Claisen rearrangements with Wittig rearrangement

Chiral Substrates with Other Achiral Reagents Diastereoselective Claisen Rearrangement and Wittig Reactions... 

Ireland-Claisen rearrangement as an alternative approach to the syn isomer with a high degree of diastereoselectivity was also examined. This reaction might be similar to the system of ester-enolate [2,3]-Wittig shift in the case of OR (R=protective group). 

S ily 1) ally lie ethers 234 readily undergo 2,3-Wittig rearrangement upon treatment with an amide base to give, after methylation, 235 (equation 192)37,343. Tandem Claisen-2,3-Wittig-oxy-Cope rearrangement has been observed when 236 is treated under similar... 

The allylic halide needed for the alkylation is easily made by some aldol or Wittig-style reaction to give 63 followed by reduction and conversion of OH to Br. Alkylation of phenols (p a 10) with allylic halides is very easy as a weak base such as carbonate is enough and the Claisen rearrangement merely requires heating.15... 

Other Uses. Reagent 1 has been used for enantioselec-tive enolborination, albeit with poor (1.1 1) selectivity. Similar bis-sulfonamide-derived boron Lewis acids have been used for aldol additions, "" ester-Mannich reactions, Diels-Alder reactions, Ireland-Claisen reactions, and [2,3]-Wittig rearrangements. Similar bis-sulfonamide-derived aluminum Lewis acids have been used for aldol additions, Ehels-Alder... 

Synthesis of trifluoromethylated compounds 152 has been achieved via ester-enolate [2,3]-Wittig and [3,3]-lreland-Claisen rearrangements. Perfluorocyclo-butane phosphonium ylides, e.g. 153, have been used as a masked fluoride anion source in their reactions with alcohols and carboxylic acids which lead to alkyl-and acyl-fluorides. Ylides 153 are also reported to cleave Si-C and Si-O bonds, cause dimerisation of fluoro-olefins, and also react with acid chlorides or other activated aromatic compounds under halogen exchange. ... 

Along with the Claisen rearrangement, other related reactions are applicable for the preparation of natural products. For instance a [2.3]-Wittig reaiTangement is one step in the stereospecific synthesis of HMG-CoA reductase inhibitor pravastatin and in the total synthesis of the HMG-CoA synthase inhibitor 1233A according to the general scheme (equation 253). 

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