At my group meeting earlier today, we were having a problem set related to the FMO theory. This brought to mind a discussion I had with a good friend of mine, Sergey Kozmin, of the University of Chicago (http://kozmin-group.uchicago.edu), who visited our house in Oakville this past weekend. As a matter of fact, this is a surreal coincidence because 24 hours prior to that I saw Vladimir Gevorgyan in Paris, who is also from Chicago (and, like Sergey and myself, hails from the former Soviet Union). In Bill Shatner’s words: “Is it weird, or what?” (https://www.youtube.com/watch?v=MmNgMJWEYJQ).
Continuing along the “weird” angle, I also like when well-known reactions we take for granted behave anomalously. Above is a classic paper by Daniel Singleton that probes the Diels-Alder process with vinyl boranes. Sergey brought this to my attention. What can possibly lurk out there in the old stomping grounds of [4+2] cycloadditions, you might say? Intriguingly, the LUMO coefficients at the vinylic carbon and boron centers are rather close. As a consequence, while the product of the reaction is the expected 6-membered ring, it is the [4+3] transition state that takes hold in this system, defining an interesting secondary orbital interaction. There have been other papers on this subject since Singleton’s report, so I encourage you to look into this literature.