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Controlling the selectivity of an intramolecular Friedel–Crafts alkylation with alkenes using selenium under mild conditions

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Abstract

An efficiently divergent intramolecular Friedel–Crafts alkylation by unactivated alkenes with seleniranium ion-controlled Markovnikov/anti-Markovnikov specificities under mild conditions has been investigated. 2-Benzoxepin, isochroman, and isochromene can be produced in one-pot procedures from the same substrate in high yields and with high regio- and stereospecificity. The products are challenging to access via 7-endo-trig carbocyclizations and by 7-endo-trig carbocyclization/rearrangement/6-exo-trig oxycyclization and 6-exo-trig carbocyclization/deselenenylation reaction sequences, respectively. Mechanistic experiments indicated that in addition to the stereospecific anti-addition processes of the cyclization reactions, the formation of a stable carbocation after ring opening of the seleniranium ion leads to an NPSP-mediated 7-endo-trig carbocyclization; the steric hindrance of the seleniranium intermediate controls the regioselectivity when using TPSCA at 60 °C, which promotes 6-exo-trig carbocyclization. Two distinct catalytic cycles were proposed, and the structures of transition states and products were identified by ab initio calculations and X-ray analyses.

Graphical abstract: Controlling the selectivity of an intramolecular Friedel–Crafts alkylation with alkenes using selenium under mild conditions

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Supplementary files

Article information


Submitted
05 Feb 2020
Accepted
10 Mar 2020
First published
10 Mar 2020

Org. Biomol. Chem., 2020, Advance Article
Article type
Paper

Controlling the selectivity of an intramolecular Friedel–Crafts alkylation with alkenes using selenium under mild conditions

M. Liao, M. Zhang, D. Hu, R. Zhang, Y. Zhao, S. Liu, Y. Li, W. Xiao and E. Tang, Org. Biomol. Chem., 2020, Advance Article , DOI: 10.1039/D0OB00257G

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