Site-Selective Approach to β-Fluorination: Photocatalyzed Ring Opening of Cyclopropanols

Abstract

To expand upon the recent pioneering reports of catalyzed sp(3) C-H fluorination methods, the next rational step is to focus on directing "radical-based fluorination" more effectively. One potential solution entails selective C-C bond activation as a prelude to selective fluorination. Herein, we report the tandem photocatalyzed ring-opening/fluorination reactions of cyclopropanols by 1,2,4,5-tetracyanobenzene (TCB) and Selectfluor to afford a process tantamount to site-selective β-fluorination of carbonyl-containing compounds. This new approach provides a synthetically mild and operationally simple route to otherwise difficult-to-prepare β-fluorinated products in good yields and with good-to-excellent regioselectivity. Remarkably, substrates that contain other usually reactive (e.g., benzylic) sites undergo ring-opening fluorination preferably. The versatility of this method to give cyclic β-fluorides from tertiary cyclopropanols and γ-fluoro alcohols is also highlighted.

Keywords: CC activation; cyclopropanols; fluorination; photochemistry; radical ions.