Acyloin condensation

As acyloin condensation is known in organic chemistry, the condensation of two esters to α - hydroxy carbonyl compounds ( acyloins ) by reacting in the heat with sodium in toluene or xylene.

Overview reaction

When acyloin condensation react two ester to a acyloin:

The radicals R1 and R2 are organyl radicals. The green binding in acyloin is the newly forged connection between the two esters.

Mechanism

The mechanism of the acyloin condensation is illustrated by the above example.

First, the ester 1 reacts with sodium to the radical anion 2, the dimerisert with another radical anion to the dianion 3. By elimination of two alcoholate groups ( R2O ) produced a diketone 4 which is reduced with excess sodium to the dianion 5. This dianion is then in aqueous workup to the α -hydroxy ketone 6, the acyloin hydrolyzed.

Rühlmann variant

To dramatically improve the yield of trimethylsilyl chloride ( TMSCl ) may be added which serves as a capture reagent for the alkaline alcoholates. Competitive reactions are suppressed.

Hydrolysis of the silyl ether to give the acyloins.

Intramolecular variant

The intramolecular variant ( Prelog Stoll cyclization ) is possible from starting materials with two ester groups. On this method are known from the corresponding dicarboxylic acid diesters corresponding ring systems accessible - depending on the chain length of the feedstock. The yields of the cyclic variation vary with respect to the chain length - some systems are easier than others. (10 - or 12 - membered) of preparative importance, especially the formation of larger rings is using the Ziegler- Ruggli dilution principle. The presence of double or triple bonds in the carbon system is not in general interfere with the reaction.