Highly Stereoselective Intramolecular Carbofluorination of Internal α,β-Ynones Promoted by Selectfluor

Abstract

Herein, we report a metal-free intramolecular carbofluorination protocol for the synthesis of tetrasubstituted monofluoroalkenes from internal α,β-ynones and Selectfluor with both high stereoselectivity and broad functional group tolerance. The chelation between tetrafluoroborate anion and the oxygen present in the aldehyde group rendered the reaction highly stereoselective, with the tetrafluoroborate serving as the direct fluorine source. Therefore, with addition of sodium tetrafluoroborate, Selectfluor could be reused several times without sacrificing reactivity.

Fluorohydroxylation and Hydration Reactions of para-Quinone Methides Promoted by Selectfluor

“…Although the exact reaction processes are not very clear, on the basis of the above control reactions and relevant literature, ,− the possible pathways for the synthesis of 3 , 4 , and 5 are proposed in Figure . In the synthesis of 3 , 14d first, the 4 Å molecular sieve absorbed the H 2 O molecules in the reaction system to prevent them from reacting with p -QMs prematurely.…”

“…Finally, E was further tautomerized to afford 4 (Figure b). In the process of the synthesis of 5 (as referred to the reported literature), p -QMs combined with Selectfluor via an electrostatic interaction between the fluorine atom of Selectfluor and the ketone, and aryl also has the electron-withdrawing groups, whose two factors enhanced its δ-position electrophilicity, allowing it to undergo a 1,6-conjugate addition reaction with a weak nucleophile H 2 O molecule to obtain intermediate F . Under the oxidation of the Selectfluor reagent, two molecules of F lost a H 2 O molecule to provide ether-type product 5 (Figure c).…”

A Straightforward Approach to Fluorinated Pyrimido[1,2-b]indazole Derivatives via Metal/Additive-Free Annulation with Enaminones, 3-Aminoindazoles, and Selectfluor

“…On the basis of these experimental results together with previously reported works, 17 Finally, the target product 4a was generated via dehydration process.…”

Cu-catalyzed cascade difluoroalkylation/5-endocyclization/β-fluorine cleavage of ynones

“…Alternatively, the carbofluorination of alkynes serves as a more direct and efficient approach to these scaffolds. 4 For example, Zhang and co-workers discovered an Ag-catalyzed synthesis of monofluoroethenyl cyclopentanones via the radical ring expansion/fluorination of alkynyl cyclobutanols with Selectfluor. 4 c Jiang’s group reported a metal-free intramolecular carbofluorination of 2-(3-arylpropioloyl)-benzaldehydes, leading to α-monofluoroalkenyl indanones with high stereoselectivity.…”