Tebbe-Claisen rearrangement

The asymmetric total synthesis of the putative structure of the cytotoxic diterpenoid (-)-sclerophytin A was realized via a Tebbe-Claisen rearrangement of a tricyclic lactone precursor in the laboratory of L.A. Paquette/ The tricyclic lactone was subjected to the Tebbe methylenation protocol to provide the allyl vinyl ether that was then heated to 130-140 °C in p-cymene to undergo the Claisen rearrangement in good yield. 

The opening move was the transformation of the known glucopyranoside 355 into exomethylene vinylpyranose 356. TIBAL-promoted Claisen rearrangement of 356 provided the cyclooctene derivative 357 almost quantitatively, which was then transformed to protected cyclooctanose 358 by methylation followed by hydroboration-oxidation. Installation of the hydroxymethyl function at C5 required three further operations oxidation of the Cs-hydroxyl, Tebbe methylenation, and hydroboration-oxidation. In the event, a mixture of epimeric... 

Recently, Claisen rearrangement of allyl-vinyl ether prepared from glycal ester with Tebbe reagent was reported [91]. In contrast to the Ireland-Claisen rearrangement, in principle, a non-enolizable ester can be employed (O Scheme 63). This method was applied for the synthesis of C-disaccharide. 

The enantioselective total synthesis of the cyclooctanoid natural product (+)-epoxydictymene was accomplished in the laboratory of L.A. Paquette. The entire tricyclic framework was constructed by the application of a Claisen rerrangement via a chairlike transition state. The precursor for this / 3,37-sigmatropic rearrangement was obtained by treating a lactone precursor with the solution of the Tebbe reagent in the presence of pyridine. The corresponding enol ether was formed in almost quantitative yield, and immediately after isolation it was treated with triisobutylaluminum to effect the Claisen rearrangement. 

Chlorodimethylaluminum (generated from the methylenation reagent) is presumed to be the catalyst in the one-pot Tebbe methylenation -Claisen rearrangement procedure. This process proceeds with 98% E selectivity17s. 

Ester 155 was converted by the Tebbe method to the methylene analogue (92%) which underwent Claisen rearrangement to give the C-linked uronic add derivative 156 (56%). ... 

Using double Tebbe methylenation (77 to 78) followed by a Claisen rearrangement, Paquette and co-workers developed a concise, reliable, and efficient scheme for 4-cyclooctenones. Using this methodology, Paquette reported an alternate enantioselective route to a key bicyclic intermediate,... 

SCHEME 9.5 Fairbanks s approach to a-(l-6)-C-disaccharides by tandem the Tebbe methylenation and Claisen rearrangement. 

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