Science of Synthesis

Harris, P. A., Science of Synthesis Knowledge Updates, (2021) 3, 181.

Azobenzenes ‌4‌ and terminal arylalkynes ‌5‌ undergo a rhodium-catalyzed cascade annulation to afford indolo[1,2-b]cinnolines ‌6‌ (‌Scheme 2‌).[‌1‌] The optimal reaction conditions require copper(II) acetate as an oxidant and copper(I) iodide, which is thought to coordinate with the terminal alkyne to generate a copper acetylide. Electron-donating groups on the arylalkyne are favorable for the reaction compared to electron-withdrawing groups, whereas ortho-substituted arylalkynes do not react, probably due to steric factors. The reaction displays high regioselectivity with unsymmetrical azobenzenes, with the aryl ketone forming closest to the substituted phenyl ring of the azobenzene for reasons not clearly understood.

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