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Claisen rearrangement concerted reaction

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 ... [Pg.66]

Like the Diels-Alder reaction discussed in Sections 14.4 and 14.5, the Claisen rearrangement reaction takes place through a pericyclic mechanism in which a concerted reorganization of bonding electrons occurs through a six-membered, cyclic transition state. The 6-allyl-2,4-cyclohexadienone intermediate then isomerizes to o-allylpbenol (Figure 18.1). [Pg.660]

Scheme 6.17 gives some examples of the orthoamide and imidate versions of the Claisen rearrangement. Entry 1 applied the reaction in the synthesis of a portion of the alkaloid tabersonine. The reaction in Entry 2 was used in an enantiospecific synthesis of pravastatin, one of a family of drugs used to lower cholesterol levels. The product from the reaction in Entry 3 was used in a synthesis of a portion of the antibiotic rampamycin. Entries 4 and 5 were used in the synthesis of polycyclic natural products. Note that the reaction in Entry 4 also leads to isomerization of the double bond into conjugation with the ester group. Entries 1 to 5 all involve cyclic reactants, and the concerted TS ensures that the substituent is introduced syn to the original hydroxy substituent. [Pg.579]

This reaction also is concerted and proceeds via a six-membered transition state, but here the species (59), corresponding to the ene-one intermediate (53a) in the aromatic Claisen rearrangement, is in fact the end-product. This is so because there is in (59) no energetic driving force, comparable to re-aromatisation in (53a— 52a), to promote its enolisation. [Pg.356]

Originally very few types of such rearrangements were known e.g., Copes rearrangement, Claisen rearrangement and some 1, 5 hydrogen shift in some dienes, but now many others have been discovered. The common feature of such reactions is that they are concerted, uncatalysed and involve a bond migration through a cyclic transition state. [Pg.72]

Let s now consider concerted skeletal rearrangements which allow the direct transformation of a sugar structure into a carbocyde. The Claisen rearrangement has been used for the direct conversion of sugar C-glycosides to eight membered carbocycles, respectively. The reaction has precedents in the transformation of 2-methylene-6-vinyl-tetrahydropyrans to cyclooctenone derivatives, a transformation that has been applied in the synthesis of several natural products [54],... [Pg.9]


See other pages where Claisen rearrangement concerted reaction is mentioned: [Pg.715]    [Pg.632]    [Pg.1454]    [Pg.374]    [Pg.31]    [Pg.860]    [Pg.861]    [Pg.519]    [Pg.302]    [Pg.1143]    [Pg.226]    [Pg.674]    [Pg.31]    [Pg.194]    [Pg.236]    [Pg.164]    [Pg.5]    [Pg.13]    [Pg.20]    [Pg.21]    [Pg.858]    [Pg.189]    [Pg.197]    [Pg.362]   


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Claisen rearrangement reaction

Concerted

Concerted reaction

Concerts

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