Here is a question for tonight: how many cases are out there where a single hydrogen bond dominates the regiochemical outcome of a chemical transformation? Let’s say we are comparing the protio version to its methylated congener, which is arguably the smallest steric perturbation that does not produce a confounding effect. Here is a case from Paul Carlier’s lab published some time ago in Organic Letters. If you look at the two epoxide-containing anilines depicted below, you will note that they differ by a methyl group. Their behavior is strikingly dissimilar, demonstrating how a single hydrogen bond can affect the reactive conformation. The reactions were run neat, by the way. Both outcomes are driven by the logic of trans-diaxial epoxide ring opening, yet the NH-to-O interaction flips the reactive conformation in the first case compared to the second one. If you are looking for a powerful demonstration of the Fürst-Plattner rule, there is probably no better way to show how a relatively weak interaction can control the reaction outcome.
Very elegant example. Thanks for posting this.
Glad you like it!
It’d be interesting to know what the outcomes would be if it were run in solvent rather than neat.
There will probably be a drastic change indeed…