Subject Claisen rearrangement

Enolates of allyl esters of a-amino acids are also subject to chelation-controlled Claisen rearrangement.249... 

The ester 7-1 gives alternative stereoisomers when subjected to Claisen rearrangement as the lithium enolate or as the silyl ketene acetal. Analyze the respective transition structures and develop a rationale to explain these results. 

CYCLOHEXEN-l-ONE. Importantly, only 1.6 equivalents of Ag20 are required for efficient coupling. The final preparation in this series illustrates the hydrosilation of racemic 3-butyn-2-ol catalyzed by a phosphine based platinum(O) catalyst. The resultant racemic (E)-vinylsilane is then resolved with a commercially available lipase and subjected to a Johnson ortho ester Claisen rearrangement to afford [3R- AND 3S-]-(4E)-METHYL... 

This section will focus on recent examples of asymmetric [3,3]-sigmatropic rearrangements involving dienes and polyenes. Attention will be given to Cope and Claisen rearrangements, as well as to several of their variants. For more exhaustive reviews of the subject, the reader is referred elsewhere69,70. 

Desmethylindolactam G (50, R=H, replace zPr by H) was subjected to the same sequence (50 54). The first allylation step succeeded with 52% yield, but the aza-Claisen rearrangement/cationic cyclization gave only 9.5% of the product mixture 52-54 (replace /Pr by H). 

These ideas will be discussed in the following subsections, where most of the attention will be devoted to the mechanistic smdies with aromatic esters, which have been the subject of an overwhelming majority of the research efforts. Nevertheless, the same reaction mechanism has been shown to be valid for the PFR of anilides, thioesters, sulfonates, and so forth. Furthermore, it is also applicable to the photo-Claisen rearrangement [i.e. the migration of alkyl (or allyl, benzyl, aryl,)] groups of aromatic ethers to the ortho and para positions of the aromatic ring [21,22]. 

Schkeryantz and Pearson (59) reported a total synthesis of ( )-crinane (298) using an intramolecular azide-alkene cycloaddition (Scheme 9.59). The allylic acetate 294 was first subjected to an Ireland-Claisen rearrangement followed by reduction to give alcohol 295, which was then converted into the azide 296 using Mitsunobu conditions. Intramolecular cycloaddition of the azide 296 in refluxing toluene followed by extrusion of nitrogen gave the imine 297 in quantitative yield. On reduction with sodium cyanoborohydride and subsequent reaction with... 

Thus, ketose 361 was first methylated and then subjected to a three step transformation including desilylation followed by iodination and hydride-promoted HI elimination. This furnished vinyl ketoside 362 whose treatment with excess of TIBAL ensured smooth Claisen rearrangement to afford cyclooctenic carbocycle 363 in excellent yield. 

A solution of the silylketene acetal 4 in dodecane was subjected to thermolysis at 200 C for 140 minutes. The Cope-Claisen rearrangement product 5 was then treated with KF in HMPA followed by esterification to afford the methyl ester 6. 

In a related study, the enolate of cyano ketone 198 was O-allylated and subjected to Claisen rearrangement (Scheme 31). The allyl group migrated only to the exo face... 

Cope and Claisen rearrangements are the [3,3]-sigmatropic rearrangements and are among the most commonly used sigmatropic reactions. They have been the subject of numerous... 

Oxopentanals may be synthesized from allylic alcohols by 3,3-sigmatropic rearrangement of their vinyl ethers, and subsequent oxidation of the terminal double bond. ° Cinnamyl alcohol (31) was converted to the allyl vinyl ether (32), which was subjected to Claisen rearrangement to give 3-phenyl-4-pentenal (33) in 30% yield. Oxidation of the terminal double bond of (33) gave 3-phenyl-4-oxopentanal (34) in 76% yield, which was converted to 2-methyl-3-phenylfuran (35) in quantitative yield (Scheme 9). 

This review aims to siunmarize and update the various roles exerted by sulfur-containing fimctionaUties in [3,3]-sigmatropic rearrangements. Some of the subject matter discussed herein has been reviewed before [1-5], therefore, we have made an effort to discuss in depth just the more recent results, as well as mechanistically related transformations that were not included in previous reviews on Claisen and thio-Claisen rearrangements. 

The palladium(0)-catalyzed asymmetric O-allylation of phenols has been described using five-, six- and seven-membered ring allylic carbonates and acyclic allylic carbonates (eq 9). The products from these reactions were subjected to a Claisen rearrangement to provide C-alkylated phenols. A study of various ligands for the reaction of phenol with 2-cyclohexenyl-l-methyl carbonate clearly showed that the Trost ligand is superior. ... 

Cyclic 1,2-diketones, such as3-methylcyclopentane-l,2-dione, act as oxygen nucleophiles in palladium(0)-catalyzed reactions with a range of cyclic and acyclic allylic esters. The products of these reactions were subjected to a lanthanide-catalyzed Claisen rearrangement to access the C-alkylated products. 

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