This a little overdue…Some interesting chemistry reported in Journal of the American Chemical Society….Interesting not for the products that it produces but for the proposed mechanism, an intermolecular ene-reaction. From a retrosynthetic point of view one can imagine that the product of thisreaction could also be formed just as easily from the corresponding aldehyde via and Aldol reaction instead. However, the authors provide evidence to show that the reactants, as their enols, go through an ene-type process.
Given that this reaction occurs at room temperature simply by mixing the two substrates together is also noteworthy and makes me wonder why nobody had reported this before.
April 3, 2007 at 3:54 am
It is not realy ene reaction in classical sense - it is more akin to acid-catalyzed aldol. The keto ester is pretty acidic, it protonates the vinyl ether to make O-alkyl oxonium of the aldehyde which then easily condenses with the enolate. I don’t think it is a synchronnous transition state (like for example with ethyl glyoxylate and beta pinene) - even though you can draw it that way.
April 3, 2007 at 9:00 pm
Sort of a “flipped” aldol since the acidic enol-H “protonates” the alpha-carbon of the aldehyde instead of the oxygen, like in the normal aldol.
HC=CH-O-H—O=CHR normal aldol
HC=CH-O-H—C(R)=CHOR’ “ene/aldol”