Rearrangement of 1,5-Diene

Another example of a reaction in which the stereochemistry of the process provides some valuable information about the mechanism is the thermal rearrangement of 1,5-dienes and substituted analogs ... 

The most important sigmatropic rearrangements from the synthetic point of view are the [3,3] processes involving carbon-carbon bonds. The thermal rearrangement of 1,5-dienes by [3,3] sigmatropy is called the Cope rearrangement. The reaction establishes equilibrium between the two 1,5-dienes and proceeds in the thermodynamically favored direction. The conversion of 24 to 25 provides an example ... 

The thermal rearrangement of 1,5-dienes 1 to yield the isomeric 1,5-dienes 2, is called the Cope rearrangemenC —not to be confused with the thermolysis of amine oxides, which is also named after Arthur C. Cope. 

Among the best known examples, involving a carbon moiety, is the shift from one carbon atom to another observed in the Cope rearrangement of 1,5-dienes (49— 50 not to be confused with the... 

Oxy-Cope rearrangement (7, 302-303 8, 412-414). Further studies indicate that the rearrangement of 1,5-diene alkoxides can be used for stereoselective generation of asymmetry. An application is the stereoselective synthesis of eryf/iro-juvabione (1), a sesquiterpene from Abies balsamea, shown in equation (I). ... 

Rearrangement of 1,5-dienes is known as the Cope rearrangement and rearrangement of allyl phenyl ethers and allyl vinyl ethers is known as the Claisen rearrangement The... 

TCNE takes place (Scheme 57). Tomioka reported the (3 + 2) photocycloaddition between 1,1,2-triarylcyclopropanes and vinyl ethers in the presence of p-DCB [162]. Mizuno and Otsuji reported the (4 -l- 2) photocycloaddition between 1,2-diarylcyclopropanes and DCA [23]. The 1,4-radical cation produced as an intermediate of the Cope rearrangement of 1,5-dienes via photoinduced electron transfer can be trapped by molecular dioxygen, giving bicyclic dioxanes (Scheme 58) [163]. This photooxygenation takes place in a stereospecific manner. 

Cope rearrangement The [3,3] sigmatropic rearrangement of 1,5-dienes. If the reagent is symmetrical about the 3,4 bond then the product is indistinguishable from the starting material. 

Two common six-membered rearrangements of 1,5-dienes have Y as either oxygen (Claisen rearrangement) or carbon (Cope rearrangement). Both are reversible and favor the more stable product. The preceding example problem demonstrated that they were thermally allowed An+2 suprafacial retention processes. As in the Cope example problem above, the transition state for the reaction commonly resembles the chair conformation of cyclohexane. Figure 12.29 shows a biochemical example of the Claisen rearrangement. 

The rearrangement of 1,5-dienes with a hydroxy group at C-3 or C-4 is referred to as the oxy-Cope rearrangement638 722 723. The method leads primarily to an enol, which spontaneously tautomerizes to yield a carbonyl compound723. The widespread use of the oxy-Cope rearrangement today ean be attributed to the following features ... 

The Cope rearrangement of 1,5-dienes is the all-carbon analog of the Claisen... 

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