Organic Letters
ORCID
Letter
(15) Control experiments with various spiked metal complexes did not
show any promoting effect.
Notes
(16) Grushin, V. Organometallics 2001, 20, 3950.
(17) For C−H alkenylation of oxazoles, see: (a) Meng, L.; Kamada, Y.;
Muto, K.; Yamaguchi, J.; Itami, K. Angew. Chem., Int. Ed. 2013, 52,
10048. (b) Lee, W.-C.; Wang, T.-H.; Ong, T.-G. Chem. Commun. 2014,
50, 3671.
The authors declare no competing financial interest.
(18) (a) DFT calculations were performed at the SMD(toluene)-
B3LYP-D3(BJ)/Def2-TZVP//B3LYP/Def2-SVP level of theory by
using Gaussian 09 program packages. See the SI for computational
details. For computational studies on SET-mediated C−H arylation
with aryl iodides, see: (b) Pichette Drapeau, M.; Fabre, I.; Grimaud, L.;
Ciofini, I.; Ollevier, T.; Taillefer, M. Angew. Chem., Int. Ed. 2015, 54,
10587. (c) Reference 8g.
(19) For a previous report on the redox properties of dppf, see: Pilloni,
G.; Longato, B.; Corain, B. J. Organomet. Chem. 1991, 420, 57.
(20) For a computational study on the bicarbonate radical, see: Buhl,
M.; DaBell, P.; Manley, D. W.; McCaughan, R. P.; Walton, J. C. J. Am.
Chem. Soc. 2015, 137, 16153.
ACKNOWLEDGMENTS
■
We gratefully thank the National Natural Science Foundation of
China (21421062, 21502098, 21672105, 21772098) for financial
support of this work.
REFERENCES
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■
Chem., Int. Ed. 2009, 48, 9792. (b) Verrier, C.; Lassalas, P.; Thev
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eau, L.;
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(21) The ΔG of 19.7 kcal/mol is calculated for free anion tBuO−.
KOtBu and NaOtBu exist as oligomers in solution. Their dissociation
behavior can be strongly influenced by solvents and additives, which
need to be taken into consideration when analyzing tBuO−-mediated
SET reactions. Previous reports have shown that the use of ligand is
critical to promote these SET processes (see ref 8). Dppf-mediated SET
of KOtBu is likely a complex process. A more comprehensive
investigation of the dppf/KOtBu system will be the subject of a future
account.
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(22) This value might be influenced by solvent and additives in the
solution.
(23) DFT calculations indicate that P7 dppf(O) is comparable to dppf
in regard to forming complexes with CsCO3− and undergoing SET with
−
ArI. P8 dppf(O2) forms a stronger complex with CsCO3 , but the SET
(5) For a recent review on radical C−H arylation of arenes, see: Chan,
T. L.; Wu, Y.; Choy, P. Y.; Kwong, F. Y. Chem. - Eur. J. 2013, 19, 15802.
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ability of the resulting complex is weaker. P5 forms a weaker complex
−
with CsCO3− than dppf. P1 cannot form a complex with CsCO3 . See
(7) Studer, A.; Curran, D. P. Angew. Chem., Int. Ed. 2011, 50, 5018.
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(24) Like dppf, Br− is also a poor electron door for SET reduction of
ArI.
(25) DFT calculations showed that HOMO orbital of VII lies on the
bicarbonate group. Thus, bicarbonate might be better viewed as the
electron donor in this reaction system.
(26) Redox cycle pathway a in which VIII serves as D(+1) which
accepts an electron from V cannot be completely ruled out.
(27) DFT calculations suggest that CsI, Cs2CO3, or (Cs2CO3)Cs+
species are likely involved in the decarboxylation process. See the SI for
more details.
(28) Control experiments show that heating dppf with Cs2CO3 in
toluene at 110 °C for 24 h under O2-free conditions leads to the
formation of 9% of P-oxygenation product P7 (a plausible reaction
equation is shown below). Heating of P7 with Cs2CO3 in toluene led to
the formation of 17% of P8. In comparison, heating of P5 with Cs2CO3
in toluene did not form any P-oxygenation product. See the SI for more
details.
(11) For applications of ferrocene in redox-catalyzed reactions, see:
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̈
Chem., Int. Ed. 2013, 52, 10792. (b) Zhang, B.; Studer, A. Org. Lett. 2014,
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(13) The unique effect of Cs2CO3 base in radical-mediated reactions
has been reported; however, the underlying mechanism remains elusive:
(a) Zhang, J.; Wu, H.-H.; Zhang, J. Eur. J. Org. Chem. 2013, 2013, 6263.
(b) Liang, Y.-F.; Jiao, N. Angew. Chem., Int. Ed. 2014, 53, 548. (c) Xu, T.;
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B.; Studer, A. Org. Lett. 2014, 16, 3990 For a CoCO3 additive, see:.
(e) Li, Y.; Wang, M.; Fan, W.; Qian, F.; Li, G.; Lu, H. J. Org. Chem. 2016,
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(14) tBuO− is a more nucleophilic base than Cs2CO3 and may be
incompatible with certain substrates.
D
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