A new asymmetric activation strategy for hydrazones as acyl anion equivalents in the bimetallic catalyzed carbonyl-ene reaction

A new asymmetric activation strategy for hydrazones as acyl anion equivalents is developed in the bimetallic catalyzed carbonyl-ene reaction of isatins and hydrazones. Under mild conditions, optically active functionalized 3-hydroxy-2-oxindoles were furnished in up to 98% yield with up to 97% enantioselectivity. In this process, formaldehyde tert-butylhydrazone which is seldom employed in asymmetric carbonyl-ene reactions accelerated by a metallic catalyst can be activated well by a Bronsted base. A possible catalytic cycle is proposed.

Automated summary

A new asymmetric activation strategy is developed for hydrazones as acyl anion equivalents in the bimetallic catalyzed carbonyl-ene reaction, resulting in high yields and high enantioselectivity. By utilizing a Bronsted base, formaldehyde tert-butylhydrazone can be well activated in this process.