The Carroll rearrangement is a

rearrangement reaction In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another at ...

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

and involves the transformation of a β- keto

allyl In organic chemistry, an allyl group is a substituent with the structural formula . It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . In 1844, Theodor Wertheim isolated a ...

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

into a α-allyl-β-ketocarboxylic acid. This

organic reaction Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, mechanistic organ ...

is accompanied by

decarboxylation Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...

and the final product is a γ,δ-allylketone. The Carroll rearrangement is an adaptation of the

Claisen rearrangement The Claisen rearrangement is a powerful carbon–carbon chemical bond, bond-forming chemical reaction discovered by Rainer Ludwig Claisen. The heating of an allyl Vinyl group, vinyl ether will initiate a Sigmatropic reaction, ,3sigmatropic r ...

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 In organic chemistry, enols are a type of functional group or intermediate in organic chemistry containing a group with the formula (R = many substituents). The term ''enol'' is an abbreviation of ''alkenol'', a portmanteau deriving from "-ene ...

which then rearranges in a sigmatropic Claisen rearrangement. The follow-up is a decarboxylation. This rearrangement is used in the conversion of

linalool Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Together with geraniol, nerol, and citronellol, linalool is one of the rose alcohols. Linalool has multiple commercial app ...

to geranylacetone. LinaloolToGeranylacetone

Palladium-catalyzed processes

With

palladium Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...

(0) as a

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

, the reaction (Tsuji, 1980) is much milder (path B) with an intermediate allyl cation / carboxylate

organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

complex.

Decarboxylation precedes allylation as evidenced by this reaction catalyzed by

tetrakis(triphenylphosphine)palladium(0) Tetrakis(triphenylphosphine)palladium(0) (sometimes called quatrotriphenylphosphine palladium) is the chemical compound d(P(C6H5)3)4 often abbreviated Pd( PPh3)4, or rarely PdP4. It is a bright yellow crystalline solid that becomes brown upon d ...

Asymmetric decarboxylative allylation

By introducing suitable chiral ligands, the reaction becomes

enantioselective In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during a non- stereospecific creation of a new stereocenter or during a non-stereospecific transformation o ...

. The first reported asymmetric rearrangement is catalyzed by

tris(dibenzylideneacetone)dipalladium(0) Tris(dibenzylideneacetone)dipalladium(0) or d2(dba)3is an organopalladium compound. The compound is a complex of palladium(0) with dibenzylideneacetone (dba). It is a dark-purple/brown solid, which is modestly soluble in organic solvents. Bec ...

and the

Trost ligand The Trost ligand is a diphosphine used in the palladium- catalyzed Trost asymmetric allylic alkylation. Other C2-symmetric ligands derived from ''trans''-1,2-diaminocyclohexane (DACH) have been developed, such as the (''R'',''R'')-DACH- naphthy ...

:''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) AsymmetricCarrol2005

A similar reaction uses additional

naphthol Naphthol may refer to: * 1-Naphthol 1-Naphthol, or α-naphthol, is an organic compound with the formula . It is a fluorescent white solid. 1-Naphthol differs from its isomer 2-naphthol by the location of the hydroxyl group on the naphthalene ...

This reaction delivers the main

enantiomer In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

with 88%

enantiomeric excess In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a sing ...

. 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: DecarboxylativeAllylation

The scope is extended to asymmetric α-alkylation of

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

s masked as their enol

carbonate ester In organic chemistry, a carbonate ester (organic carbonate or organocarbonate) is an ester of carbonic acid. This functional group consists of a carbonyl group flanked by two alkoxy groups. The general structure of these carbonates is and they a ...

s:''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) DecarboxylativeAllylationTrost2005

References

{{DEFAULTSORT:Carroll rearrangement Rearrangement reactions Palladium Name reactions Allyl complexes