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 in the presence of base and with high reaction temperature 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.
Palladium-catalyzed processes
With palladium as a catalyst, the reaction is much milder with an intermediate allyl cation / carboxylate organometallic complex.Decarboxylation precedes allylation as evidenced by this reaction catalyzed by tetrakis(triphenylphosphine)palladium(0):
Asymmetric decarboxylative allylation
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.
The same catalyst but a different ligand is employed in this enantioconvergent reaction:
The scope is extended to asymmetric α-alkylation of ketones masked as their enol carbonate esters: