Claisen rearrangement enolate

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)... 

CHCI3, reflux (Ireland ester enolate Claisen rearrangement)... 

Several applications of this methodology are known. For the determination of the relative configuration of the stereocenter and the axial chiral unit of 71, the product of a diastereoselective ester enolate Claisen rearrangement of 70, with AgBF4 a cycli-zation to 72 was initiated. Then the carboxylic acid was reduced to alcohol 73 and the position of the substituents was investigated by NMR and by the use of NMR shift-reagents (Scheme 15.16) [32], Control experiments ensured the stereospecifi-city of the cyclization and the reduction step. There are further examples of this strategy [33]. 

Selective protection of the primary alcohol gave 138 (P=TBDMS), which was then esterified with ( )-3-hexenoic acid to produce the key intermediate 139 for cyclization. Ireland ester-enolate Claisen rearrangement and hydrolysis produced a protected hydroxyacid, which, after reduction of the acid and deprotection of the alcohol, yielded meso diol 128 more quickly and efficiently than in the previous synthesis. The meso diol was then converted to the racemate of the lactol pheromone 130 as previously described. 

In one final improvement to the synthesis of the racemate, after it had been shown that even the unnatural enantiomer of the pheromone attracted bugs, the Z-isomer of diene ester 139 was used in the ester-enolate Claisen rearrangement, resulting in a slightly higher yield, and avoiding the use of HMPA as a solvent in that step [113]. 

It has been shown that the Claisen rearrangement of lithium enolates of amino acid enynol esters allows the synthesis of very sensitive y, 5-unsaturated amino acids with conjugated enyne side chains.The chelate-enolate Claisen rearrangement has also been applied to the synthesis of unsaturated polyhydroxylated amino acids, polyhydroxylated piperidines, and unsaturated peptides. ... 

The stereoselectivity of ester enolate Claisen rearrangements can also be controlled by specific intramolecular interactions.168 169 The enolates of a-alkoxy esters give the Z-silyl derivatives because of chelation by the alkoxy substituent. 

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). ... 

R. E. Ireland and J. P. Vevert, A chiral total synthesis of (—) and (+) nonactic acids from carbohydrate precursors and the definition of the transition for the enolate Claisen rearrangement in heterocyclic systems, J. Org. Chem. 45 4259 (1980). 

Hydroxy-3-tetrahydrofuranols are available by lengthy transformation of sugars and are readily converted into esters which undergo enolate Claisen rearrangement (Scheme... 

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...

The ester enolate Claisen rearrangements of amino acid propargylic esters (106) have been used137 to produce a-allenic amino acids (107), and y, d-un saturated amino acids... 

The method involves a highly enantioselective rearrangement of an epoxide and a subsequent Ireland-Claisen rearrangement (see Scheme 31). The enolate Claisen rearrangements of [4-7- /4-4-(l-acyloxy-2,4,6-octatrienyl)]tricarbonyl iron complexes... 

R. E. Ireland, S. Thaisrivongs, N. Vanier, and C. S. Wilcox, Enolate Claisen rearrangements from furanoid and pyranoid glycals, J. Org. Chem., 45 (1980) 48-61. 

Step b [3,3] sigmatropic shift (ester enolate Claisen rearrangement) via a chair transition state on the sterically more accessible (3-face of the butenolide (B below). 

H.-J. Altenbach, Ester Enolate Claisen Rearrangements , in Organic Synthesis Highlights (J. Mulzer, H.-J. Altenbach, M. Braun, K. Krohn, H.-U. ReiBig, Eds.), VCH, Weinheim, New York, 1991, 116-118. S. Pereira, M. Srebnik, The Ireland-Claisen Rearrangement, AldrichimicaActa 1993, 26, 17-29. 

Stereoselective synthesis of functionalized carbocyclic and heterocyclic compounds via tandem ester enolate Claisen rearrangement/RCM has been reported (Eq.79) [131,132],... 

Ester enolate Claisen rearrangement (4, 307- K)8 6, 276-277 7, 209-210). Lithium hexamethyldisilazide is comparable to LDA in combination with HMPT for stereoselective Claisen rearrangement of ester cnolates. ... 

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