Claisen rearrangement 3,3 -sigmatropic rearrangement

Karahanaenone is formed by a [3,3] sigmatropic rearrangement (Claisen rearrangement). 

Chorismate mutase catalyzes the conversion of chorismate to prephenate (Equation 17.44). This reaction is unusual, in that it is the only pericyclic [3,3] sigmatropic rearrangement (Claisen rearrangement) that is catalyzed by an enzyme. 

C,oH oOg, Mu 226.19. P. is unstable in the free form and undergoes decarboxylation with elimination of water to give phenylpyruvic acid. It is an intermediate in the biosynthesis of many aromatic natural products by the shikimate pathway (see chorismic acid, shi-kimic acid). The biosynthesis of P. proceeds from chorismic acid by enzyme-catalyzed [3,3]sigmatropic rearrangement (Claisen rearrangement) under the action of chorismate mutase (EC 5.4.99.5). 

The reaction, which is in fact practised industrially, is the Saucy-Marbet reaction, where 2- methoxypropene, obtained by thermolysis of 2,2-dimethoxypro-pane, is converted into 2-methylbut-3-en-2-ol. The intermediate, which is not isolated, undergoes a sigmatropic rearrangement (Claisen rearrangement) to give 6-methylhept-5-en-2-one. 

Continuous efforts for the elucidation of reaction mechanism of the aromatic Claisen rearrangement have been made since the reaction was discovered [4]. The reaction is considered to be a concerted pericyclic pathway. The first step is the [3,3]-sigmatropic rearrangement (Claisen rearrangement) resulting in the bond... 

Strong heating of 2-substituted 5-propargylsulfanyl-3-aryl-3//-pyrimidin-4-ones, and their 5-allylsulfanyl derivatives, has been shown to lead to 2-substituted 3-aryl-6-methyl-3//-thieno[3,2-d]pyrimidin-4-ones and their 6,7-dihydro derivatives. The proposed mechanism in both cases is a [3,3]-sigmatropic thia-Claisen rearrangement followed by tautomerization and a 5-exodig or 5-exo-trig cyclization.38... 

Citral is a key intermediate in the synthesis of vitamin A, and in Chapter 31 you had a go at designing a synthesis of it. BASF manufacture citral by a remarkable process that involves two successive [3,3] -sigmatropic rearrangements, Claisen followed by a Cope. 

One key element of the total synthesis of (-)-dactylolide (-)- developed by McLeod et al. is a [3,3]-sigmatropic Ireland-Claisen rearrangement which allows the selective formation of the stereogenic centre at C-19. 

Allyloxy-substituted 4,5-diphenyloxazoles undergo [3,3]-sigmatropic aza-Claisen rearrangements to 3-allyl-2(3//)oxazolones <84JOC399>. The 2-propynyloxy-oxazole (61) affords an allene... 

Tandem [3,3]—[3,3] Sigmatropic Rearrangements Claisen-Cope Rearrangements... 

PROBLEM 20.45 We saw on page 1063 that chorismate undergoes a [3,3] sigmatropic shift (Claisen rearrangement) to prephenate catalyzed by the enzyme chorismate mutase. This enzyme-catalyzed reaction occurs more than 1 million times faster than the corresponding nonenzymatic reaction. How does the enzyme effect rate enhancement Both enzymatic and nonenzymatic reactions proceed through a chairlike transition state. However, the predominant conformer of chorismate in solution, as determined by H NMR spectroscopy, is the pseudodiequatorial conformer 2, which cannot undergo the reaction. 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

Sigmatropic rearrangement (Section 24 13) Migration of a a bond from one end of a conjugated tt electron system to the other The Claisen rearrangement is an example... 

This reaction proceeds by a concerted, [3,3] sigmatropic rearrangement (cf. the Claisen rearrangement) where one carbon-carbon single bond breaks, while the new one is formed. It is a reversible reaction the thermodynamically more stable isomer is formed preferentially ... 

Two other important sigmatropic reactions are the Claisen rearrangement of an allyl aryl ether discussed in Section 18.4 and the Cope rearrangement of a 1,5-hexadiene. These two, along with the Diels-Alder reaction, are the most useful pericyclic reactions for organic synthesis many thousands of examples of all three are known. Note that the Claisen rearrangement occurs with both allylic aryl ethers and allylic vinylic ethers. 

N,O-acetal intermediate 172, y,<5-unsaturated amide 171. It is important to note that there is a correspondence between the stereochemistry at C-41 of the allylic alcohol substrate 173 and at C-37 of the amide product 171. Provided that the configuration of the hydroxyl-bearing carbon in 173 can be established as shown, then the subsequent suprafacial [3,3] sigmatropic rearrangement would ensure the stereospecific introduction of the C-37 side chain during the course of the Eschenmoser-Claisen rearrangement, stereochemistry is transferred from C-41 to C-37. Ketone 174, a potential intermediate for a synthesis of 173, could conceivably be fashioned in short order from epoxide 175. 

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