2,3-Wittig rearrangements 3.3- Claisen rearrangement

Sequential [2,3]-Wittig and Claisen rearrangements provide an effective synthesis of ,E-alka-4,7-dienoic acids, esters, or aldehydes depending on the type of Claisen rearrangement employed (Scheme 16). ... 

The retron for the Claisen rearrangement transform (see above) is easily established by the application of a Wittig disconnection at each of the equivalent terminal double bonds of 57... 

Isomerization of vinylaziridines is widely used in organic synthesis. Six types of isomerization of vinylaziridines are shown in Scheme 2.40. Outlined in this section are i) azepine formation by aza-[3,3]-Claisen rearrangement of 1,2-divinyl- or 2,3-divinylaziridines 153 (Section 2.4.1), ii) pyrroline formation from 155 (Section 2.4.2), Hi) aza-[2,3]-Wittig rearrangement of anionic species 157 (Section 2.4.3),... 

The aza-[2,3]-Wittig rearrangement [47] and the related aza-[3,3]-Claisen rearrangement [48] of vinylaziridines are elegant examples of expansion of the aziridine ring in a stereocontrolled fashion (Scheme 38). 

A combination of a Claisen rearrangement, a Wittig rearrangement and a Wittig reaction was described by Mali and coworkers for the synthesis of 6-prenylcou-marins. In these transformations, 2-prenyloxybenzaldehydes was employed as substrate [105]. 

A solvent-free synthesis of benzo[b]furan derivatives 10-79, a class of compounds which is often found in physiologically active natural products, was described by Shanthan Rao and coworkers. These authors heated phosphorane 10-71 for 8 min in a microwave oven and obtained the benzo[b]furan 10-74 in 73% yield (Scheme 10.18) [25]. The sequence is initiated by an intramolecular Wittig reaction, providing alkyne 10-72 this underwent a subsequent Claisen rearrangement to give the intermediate 10-73. Also in this case, normal oil-bath heating gave much lower yields (5%) of the desired product the authors hypothesize that the micro-... 

X.J. Wang, S.A. Hart, B. Xu, M.D. Mason, J.R. Goodell, F.A. Etzkorn, Serine-c/s-proline and Serine-frans-proline isosteres Stereoselective synthesis of (Z)- and ( )-alkene mimics by still-wittig and ireland-claisen rearrangements, J. Org. Chem. 

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). 

A well-developed concept to achieve high stereocontrol in the formation of a quaternary chiral center has been introduced by Fraser-Reid, using the Claisen rearrangement along two lines. In the first approach a type III branched-chain sugar is prepared by Wittig... 

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... 

Naturally occurring 6-prenylcoumarins have been synthesised from 2-prenyloxy-benzaldehydes through tandem Wittig reaction and Claisen rearrangement. Several of the... 

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