The chemistry world can be a very small place. Last semester, for example, I TA’ed for a professor who had my undergrad organic professor as her organic TA in undergrad. What does this have to do with Wednesday’s problem? To put it plainly, I don’t remember ever learning oxymercuration from the aforementioned prof. In all fairness to RBG I spent many hours asleep in that class, having it a mere eight hours after the 12-4am dorm night-desk shift. Still though, before last semester, mercury was basically the element that filled thermometers to me and little else. But Wednesday’s problem demonstrates that under the right conditions, mercury can do magic!
The cornerstone of the problem is the Ritter reaction, in which an isonitrile attacks an electrophile before being attacked by some nucleophile (classically, water) at carbon. The overall transformation leads to substituted amides in the classical case, but with other nucleophiles around, interesting architectures can fall out. In Stevens’s case, mercury-mediated fragmentation of the pinene skeleton generated both the electrophile (a carbocation) and the nucleophile (a double bond) in one fell swoop! The fragmentation can be rationalized by the release of ring strain associated with the starting cyclobutane. Attack by the isonitrile and trapping by the alkene, with loss of mercury to form the exocyclic alkene, leads to the intermediate X, an imine. The imine is then reduced on its top face to form the final product. Stevens makes a big deal of the reduction stereochemistry in the paper, although it makes sense to me considering the “roof-like” bicyclic structure of the imine.
Same time, same place, next week…be there or be square.