:Carroll rearrangement
{{Short description|Chemical reaction}}
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.Carroll, 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". Journal of the Chemical Society 1940, 704–706. {{doi|10.1039/JR9400000704}} 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.{{citation | editor=Arza Seidel|display-editors=etal| author=Charles S. Sell | chapter=Terpenoids | title=Kirk-Othmer Chemical Technology of Cosmetics | year=2013 | pages=247–374|publisher=John Wiley & Sons | isbn=978-1-118-40692-2}}
Palladium-catalyzed processes
With palladium(0) as a catalyst, the reaction (Tsuji, 1980) is much milder (path B) with an intermediate allyl cation / carboxylate 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}}
File:Carrol_rearrangement_reaction_mechanism.png
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 reactionKuwano, R.; Ishida N.; Murakami, M. "Asymmetric Carroll rearrangement of allyl α-acetamido-β-ketocarboxylates catalysed by a chiral palladium complex". Chemical Communications 2005, (31), 3951–3952. {{doi|10.1039/b505105c}} uses additional naphthol.
File:AsymmetricCarrolRearrangement.png
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: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}}
File:DecarboxylativeAllylation.png
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|authpr=Barry M. Trost and Jiayi Xu
J. Am. Chem. Soc.; 2005; 127(49) pp 17180 - 17181; (Communication) {{doi|10.1021/ja055968f}}
References
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{{Organic reactions}}
{{DEFAULTSORT:Carroll rearrangement}}