Abstract
A cationic iridium/binap catalyst enabled the asymmetric [3+2] annulation of cyclic N-acyl ketimines with internal alkynes via C-H activation to give spiroaminoindene derivatives with high enantioselectivity. The stereochemical course of this annulation was switchable by acid additives.
Highlights
A cationic iridium/binap catalyst enabled the asymmetric [3+2] annulation of cyclic N-acyl ketimines with internal alkynes via C–H activation to give spiroaminoindene derivatives with high enantioselectivity
We reported that a cationic iridium(cod) complex catalyzes a [3+2] annulation of aromatic ketimines with alkynes via C–H activation to give spiroaminoindenes (Scheme 1a).[7]
One is the transfer of a transient axial chirality of intermediate C to the chiral annulation product 3,8 and the other is the use of the cationic iridium species as a chiral Lewis acid to invoke the enantioselective cyclization of intermediate C.9
Summary
A cationic iridium/binap catalyst enabled the asymmetric [3+2] annulation of cyclic N-acyl ketimines with internal alkynes via C–H activation to give spiroaminoindene derivatives with high enantioselectivity. We reported that a cationic iridium(cod) complex catalyzes a [3+2] annulation of aromatic ketimines with alkynes via C–H activation to give spiroaminoindenes (Scheme 1a).[7] Mechanistic studies revealed that the reaction proceeds via sequential ortho-alkenylation and intramolecular cyclization. It was found that the reaction of ketimines having substituted phenyl groups gave the annulation products in high yields and enantioselectivity.
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