Mechanism Monday – The Synthesis of furo-fused oxazinanes via gold asymmetric catalysis

Recently, the team of Prof. Zhang (East China Normal University, Shanghai) reported a new asymmetric heterocycle synthesis using gold catalysis (yes, you have understood by now, I am quite a big fan of gold catalysis). I propose two examples to solve, they are directly extracted from the paper. For the sake of the exercise, determining the stereochemistry of the transition states are optional.

12And this one for a little twist (R and R1 are aromatic):

12b

Reference: Angew. Chem. Int. Ed. 2014, 4350-4354. link

9. Mechanism Monday – The Endgame of Overman’s Total Synthesis of Actinophyllic Acid

Well, this is what I consider a classic. I have proposed it a couple of times in group meetings and it has never ceased to amaze me.

This, Ladies and Gentlemen, is what I call a spectacular endgame! Four reactions for the price of one!

Have a close look at it, give it a try, and get back to the original paper once you have found a satisfactory mechanism.

9Reference: J. Am. Chem. Soc. 2010 4894-4906 link

8. Mechanism Monday: the Gold-catalysed spiroannulation of enynes and cyclopropenones by Matsuda et al.

Though the field is not that new and was explored in much details by many, I still find gold catalysis has a strong appeal. A good reason for this is that I have found gold-catalysed reactions to occur following an original mechanism that would seem queer in other Lewis-acid or transition-metal-catalysed reactions.

The following reaction between an enyne and a cyclopropenone was reported earlier this year by Matsuda and Sakurai from the Tokyo University of Science. Trying to find the mechanism is trickier than it looks at first and I found it to be a good exercise on gold catalysis .

8.a

Reference :

J. Org. Chem. 2014, 2739-45. link

5. Mechanism Monday: the acid-promoted cascade cyclisations of N-Cinnamoyl-1-naphtylamines

A recent paper of Dr. Frank D. King and co-workers (from University College London) was dealing with the acid-mediated cyclisation patterns of N-cinnamoyl-1-naphtylamines.1 While most results were matching what one would expect, the authors observed two new products appearing when the nitrogen atom was bearing a benzyl group. They proposed structures for these unexpected products, so the question is, what would you propose for the mechanism?

5.aNot too difficult, I agree, but a nice warm-up exercise to start a group meeting.

Reference:
1. J. Org. Chem. 2013, 78, 10938-10946 link