Catalytic Alkene Carboaminations Enabled by Oxidative Proton-Coupled Electron Transfer

Article abstract of DOI:10.1021/jacs.5b05377

Here we describe a dual catalyst system comprised of an iridium photocatalyst and weak phosphate base that is capable of both selectively homolyzing the N-H bonds of N-arylamides (bond dissociation free energies ～ 100 kcal/mol) via concerted proton-couple

Full text of DOI:10.1021/jacs.5b05377

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Catalytic Alkene Carboaminations Enabled by Oxidative Proton-
Coupled Electron Transfer
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Gilbert J. Choi and Robert R. Knowles*
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
Supporting Information Placeholder
Oxidative PCET Activation of Amide N-H Bonds
e–
ABSTRACT: Here we describe a dual catalyst system com-
prised of an iridium photocatalyst and weak phosphate base that is
Ar
Ar
capable of both selectively homolyzing the N-H bonds of N-aryl
amides (BDFEs ~ 100 kcal/mol) via concerted proton-coupled
electron transfer (PCET) and mediating efficient carboamination
reactions of the resulting amidyl radicals. This manner of PCET
activation, which finds its basis in numerous biological redox
processes, enables the formal homolysis of a stronger amide N-H
bond in the presence of weaker allylic C-H bonds, a selectivity
that is uncommon in conventional molecular H-atom acceptors.
Moreover, this transformation affords access to a broad range of
structurally complex heterocycles from simple amide starting
materials. The design, synthetic scope and mechanistic evaluation
of the PCET process are described.
concerted
PCET
Mn–1
Mn
N
R
N
R
H
B
H B
O
O
H+
N-H BDFE for N-aryl amide ~100 kcal/mol
PCET 'BDFE' (kcal/mol) =1.37 pKa(H-B) + 23.06 E(Mn) + Csolv
Catalytic Alkene Carboamination Enabled by PCET
Ir(III) redox cat.
cat. phosphate base
Ar
R3
O
R1
O
N
Ar
N
H
R2
olefin acceptor
R2
R1
visible hν
O
R1
PCET
Ar
N
R2
Hydrogen atom transfer (HAT) is a powerful mechanism for
homolytic bond activation that plays a central role in organic
free radical chemistry. However, in HAT reactions involving
conventional acceptors, such as main group radicals and high-
valent metal oxo complexes, the rates of abstraction are highly
correlated with the strengths of the bonds being broken.1 In
turn, this has limited the development of catalytic HAT meth-
ods that enable the selective homolysis of strong E-H bonds
found in many common organic functional groups, such as
alcohols and amides, in preference to weaker C-H bonds pre-
sent in the same substrates.2
Figure 1. PCET activation of amide N-H bonds and application to the
development of a catalytic protocol for alkene carboamination.
oxidants.5 Lastly, the driving force for the PCET step can be
rationally modulated over a wide range of energies by inde-
pendently varying the pKa of the proton acceptor and the re-
duction potential of the oxidant (vide infra).6 Taken together,
these attributes provide a basis for the rational identification
oxidant/base combinations that are thermodynamically compe-
tent to selectively homolyze strong E-H bonds with BDFEs in
excess of 100 kcal/mol.
We recently questioned whether proton-coupled electron
transfer (PCET) could serve as an alternative mechanism for
homolytic bond activation that addresses this limitation.3 In
PCET oxidations, an electron and proton originating from a
single donor are transferred to two independent acceptors – a
Brønsted base and a one-electron oxidant – in a concerted
elementary step. While these exchanges constitute a formal
loss of H• and furnish a neutral free radical product in a man-
ner similar to HAT, the chemoselectivities and energetic char-
acteristics of PCET reactions are distinct. First, multisite
PCET oxidations require the formation of a hydrogen bond
between the transferring proton and the Brønsted base prior to
electron transfer.4 As typical C-H bonds are poor H-bond part-
ners, we postulated that PCET might enable the homolytic
activation of stronger O-H and N-H bonds selectively via the
formation of more favorable non-covalent complexes. Moreo-
ver, these hydrogen bonding interactions should significantly
decrease the potential requirements for the electron transfer
process, enabling the use of comparatively mild one-electron
In line with the ideas above, we report here a dual oxi-
dant/base catalyst system for the oxidative PCET activation of
the strong N-H bonds in N-aryl amide derivatives (N-H
BDFEs ~ 100 kcal/mol) and utilization of the resulting amidyl
radicals in a new catalytic protocol for alkene carboamination
(Figure 1).7 These reactions, which install vicinal C-N and C-
C bonds across an unactivated alkene in a single transfor-
mation, are complementary in scope to many established cata-
lytic carboamination technologies and have the potential to
simplify the synthesis of a range of complex heterocyclic
compounds. Moreover, while most state of the art technologies
in synthetic amidyl chemistry rely on radical generation via
either N-functionalized substrates8 or the use of strong stoichi-
ometric oxidants,9 the reaction described here constitutes a
rare example of catalytic amidyl generation via direct homoly-
sis of the N-H bond in a simple amide precursor.10 The design,
scope and mechanistic evaluation of the PCET process are
described herein.
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Table 1. Reaction optimization
Scheme 1. Proposed catalytic cycle
1
2
3
4
5
6
7
8
O
3 mol% photocatalyst
25 mol% Brønsted base
O
Ph
CO2Me
Ph
O
Me
hν
N
O
Ph
N
Mn
B
N
H
Me
Ph
CO2Me
N
H
Me
Me
3.0 equiv. methyl acrylate
0.4 M CH2Cl2
Me
Me
Me Me
Blue LEDs, rt, 12 hr
1
2
proton
transfer
concerted
PCET
'BDFE'a
Entry
Photocatalyst
Base
Yield (%)
H
B
H
B
CO2Me
Ph
O
NBu4OP(O)(OBu)2
1
2
Ir(ppy)2(phen)PF6
80
82
82
83
83
85
87
89
90
92
92
93
93
95
97
98
99
103
104
108
0
0
O
N
Ph
Mn
Mn-1
lutidine
NBu4OP(O)(OBu)2
lutidine
N
Me
Ir(ppy)2(phen)PF6
Me
Me
3
Ir(Fmppy)2(dtbbpy)PF6
Ir(Fmppy)2(dtbbpy)PF6
Ir(Fmppy)2(phen)PF6
Ir(Fmppy)2(phen)PF6
Ir(ppy)2(phen)(PF6)
0
Me
9
4
0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
C-N bond
formation
electron
transfer
NBu4OP(O)(OBu)2
lutidine
5
trace
0
6
DMAP
7
trace
0
CO2Me
Ph
Ph
DMAP
H
B
H
B
8
Ir(Fmppy)2(dtbbpy)PF6
Ir(Fmppy)2(phen)PF6
Ir(ppy)2(phen)PF6
O
O
N
Me
C-C bond
formation
N
DMAP
9
6
Mn-1
Mn-1
Me
Me
Me
NBu4OBz
NBu4OP(O)(OBu)2
lutidine
10
11
12
13
14
15
16
17
18
19
20
20
76
22
56
35
92
24
34
16
76
50
Ir(dF(CF3)ppy)2(dtbbpy)PF6
Ir(dF(CF3)ppy)2(dtbbpy)PF6
Ir(Fmppy)2(dtbbpy)PF6
Ir(Fmppy)2(phen)PF6
Ir(dF(CF3)ppy)2(bpy)PF6
Ir(dF(CF3)ppy)2(bpy)PF6
Ir(dF(CF3)ppy)2(dtbbpy)PF6
Ir(dF(CF3)ppy)2(bpy)PF6
Ir(dF(CF3)ppy)2(dtbbpy)PF6
Ir(dF(CF3)ppy)2(bpy)PF6
NBu4OBz
NBu4OBz
NBu4OP(O)(OBu)2
lutidine
CO2Me
Reaction design Our initial efforts focused on identifying
combinations of Brønsted bases and excited state oxidants
that, while incapable of reacting with the amide substrates
individually, are thermodynamically competent in combina-
tion to effect PCET homolysis of the N-H bond in model am-
ide 1 (Scheme 1). In these reactions, we envisioned that the
Brønsted base would first form a hydrogen bond complex with
the secondary amide substrate, modulating its oxidation poten-
tial to facilitate PCET with the excited state of the photoredox
catalyst. The nascent amidyl radical intermediate would then
cyclize onto the pendant olefin to form a new C-N bond and
an adjacent carbon-centered radical. This radical would in turn
undergo intermolecular addition to an acrylate acceptor to
form a new C-C bond and an α-carbonyl radical that would
accept an electron from the reduced state of the photocatalyst
to furnish an enolate. Favorable proton transfer between the
enolate and the conjugate acid produced in the PCET event
would furnish the desired carboamination product and regen-
erate the catalytically active forms of the oxidant/base pair.
DMAP
DMAP
NBu4OBz
NBu4OBz
Entry
Change from best conditions (entry 15)
Yield (%)
21
22
23
24
25
26
27
no light
0
no photocatalyst
0
no NBu4OP(O)(OBu)2
1 mol% Ir(dF(CF3)ppy)2(bpy)PF6
10 mol% NBu4OP(O)(OBu)2
1.1 equivalents of acrylate
0.1 M in CH2Cl2
<5
76
78
68
80
Optimization reactions performed at 0.05 mmol scale. Yields deter-
mined by 1H-NMR analysis of the crude reaction mixture relative to an
a
internal standard. ‘BDFE’ values in kcal/mol calculated from pKa and
potential data in MeCN, with a Csolv value of 54.9 kcal/mol. Structures
and potential data for all photocatalysts is included in the Supporting
Information.
To identify effective catalyst combinations for N-H homol-
ysis, we made use of a simple thermodynamic formalism in-
troduced by Mayer and coworkers that defines an effective
bond strength (‘BDFE’) for any given base/oxidant pair as a
function of the pKa and redox potential of its constituents
(Figure 1) and a constant term relating to the energetics of
proton reduction.11 In turn, these values enable the thermo-
chemistry of any proposed PCET event to be estimated by
comparing the effective BDFE of the chosen base/oxidant pair
to the strength of the bond being homolyzed. Importantly, as
these two key parameters are independent variables, the for-
mal bond strength can be rationally varied with respect to the
strength of the target bond. We tested the validity of this ap-
proach through combinatorial evaluation of five iridium pho-
tocatalysts and four Brønsted bases with effective bond
strengths ranging from 80 to 108 kcal/mol in the carboamina-
tion of anilide 1 (N-H BDFE = 99 kcal/mol) (Table 1).12,13 In
these experiments, we observed that combinations with
‘BDFE’ values significantly lower than the strength of the
substrate N-H bond were not successful catalysts for carbo-
amination (entries 1–9). However, all combinations with ef-
fective BDFEs approaching or exceeding the N-H BDFE of 1
resulted in catalytic generation of 2, though with varying de-
grees of efficiency (entries 10–20). Notably, all of the iridium
complexes and bases evaluated proved active in at least one
combination, including those with pKas and potentials far re-
moved from those of the amide substrate (pKa ~ 32, Ep = +1.2
V vs. Fc/Fc+ in MeCN) (entry 10).12,13 Taken together, these
results are consistent with a PCET mechanism of amidyl for-
mation (vide infra) and support the notion that thermochemis-
try is a principal determinant in the kinetic viability of N-H
activation. In addition, these studies highlight the ability of
PCET to enable access to catalytically active H• acceptor sys-
tems with effective bond strengths higher than those attainable
with any known molecular H-atom transfer catalysts (entry
20).
From the successful combinations tested, we elected to fur-
ther study the Ir(dF(CF3)ppy)2(bpy)PF6/dibutyl phosphate pair
(entry 15, ‘BDFE’ = 97 kcal/mol). Control reactions omit-
ting either the Ir photocatalyst or visible light irradiation pro-
vided none of the desired carboamination product (entries 21,
22). Similarly, reactions run in the absence of the phosphate
base resulted in <5% conversion of the amide starting material
(entry 23). The carboamination reaction was also successful,
2
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cyclic tetrasubstituted olefin substrate, furnishing spirocycle 7
Table 2. Substrate scope studies
O
X
1
2
3
4
5
6
7
8
3 mol% Ir(dF(CF3)ppy)2(bpy)PF6
25 mol% NBu4OP(O)(OBu)2
in good yield and with moderate diastereoselectivity. To the
best of our knowledge, tetrasubstituted olefins are not sub-
strates in any other reported catalytic carboamination technol-
ogy. Fused bicyclic systems could also be generated using this
method. For example, a cyclohexenol-derived carbamate was
cyclized to furnish 8 in 86% yield as 8:1 mixture of diastere-
omers at the quaternary carbon center. Additionally, a protect-
ed glucal substrate was successfully carboaminated to provide
carbohydrate derivate 9 with high levels of diastereoselectivi-
ty. A carbamate substrate derived from an acyclic chiral allylic
alcohol cyclized to provide access to a trans-fused oxazoli-
dinone 10 with excellent diastereoselectivity. Geminal substi-
tution adjacent to the olefin is tolerated and enables the use of
both monosubstituted and 1,2-disubstituted olefins substrates,
with moderate diastereoselectivity observed in the latter case
(11 and 12). Simple monosubstituted olefins could be also
carboaminated efficiently when more activated olefin accep-
tors were employed (13).
Ar
O
R1
N
Ar
EWG
N
H
X
R2
olefin acceptor
CH2Cl2
Blue LEDs, rt
R1 R2
O
O
O
N
Ph
Ph
Ph
N
N
N
O
Me
CO2Me
CO2Me
CO2Me
Me Me
Me Me
Me Me
2
95%
3
87%
4
63%
9
O
O
O
O
Ph
Ph
O
COMe
N
N
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Me
N
S
COMe
CO2Me
Ph
Me
Me Me
Me Me
5
72%
6
80%
7 82%
6:1 dr
O
N
O
O
COMe
Ph
Ph
O
N
O
N
Me
Me
Ph
COMe
O
Me
O
Me Me
iPr
O
COMe
O
8 86%
8:1 dr
9 63%
>20:1 dr
10 77%
>20:1 dr
With respect to the aryl amine component, numerous para-
substituted substrates were accommodated (14–17) including
both electron-rich and electron-deficient examples. Similarly,
substrates bearing both meta- and ortho-substituted arenes
could be carboaminated in good yields (18 and 19). In addi-
tion, heterocyclic arenes, such as pyridine and benzothiazole
could be incorporated into the amide moiety and cyclized with
good efficiency (20 and 21). Notably, the potential required
for direct ET oxidation of p-CN carbamates such as 15 is more
than 600 mV more positive than that of the Ir(III) excited state
(E1/2 = +1.0 V vs. Fc/Fc+ in MeCN), highlighting the ability of
simple H-bonding interactions to facilitate otherwise challeng-
ing charge transfer events.14,15 Lastly, a variety of electron-
deficient olefin partners were found to effectively couple, in-
cluding methyl acrylate, methyl vinyl ketone, acrolein, acrylo-
nitrile, and 2-vinylpyridine (20–23).
O
O
O
Ph
Ph
Ph
N
N
N
O
CO2Me
COMe
COMe
Me
Me
Me
Me
Ph
Me
11 76%
12 76%
5:1 dr
13 90%
1:1 dr
OMe
CN
F
OCF3
25
26
27
28
29
30
O
O
O
O
O
N
N
N
N
CO2Me
CO2Me
CO2Me
CO2Me
Me Me
Me Me
Me Me
Me Me
14 78%
15 94%
16 86%
17 70%
N
N
Me
O
O
Br
O
S
31
32
O
O
N
N
N
N
O
CO2Me
COMe
CO2Me
CO2Me
33
34
35
36
37
38
39
40
Me Me
Me Me
Me Me
Me Me
Mechanism of amidyl formation To assess the role of
PCET in these reactions, we studied the mechanism of amidyl
formation using luminescence quenching techniques and N-
phenyl acetamide (26) as a model substrate. Stern-Volmer
analysis revealed that 26 (Ep = +1.2 V vs. Fc/Fc+ in MeCN)
does not quench the excited state of Ir(dF(CF3)ppy)2(bpy)PF6
(*E1/2 = +1.0 V vs. Fc/Fc+ in MeCN) in acetonitrile at 25 °C.14–
16 However, solutions containing both amide 26 and tetrabutyl
ammonium dibutyl phosphate resulted in a significant de-
crease in the observed emission intensity. Variation of the
phosphate base and amide concentrations in these assays
demonstrated that the rate law for the quenching process ex-
hibits a first order kinetic dependence on the concentration of
each component. Additionally, an isotope effect of 1.15 ± 0.04
was observed in independent experiments conducted with the
N-H and N-D isotopologues of 26, consistent with the notion
that the labeled bond plays a specific role in the quenching
process.17 Notably, the phosphate base alone was also found to
weakly quench the Ir excited state (ksv = 41 M-1), but not suffi-
ciently to account for the much greater degree of quenching
18 82%
19 60%
20 70%
21 63%
O
O
O
Ph
CN
N
N
H
Me
EWG
Me Me
22 94%
23 50%
24 78%
25 76%
Reactions performed at 0.5 mmol scale. Yields are for purified mate-
rial and are the average of two experiments. Diastereomeric ratios
determined by 1H-NMR analysis of the crude reaction mixtures.
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
though lower yielding, when carried out at lower concentra-
tions, with lower catalyst loadings, or with 1.1 equivalents of
the acrylate acceptor (entries 24–27).
Substrate Scope Using the optimal conditions outlined
above, we next examined the scope of this process. On pre-
parative scale, carboamination of the model substrate 1 fur-
nished amide 2 in 95% isolated yield after 18 hours of irradia-
tion with blue LEDs at rt (Table 2). Carbamates were also
excellent substrates, providing straightforward access to vici-
nal amino alcohols derivatives such as 3 from simple allylic
alcohol starting materials. Structurally related urea and thia-
zolidinone products 4 and 5 could also be accessed in good
yields. Notably, this method was also found to accommodate
tetrasubstituted olefin substrates, providing access to products
containing vicinal tertiary carbinamine and quaternary carbon
centers, such as 6. This observation was extended to an endo-
observed when amide 26 was also present in solution (ksv
=
731 M-1).
While the results above indicate that the excited state iridi-
um complex does not oxidize the amide substrate directly,
they are consistent in principle with either concerted PCET
activation or rate-limiting deprotonation of the amide substrate
3
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Soc. 2006, 128, 13076. (e) Markle, T. F.; Mayer, J. M. Angew. Chem. Int.
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by the phosphate base followed by fast oxidation of the result-
1
2
3
4
5
6
7
8
ing anilide anion. However, the large pKa difference between
the amide and the phosphate (ΔpKa ~ 20) suggests that the
latter pathway would not be kinetically competitive with lumi-
nescent decay of the Ir excited state (τ = 2.3 µs in MeCN at
rt).14 As the feasibility of both sequential transfer mechanisms
can be discounted, the measured rate law and isotope effect
are consistent with a concerted PCET mechanism of amidyl
formation.18
(6) (a) C. J. Fecenko, T. J. Meyer and H. Thorp, J. Am. Chem. Soc.,
2006, 128, 11020. (b) C. J. Fecenko, H. Thorp and T. J. Meyer, J. Am.
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9
In conclusion, we have developed a novel PCET-based pro-
tocol for alkene carboamination. Notably, these studies
demonstrate that concerted multisite PCET is a viable mecha-
nism for the direct homolytic activation of strong N-H bonds,
providing catalytic access to amidyl radical intermediates from
simple anilide starting materials. Differential H-bonding abil-
ity enables these PCET activations to be completely chemose-
lective for the N-H bond even when much weaker allylic C-H
bonds are present in the same substrates. Additionally, the
qualitative success of effective BDFEs in enabling catalyst
selection suggests this simple metric will become an enabling
tool in PCET reaction design.19 These results provide further
support for the view that concerted PCET mechanisms can be
successfully translated to small molecule catalysis platforms
and enable the development of new synthetic methods.
10
11
12
13
14
15
16
17
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ASSOCIATED CONTENT
Supporting Information
Experimental procedures and characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
rknowles@princeton.edu
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
Financial support was provided by Princeton University and the
NIH (R01 GM113105). R.R.K is a fellow of the A. P. Sloan
Foundation.
(13) See Supporting Information for potential and pKa data used in ef-
fective bond strength calculations. From reference 11a, the Csolv constant
term for MeCN used in these calculations is 54.9 kcal/mol.
(14) Hanss, D.; Freys, J. C.; Bernardinelli, G. R.; Wenger, O. S. Eur. J.
Inorg. Chem. 2009, 4850.
(15) See Supporting Information for voltammetric data.
(16) Stern Volmer experiments were carried out in MeCN to allow
comparisons to literature potential, lifetime and pKa data. Carboamination
of 1 under standard conditions in MeCN are effective and provide 2 in
42% yield.
REFERENCES
(1) (a) Evans, M. G.; Polanyi, M. Trans. Faraday Soc. 1938, 34, 11.
(b) Kochi, J. K., Ed., Free Radicals; Wiley: New York, 1973. (c) Roth, J.
P.; Yoder, J. C.; Won, T. J.; Mayer, J. M. Science 2001, 294, 2524. (c)
Mayer, J. M. Acc. Chem. Res. 2011, 44, 36.
(17) For examples and theoretical justification of small isotope effects
in multisite PCET reactions, see: (a) Warren, J. J.; Menzeleev, A. R.;
Kretchmer, J. S.; Miller, T. F., III; Gray, H. B.; Mayer, J. M. J. Phys.
Chem. Lett. 2013, 4, 519. (b) Warren, J. J.; Mayer, J. M. J. Am. Chem.
Soc. 2011, 133, 8544. (c) reference 6c (d) Hammes-Schiffer, S.; Sou-
dackov, A. V. J. Phys. Chem. B 2008, 112, 14108. (e) Megiatto, J. D.;
Méndez-Hernández, D. D.; Tejeda-Ferrari, M. E.; Teillout, A.-L.; Llanso-
la-Portolés, M. J.; Kodis, G.; Poluektov, O. G.; Rajh, T.; Mujica, V.;
Groy, T. L.; Gust, D.; Moore, T. A.; Moore, A. L. Nature Chem. 2014, 6,
423. (f) Edwards, S. J.; Soudackov, A. V.; Hammes-Schiffer, S. J. Phys.
Chem. A 2009, 113, 2117.
(18) For examples of concerted PCET with excited state redox partners:
(a) Wenger, O. S. Acc. Chem. Res. 2013, 46, 1517. (b) Gagliardi, C. J.;
Westlake, B. C.; Kent, C. A.; Paul, J. J.; Papanikolas, J. M.; Meyer, T. J.
Coord. Chem. Rev. 2010, 254, 2459.
(19) As pointed out by a reviewer, the thermochemical considerations
reflected in the effective BDFE formalism are best viewed as a necessary
but not a sufficient condition to ensure a given PCET activation.
(2) Luo, Y. R. Handbook of Bond Dissociation Energies in Organic
Compounds; CRC Press: Boca Raton, Fl, 2003.
(3) (a) Reece, S. Y.; Nocera, D. G. Annu. Rev. Biochem. 2009, 78, 673.
(b) Mayer, J. M. Annu. Rev. Phys. Chem. 2004, 55, 363. (c) Hammes-
Schiffer, S.; Stuchebrukhov, A. A. Chem. Rev. 2010, 110, 6939. (d) Wein-
berg, D. R.; Gagliardi, C. J.; Hull, J. F.; Murphy, C. F.; Kent, C. A.;
Westlake, B. C.; Paul, A.; Ess, D. H.; McCafferty, D. G.; Meyer, T. J.
Chem. Rev. 2012, 112, 4016.
(4) For discussions of the role of H-bonding in concerted PCET, see:
(a) Turro, C.; Chang, C. K.; Leroi, G. E.; Cukier, R. I.; Nocera, D. G. J.
Am. Chem. Soc. 1992, 114, 4013. (b) Kirby, J.; Roberts, J.; Nocera, D. G.
Significant Effect of Salt Bridges on Electron Transfer. J. Am. Chem. Soc.
1997, 119, 9230. (c) Young, E. R.; Rosenthal, J.; Hodgkiss, J. M.; Nocera,
D. G. J. Am. Chem. Soc 2009, 131, 7678. (d) Sjodin, M.; Irebo, T.; Utas, J.
E.; Lind, J.; Merenyi, G.; Akermark, B.; Hammarstrom, L. J. Am. Chem.
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O
Ir(III) redox cat.
cat. phosphate base
O
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Me
COMe
Ph
N
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Ph
olefin acceptor
visible hν
Me
oxidative
PCET
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Me
24 examples
Ph
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Selective Homolysis of Amide N-H Bonds via PCET
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