Cope reaction

The photochemical behavior of the isomeric 3-methyl-2-phenyl-2-allyl-l-azirine (66) system was also studied. Irradiation of (66) in cyclohexane gave a quantitative yield of azabicyclohexenes (67) and (68). Control experiments showed that (65) and (66) were not interconverted by a Cope reaction under the photolytic conditions. Photocycloaddition of (66) with an added dipolarophile afforded a different 1,3-dipolar cycloadduct from that obtained from (65). The thermodynamically less favored endo isomer (68b) was also formed as the exclusive product from the irradiation of azirine (66b). 

Examine transition-state structures and bond density surfaces for the Diels-Alder, ene and Cope reactions. 

Participation of aromatic groups in oxy-Cope reaction sequences enables the synthesis of highly substituted polyquinane ring systems (Scheme 10, <96JOC7976>). 

C4-insertions by means of a sigmatropic rearrangement process have been described using either a thermal Cope reaction, anionic Claisen amide enolate and zwitterionic aza-Claisen rearrangements. 

An important improvement in the oxy-Cope reaction was made when it was found that the reaction is strongly catalyzed by base.212 When the C(3) hydroxy group is converted to its alkoxide, the reaction is accelerated by a factor of 1010-1017. These base-catalyzed reactions are called anionic oxy-Cope rearrangements, and their rates depend on the degree of cation coordination at the oxy anion. The reactivity trend is K+ > Na+ > Li+. Catalytic amounts of tetra-rc-butylammonium salts lead to accelerated rates in some cases. This presumably results from the dissociation of less reactive ion pair species promoted by the tetra-rc-butylammonium ion.213... 

The reaction in Entry 5 is a case in which the thermal conditions were preferable to the basic conditions because of the base sensitivity of the product. Entries 6 to 10 show anionic oxy-Cope reactions. Entries 6 and 7 are early examples of the application of the reaction in synthesis. Entries 8 and 9 involve rearrangements of bicyclo[2.2.1]hept-2-en-2-ol derivatives to give cw-fused bicyclo[4.3.0]non-7-en-3-ones. 

The reaction that is perhaps of the greatest synthetic utility—because it proceeds at relatively low temperatures—is the Cope reaction of tertiary amine oxides, e.g. (82) ... 

The six-membered rings in these T.S.s are more flexible than the five-membered T.S.—(81) above—and need not be planar (cf cyclohexanes v. cyclopentanes). Elimination may thus proceed, in part at least, from conformations other than the syn-periplanar, with the result that the degree of SYN stereoselectivity in these eliminations may sometimes be lower than that observed in the Cope reaction. Both reactions require higher temperatures than for the Cope reaction, carboxylic esters particularly so. 

Serrano s group described asymmetric domino Diels-Alder/Cope reactions using 1,3-nitrocyclohexadienes containing a sugar moiety such as 4-39 and cy-... 

Oxidation of lappaconitine and elatine alkaloids leads to de-ethylation by a Cope reaction, with the formation of nitrones (Scheme 2.15) (94). 

In some cyclic system the chair transition is sterically impossible to attain, and the Cope reaction still goes but by a boat transition state. 

In unsubstituted phenyl ethers, the enolisation is faster than the Cope reaction. This is why the product is predominantly ortho isomer. When both the ortho positions are substituted, the allyl group undergoes a second migration via a concerted sigmatropic mechanism giving a para substituted phenol. This is called para Claisen condensation. 

The first evidence that the radical cation generated by a single-electron transfer (SET) of an unsymmetrical 1,5-diene 408 can undergo a [3,3]-sigmatropic shift (Cope reaction)... 

There is no unity of opinion in the literature concerning a classification, i.e, whether to call these transformations aza-Claisen or aza-Cope rearrangements. It is accepted that the term aza-Claisen should be reserved only for those processes in which a carbon atom in the allyl vinyl ether system has been replaced by nitrogen357. Three different types of aliphatic 3-aza-Cope reactions which were studied theoretically are the rearrangements of 3-aza-l,5-hexadienes (610, equation 262), 3-azonia-l,5-hexadienes (611, equation 263) and 3-aza-l,2,5-hexatrienes (612, equation 264) (the latter is a ketenimine rearrangement )357. 

Figure 12 Oxy-Cope reaction catalyzed by antibody AZ28 raised against the hapten y and X-ray structure of the antibody AZ28-hapten y complex.

Conjugated dienes, 11 Conjugation, 11, 368 Conrotation, 345 Coordination polymerisation, 322 Copolymerisation, 322 Cope reaction, 268 Cope rearrangement, 354 Cracking, 112, 305 Cram s rule, 235 Cross-linking, 323... 

Nowadays, these coping reactions still present in stressful situations when the individual is worried, frustrated and frightened. 

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