The copper works by transmetallating the Grignard reagent to give an organocopper reagent— simply put, the magnesium is exchanged for copper. Organocoppers are softer than Grignard reagents, and add in a conjugate fashion to the softer C=C double bond. Once the organo copper has added, the copper salt is available to transmetallate some more Grignard, and only a catalytic amount is required.

The organocopper is shown here as ‘Me–Cu’ because its precise structure is not known. But there are other organocopper reagents that also undergo conjugate addition and are much better understood. The simplest result from the reaction of two equivalents of organo lithium with one equivalent of a copper (I) salt such as CuBr in ether or THF solvent at low temperature. The lithium cuprates (R₂CuLi) that are formed are not stable and must be used immediately.

The addition of lithium cuprates to α,β-unsaturated ketones turns out to be much better if trimethylsilyl chloride is added to the reaction—we shall explain what this does shortly, but for the moment here are two examples of lithium cuprate additions.

The silicon works by reacting with the negatively charged intermediate in the conjugate addition reaction to give a silyl enol ether—a type of molecule. Here is a possible mechanism for a reaction between Bu₂CuLi and an α,β-unsaturated aldehyde in the presence of Me₃SiCl. The silyl enol ether simply hydrolyses to the ketone at the end of the reaction.

مواضيع ذات صلة

Hydroboration

تثبيت النتروجين Nitrogen Fixation

دورة اليوريا urea cycle

المصير الايضي للأحماض الامينية

ايض الأحماض الامينية والبروتينات metabolism of amino acids and proteins

اكسدة الأحماض الدهنية Oxidational of fatty acids

ايض الدهون metabolism of lipids

ايض الكاربوهيدرات metabolism of carbohydrates

انتقال الالكترونات والفسفرة التاكسدية Electron transport and Oxidative phosphorylation

الفسفرة التاكسدية Oxidative phosphorylation

دورة حامض الكلايوكسيليك Glyoxylic acid cycle

عملية التركيب الضوئي photo synthesis