Carroll-Claisen

An alternative route to y,5-unsaturated ketones is via the Carroll-Claisen rearrangement, which uses allylic esters of 3-keto acids (which exist mainly in the enol form) as substrates. These are readily prepared by condensation of allylic alcohols with acetoacetic esters or diketene. Following rearrangement, the intermediate keto acid undergoes in situ decarboxylation on heating. 

In an imioortant industrial process, the Carroll reaction , an ahphatic version of the Claisen rearrangement occurs. See if you can find the right mechanism ... 

Claisen and Carroll rearrangements of hydroxyalkenylsilanes provide an asymmetric synthesis of allylsilanes from optically active secondary alcohols39,40. 

The Claisen rearrangement, discovered in 1912, has proven to be a powerful tool for the stereoselective generation of C—C bonds69. It is widely employed in complex multistep syntheses (see, for example, References 86-89) and has inspired many variations, including the Carroll (1940), Eschenmoser (1964), Johnson (1970), Ireland (1972) and Reformatsky-Claisen (1973) reactions69. 

The Carroll rearrangement, a variation on the ester Claisen rearrangement, is a useful method for the preparation of y, 8-unsaturated ketones from allyl acetoacetates, and has been adapted to provide a method for the synthesis of a number of specific arylacetones. Thus, treatment of the p-quinol 1 with diketene and a catalytic amount of DMAP at room temperature gave a 72% yield of the arylacetone 2 together with 5% of the benzofuran 3. 

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... 

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-... 

Related reactions Carroll rearrangement, Claisen-lreland rearrangement, Eschenmoser-Claisen rearrangement, Johnson-Claisen rearrangement ... 

Use of the Claisen rearrangement achieves the same conversion of methylbutenol into methylheptenone as does the Carroll reaction, but without the loss of carbon dioxide.The methanol produced instead can be recovered and recycled. In this process, as shown in Scheme 4.7, methylbutenol is treated with the readily available 2-methoxypropene to give the allyl vinyl ether, which then undergoes a Claisen rearrangement to give methylheptenone. 

CARROLL Rearrangement of Allyl Acetoacetic Esters Thermal condensation of allyl alcohols with ethyl acetoacetate in the presence of a catalyst, with loss of C02 a one pot ester exchange-Claisen-lreland rearrangement with loss of C02 (see 1st edition). 

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. 

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