Allyl ester enolates Claisen rearrangement

This effect is the basis of the synthetic importance of ester enolate Claisen rearrangements in which enolates or silyl enol ethers of allylic esters are rearranged into 4-pentenoate esters. 

When ethyl trifluoroacetylacetate is treated with an allylic alkoxide, tran-sesterification is followed by ester enolate Claisen rearrangement m a process that on decarboxylation yields stereospecifically the tnfluoromethyl ketone product [22] (equation 19)... 

The full paper on the synthesis of onikulactone and mitsugashiwalactone (Vol. 7, p. 24) has been published.Whitesell reports two further useful sequences (cf. Vol. 7, p. 26) from accessible bicyclo[3,3,0]octanes which may lead to iridoids (123 X=H2, Y = H) may be converted into (124) via (123 X = H2, Y = C02Me), the product of ester enolate Claisen rearrangement of the derived allylic alcohol and oxidative decarboxylation/ whereas (123 X = 0, Y = H) readily leads to (125), a known derivative of antirride (126) via an alkylation-dehydration-epoxi-dation-rearrangement sequence. Aucubigenin (121 X = OH, R = H), which is stable at —20°C and readily obtained by enzymic hydrolysis of aucubin (121 X = OH, R = j8-Glu), is converted by mild acid into (127) ° with no dialdehyde detected sodium borohydride reduction of aucubigenin yields the non-naturally occurring isoeucommiol (128 X=H,OH) probably via the aldehyde (128 X = O). ... 

The chelated ester enolate Claisen rearrangement of allylic glycinates 9 is carried out with zinc(II) chloride, which is added to the enolate at — 78 C (Table 19). The rearrangement occurs as the reaction mixture is allowed to warm to room temperature over 1 hour. The 2-amino-3,3-difluoro-4-[(2-methoxyethoxy)methoxy] alk-4-enoic acids 10 arc converted directly into the corresponding methyl esters, which can be hydrolyzed to the methyl 2-amino-3,3-difluoro-4-oxoal-kanoates. 

Table 19. Synthesis of 2-Amino-3,3-difluoro-4-[(2-methoxyethoxy)meth-oxy]alk-4-cnoic Acids 10 by the Chelated Ester Enolate Claisen Rearrangement of Allylic Glycinates 943...

Kazmaier, U. Synthesis of y,5-unsaturated amino acids via ester enolate Claisen rearrangement of chelated allylic esters. Amino Acids... 

Scheme4.23 Asymmetric ester enolate Claisen rearrangement of (N)-trifluoroacetyl-glycine allylic esters.

Diastereoselective control during enolization of allyl esters for Claisen rearrangement leads to predefined stereomers, and amide bases such as enantiomeric 189 are capable of generating chiral products. ... 

Other donor substituents, e.g., trimethylsilyloxy, at C(2) are strongly accelerating. This effect is the basis of the synthetic importance of ester enolate Claisen rearrangements, in which enolates or silyl ketene acetals of allylic esters are rearranged into 4-pentenoate esters. This reaction is known as the Ireland-Claisen rearrangement. 

Claisen rearrangement. The ester enolate Claisen rearrangement of allyl esters of protected amino acids proceeds after replacing the lithium ion with Zn. 

An electrochemical oxidative decarboxylation in combination with an ester enolate Claisen rearrangement was reported by Wuts et al. (Scheme 5.2.26) [51]. A variety of allylic esters such as 97 was subjected to an Ireland-Qaisen rearrangement, and the resulting acids (98) obtained were submitted to electrolytic decarboxylation in a divided cell to afford ketals 99. The use of the divided cell was necessary to suppress side reactions such as alkene reduction. 

To expand the scope of the diastereoselective C-C bond formation by the ester enolate Claisen rearrangement, the rearrangement of allylic esters of )S-hydroxy acids is noted to introduce three continuous asymmetric centers. Fujisawa et al. investigated the rearrangement of E- and Z-crotylesters 205 under different reaction conditions [119]. 

Rearrangement of allyl trimethylsilyl ketene acetal, prepared by reaction of allylic ester enolates with trimethylsilyl chloride, to yield Y,5-unsaturated carboxylic a-cids. The Ireland-Claisen rearrangement seems to be advantageous to the other variants of the Claisen rearrangement in terms of E/Z geometry control and mild conditions. 

Chelate enolate Claisen rearrangements of a-amido substituted allylic esters... 

The rearrangement of ester enolates (Ireland rearrangement)36 41 87,88-91-257,292 467-469 derived from allyl esters is perhaps the most flexible Claisen variation, allowing the diasiereo-and enantioselective controlled synthesis of y.fS-unsaturated acids either by a change of the double-bond configuration of the allylic alcohol moiety or variation of the solvent system. 

A synthesis of a-substituted S-unsaturated acids exploits the facile Claisen rearrangement of allyl ester enolates, which can be generated by conjugate addition of organocopper reagents to ally 2-alkenoates. ... 

Amathaspiramide F has also been synthesized by Sakaguchi and coworkers [64, 65], and they started the synthesis by taking a-hydroxy-a-ethynylsilane as a starting material. The key step of the synthesis was enolate Claisen rearrangement. While ( )-amathaspiramide F has been synthesized by Soheili and Tambar [66]. They started the synthesis by taking substituted phenyl allyl carbonate and A-substituted proline ester. 

A novel synthesis of (+)-avenaciolide (341) centres on the stereospecific elaboration of the anti-ester (339) by an enolate Claisen rearrangement of the corresponding ( Z)-allylic glycolate and a highly stereoselective selenolactonization of the derived... 

Historically, as early as 1937, the first enolate Claisen rearrangement, though it was not formally recognized as such, was documented. Tseou and Wang [12] reported the formation of 4-pentenoic acid in low yields on heating neat allyl acetate with sodium metal for 3 h to ca. 100°C while attempting the acetoacetic ester synthesis (Scheme 5.1.1). 

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