Over the past few days I was at the Vanderbilt University in Nashville, TN. Jeff Johnston (http://www.johnstonchemistry.org) put together a mini-symposium consisting of Professor Viresh Rawal of the University of Chicago (http://rawalgroup.uchicago.edu) and myself. Everything was sponsored by Sigma-Aldrich and I fully enjoyed this opportunity to visit the South and learn about what goes on at Vanderbilt as well as in Viresh’s lab.
I learned a lot by hearing about the imaginative research programs led by Viresh and Jeff. Proton management turned into the common theme of the visit. One interesting piece of history I was not aware of was Margaret Etter’s work from 25 or so years ago. In it, the urea-driven activation of carbonyl compounds is described, which is foundational to many organocatalytic reactions. I think students should be aware of this work. Viresh’s talk reminded me about his remarkable discovery that TADDOL ligands are excellent catalysts for a range of asymmetric reactions. The activation here is derived from the enhanced acidity of the OH functionality that is augmented by the nearby OH in organic solvents. Over the years, Viresh’s lab has characterized several co-crystals formed between carbonyl compounds and TADDOL, which support the lowered pKa of the OH functionality. Last but not least, I want to mention one of Jeff’s cool recent uses of his chiral proton catalysts. In a JACS paper that appeared not long ago, he showed how carbon dioxide could be efficiently fixated using asymmetric catalysis. This is an exceptionally interesting article. Overall, this was a fun trip and I am very grateful to Jeff for putting the agenda together.
It’s probably worth to mention that enantioselective transformations using TADDOL as a hydrogen bonding catalyst/reagent have been reported some time before Rawals beautiful application. Angew. Chem. Int. Ed. 2001, 40, 92 ± 138 provides a nice “historic” overview by the TADDOL-inventor, Dieter Seebach.
By all means, I completely agree with you!