Eschenmoser-Claisen

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. 

Eschenmoser reagent 784 Eschenmoser coupling -.oxidative 102 Eschenmoser sulfide contraction 102, 117ff 122, 474, 478 -.alkylative 119 -.oxidative 119 Eschenmoser-Claisen rearrangement 605 ff., 617 f.. estrone 153 ff. 

Sigmatropic rearrangement of A, 0-ketene acetals to yield Y,5-unsaturated amides. Since Eschenmoser was inspired by Meerwein s observations on the interchange of amide, the Eschenmoser-Claisen rearrangement is sometimes known as the Meerwein-Eschenmoser-Claisen rearrangement. 

D-Mannitol (63) has been used for the synthesis of y-butyrolactones, making again use of a Claisen rearrangement as the key step (Scheme 10). The C2-symmetrical 1,4-diol 65, obtained from 63 via the alkene 64 [28], could be converted to 67 by applying the Eschenmoser-Claisen variant. Cyclization to 68 was readily achieved upon heating 67 in xylene, establishing two differ-... 

Chirality transfer also belongs to this class of methods. Thus, the configuration of (S)-(E)-Ar,jV-dimethyl-3-trimethylsilyl-4-hexenamide [(S)-(Zi)-2 on p 422] was solely assigned81 on the basis of the established stereochemistry of the Eschenmoser Claisen rearrangement (see P 475). 

Claisen-Eschenmoser Reaction (Eschenmoser-Claisen Rearrangement) Amides are produced after rearrangement with heating. 

A. E. Wick, D. Felix, K. Steen, and A. Eschenmoser, Claisen sche umlagerungen bei allyl- und benzylalkoholen mit hilfe von acetalen des A((V-dimethylacetamids, Helv. Chim. Acta 47 2425 (1964). 

FIuoroaHylic alcohols 1 are converted via the Eschenmoser Claisen rearrangement into the... 

Chiral 3-(trifluoromethyl)alk-4-enamides 4 can be prepared in the highly stereoselective Eschenmoser-Claisen rearrangement of chiral allylic alcohols 3 (Table 23).35 The. E-isomers of allylic alcohols 3 give 100% chirality transfer and slightly higher yields than the Z-isomers. 

Table 23. Synthesis of Chiral /V,V-DimethyI-3-(trifluoromcthyl)alk-4-en-amidcs 4 by Eschenmoser-Claisen Rearrangement35...

Table 24. Synthesis of 2-Fluoro-3-methylpent-4-enamides 7 by Eschenmoser-Claisen Rearrangement 4...

In an attempt to achieve an enantioselective Eschenmoser-Claisen rearrangement with amide salts 6, (2R,5R)-l-(fluoroacetyl)-2,5-dimethylpyrrolidine was methylated to give chiral 6d. 5 Reaction of 6d with the lithium salt of (fj-crotyl alcohol gives amide 7d as a mixture of diastereomers, in which the. vj rt-isomers predominate. 

Figure 8.6 Preparation of enantiomeric forms of dimethylalkanes with 1,4-branching patterns, via stereoselective Eschenmoser-Claisen rearrangements.

The Claisen rearrangements of allyl vinyl ethers yield y, 8-unsaturated carbonyl compounds. When R = NR2 the rearrangement is known as the Eschenmoser-Claisen... 

NR2 Eschenmoser-Claisen rearrangement R" = OR Johnson-Claisen rearrangement... 

Geminal Doubly Branched-Chain Sugars by Eschenmoser-Claisen Rearrangement 1157 ... 

The reaction outlined in O Scheme 59 is an example of a variant of the Claisen rearrangement of allyl ketene aminal (so-called Eschenmoser-Claisen rearrangement) [87], The reaction dose not require an acid catalyst glycal was just heated with dimethylacetamide dimethyl acetal to form ketene aminal, which underwent the sigmatropic rearrangement to form the corresponding )/,5-unsaturated amide. 

During the asymmetric total synthesis of (+)-pravastatin by A.R. Daniewski et al., one of the stereocenters was introduced with the Eschenmoser-Claisen rearrangement. The tertiary alcohol intermediate was heated in neat N,N-dimethylacetamide dimethyl acetal at 130 °C for 48h, during which time the by-product methanol was distilled out of the reaction mixture to afford the desired amide in 92% yield. 

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