Pd-catalyzed Stereodivergent [4+2] Annulation to Access [6.7]-Fused N-Heterocycles

Abstract

Stereodivergent synthesis of N-heterocycle frameworks bearing 1,3-nonadjacent stereogenic centers through a single transformation remains a high-priority challenge in organic synthesis. Herein, we highlight our recent discovery of stereodivergent access to such useful structural motifs using Pd-catalyzed [4+2] annulation reactions of vinyl benzoxazinaones and seven-membered cyclic N-sulfonyl aldimines. A wide range of N-heterocycles with 1,3-nonadjacent stereogenic centers were obtained in high efficiency and stereodivergency. Importantly, the polarity of solvents was found to play a key role in switching of diastereoselectivity. Furthermore, good enantioselectivities of these reactions were achieved by the employment of commercially available Wingphos as the chiral ligand.