Organocatalyzed Enantioselective [2 + 2] Cycloaddition of C, N-Cyclic Ketimines and Allenoates

Org Lett. 2024 Jan 12;26(1):225-230. doi: 10.1021/acs.orglett.3c03848. Epub 2023 Dec 26.

Abstract

We report a novel enantioselective and regioselective [2 + 2] cycloaddition of allenoate and C,N-cyclic ketimine catalyzed by a quinidine derivative. The methodology enables the synthesis of fused tricyclic azetidines with a quaternary stereogenic center exhibiting high enantioselectivities. The broad range of substrates demonstrates the generality of the protocol, and the resulting functional products can be easily converted to a variety of valuable synthons. To elucidate the plausible reaction mechanism and how the catalyst affects absolute stereocontrol over the products, we conducted the corresponding density functional theory (DFT) calculations.