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Copper(II) Acetate-Induced Oxidation of Hydrazones to Diazo Compounds under Flow Conditions Followed by Dirhodium-Catalyzed Enantioselective Cyclopropanation Reactions.

Bo WeiTaylor A HatridgeChristopher W JonesHuw M L Davies
Published in: Organic letters (2021)
A tandem system comprising in-line diazo compound synthesis and downstream consumption in a rhodium-catalyzed cyclopropanation reaction has been developed. Passing hydrazone through a silica column absorbed with Cu(OAc)2-H2O/N,N-dimethylaminopyridine oxidized the hydrazone to generate an aryldiazoacetate in flow. The crude aryldiazoacetate elutes from this column directly into a downstream cyclopropanation reaction, catalyzed by the chiral dirhodium tetracarboxylates, Rh2(R-p-Ph-TPCP)4 and Rh2(R-PTAD)4. This convenient flow to batch method was applied to the synthesis of a range of 1,2-diarylcyclopropane-1-carboxylates in high yields and with high levels of enantioselectivity.
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