Visible Light-Induced Direct S₀ → T_n Transition of Benzophenone Promotes C(sp³)–H Alkynylation of Ethers and Amides

Abstract

Benzophenone has an S 0 → S 1 absorption band at 365 nm. However, the rarely reported S 0 → T n transition occurs upon irradiation at longer wavelengths. Herein, we employed benzophenone as a catalyst and exploited its S 0 → T n transition in C(sp 3 )−H alkynylations with hypervalent iodine reagents. The selective benzophenone excitation prevented alkynylating reagent decomposition, enabling the reaction to proceed under mild conditions. The reaction mechanism was investigated by spectroscopic and computational studies.

From Photoredox Catalysis to the Direct Excitation of EthynylBenziodoXolones: Accessing Alkynylated Quaternary Carbons from Alcohols via Oxalates

“…An NMR sample of the crude was prepared with 1 equiv of CH 2 Br 2 (7.0 μL, 0.10 mmol, 1 equiv) in CD3 CN. The 1 H NMR yield was determined using the signal at 5.53 ppm (dd, J = 8.6, 4.8 Hz, 1H, NCHCH 2 O): 35% 1 H NMR (400 MHz, Acetonitrile-d3) δ 8.06 (dd, J = 7.9, 1.2 Hz, 1H, ArH), 7.81 (dd, J = 7.8, 1.7 Hz, 1H, ArH), 7.58 -7.47 (m, 3H, ArH and PhH), 7.47 -7.33 (m, 3H, PhH), 7.27 (td, J = 7.7, 1.8 Hz, 1H, ArH), 5.53 (dd, J = 8.6, 4.8 Hz, 1H, NCHCH 2 O), 4.64 (dd, J = 11.3, 8.6 Hz, 1H, NCHCH 2 O), 4.50 (dd, J = 11.2, 4.8 Hz, 1H, NCHCH 2 O), 3.75 -3.52 (m, 2H, CH 2 ), 2.39 -2.30 (m, 2H, CH 2 ), 2.12 -2.02 (m, 2H, CH 2 ).Corresponds to the reported literature data 27. Deboronative alkynylation potassium 2,3-dihydro-1H-inden-2-yl-tris(fluoranyl)borate(12) a reported procedure,28 a flame dried round bottom flask containing a solution of BH 3 .THF (34.0 mL, 34.0 mmol, 1.00 M, 2.00 equiv) in THF was cooled to 0 °C.…”

“…NMR (400 MHz, CDCl 3 ) δ 7.45−7.41 (m, 2H, ArH), 7.31−7.28 (m, 3H, ArH), 4.81 (dd, J = 7.2, 5.2 Hz, 1H, CH x O), 4.04−3.99 (m, 1H, CH x O), 3.89−3.83 (m, 1H, CH x O), 2.29−2.19 (m, 1H, CH x ), 2.15−2.04 (m, 2H, CH x ), 1.99−1.90 (m, 1H, CH x ). Corresponds to the reported literature data.Following a modified reported procedure,27 an oven dried dram vial, equipped with a magnetic stir bar was charged with 2a (35 mg, 0.10 mmol, 1.0 equiv) and 5a (15 mg, 0.050 mmol, 0.50 equiv). After 3 vacuum/nitrogen cycles refilling with Ar on the last cycle, degassed CH 2 Cl 2 (0.40 mL) was added followed by N-vinylpyrolidinone (10) (16.7 mg, 16.0 μL, 150 μmol, 1.50 equiv).…”

Uranyl-catalyzed C-H Alkynylation and Olefination

“…By using alkenyl or allyl bromides, we were delighted to discover that C(sp 3 )-C(sp 2 ) and C(sp 3 )-C(sp 3 ) coupling products (32 & 39) were readily furnished under the same conditions (Figure 3). Unsaturated bromides bearing halogen (33,40), tri uoromethoxy (34), methoxy (35), acetoxy (36), thiophene (37), naphthyl (41) substitutions were tolerated under the conditions. Disubstituted ethylene bromide was applicable for generating the desired products in good yields (38).…”

“…However, modi cation of the hydrocarbons and use of expensive catalysts inevitably restricts the application of such strategies. Recently, prefunctionalized alkynyl reagent such as sulfones or hypervalent iodines were employed in Giese-type reactions for radical alkynylation [34][35][36][37] (Fig. 1B).…”

Vinylbenziodoxol(on)es: Synthetic Methods and Applications

“…Nemoto and coworkers reported in 2020 the C(sp 3 )−H olefination of THF ( 26 ) by using Ar‐VBX reagents 2 in presence of benzophenone ( 28 ) as organic triplet‐sensitizer at 400 nm ( Scheme 11). [71] Good yields were obtained. However, the irradiating conditions led to isomerization of the C=C bond.…”