Paul Schleyer sent me an email about a pattern he had spotted, between my post on F 3 SSF and some work he and Michael Mauksch had done 13 years ago with the intriguing title “ Demonstration of Chiral Enantiomerization in a Four-Atom Molecule “.[cite]http://doi.org/d8g2nw[/cite] Let me explain the connection, but also to follow-up further on what I discovered in that post and how a new connection evolved.
This is an interesting result I got when studying the [1,4] sigmatropic rearrangement of heptamethylbicyclo-[3.1.0]hexenyl cations. It fits into the last lecture of a series on pericyclic mechanisms, and just before the first lecture on conformational analysis. This is how they join.
Following on from our first mechanistic reality check, we now need to verify how product A might arise in the mechanism shown below, starting from B . This pathway backtracks the original one in reversing the final arrow of that process (shown in red in previous post and in magenta here for the arrow in reverse), to go uphill in energy to reach the secondary (unstabilised) carbocation.