Fig. 1 The combination of PCET and an RNR class I reaction enables heteroarene C─H alkylation using ketones and aldehydes as alkyl radical equivalents. (A) The polarity of the C═O bond. HAT, hydrogen atom transfer. (B) A new catalyst system for reductive PCET. (C) The RNR class I reaction. (D) The method reported herein.
Fig. 3 Mechanistic studies in support of the proposed pathway. (A) Ir[dF(CF3)ppy]2(dtbbpy)PF6 emission quenching with TTMS. (B) Proof of the corresponding α-oxy radicals. (C) Mechanistic studies support the spin-center shift elimination pathway. (D) Confirmation of the source of hydrogen atoms at the benzylic position of product. rt, room temperature.
- Table 1 Optimization of conditions for alkylation of 4-hydroxyquinazoline with acetone.
Reaction conditions: 4-hydroxyquinazoline (0.3 mmol), photocatalyst (0.003 mmol), reductant (0.6 mmol), TFA (0.6 mmol), and acetone (3.0 ml) under Ar atmosphere. The yield was determined by 1H NMR spectroscopy using dibromomethane as the internal standard. Reaction was performed in the absence of light for entry 9. Reaction was performed in the absence of photocatalyst for entry 10. Reaction was performed in the absence of TTMS for entry 11. Reaction was performed in the absence of TFA for entry 12. rt, room temperature; NR, no reaction; DIPEA, N,N-diisopropylethylamine; HEH, diethyl 1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate.
Entry Photocatalyst Reductant Yield (%) 1 Ir[dF(CF3)ppy]2(dtbbpy)PF6 TTMS 96 2 Ir(ppy)3 TTMS NR 3 [Ru(bpy)3](PF6)2 TTMS NR 4 Eosin-Y TTMS NR 5 Ir[dF(CF3)ppy]2(dtbbpy)PF6 Et3SiH 82 6 Ir[dF(CF3)ppy]2(dtbbpy)PF6 Ph3SiH NR 7 Ir[dF(CF3)ppy]2(dtbbpy)PF6 DIPEA NR 8 Ir[dF(CF3)ppy]2(dtbbpy)PF6 HEH 40 9 Ir[dF(CF3)ppy]2(dtbbpy)PF6 TTMS NR 10 — TTMS NR 11 Ir[dF(CF3)ppy]2(dtbbpy)PF6 NR 12 Ir[dF(CF3)ppy]2(dtbbpy)PF6 TTMS NR - Table 2 Exploration of substrate scope.
Reactions were performed on a 0.3-mmol scale, unless otherwise noted. Isolated yields are given. We used Hantzsch dihydropyridine as reductant for 48. See the Supplementary Materials for experimental details.
Supplementary Materials
Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaax9955/DC1
Section S1. General information
Section S2. Reaction optimization
Section S3. Investigation of the mechanism
Section S4. Experimental procedures and product characterization
Section S5. Copies of 1H NMR and 13C NMR spectra for new compounds
Table S1. Screening of different solvents.
Table S2. Screening of the amount of cyclohexanone.
Table S3. Light on and off experiments.
Table S4. Control experiments of intermediate 66.
Fig. S1. Control experiments.
Fig. S2. Emission quenching experiments (Stern-Volmer studies).
References (33, 34)
Additional Files
Supplementary Materials
This PDF file includes:
- Section S1. General information
- Section S2. Reaction optimization
- Section S3. Investigation of the mechanism
- Section S4. Experimental procedures and product characterization
- Section S5. Copies of 1H NMR and 13C NMR spectra for new compounds
- Table S1. Screening of different solvents.
- Table S2. Screening of the amount of cyclohexanone.
- Table S3. Light on and off experiments.
- Table S4. Control experiments of intermediate 66.
- Fig. S1. Control experiments.
- Fig. S2. Emission quenching experiments (Stern-Volmer studies).
- References (33, 34)
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