Modified Ireland-Claisen rearrangement

Two groups have reported on the use of the Claisen rearrangement to obtain 2,3-unsaturated C-glycosides. Fraser-Reid and colleagues found the standard reaction applied to derivatives of the allylic alcohol (77) inefficient because of the poor yields of the derived vinyl ethers or because allylic esters e.g. (78) predominated. They were successful, however, in obtaining compounds (79) and (80) by modified procedures (Scheme 5). An alternative synthesis of saturated, and hence unsaturated, C-glycosides was developed as illustrated in Scheme 6. In parallel work Ireland and co-workers used the enol silyl ether approach as shown in Scheme 7 and employed the products in polyether antibiotic syntheses. ... 

The Claisen Rearrangements and Their Modified Versions The Carroll, Eschenmoser, Ireland,... 

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