Claisen process

Neier and coworkers have used a domino Diels-Alder/Ireland-Claisen process for the synthesis of (rac)-juvabione 4-46 and (rac)-epijuvabione [15]. Since neither the Diels-Alder reaction of the acetal 4-44 and methyl acrylate nor the sigmatropic rearrangement seemed to be stereoselective, these authors obtained the cyclohexene derivative 4-45 as a mixture of three diastereomers (Scheme 4.9). 

In the above examples, in spite of the allyhc nature of the starting sulfoxides, the [2,3]-sigmatropic rearrangement does not interfere with the thio-Claisen process, hi this context, the group of Majiundar recently found contradicting results (Scheme 5). These authors examined the thermally pro-... 

Allylation of the 2,3-Wittig products (167) leads to diallylic ethers (171) in which one of the allylic double bonds is part of a 1,5-diene system. These ethers undergo 3,3-oxy-Cope rearrangement to afford vinyl allyl ethers (170), which rearrange in situ by a 3,3-Claisen process to yield the ( )-dienals (169). Some typical results are summarized in Table 14. The cyclopentanols (175) were shown to arise from aldehydes (169) by an intramolecular thermal ene reaction. ... 

As the last step in the tandem Cope-Claisen rearrangement is the irreversible Claisen process, any unfavorable Cope equilibrium should be transposed to the tandem products. Thus, vinyl ether 1 is channeled to aldehyde 3 containing a less highly substituted double bond by such a Cope-Claisen process1165. 

Thio-Claisen and aza-Claisen examples. Aza-Claisen process can be subdivided into zwitterionic aza-Claisen, amide enolate Claisen,... 

One of the traditional methods for applications of the aliphatic Claisen rearrangement has used Mercuric salts to prepare vinyl ether as illustrated in the use of the allylic alcohol (28) en route to aldehyde 29. The chemical development group at Boehringer-Ingelheim has developd a mild palladium acetate-phenanthroline catalyst 31 for the sequential allyl vinyl ether-Claisen process utilizing commercially available triethyleneglycol divinyl ether which avoids the use of mercuric acetate. ... 

Recently, Jacobson reported an organocatalytic version of the Claisen process where guadinium derivative 95 efficiently promoted the reaction of 94 to generate ketoester 96 with high enantioselectivity... 

The Meerwein-Eschenmoser Claisen rearrangement is a variant of the Claisen process which is described by the thermal rearrangement of ketene... 

To cite at least one example of an a2a-Claisen process we choose the ketene adduct 218, which combines important mechanistic aspects with remarkable preparative value. 

In both cases, very good yields went along with excellent selectivity. In a very simple approach to divert a 3,3-sigmatropic Claisen process into a 2,3-Wittig rearrangement, the carbonyl group of 401 was replaced by its dimethylhydrazone (see 404). 

You will have noted that the conditions of the Claisen condensation, ester plus alkoxide in alcohol, are identical to those used in base-catalyzed transesterifications (Section 20-4). Why, then, did we not see condensation products in such ester exchanges The answer is that transesterilication is much faster than the Claisen process (see step 1 above). Indeed, in order to avoid product mixtures, the latter always employs alkoxides that are identical to that in the ester function, in this way relegating transesterilication to a nonproductive background transformation. 

The mechanism of addition of allylzinc reagents to vinylmetallics (including vinyllithium) has been probed using DFT calculations with both the metallo-ene and metallo-Claisen processes being studied. Finally, an ab initio analysis of the structures of lithium and sodium pentadienyl points to the stability of a U-shaped structure which maximises metal centre coordination. ... 

These results differ considerably from those obtained by Lubineau reactions. In the Lubineau series, a Knoevenagel condensation followed by an oxa-Michael/intermolecular retro-Claisen process is proposed. As a result of the Lubineau sequence, the loss of an acetate-fragment occurs in reactions with acetylacetone. 

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