8. Mechanism Monday: the Gold-catalysed spiroannulation of enynes and cyclopropenones by Matsuda et al.

Though the field is not that new and was explored in much details by many, I still find gold catalysis has a strong appeal. A good reason for this is that I have found gold-catalysed reactions to occur following an original mechanism that would seem queer in other Lewis-acid or transition-metal-catalysed reactions.

The following reaction between an enyne and a cyclopropenone was reported earlier this year by Matsuda and Sakurai from the Tokyo University of Science. Trying to find the mechanism is trickier than it looks at first and I found it to be a good exercise on gold catalysis .

8.a

Reference :

J. Org. Chem. 2014, 2739-45. link

4. Electrochemical chlorination of 1,3-dicarbonyls

A recent paper of Prof. Fumitoshi Kakiuchi et al. (from Keio University in Yokohama, Japan) deals with the copper-catalysed α-chlorination of 1,3-dicarbonyl compounds.

You might be thinking that it is just another paper on an overused method, but there is a twist here that I particularly liked. The source of chlorine here is nothing but hydrochloric acid, probably the cheapest and simplest source of chlorine atoms, without the issue of handling a toxic gas like Cl2. I guess there is no point in mentioning N-chlorosuccinimide. The trick for the transformation of a fairly inert Cl into a formal Cl+ is the use of electrochemistry. A mild current at the appropriate intensity provides just enough oxidation to provide monochlorinated 1,3-dicarbonyls in ok-to-high yields.

4.a

While I doubt I will ever use this method in a lab (I am not too experienced with organic electrochemistry), I can see the potential of it on an industrial scale: reducing costs of reagents, reducing waste, and perhaps you could even use the H2 produced by the reaction to power an auxiliary generator or something.

Asian J. Org. Chem. 2013, 2, 935-937 link