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16-September-2008 16:20:31 - Nucleophilic conjugate addition Redirected from Conjugate addition Nucleophilic conjugate addition Nucleophilic conjugate addition Nucleophilic conjugate addition is a type of organic reaction. Ordinary nucleophilic additions or 1,2-nucleophilic additions deal mostly with additions to carbonyl compounds. Simple alkene compounds do not show 1,2 reactivity due to lack of polarity, unless the alkene is activated with special substituents. With α,β-unsaturated carbonyl compounds such as cyclohexenone it can be deduced from resonance structures that the β position is an electrophilic site which can react with a nucleophile. The negative charge in these structures is stored in as an alkoxide anion. Such a nucleophilic addition is called a nucleophilic conjugate addition or 1,4-nucleophilic addition. The most important actived alkenes are the aforementioned conjugated carbonyls and acrylonitriles. Contents 1 Reaction mechanism 2 Reactions 3 Scope 4 Toxicology 5 References Reaction mechanism A nucleophile reacts with a α,β-unsaturated carbonyl compound in the β position. The negative charge carried by the nucleophile is now delocalized in the alkoxide anion and the α carbon carbanion by resonance. Protonation leads through Keto-enol tautomerism to the saturated carbonyl compound. Reactions Conjugated carbonyls react with secondary amines to form 1,4-keto-amines. For example the conjugate addition of methylamine to 2-cyclohexenone gives the compound 3-N-methylamino-cyclohexanone. Conjugated carbonyls react with hydrogen cyanide to 1,4-keto-nitriles. In the Nagata reaction the cyanide source is diethylaluminum cyanide. The Gilman reagent is an effective nucleophile for 1,4-additions to conjugated carbonyls. The Michael reaction involves conjugate additions of enolates to conjugated carbonyls. The Stork enamine reaction involves the conjugate addition of enamines to conjugated carbonyls. Scope Conjugate addition is effective in the formation of new carbon-carbon bonds with the aid of organometallic reagents such as the organo zinc iodide reaction with methylvinylketone.1 4R',5R'-5-5-Ethyl-2,2-dimethyl-1,3-dioxolan-4-yl -pentan-2-one An example of an asymmetric synthesis by conjugate addition is the synthesis of R-3-phenyl-cyclohexanone from cyclohexenone, phenylboronic acid, a rhodium acac catalyst and the chiral ligand BINAP.2 :R-3-phenyl-cyclohanone In another example of asymmetric synthesis the α,β-unsaturated carbonyl compound first reacts with a chiral imidazolidinone catalyst and chiral auxiliary to an iminium compound in an alkylimino-de-oxo-bisubstitution which then reacts enantioselective with the furan nucleophile. The immediate reaction product is an nucleophilic enamine and the reaction cascades with abstraction of chlorine from a chlorinated quinone. After removal of the amine catalyst the ketone is effectively functionalized with a nucleophile and an electrophile with syn:anti ratio of 8:1 and 97% enantiomeric excess.3 Enantioselective Organo Cascade Catalysis This principle is also applied in an enantioselective multicomponent domino conjugated Addition of nucleophilic thiols such as benzyl mercaptan and electrophilic DEAD.4 Enantioselective Conjugated Addition of Thiols to ,Unsaturated Aldehydes Toxicology Suitably soluble Michael acceptors are toxic, because they alkylate DNA by conjugate addition. Such modification induces mutations, which are cytotoxic and carcinogenic. However, glutathione is also able to react with them and for example dimethyl fumarate reacts with it. References ^ Asymmetric Synthesis of exo-Isobrevicomin and exo-Brevicomin via Conjugated Addition of Primary Alkyl Iodides to a, b-Unsaturated Ketones Andréa L. de Sousa and Inês S. Resck J. Braz. Chem. Soc. vol.13 no.2 São Paulo 2002 Online Article ^ R-3-phenyl-cyclohanone Tamio Hayashi, Makoto Takahashi, Yoshiaki Takaya, and Masamichi Ogasawara Organic Syntheses, Coll. Vol. 10, p.609 2004; Vol. 79, p.84 2002. Online article ^ Enantioselective Organo-Cascade Catalysis Yong Huang, Abbas M. Walji, Catharine H. Larsen, and David W. C. MacMillan J. Am. Chem. Soc.; 2005; 12743 pp 15051 - 15053; Communication DOI: 10.1021/ja055545d Abstract ^ Asymmetric Multicomponent Domino Reactions and Highly Enantioselective Conjugated Addition of Thiols to ,α,β-Unsaturated AldehydesMauro Marigo, Tobias Schulte, Johan Franzén, and Karl Anker Jorgensen J. Am. Chem. Soc.; 2005; 12745 pp 15710 - 15711; Communication DOI: 10.1021/ja055291 Abstract Retrieved from http://en..org/wiki/Nucleophilic_conjugate_addition Categories: Addition reactions Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Español This page was last modified on 2 August 2008, at 11:53
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