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(
S.O.P., Y.L., C.J.H., J.R.A.) for financial supDpoOrIt:.10N.1.0J.3T9.,/CE5.CHC.D0.4,6a7n7Gd
K.M.M. thank the NSF Graduate Research Fellowship for funding
and Z.M.H. acknowledges the California NanoSystems Institute for
an Elings Prize Fellowship in Experimental Science.
our protocol. Further, during the course of purification, we
were also able to isolate the PTH catalyst used in the reaction.
This catalyst sample was then re-used in the reduction of 5,
and quantitative conversion to the desired product was
observed after 1.5 h, again highlighting the simplicity and
inherent robustness of PTH.
Notes and references
1.
(a) C. K. Prier, D. A. Rankic, and D. W. C. MacMillan, Chem.
Rev., 2013, 113, 5322–5363. (b) D. M. Schultz and T. P.
Yoon, Science, 2014, 343, 1239176–1239176. (c) J. M. R.
Narayanam and C. R. J. Stephenson, Chem. Soc. Rev., 2010,
Scheme 1 a) Reaction in the presence of air (triplet quencher)
proceeds b) Preparative scale reaction conducted without
degassing demonstrates modularity and scalability c) Cyclization
suggests radical mechanism.
40, 102. (d) D. A. Nicewicz and T. M. Nguyen, ACS Catal.,
2
014, 4, 355–360.
(
a) Open to air:
PTH
NBu3, HCOOH
2.
3.
D. A. Nicewicz and D. W. C. Macmillan, Science, 2008, 322,
7–80.
I
H
7
3
80 nm light
MeCN, rt
J. M. R. Narayanam, J. W. Tucker, and C. R. J. Stephenson, J.
Am. Chem. Soc., 2009, 131, 8756–8757.
S. Fukuzumi, K. Hironaka, and T. Tanaka, J. Am. Chem. Soc.,
1
57 %
2
h
4
.
.
(b) Gram-scale reaction in air:
1
983, 105, 4722–4727.
PTH
5
J. D. Nguyen, E. M. D'Amato, J. M. R. Narayanam, and C. R.
J. Stephenson, Nature Chem, 2012, 4, 854–859.
C. D. McTiernan, S. P. Pitre, H. Ismaili, and J. C. Scaiano,
Adv. Synth. Catal., 2014, 356, 2819–2824.
I
NBu , HCOOH
H
3
3
80 nm light
MeCN, rt
20 h
BnO2C
BnO2C
6.
5
87 %, 1.5 g
7.
C. D. McTiernan, S. P. Pitre, and J. C. Scaiano, ACS Catal.,
2014, 4, 4034–4039.
(c) Radical cyclization:
PTH
NBu3, HCOOH
8.
9.
I. Ghosh, T. Ghosh, J. I. Bardagi, and B. Konig, Science,
Br
2
014, 346, 725–728.
O
O
380 nm light
MeCN, rt
72 h
S. M. Senaweera, A. Singh, and J. D. Weaver, J. Am. Chem.
Soc., 2014, 136, 3002–3005.
47 %
2
3
24
10.
G. Revol, T. McCallum, M. Morin, F. Gagosz, and L.
Barriault, Angew. Chem. Int. Ed., 2013, 52, 13342–13345.
P. Knochel, W. Dohle, N. Gommermann, F. F. Kneisel, F.
Kopp, T. Korn, I. Sapountzis, and V. A. Vu, Angew. Chem.
Int. Ed., 2003, 42, 4302–4320.
Additional, mechanistic experiments were conducted
providing strong evidence of an oxidative-quenching cycle with
deuterium studies supporting the primary source of hydrogen
atoms being the tributylamine (For in-depth discussion see SI
and Scheme S1). Furthermore, evidence of a radical-based
mechanism was obtained via a successful radical cyclization of
substrate 23 (Scheme 1b). The desired product 24 was
obtained in 47 % yield, providing strong support for the 15.
a radical process, as well as
preliminary evidence illustrating that generated radical 16.
1
1.
2.
1
W. F. Bailey and J. J. Patricia, J. Organomet. Chem, 1988,
352, 1–46.
1
1
3.
4.
W. P. Neumann, Synthesis, 1987, 665–683.
A. Krief and A.-M. Laval, Chem. Rev., 1999, 99, 745–778.
K. Miura, Y. Ichinose, K. Nozaki, K. Fugami, K. Oshima, and
K. Utimoto, Bull. Chem. Soc.Jpn, 1989, 62, 143–147.
M. R. Medeiros, L. N. Schacherer, D. A. Spiegel, and J. L.
Wood, Org. Lett., 2007, 9, 4427–4429.
reaction proceeding via
intermediates can be used for carbon–carbon bond forming
1
1
7.
8.
Based on Sigma-Aldrich price on January 21, 2015.
H. Kim and C. Lee, Angew. Chem. Int. Ed., 2012, 51, 12303–
reactions.
In conclusion, we have developed a highly reducing, organic
photocatalytic platform with broad applicability for the
generation of carbon-centered radical intermediates on route
to efficient dehalogenations of aryl and alkyl iodides, bromide
and chlorides. In addition to offering an inexpensive, metal-
free alternative to current halide reductions, this approach is
highlighted by a robust and facile nature with high yields being
obtained even in the presence of air. Moreover, in contrast to 21.
classic photoredox systems, preliminary evidence suggests that
PTH is primarily operating through the singlet state. Further
investigations regarding the mechanism, the tunability of the
catalyst, and its potential to open doors for new organic bond
forming transformations are currently in progress.
1
2306.
19.
N. J. Treat, H. Sprafke, J. W. Kramer, P. G. Clark, B. E.
Barton, J. Read de Alaniz, B. P. Fors, and C. J. Hawker, J.
Am. Chem. Soc., 2014, 136, 16096–16101.
20.
To eliminate any question of difference in catalyst loading
causing the increased performance, 5 mol % Ir(ppy) was
3
also tested and gave a slightly lower yield after 1 h (19 %).
J.-B. Xia, C. Zhu, and C. Chen, Chem. Commun., 2014, 50,
11701–11704.
A. J. Fry and R. L. Krieger, J. Org. Chem., 1976, 41, 54–57.
S. Rondinini, P. R. Mussini, P. Muttini, and G. Sello,
Electrochimica acta, 2001, 46, 3245–3258.
2
2
2.
3.
2
4.
5.
J. W. Tucker and C. R. J. Stephenson, J. Org. Chem., 2012,
77, 1617–1622.
2
Although these results in the presence of oxygen support
singlet catalysis, a combination of both singlet and triplet
states operating under our oxygen free conditions cannot
be completely ruled out at this time.
Acknowledgements
We thank the MRSEC program of the National Science Foundation
DMR 1121053, C.J.H., J.R.A.) and The Dow Chemical Company
(
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