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. [Carrol, M. F. "131. Addition of α,β-unsaturated alcohols to the active methylene group. Part I. The action of ethyl acetoacetate on linalool and geraniol". "J. Chem. Soc." 1940, 704–706. doi|10.1039/JR9400000704.] This organic reaction is accompanied by decarboxylation and the final product is a γ,δ-allylketone. The Carrol rearrangement is an adaptation of the Claisen rearrangement and effectively a decarboxylative Allylation.

Reaction mechanism

The Carrol rearrangement (1940) in the presence of base and with high reaction temperature (path A) takes place through an intermediate enol which then rearranges in an electrocyclic Claisen rearrangement. The follow up is a decarboxylation. With palladium(0) as a catalyst, the reaction (Tsuji, 1980) is much milder (path B) with an intermediate allyl cation / carboxylic acid anion organometallic complex ["Palladium-catalyzed rearrangement of allylic esters of acetoacetic acid to give γ,δ-unsaturated methyl ketones" Tetrahedron Letters, Volume 21, Issue 33, 1980, Pages 3199-3202 Isao Shimizu, Toshiro Yamada and Jiro Tsuji doi|10.1016/S0040-4039(00)77444-2] .

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 ["Enantioselective Palladium-Catalyzed Decarboxylative Allylic Alkylations" Shu-Li You and Li-Xin Dai Angew. Chem. Int. Ed. 2006, 45, 5246 – 5248 DOI|10.1002/anie.200601889] .

The first reported asymmetric rearrangement is catalyzed by tris(dibenzylideneacetone)dipalladium(0) and the Trost ligand "Asymmetric Allylic Alkylation of Ketone Enolates: An Asymmetric Claisen Surrogate" Erin C. Burger and Jon A. Tunge Org. Lett.; 2004; 6(22) pp 4113 - 4115; (Letter) DOI|10.1021/ol048149t] :

A similar reaction [Kuwano, R.; Ishida N.; Murakami, M. "Asymmetric Carroll rearrangement of allyl α-acetamido-β-ketocarboxylates catalysed by a chiral palladium complex". "Chem. Commun." 2005, (31), 3951–3952. doi|10.1039/b505105c.] uses additional naphthol.

This reaction delivers one enantiomer with 88% ee. 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 ["Deracemization of Quaternary Stereocenters by Pd-Catalyzed Enantioconvergent Decarboxylative Allylation of Racemic b-Ketoesters" Justin T. Mohr, Douglas C. Behenna, Andrew M. Harned, and Brian M. Stoltz Angew. Chem. Int. Ed. 2005, 44, 6924 –6927 DOI|10.1002/anie.200502018] :

The scope is extended to asymmetric α-alkylation of ketones masked as their enol carbonate esters ["Palladium-Catalyzed Asymmetric Allylic α-Alkylation of Acyclic Ketones" Barry M. Trost and Jiayi Xu
J. Am. Chem. Soc.; 2005; 127(49) pp 17180 - 17181; (Communication) DOI|10.1021/ja055968f
] :


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