B.R.S.M. Help! I'm trapped in a molecule factory!


I’ll see your Diels-Alder and raise you one 1,3-dipolar cycloaddition

On Monday, See Arr Oh over at Just Like Cooking posted on this non-obvious Diels-Alder reaction recently published by the Vanderwal group, suggesting that it'd make good problem session fodder. And I agree:

Fortunately, this tied in perfectly with my plans to run our group problem session next week on a pericyclic theme and so it was duly incorporated. If you're interested in what else featured, I also included a question on the origin of the metastability of Dewar Benzene (which I've blogged about before).

After a few easier questions I finished up by asking people to suggest a mechanism for this interesting sequence published a few years back.

Have a think and then read on for a possible answer!

Okay, here's one plausible mechanism that the authors themselves put forward (J. Org. Chem., 2006, 71, 2417). I find the step that breaks the N-O bond a bit troubling (bottom right), but other than that it's not too bad. The halomethylcyclopropane-halocyclobutane rearrangement is apparently quite a well studied thing.

More total synthesis soon, I promise!

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  1. Great mech! I love rearrangments like these, and when I saw the “bow-tie” of gem cyclopropanes, I knew de Meijere had to be involved.

    One (small) criticism: I think your alkoxide has moved. In the SM, it’s in the “4” position, and it looks to have migrated to “3” on the indolizinone. What do you think?

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