Carroll Variants

Among the most favorable features of the Carroll variant of the Claisen rearrangement are the relative ease of preparation of the parent system by condensation of allylic alcohols with acetoacetic estet or di-ketene and the defined configuration of the intermediately generated double bond. The Carroll rearrange-... 

Since its discovery in 1912, the Claisen rearrangement of allyl vinyl ethers (1 - 2 equation 1) has become one of the most powerful tools for stereoselective carbon-carbon bond formation. Much of its current popularity is due to the subsequent development of a series of new variants of this 3,3-sigma-tropic rearrangement. In 1940, Carroll reported the base-catalyzed rearrangement of -keto esters and allylic alcohols to alkenic ketones (3 4 5 equation 2). Twenty years later. Saucy and Marbet dem-... 

Whereas Eschenmoser and Johnson variants of the Claisen rearrangement utilize an excess of amide acetal and orthoester precursors, respectively, for generation of the vinyl ether functionality, the Carroll... 

The Carroll rearrangement, first reported in 1940210-212, is an old and well-established versatile yet complementary variant of the Claisen rearrangement. The mechanism of this reaction was proposed in 1943 by Kimel and Cope213. With respect to the stereoselectivity, the most favorable feature of the Carroll rearrangement is the defined configuration of the double bond generated in the intermediate hydrogen-bonded enol. 

Furthermore, unlike its thermal variant, the Pd-catalyzed Carroll rearrangement does not involve the enolate of the /3-dicarbonyl, as evidenced by the ready rearrangement of the /3,/3-dialkyl substrate 30 (Scheme 15) in the presence of Pd (note that this reaction does not occur under thermal conditions).f" f" ... 

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