A Metal-Free and Redox-Neutral Benzylic C-O Cyclization for Succinct Access of Helical Chromenes

Tianyi Liu; Kin Boon Gan; Rong-Lin Zhong; Xinwei He; Fuk Yee Kwong

doi:10.1021/acs.orglett.2c02728

A Metal-Free and Redox-Neutral Benzylic C-O Cyclization for Succinct Access of Helical Chromenes

Org Lett. 2022 Sep 23;24(37):6805-6809. doi: 10.1021/acs.orglett.2c02728. Epub 2022 Sep 13.

Authors

Tianyi Liu^{1

2}, Kin Boon Gan^{1

2}, Rong-Lin Zhong^{1

3}, Xinwei He^{1

4}, Fuk Yee Kwong^{1

2}

Affiliations

¹ State Key Laboratory of Synthetic Chemistry and Department of Chemistry, The Chinese University of Hong Kong, New Territories, Hong Kong, China.
² Shenzhen Municipal Key Laboratory of Chemical Synthesis of Medicinal Organic Molecules, Shenzhen Research Institute, The Chinese University of Hong Kong, No. 10, Second Yuexing Road, Shenzhen 518507, P. R. China.
³ Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130023, P. R. China.
⁴ Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials (State Key Laboratory Cultivation Base), College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241002, P. R. China.

PMID: 36098713
DOI: 10.1021/acs.orglett.2c02728

Abstract

A redox-neutral benzylic C-O cyclization under beneficial transition-metal-free conditions is reported. Key to the success of this process is the utilization of the Tf anion as the leaving group for achieving the redox-neutral transformation. This protocol delivers a series of captivating helical compounds having various functionality in good-to-excellent yields. It is particularly noteworthy that sterically hindered helical compounds are conformationally stable. In addition to simple helical chromenes, the bihelical multiple-ring systems which are potentially useful in material chemistry are also easily attained by employing this method. DFT calculation revealed that quinone intermediate is the key species, among four possible mechanisms, for accomplishing the desired cyclization via an oxa-6π-electrocyclization pathway.