1912, 45, 3157. Mechanism of the Claisen Rearrangement. The Claisen Reaction: Stereochemical Considerations L. Claisen, Chem. In the branch that leads to the production of tyrosine and phenylalanine, chorismate mutase (CM, chorismate-pyruvate mutase, EC 5.4.99.5) is a key enzyme … O Me O MeO Me O Me Pre-existing chirality determines the stereoselectivity of the rearrangement Me H Me H Me H Me O Me H Me O Me Me H MeMeO typically not observed As a general rule, unless there are strange geometrical constraints Woodward–Hoffmann rules show a suprafacial, stereospecific reaction pathway. Save as PDF Page ID 90955; Cope and Claisen rearrangements; Contributors and Attributions; Objectives . The Claisen Reaction: Stereochemical Considerations L. Claisen, Chem. Apparently first reported by Gosteli in 1972, this variation of a Claisen rearrangement enjoyed a shadowy existence for three decades until its potential for the development of a catalytic asymmetric Claisen rearrangement was discovered. Molecules 2000, 5 ˇ Scheme 6. Key Terms. Crossover experiments eliminate the possibility of the rearrangement occurring via an intermolecular reaction mechanism and are consistent with an intramolecular process. After completing this section, you should be able to. account for the formation of a specific product from a Claisen rearrangement, without giving mechanistic details. kat. General Procedure for the Preparation of Geranyl Phenyl Ether To a stirred suspension of 176 mg sodium hydride (60% in oil, 4.4 mmol) in 20 mL THF at room temperature under argon atmosphere was added 0.376 g phenol (4.0 … The Claisen rearrangement can formally be considered as the intramolecular S n ′ addition of a carbonyl enol (X = O), thiocarbonyl enol (X = S) or enamine (X = N) to an allylic ether, sulfide or amine, respectively, forming a carbon–carbon σ-bond. The Claisen rearrangement is an exothermic, concerted (bond cleavage and recombination) pericyclic reaction. O Me O MeO Me O Me Pre-existing chirality determines the stereoselectivity of the rearrangement Me H Me H Me H Me O Me H Me O Me Me H MeMeO typically not observed As a general rule, unless there are strange geometrical constraints The Claisen rearrangement can also lead to a number of other alcohols (5) and aldehydes (6-9) with isoprenoid or related skeletons [16-20] (Scheme 6). Epoxides also undergo pinacol type rearrangement on treatment with acid O PhPh MgBr2 OHC Ph Ph O 1) RMgBr 2) H OH R! 1912, 45, 3157. The Claisen rearrangement (not to be confused with the Claisen condensation) is a powerful carbon–carbon bond-forming chemical reaction discovered by Rainer Ludwig Claisen in 1912. Summary This chapter contains sections titled: Introduction Aromatic Simple Aza‐Claisen Rearrangements Aliphatic Simple Aza‐Claisen Rearrangements Amide Acetal and Amide Enolate Claisen … The results of kinetic studies on the uncatalyzed [3,3]-sigmatropic rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers are reported. Chiral, enantiomerically enriched starting materials give products of high optical purity. 5 H2 H2. The Cope rearrangement, which is the conversion of a 1,5-hexadiene deriva-tive to an isomeric 1,5-hexadiene by the [3,3]-sigmatropic mechanism, has been studied extensively.14 As is the case for the Claisen rearrangement, the Cope rearrangement prefers … Chorismate-Mutase-Catalyzed Claisen Rearrangement Hong Guo and Niny Rao 1.1 Introduction Chorismic acid is the key branch point intermediate in the biosynthesis of aro-matic amino acids in microorganisms and plants (Scheme1.1a) [1]. catalyzed [3,3]-sigmatropic rearrangement that we expect will provide a new avenue for the development of an enantioselective catalytic Claisen process.6 In 1978, Bellus and Malherbe reported the conceptually novel ketene-Claisen reaction.7 In an attempt to perform a [2 + 2] cycloaddition, the authors discovered that treatment of an allyl To our knowledge, these studies collectively represent the first example of an enantioselective acyl-Claisen reaction. The reaction proceeds preferably via a chair transition state. Ber. Claisen rearrangements • One of the most useful sigmatropic rearrangements is the Claisen rearrangement and all it’s variants 3 Claisen rearrangement Johnson-Claisen rearrangement Eschenmoser-Claisen rearrangement OH+ OEt Hg+ O O H heat OH+ Me OMe MeOOMe H+ O OMe O OMe heat OH+ Me NMe 2 MeOOMe H+ O NMe2 O NMe2 heat Ireland-Claisen rearrangement OH+ Me O Me …
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