Named Organic Reactions
Chapter One
A
Acyloin Ester Condensation
[alpha]-Hydroxyketones from carboxylic esters
Upon heating of a carboxylic ester 1 with sodium in an inert solvent, a condensation
reaction can take place to yield a [alpha]-hydroxy ketone 2 after hydrolytic
workup. This reaction is called Acyloin condensation, named after the products
thus obtained. It works well with alkanoic acid esters. For the synthesis of the
corresponding products with aryl substituents (R = aryl), the Benzoin condensation
of aromatic aldehydes is usually applied.
For the mechanistic course of the reaction the diketone 5 is assumed to be
an intermediate, since small amounts of 5 can sometimes be isolated as a minor
product. It is likely that the sodium initially reacts with the ester 1 to give the
radical anion species 3, which can dimerize to the dianion 4. By release of
two alkoxides R'[O.sup.-] the diketone 5 is formed. Further reaction with sodium
leads to the dianion 6, which yields the [alpha]-hydroxy ketone 2 upon aqueous ... read full excerpt from Named Organic Reactions, 2nd Edition ebook
