Chiral Ferrocenyl N,N Ligands with Intramolecular Hydrogen Bonds for Highly Enantioselective Allylic Alkylations
Lin Yao, Huifang Nie, Dongxu Zhang, Libin Wang, Yuhao Zhang, Weiping Chen, Zhenhua Li, Xueying Liu, Shengyong Zhang
文献索引：10.1002/cctc.201701461
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摘要
Abstract Several new ferrocene-derived bidentate N ligands, which contain multiple chiral factors, have been designed and synthesized by a rational combination of oxazoline and pyridine. Their catalytic performances were investigated preliminarily in Pd-catalyzed asymmetric allylic alkylation, and excellent reactivities and enantioselectivities (up to 99 % yield and 98 % ee) were realized if we used the ligand with a matched chirality. DFT calculations were used to illustrate that an intramolecular hydrogen bond formed between the hydroxyl group and the oxazoline fragment of the ligand contributed to the optimal conformation of the ligand-Pd-allyl complex. Intramolecular hydrogen bond makes sense: A series of new chiral ferrocenyl N,N-ligands is designed and synthesized. Their application in Pd-catalyzed allylic alkylations shows the great potential of the developed ligands in asymmetric catalysis (up to 99 % yield, 98 % ee), and DFT calculations indicated that the intramolecular hydrogen bond formed within the ligand plays a vital role in this catalysis.