Long time readers know how much I adore the thiol-ene reaction for making polymeric coatings (see for instance, these posts 1, 2, 3 or this 2- part video). It's fast, really fast (I've made coatings that go from pure monomer to cured coating in 0.1 seconds), it doesn't suffer from oxygen inhibition, it's solvent free and works well with endless varieties of terminal enes. So when I see a new report in Angewandte Chemie entitled "Repairing the Thiol-Ene Coupling Reaction", my first thought was don't fix what ain't broke. Unless you can eliminate the smell of the thiols. Then by all means, feel free to do so. My wife will be endlessly thankful as will my labmates.
But it does turn out that my beloved reaction has a technical flaw. It doesn't work well with allyl ethers, such a R-O-CH2-CH=CH2, giving either poor yields after tremendous increases in thiol (oh, great!), or multiple reaction products.
But it turns out that the addition of catechol is able to overcome this. (The authors used 4-tert-butylcatechol since it was more soluble in the reactants, but it's the catechol that is doing all the work.) The proposed mechanism is this:
So can this reaction be done with my standard UV absorbing photoinitiators? I have my doubts, since the triethyl borane and the catechol directly react via an undescribed mechanism. But it would be fun to try someday. Maybe the next time that my wife is out of town - for a week or more so that I have plenty of time to do the laundry. However, if you look at the videos linked to earlier, you will see me discuss results of thiol-ene polymerization using allyl ethers. I never knew of the problem back then so I just plugged along, but a more thorough analysis of the product would be needed now. So maybe...
P.S., This article had a structure that I've never encountered before: