- Carroll rearrangement
The Carroll rearrangement is a
rearrangement reaction inorganic chemistry and involves the transformation of a β-ketoallyl 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.] Thisorganic reaction is accompanied bydecarboxylation and the final product is a γ,δ-allylketone. The Carrol rearrangement is an adaptation of theClaisen 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 electrocyclicClaisen rearrangement . The follow up is a decarboxylation. With palladium(0) as acatalyst , the reaction (Tsuji, 1980) is much milder (path B) with an intermediate allyl cation / carboxylic acid anionorganometallic 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 andJiro 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 DaiAngew. 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 theTrost ligand "Asymmetric Allylic Alkylation of Ketone Enolates: An Asymmetric Claisen Surrogate" Erin C. Burger and Jon A. TungeOrg. 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 theacetamido 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. StoltzAngew. Chem. Int. Ed. 2005, 44, 6924 –6927 DOI|10.1002/anie.200502018] :The scope is extended to asymmetric α-alkylation of
ketone s masked as their enolcarbonate ester s ["Palladium-Catalyzed Asymmetric Allylic α-Alkylation of Acyclic Ketones"Barry M. Trost and Jiayi XuJ. Am. Chem. Soc. ; 2005; 127(49) pp 17180 - 17181; (Communication) DOI|10.1021/ja055968f] :References
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