Streamlined Access to Steroid-Like Frameworks With Vicinal Tertiary and Quaternary Centers via Pd-Catalyzed Asymmetric Bisallylation.

Abstract

Despite remarkable advances in all-carbon quaternary stereocenter construction, catalytic enantioselective assembly of sterically congested vicinal tertiary-all-carbon quaternary stereodyads remains underdeveloped. Stereocontrolled access to such motifs embedded in steroid-like frameworks represents a particularly formidable challenge. Herein, we disclose a highly efficient Pd-catalyzed enantioselective bisallylation/ring-closing metathesis (RCM) cascade, enabling modular asymmetric assembly of enantioenriched polycyclic architectures from simple coumarin-derived precursors. With the newly developed chiral biaryl monophosphine ligand-Pd2(dba)3 system, the reaction proceeds with exceptional enantiocontrol and diastereoselectivity. Synthetic versatility is demonstrated by divergent transformations into diverse high-value chiral building blocks. Computational studies reveal that the formation of the bis-π-allylpalladium intermediate is the rate-determining step of this sequential process. Notably, this simple yet powerful catalytic system is also applicable to cyclic N-sulfonyl imines, offering a general and robust platform for the facile synthesis of enantioenriched homoallylic amines and structurally intricate N-polycyclic skeletons.