Introducing: the metathesis-modified Himbert reaction!
Wait...the what?
Browse on over to Org. Lett. ASAP for a crazy two-stepper you're sure to love. Here's the opening scheme, so sharpen those pencils, and try some electron-pushing before I tell you the secret:
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Give up? I tried all sorts of pi-arene cyclizations, and drew out amide tautomers until my eyes bled. But the real answer, clues author Prof. Chris Vanderwal, lies 30 years in the past. A brief (2/3 page!) 1982 communication in ACIEE related a rare bird indeed: an unactivated benzene ring participating as a diene, with no added metal catalysts, pressure, acids, or bases. Upon heating, the tethered alkyne isomerizes to an allenamide, which gladly serves as the dienophile (somewhere, Richard Hsung is smiling).
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| Source: Himbert, Henn ACIEE 1982, p. 620 |
Vanderwal's insight comes next: seeing a strained [2.2.2] diene, he figures he can pop it open with some metathesis magic. A touch of Hoveyda-Grubbs, some ethylene, and a little heat rearrange the strained system to a complex 7-6-5 tricyclic lactam. His group prepares quite a few of these scaffolds, and hopes to utilize them to access several of the Erythrina alkaloids.
P.S. First one to use this problem for 'mechanisms' group meeting wins!
