Cope and Claisen Rearrangements

Step through the sequence of stmctures depicting Cope rearrangement of 1,5-hexadiene. Plot energy (vertical axis) vs. the length of either the carbon-carbon bond being formed or that being broken (horizontal axis). Locate the transition state. Measure all CC bond distances at the transition state, and draw a structural formula for it 

Would you describe the transition state for the Claisen rearrangement as early (like reactants), late (like products) or in between Given the overall thermodynamics of reaction, do you conclude that the Hammond Postulate applies Explain. 

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Both Cope and Claisen rearrangements involve reorganization of an odd number of electron pairs (two tt bonds and one a bond), and both react by suprafacial pathways (Figure 30.13). 

SCHEME 19. Activation volumes of Cope and Claisen rearrangements in polar 1,5-hexadiene systems... 

In addition to the numerous pericyclic aromatic TSs, other reactions deserve attention. These include the Cope and Claisen rearrangements, the pericyclic reactions with Mobius TSs, the Bergman cyclizations [77,116], and the TSs for 1,5-H shifts [100,117],... 

Therefore, the [3, 3] sigmatropic rearrangement has become a useful tool in synthetic organic chemistry. The following are some examples which include Cope and Claisen rearrangement. 

So we find that both Cope and Claisen rearrangements are [3, 3] sigmatropic rearrangements and proceed by suprafacial-suprafacial pathway. 

This section will focus on recent examples of asymmetric [3,3]-sigmatropic rearrangements involving dienes and polyenes. Attention will be given to Cope and Claisen rearrangements, as well as to several of their variants. For more exhaustive reviews of the subject, the reader is referred elsewhere69,70. 

The Cope and Claisen rearrangements are important sigmatropic reactions. Both... 

In this section, the aliphatic Cope and Claisen rearrangements, as depicted in the transformation of I to 2 in Scheme 2, are discussed, as well as variations of the latter (i.e.. Johnson-Claisen, Ireland-Claisen, Reformatsky Claisen, F.schenmoser-Claisen. Ficini Claisen, and hetero-Claisen rearrangements). When X is oxygen, replacement of Cl and C2 with an aromatic ring... 

The Cope and Claisen rearrangements are markedly similar reactions, although they differ in thermodynamic driving force. Whereas the Cope rearrangement of 1,5-hexadiene is thermoneutral (reactant and product are the same), the analogous Claisen rearrangement of allyl vinyl ether is exothermic. Do thermodynamic differences lead to differences in transition state geometries ... 

Cope and Claisen rearrangements proceed under milder conditions in the presence of Pd(II) catalyst [194,199]. Cope rearrangement of the linear 1,5-diene 467 to 468... 

MM has been used to study the transition states involved in SN2 reactions, hydroborations, cycloadditions (mainly the Diels-Alder reaction), the Cope and Claisen rearrangements, hydrogen transfer, esterification, nucleophilic addition to... 

Another series of publications from Ken s group compared kinetic isotope effects, computed for different possible transition structures for a variety of reactions, with the experimental values, either obtained from the literature or measured by Singleton s group at Texas A M. These comparisons established the most important features of the transition states for several classic organic reactions — Diels-Alder cycloadditions, Cope and Claisen rearrangements, peracid epoxidations, carbene and triazolinedione cycloadditions and, most recently, osmium tetroxide bis-hydroxylations. Due to Ken s research, the three-dimensional structures of many transition states have become nearly as well-understood as the structures of stable molecules. 

Shifts in Neutral Species Shifts in Charged Species Shifts in Electron Deficient Centers Application of EMO Method Cope and Claisen Rearrangements Cope Rearrangement Oxy-Cope Rearrangement Claisen Rearrangement Some Other Examples Abnormal Claisen Rearrangement... 

Wiest, O. Black, K. A. Houk, K. N. Density functional theory isotope effects and activation energies for the Cope and Claisen rearrangements, J. Am. Chem. Soc. 1994, 116, 10336-10337. 

Cope and Claisen rearrangements are the [3,3]-sigmatropic rearrangements and are among the most commonly used sigmatropic reactions. They have been the subject of numerous... 

These rearrangements involve a six-membered transition state (Scheme 8.5). It is found that a chair-like transition state is usually preferred for the Cope and Claisen rearrangements. 

Three fundamental types of isomerization may be distinguished. The first is double-bond migration, as in the isomerization of pent-l-ene to (Z)-pent-2-ene. The second involves skeletal rearrangements, such as the conversion of bicyclo[3.1.0]hex-2-ene derivatives to the corresponding cyclohexadienes. The third, and possibly most useful type, is the catalysis of group migrations, particularly in the Cope-and Claisen rearrangements. 

The Cope- and Claisen rearrangements are also catalyzed by square-planar transition metal complexes. Palladium complexes have been responsible for spectacular increases in the rates of Cope rearrangements by factors of up to 10 . Certain other sigmatropic rearrangements are also catalyzed by transition metal complexes. 

The most important reactions involving skeletal changes together with substituent group migration are the Cope-and Claisen rearrangements. These are both classified as... 

The N-analogs1 8 of the Cope and Claisen rearrangement have been widely used for syntheses of amines and /V-heterocyclcs, for example, the l,l -diaza-Cope rearrangement is the key step in the Fischer indole synthesis. 

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