Catalytic enantioselective intramolecular hydroamination of alkenes using chiral aprotic cyclic urea ligand on manganese (II)
Bin Cui, Yuting Zheng, Hui Sun, Huijian Shang, Man Du, Yuxuan Shang, Cafer T. Yavuz
Abstract
Asymmetric catalysis for enantioselective intramolecular hydroamination of alkenes is a critical method in the construction of enantioenriched nitrogen-containing rings, often prevalent in biologically active compounds and natural products. Herein, we demonstrate a facile enantioselective intramolecular hydroamination of alkenes for the synthesis of chiral pyrrolidine, piperidine, and indoline moieties, using a manganese (II) chiral aprotic cyclic urea catalyst. The cyclic ligand hinders the inversion of the N atom of the urea and effectively discriminate between the enantiomers of substrates. High-resolution mass spectrometry, deuterium labeling experiments, and molecular orbital energy analysis clearly reveal the intermediates and mechanism of the transformation. As a key step, oxygen coordination by chiral aprotic urea presents a robust control over the asymmetric intra-HA reaction through the involvement of a convergent assembly of two vital intermediates (Mn-N and C-Mn-Br), providing access to chiral cyclic amine systems in high yields with excellent enantioselectivity. Nitrogen-containing rings containing chiral carbon centers are a staple of bioactive molecules and natural products of interest, and synthetic methodologies for their development are a continual focus of organic chemists. Here, the authors disclose a protocol for the synthesis of enantioenriched saturated azacycles, via intramolecular hydroamination of alkenes, using a chiral cyclic urea ligand with manganese.