Claisen rearrangement Ireland modification

The Ireland variation is, without doubt, the most important method among the variants of the Claisen rearrangement. The modification consists of the rearrangement of an allyl ester in the form of an ester enolate or silyl ketene acetal to give a y.d-unsaturated acid40 41-80,87 88. 

As with the Claisen Rearrangement, the Ireland modification also proceeds with a high degree of stereoselectivity ... 

The Ireland modification utilizes silyl ketene acetals derived from allyl ester eno-lates and provides a general method to effect stereocontrolled Claisen rearrangements under mild conditions, making it possible to apply the reaction to acid-sensitive and thermally labile substrates. Moreover, by proper choice of the reaction conditions, one can control the geometry of the enol ethers and hence the stereochemistry of the new C-C bond that is produced in the rearrangement step." ... 

Most [3,3]-sigmatropic rearrangements take place thermally, and the Cope, oxy-Cope and Claisen rearrangements are among the most important rearrangements in this class. Important variants of the Claisen rearrangement include the Johnson modification via orthoesters, the Eschenmoser modification via ketene N,O-acetals, the Ireland modification via ketene silylacetals and the Corey modification via boron ester enolates [696], The aza-Claisen rearrangement has also seen... 

Hunsdiecker Reaction Hydroboration Reaction Hydroformylation Reaction Ireland-Claisen Rearrangement Irvine-Purdie Methylation Isler Modification Ivanov Reaction... 

Ireland and co-workers, in their synthesis of the prostanoid skeleton, have described the use of the ester enolate modification of the aliphatic Claisen rearrangement to produce the cyclopentane ring C-8—C-12 bond, viz. (74) ->(75). Conversion of the silyl ester (75) into the lactone (76), with a trace of acid, followed by reduction with DIBAL and aldol cyclization, then led to the prostanoid (77) (Scheme 20). 

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