Photoinduced Aryl Ketone-Catalyzed Phenylation of C(sp3)–H Bonds Attached to the Heteroatom of Ethers and N-Boc-Amines via Concerted Homolytic Aromatic Substitution

Masaya Azami; Michinori Sumimoto; Reika Nakamura; Toshihiro Murafuji; Shin Kamijo

doi:10.1055/a-2338-4243

Synthesis, Table of Contents

Synthesis 2024; 56(18): 2925-2932
DOI: 10.1055/a-2338-4243

paper

Photoinduced Aryl Ketone-Catalyzed Phenylation of C(sp³)–H Bonds Attached to the Heteroatom of Ethers and N-Boc-Amines via Concerted Homolytic Aromatic Substitution

Masaya Azami

^aGraduate School of Sciences and Technology for Innovation, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8512, Japan

,

Michinori Sumimoto

^bGraduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan

,

Reika Nakamura

^cDepartment of Chemistry, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8512, Japan

,

Toshihiro Murafuji

^aGraduate School of Sciences and Technology for Innovation, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8512, Japan

,

Shin Kamijo∗

^aGraduate School of Sciences and Technology for Innovation, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8512, Japan

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Abstract

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Abstract

A single-step phenylation at the non-acidic C(sp³)–H bond attached to the heteroatom of ethers and N-Boc-amines has been achieved using photoexcited 4-benzoylpyridine as a hydrogen atom transfer (HAT) catalyst. The design of electron-deficient (trifluoromethylsulfonyl)benzene derivatives, as a phenyl precursor, was critical to realizing the present transformation. Moreover, the DFT calculations indicated that the present transformation proceeds via a concerted homolytic aromatic substitution rather than via a stepwise one involving the formation of a cyclohexadienyl radical intermediate.

Key words

C–H functionalization - phenylation - photoreaction - aryl ketone - ether - carbamate

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References

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21 The phenyl precursor without additional EWG, (trifluoromethylsulfonyl)benzene, did not give the expected product, 2-phenyltetrahydrofuran, under the standard conditions for 24 h, and recovery of the phenyl precursor was observed.
22 The DFT calculations showed that the energy barrier leading to the expected product 3o′ is higher than to its isomer 3o, see: Supporting Information for details.
23 To obtain the TEMPO-adduct of THF 4, the reaction was carried out under slightly modified conditions with a stoichiometric amount of K₂CO₃ and without addition of H₂O at rt, see: entries 3 and 9 of Table 2 for comparison.
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26 The kinetic isotope effect (KIE) was measured by independent treatment of THF (1a) and its fully deuterated analogue 1a-d with the phenyl precursor 2a under the optimized conditions. Its value was calculated to be 1.5.
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Supplementary Material

Supporting Information