Carroll rearrangement
Carroll rearrangement
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Carroll rearrangement

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Carroll rearrangement

The Carroll rearrangement is a rearrangement reaction in organic chemistry and involves the transformation of a β-keto allyl ester into a α-allyl-β-ketocarboxylic acid. This organic reaction is accompanied by decarboxylation and the final product is a γ,δ-allylketone. The Carroll rearrangement is an adaptation of the Claisen rearrangement and effectively a decarboxylative allylation.

The Carroll rearrangement (1940) in the presence of base and with high reaction temperature (path A) takes place through an intermediate enol which then rearranges in a sigmatropic Claisen rearrangement. The follow-up is a decarboxylation. This rearrangement is used in the conversion of linalool to geranylacetone.

With palladium(0) as a catalyst, the reaction (Tsuji, 1980) is much milder (path B) with an intermediate allyl cation / carboxylate organometallic complex.

Decarboxylation precedes allylation as evidenced by this reaction catalyzed by tetrakis(triphenylphosphine)palladium(0):

By introducing suitable chiral ligands, the reaction becomes enantioselective.

The first reported asymmetric rearrangement is catalyzed by tris(dibenzylideneacetone)dipalladium(0) and the Trost ligand:

A similar reaction uses additional naphthol.

This reaction delivers the main enantiomer with 88% enantiomeric excess. It remains to be seen if this reaction will have a wide scope because the acetamido group appears to be a prerequisite.

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