Radical Pentafluorosulfanylphenylation of Styrenes by Photoredox Catalysis

Abstract

Simple and versatile radical pentafluorosulfanylphenylation (SF₅-phenylation) of styrenes by photoredox catalysis has been developed. Pentafluorosulfanylphenyliodonium salts (SF₅-phenyliodonium salts), which can be easily prepared from SF₅-phenyl iodides and handled without special caution, serve as precursors of SF₅-phenyl radicals by action of a ruthenium photoredox catalyst, [Ru(bpy)₃]²⁺. Radical phenylation of styrenes combined with solvolysis or deprotonation leads to a variety of SF₅-phenyl-containing compounds via a single step.

Key words

photoredox catalysis - pentafluorosulfanyl group - diaryliodonium salt - phenyl radical - radical reaction - arylation - photochemistry

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• 9 Experimental Procedures for the Synthesis of 1a To a stirred solution of pentafluoro(4-iodophenyl)-λ⁶-sulfane (331 mg, 1.0 mmol) in CH₂Cl₂–CF₃CH₂OH (v/v = 1:1, 10.0 mL) was added 69–75 wt% grade of mCPBA (230 mg, 1.0 mmol), followed by addition of TsOH (190 mg, 1.0 mmol). The resulting solution was stirred for 3 h at 40 °C and concentrated under a stream of air, then Et₂O (20.0 mL) was added to the residue. The precipitate was filtered and dried in vacuo to afford Koser-type reagent 1′a (459 mg, 89% yield). To a stirred solution of mesitylene (108 mg, 1.0 mmol) in CF₃CH₂OH (5.0 mL) was added 1′a in one portion at r.t., and the reaction mixture was stirred for 24 h. The mixture was concentrated, and the resulting crude product was precipitated by addition of Et₂O. The precipitate was filtered and dried in vacuo to give the product 1a (509 mg, 89%). Recrystallization from MeOH–CH₂Cl₂ afforded colorless crystals suitable for single-crystal X-ray measurement. Comound 1a: ¹H NMR (500 MHz, CD₃OD, r.t.): δ = 2.37–2.38 (6 H, Me in mesityl and tosyl), 2.66 (s, 6 H, Me in mesityl), 7.22 (d, J = 7.5 Hz, 2 H, tosyl), 7.29 (s, 2 H, mesityl), 7.70 (d, J = 7.0 Hz, 2 H, tosyl), 7.96 (d, J = 8.0 Hz, 2 H, SF₅Ph), 8.05 (d, J = 8.0 Hz, 2 H, SF₅Ph). ¹⁹F NMR (376 MHz, CD₃OD, r.t.): δ = 60.1 (d, J = 148.1 Hz, 4 F), 78.9 (quin, J = 149.5 Hz, 1 F). ¹³C NMR (125 MHz, CD₃OD, r.t.): δ = 21.0 (p-Me in mesityl), 21.3 (Me in tosyl), 27.1 (o-Me in mesityl), 117.5 (mesityl), 122.5 (mesityl), 126.9 (tosyl), 129.8 (tosyl), 130.5 (m, SF₅Ph), 131.5 (mesityl), 135.8 (SF₅Ph), 141.6 (tosyl), 143.6 (tosyl), 143.7 (SF₅Ph), 146.3 (mesityl), 157.1 (apparent t, J = 22.9 Hz, SF₅Ph). HRMS (ESI-TOF): m/z calcd for [C₁₅H₁₅F₅SI]⁺: 448.9854; found: 448.9856. For related synthetic method, see: Dohi T., Yamaoka N., Kita Y.; Tetrahedron; 2010, 66: 5775.
• 10 Compound 1a: CCDC 1431812 contains the supplementary crystallographic data. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.