganic Reaction Mechanisms 1973 Reprint A
An annual survey covering the literature dated December 1972 through November 1973
- A. R. Butler, M. J. Perkins, A. R. Butler, M. J. Perkins(Authors)
- 2008(Publication Date)
- Wiley-Interscience(Publisher)
A similar conclusion was reached in the case of the rearrangement of tris- (2-methylallyl)borane.138 The thermal rearrangement of the benzylated pyrazine (148) to (149) represents the first clear-cut example of a [ 1,3]-sigmatropic shift with inversion involving nitrogen at the migration origin. The overall process showed minimal rate dependence on solvent, Molecular Rearrangements 439 proceeded with 295% stereospecificity and displayed a small extra-cage free-radical component.139 [1,3]-Sigmatropic C + N alkyl shifts have been reported in the cleavage reactions of some 1,4-diazocines.l40 These two approaches have been combined141 to examine the stereochemistry of [1,3]-sigmatropic alkyl shifts from nitrogen to carbon and their reverse in certain pyrazine-based heterocyclic systems. The shifts involved were all of the allowed suprafacial [1,3]-types. The base-induced conversion of o-dipropargylbenzeneand 2,3-&propargylnaphthalene to the corresponding allenes has been reported.141 Other Sigmatropic Migrations [ 1,5]-Migrations. An intramolecular [1,5]-shift of a formyl group has been detected in the thermolysis of methyl bicyclo[3.2.O]hept-2-en-7-ones.142 From rate studies on the thermolysis of 1 -methylcyclohexa-2,4-dienes, the formyl group undergoes [ 1,5]-sigma- tropic shift faster than hydrogen by more than two orders of magnitude, whereas the methoxycarbonyl group is slower by a factor of about 70 and acetyl shows a migration aptitude comparable to that of hydrogen.143 Thermolysis ( 150-190°, in decalin) of arylallenes causes their rearrangement via a [ l,b]-hydrogen shift to yield o-quinodi- methanes which then may cyclize to give dihydronaphthalenes and/or undergo [ l,7]-sigmatropic H-shifts to give arylbutadienes.
- Jaemoon Yang(Author)
- 2008(Publication Date)
- Wiley-Interscience(Publisher)
Still, for the convenience of following the bond connection event clearly, I prefer to draw the transition state like B. REFERENCES 1. Zimmerman, H. E.; Traxler, M. D. J. Am. Chem. Soc. 1957, 79 , 1920. 2. For definitions of syn and anti , see Masamune, S.; Ali, S. A.; Snitman, D. L.; Garvey, D. S. Angew. Chem. Int. Ed. 1980, 19 , 557. 3. (a) Day, A. C. J. Am. Chem. Soc. 1975, 97 , 2431; (b) Carey, F. A.; Sundberg, R. J., Advanced Organic Chemistry , Part A, 3rd ed.; Plenum Press: New York, 1990; Chap. 11. 4. Eliel, E. L.; Wilen, S. H.; Mander, L. N. Stereochemistry of Organic Compounds ; Wiley: New York, 1994; Chap. 11. 5. Lipkowitz, K. B.; Kozlowski, M. C. Synlett 2003, 1547. 6. (a) Andrews, P. R.; Haddon, R. C. Aust. J. Chem. 1979, 32 , 1921; (b) Copley, S. D.; Knowles, J. R. J. Am. Chem. Soc. 1985, 107 , 5306. 1 [3,3]-Sigmatropic Rearrangements GENERAL CONSIDERATIONS The Claisen and Cope rearrangements are two of the best known sigmatropic rear- rangements in organic chemistry 1 (Scheme 1.I). As the rearrangement involves six electrons in a six-atom system, these two reactions serve as excellent examples of the ubiquitous existence of a six-membered transition state in organic chemistry. In 1912, Ludwig Claisen discovered that the allyl ether 1 of ethyl acetoacetate underwent a reaction to afford 2 upon heating in the presence of ammonium chloride 2 (Scheme 1.II). Similarly, the allyl naphthyl ether 3 transformed into 1-allyl-2-naphthol (4) in 82% yield at 210 ◦ C. The reaction, now known as the Claisen rearrangement , is general for a variety of aliphatic and aromatic ethers and is recognized as one of the most synthetically useful reactions in organic chemistry. 3 The Claisen rearrangement is a thermally induced [3,3]-sigmatropic rearrange- ment of allyl vinyl ethers to form γ,δ-unsaturated carbonyl compounds.
eBook - PDFOrganic Reaction Mechanisms 2016
An annual survey covering the literature dated January to December 2016
- A. C. Knipe(Author)
- 2019(Publication Date)
- Wiley(Publisher)
1 H H H H H H H H H H H H H Scheme 1 The rearrangement of 2-vinyl aziridine 2-carboxylates to chiral cyclic sulfoximines has been reported for the stereospecific synthesis of substituted cyclic sulfoximines (Scheme 2). 2 12 Molecular Rearrangements 699 N S Mes − O N S CO 2 Me + + CO 2 Me O − Mes Scheme 2 The regioselectivity of the o-semidine, p-semidine, and diphenyline rearrangements of unsymmetrical N,N ′ -diarylhydrazines indicates that the electron-rich nitrogen atom is first protonated, and then the electron-poor non-protonated nitrogen atom undergoes an N[1,3]-sigmatropic shift to the ortho-position of the electron-rich aryl rings, gener- ating key intermediates. The intermediates can undergo a direct proton transfer to give o-semidines, or a second N[1,3]-shift of the electron-poor nitrogen atom and then pro- ton transfer to furnish p-semidines, or a [3,3]-sigmatropic shift and subsequent proton transfer to yield diphenylines (Scheme 3). 3 H 2 N NH EWG EDG NH 2 EWG EDG NH 2 or NH EWG EDG NH 2 NH EWG H 2 N EDG or + Scheme 3 A borylation/ortho-cyanation/allyl group transfer cascade initiated by a copper- catalysed electrophilic dearomatization has been reported to involve a regio- and stereo-specific 1,3-transposition of the allyl fragment facilitated by an aromatization- driven Cope rearrangement (Scheme 4). 4 de [1,4]-Sigmatropic Epimerization of the -stereocentre of sugar nitrones has been suggested to involve a [1,4]-sigmatropic rearrangement (Scheme 5). 5 [3,3]-Sigmatropic, Cope Claisen Acyclic and cyclic acyl hydrazides have been reported to catalyse a Cope rearrangement of 1,5-hexadiene-2-carboxaldehydes via iminium ion formation (Scheme 6). 6 A Cope rearrangement of 1,5-hexadiene-2-carboxaldehydes in the presence of a diazepane catalyst has been reported to offer chiral selection. 7 An enantioselective
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