Claisen-Johnson-Ireland and Oxy-Cope Rearrangements

This method was further improved when it was found that readily available allyl esters of the general formula 493 could also be involved in Claisen rearrangements via intermediate formation of ketene derivatives such as lithium enolates 494 or trimethylsilyl ketene acetals 495 (the Ireland-Claisen variant ). Moreover, rearrangement of these substrates into unsaturated acids 496 occurred easily at room temperature or below. This was in striking contrast to all previous versions of the Claisen rearrangement, which required heating at elevated temperatures (140-160 °C). The Ireland (silyl ketene acetal) variant of 

With these improvements the oxy-Cope rearrangement acquired an almost universal applicability as a powerful transformation of strategic importance. Below are given some typical examples showing the unique synthetic opportunities offered by this method. 

The transformation 505 507 represents a specific case of a general protocol 

2 Transformations of Small Ring Fragments and their Role in a Total Synthesis. Wagner-Meerwein Rearrangement, Fragmentation, 

The synthetic merits of the cycloaddition-rearrangement sequence in the construction of multi-ring frameworks are further illustrated by a concise 

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