As I wrote earlier today, I will address the question of how to make taxifolin which the paper Yang, et. al. in Journal of Medicinal Chemistry, 2009 , volume 52, issue 23, pages 7732 to 7752 does address. Now before you ask taxifolin is needed for the production of a series of herbal drugs. While for small amounts it might be perfectly OK to collect drugs from some rare plants for the production of drugs for mass treatment of humans it is often a good idea to make the drug in a factory by means of organic synthesis. This will drive down the price (with some luck) and make the drug supply independent of the plant or tree.
Before we get any further here is our synthesis target.
I would be a good idea before we go any further to ask ourselves why it is unlikely that the taxifolin will not rearrange via an enol form to give the following species.
I think that the reason why the molecule is found in the first form is that the ketone group is conjugated to benzene ring on the left, but if we move the ketone to the alternative location it is not conjugated any more. But back to the synthesis, now the best thing to do when planning a synthesis is to use the retrosynthetic method. This is to break the molecule up in your mind to work out a way to make the molecule.
After we have chosen a good disconnection we now need to work out a reagent which will represent the odd looking thing with the negative and positive charge. Now the negative charge on the oxygen can be provided by the lone pair of a phenol oxygen, while the positive charge can be provided by an epoxide (three membered cyclic ether) if we protonate the epoxide. Now it is important to note that when an epoxide is opened under acidic conditions that the regioselectivity (which way around the epoxide reacts) is dictated by the stability of the hypothetical carbocations formed when the protonated epoxide ring opens. Below is a diagram which will make it more clear.
I will discuss the chemistry required to form the epoxide compound at a later date.