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SC CHEM 334 - Michael Additions

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Chem 334 1nd Edition Lecture 21Outline of Last Lecture I. Esters as enolates and electrophilesOutline of Current Lecture II. Michael AdditionsIII. Strong NucleophilesIV. Robinson AnnulationV. Gilman ReagentsCurrent LectureMichael additions:Michael additions are nucleophile additions to alpha, beta unsaturated carbonyls, but the nucleophile adds to the carbon-carbon double bond instead of the carbonyl carbon. These are sometimes also called conjugate additions. O O R R nuc nucThe nucleophile attaches to the carbon furthest away from the carbonyl and the double bond goes away.The nucleophile doesn’t normally attack carbon-carbon double bonds. However, the C-C π bond in this case is special because the beta carbon is electrophilic due to resonance structures of the molecules, which puts a positive charge on the beta carbon.Strong nucleophiles:Strong nucleophiles, such as Gringards and organolithiums, add both to the carbonyl and the beta position. O OH O 1. Li & 2. H+wkupThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Since strong nucleophiles add to both the carbonyl and the beta position, we can use weak nucleophiles to make sure we only get the conjugate addition product. These weak nucleophiles include beta-diketones, beta-ketoesters, beta-ketonitriles, beta-diestersm and enamines. Some common conjugation addition electrophiles are alpha, beta unsaturated aldehydes, alpha, beta unsaturated ketones, alpha, beta unsaturated esters, alpha, beta unsaturated amides and alpha, beta unsaturated nitriles.Robinson Annulation:Robinson annulation is a Michael addition followed by an aldol to create a six membered ring. O O 1. OH- O 2. H+ Wkup O 3. H+/Δ OGilman Reagents:We can also use Lithium diorganocuprate nucleophiles, or Gilman reagents, in our Michael addition reactions O 1. LiCu( )2 O 2. H+


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SC CHEM 334 - Michael Additions

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