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Published on: July 19, 2019
New insights into the torquoselectivity of the Staudinger reaction
Yong Liang1, Lei Jiao, Shiwei Zhang
1Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Abstract:
To understand the torquoselectivity and the electronic effects of the Staudinger reaction, a study using a combination of experiments and DFT calculations has been conducted for the reactions of an unsymmetric cyclic ketene and cyclic imines with different electronic properties. The predominant formation of the donor-in beta-lactams, the torquoelectronically disfavored products, was observed for the first time. The Hammett analyses reveal a close relationship between the donor-out/donor-in product ratio and the electronic nature of the imines. The kinetic competition experiments and DFT calculations indicate that the two-step Staudinger reaction shows different rate-determining steps in the donor-in and donor-out pathways. Our investigations reveal that the torquoelectronic control in the Staudinger reaction is quite different from that in the ring-opening reaction of cyclobutene derivatives. The diastereoselectivity of the Staudinger reaction involving an unsymmetric disubstituted ketene cannot be simply rationalized or predicted by the torquoelectronic model.
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