Total Synthesis of 20-Norsalvinorin A. 1. Preparation of a Key Intermediate
Ylva E. Bergman, Roger Mulder and Patrick Perlmutter
Link to the Paper

So here's a nice little paper from the outback. Theres some good chemistry leading up to the Diels Alder which is what sets the majority of the Stereocenters and brings their molecule together. The most interesting part of their paper was the use of DBU, an amidine, where they used it to reverse a specific stereocenter.

I liked bringing in the chiral diene leading to a majority of the desired stereochemistry. As you can see they were able to coordinate the reaction of the more reactive alkene in the ring aswell.







This reaction was pretty slick in my opinion. Here they used an amidine to reverse the chirality of a carbon.
When I first saw this step I was stumped. Later, upon settling into my head I realized that its likely that the imine in the amidine is cooridinating the two adjacent oxygens leading to an aldol type of resonance. This kicked off the tertiary hydrogen which momentairly lost its chirality and then upon the disconnection of the amidine brought back the carboneal and lead to a trans-decalin type structre, which would be more favorable than its previous structure. You can also see how it would not reverse the chirality of the quaternary carbon being that it can not lose its chirality or go to the sp2 hybridization. I honestly think they could have heated the compound or maybe add a metal acting as a lewis acid but nonetheless its still very good chemistry.