Metal-free reductive cleavage of C-N and S-N bonds by photoactivated electron transfer from a neutral organic donor

Article abstract of DOI:10.1002/anie.201306543

A photoactivated neutral organic super electron donor cleaves challenging arenesulfonamides derived from dialkylamines at room temperature. It also cleaves a)ArC-NR and b)ArN-C bonds. This study also highlights the assistance given to these cleavage reactions by the groups attached to N in (a) and to C in (b), by lowering LUMO energies and by stabilizing the products of fragmentation. Radical fragmentations: Electron transfer from the photoactivated neutral electron donor 1 delivers high yields of S-N and C-N cleavage products for a range of nitrogen-containing species. These reactions proceed at room temperature and under mild reaction conditions in the absence of any metal reagents. DMF=N,N-dimethylformamide, Ts=4-toluenesulfonyl.

Full text of DOI:10.1002/anie.201306543

.
Angewandte
Communications
DOI: 10.1002/anie.201306543
Radical Ions
ꢀ
ꢀ
Metal-Free Reductive Cleavage of C N and S N Bonds by
Photoactivated Electron Transfer from a Neutral Organic Donor**
Steven OꢀSullivan, Eswararao Doni, Tell Tuttle,* and John A. Murphy*
Abstract: A photoactivated neutral organic super electron
donor cleaves challenging arenesulfonamides derived from
after loss of one and two electrons, respectively, and the
aromaticity of these products contributes to the driving force
for the oxidations.[1] The radical cation 4 and dication 5
derived from 3 are shown in Scheme 1. The donor 1 was the
first neutral organic compound to reductively cleave aryl
iodides to aryl radicals,[1a] while the stronger donors 2[1b] and
ꢀ
dialkylamines at room temperature. It also cleaves a) ArC NR
ꢀ
and b) ArN C bonds. This study also highlights the assistance
given to these cleavage reactions by the groups attached to N in
(a) and to C in (b), by lowering LUMO energies and by
stabilizing the products of fragmentation.
3
[1d] converted aryl iodides into aryl anions. The compounds 2
and 3 also reduced Weinreb amides,[1f] acyloin derivatives,[1h]
R
ecently, we have developed a range of highly reactive
organic electron donors, including 1–3 (Scheme 1). These
and some sulfones.[1c]
The donor 2 also cleaved arenesulfonamides, but not N,N-
dialkyl arenesulfonamides.[1c] For the sulfonamides 6, 8, and
10, the electron is transferred from the donor to the
arenesulfonyl unit, where the LUMO is located. The sub-
strates 6 and 8 underwent efficient reductive cleavage of the
compounds undergo oxidation to radical cations and dications
ꢀ
N S bond to afford the corresponding amines 7 and 9 [using
donor 2 (6 equiv), DMF, 1108C, 18 h]. In these cases, the
nitrogen leaving groups are stabilized by resonance. However,
the sulfonamide 10, which, after fragmentation, would
produce a nitrogen-centred leaving group which is unstabi-
lized by resonance, remained completely unchanged.
Most recently, our donors 2 and 3, vivid yellow and purple
solids, respectively, were tested under photoactivation con-
ditions and proved even more powerful than in the ground
ꢀ
state, in that they were now able to reductively cleave the Ar
Cl bond in chlorobenzenes, a reaction which had never been
seen with our ground-state electron donors.[1q] In addition,
they were able to donate an electron to the cis-diphenylcy-
clopropane 11, ultimately affording the 1,3-diphenylpropane
12 as a product.[1q]
These advances encouraged us to test the photoactivated 3
in other very challenging transformations, that is, the reduc-
tive cleavage of 1) difficult arenesulfonamides like 10,[2] and
2) N-benzyl groups,[3] and we report herein our results. The
donor 3 was selected since it is as strong as 2, but is much more
conveniently prepared.
Scheme 1. Protected amines and neutral organic electron donors.
DMF=N,N-dimethylformamide, Ts=4-toluenesulfonyl.
The sulfonamides 10, 14, and 16 were chosen as substrates
for reduction (Scheme 2). Fragmentation of their radical
anions would give rise to a nitrogen-centred leaving group
which would not be stabilized by resonance. Under photo-
activated conditions (l = 365 nm, 2 ꢀ 100 W) at room temper-
ature, each of the substrates underwent cleavage to afford the
parent amine in good yield after work-up. The l = 365 nm
irradiation does not overlap with the chromophore of the
sulfonamides, and hence it is the highly colored 3 which
undergoes photoactivation. This result marks the first time
that dialkyl arenesulfonamides have been reductively cleaved
by a neutral organic electron donor.
[*] S. O’Sullivan, E. Doni, Dr. T. Tuttle, Prof. Dr. J. A. Murphy
WestCHEM, Department of Pure and Applied Chemistry
University of Strathclyde
295 Cathedral Street, Glasgow G1 1XL (UK)
E-mail: tell.tuttle@strath.ac.uk
john.murphy@strath.ac.uk
[**] We thank ORSAS, EPSRC, and the University of Strathclyde for
funding. Mass spectrometry data were acquired at the EPSRC UK
National Mass Spectrometry Facility at Swansea University.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201306543.
ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. This is an open access article under the terms of the Creative
Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly
cited.
To verify the nature of the activation, two types of blank
experiments were also conducted for the substrates 10, 14,
and 16. These blank reactions were conducted a) without 3,
474
ꢀ 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 474 –478

Angewandte
Chemie
single-point energy calculation of the optimized geometry
was performed at the same level of theory within a polarizable
continuum model (CPCM)[10] with the dielectric constant of
N,N-dimethylformamide (DMF, e = 37.219; see the Support-
ing Information for details). These studies indicated that
fragmentation of the radical anion 19 into 20 and 21 is
thermodynamically preferred, both when 19 alone is consid-
ered as an entity, and also when a complex between the
radical cation of the donor and 19 is considered. Experimental
evidence in favor of the formation of an aminyl radical
following fragmentation was also seen when substrate 24 was
subjected to cleavage. Here fragmentation into the toluene-
sulfinyl radical 23 and dialkylamide anion 28 should lead to
the isolation of the corresponding amine, N-cyclopropyl-N-
tetradecylamine, upon work-up. In contrast, cleavage to 21
and the aminyl radical 29 should lead to rapid opening of the
cyclopropane ring to afford the imine 30, which could
undergo quenching of its radical in a number of ways[1k] to
form the imine product 31, and thus undergo hydrolysis under
mild work-up conditions to afford the tetradecylamine 26. In
fact, the experiment afforded 26 (85%) and 25 (78%), thus
supporting 29 as an intermediate.
The next task was to investigate whether N-benzyl groups
could be cleaved. The outcome from the substrate 8 deserves
comment because it shows no cleavage of the benzyl group.
This is in accord with expectations in this case, as the LUMO
is localized on the electron-poor p-toluenesulfonyl (tosyl)
ꢀ
group, rather than on the benzyl group. When the S N bond is
cleaved, the aniline anion 18 results, and the arene ring is too
electron-rich to receive another electron. Either during the
reaction or upon work-up, 18 undergoes protonation to 9.
To modify the structure of 8 so that cleavage of an N-
benzyl bond might occur, we designed substrates such that the
benzyl group was the site of the LUMO within the substrate.
To this end, benzyl alkyl methanesulfonamide derivatives
(33a–i) were chosen (Table 1). DFT studies (B3LYP / 6-
31G*), taking 33c and 33g as examples, in a DMF solvent
Scheme 2. Reactions of sulfonamides with the photoactivated donor 3.
but in the presence of photoactivation, and b) with 3, but in
the absence of photoactivation. In all cases, no product was
formed and the starting substrate was recovered in excellent
yield (see the Supporting Information). This reinforced the
message that photoactivation of the donor (or the donor–
substrate complex; see the Supporting Information), signifi-
cantly enhances the driving force for electron transfer.
For completeness, the more reactive substrates, 6 and 8,
were also treated with 3 under photoactivated conditions
(Scheme 2). They underwent efficient cleavage, as expected,
with the products 7 and 9, respectively, being isolated in
excellent yield after shorter reaction times in the presence of
three equivalents of 3.
For the radical anion 19, formed at the sulfonamide group
in 10 after electron transfer (Scheme 2), we calculated
whether fragmentation to either the dialkylamide anion 22
and a sulfonyl radical 23, or the dialkylaminyl radical 20 and
a sulfinate anion 21 would be preferred.[4] Density functional
theory[5,6] (DFT) calculations were employed to optimize all
structures with the gradient corrected B97-D functional with
a long-range dispersion correction.[7] All atoms were de-
scribed with the 6-311 ++ G(d,p) basis set.[8,9] Subsequent
Table 1: Reductive deprotection of benzyl methanesulfonamides (33)
with 3.
Substrate
R
Ar
33
34
Yield [%][a]
Yield [%][b]
33a
33b
33c
33d
33e
CyCH2
i-pentyl
i-butyl
C12H25
C6H5CH2
3,5-(MeO)2C6H3
3,5-(MeO)2C6H3
3,5-(MeO)2C6H3
3,5-(MeO)2C6H3
3,5-(MeO)2C6H3
33a: 9
33b: 12
33c: 0
33d: 21
33e: 7
34a: 80
34b: 80
34c: 79
34d: 64
34e*: 35
+34e: 28
34d: 80
34a: 71
34h: 84
34i: 75
33 f
33g
33h
33i
C12H25
CyCH2
n-butyl
Cy
C6H5
C6H5
4-(CF3)C6H4
4-(CF3)C6H4
33 f: 15
33g: 14
33h: 0
33i: 0
[a] Recovered starting material. [b] Yield of isolated product. Ms=me-
thanesulfonyl.
Angew. Chem. Int. Ed. 2014, 53, 474 –478
ꢀ 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
475

.
Angewandte
Communications
continuum indicated that the LUMO of these compounds was
located on the benzyl group. If electron transfer occurred to
the benzyl group, then the leaving group would likely be the
sulfonamide anion, and this would be protonated to form 34
upon work-up. Upon trying the reactions, very good yields of
N-benzyl bond cleavage were seen in each case (Table 1). The
substrate 33e features a benzyl group and a dimethoxybenzyl
group. The outcome shows competitive cleavage of these two
benzyl groups, with marginal selectivity for the formation of
34e*, which is consistent with a very slightly preferential
electron transfer to the less electron-rich aryl ring, that is, the
C6H5 ring. To show that photoactivation was required for
these reactions, 33g was subjected to a parallel reaction in
which photoactivation was omitted. This reaction afforded an
excellent recovery of the unchanged 33g (94%).
the SOMO of their radical anions) are sited on the allyl
groups, thus allowing the selectivity of the observed reactions
to be easily understood. In 35b and 35c, the LUMO lies on
the aryl ring, however, the radical anion shows spontaneous
cleavage of the allyl group. In this case, electron transfer to
the arene should occur preferentially. There is no driving
force for fragmentation of the arene radical anion in these two
cases, since that would give an alkyl leaving group unstabi-
lized by resonance, so intramolecular electron transfer to the
allyl group can occur, thus leading to the observed fragmen-
tation. To explore whether photoactivation was needed to
trigger these reactions, the substrate 35b was subjected to the
same reaction conditions, except that no photoactivation was
provided. In this case, no deprotection occurred and 35b was
recovered in quantitative yield.
Since benzyl methanesulfonamides had worked so well we
next investigated the more challenging allyl methanesulfon-
amides. Because these compounds have less extensive p sy-
stems, their LUMO energies are expected to be higher than
their benzyl counterparts. In support of this, the mixed allyl
benzyl substrate 35a showed selectivity for the benzyl
cleavage to 37 (62%; Table 2). This outcome was in line
This ability to transfer an electron to an N-allylsulfon-
amide takes the photoactivated electron donors into new
territory, as no previous deallylation reaction has been
reported. To check if the allyl group was really needed, or if
N,N-dialkyl methanesulfonamides would undergo reaction by
electron transfer to the sulfonyl group, the N,N-dioctyl
methanesulfonamide 38 was subjected to reaction with the
photoactivated 3. In this case, no new product was detected
and the starting material 38 (92%) was recovered unchanged.
Table 2: Reductive deprotection of allyl methanesulfonamides 35.
ꢀ
The ability to transfer an electron to an ArC N ring group
is evident in the above results with the substrates 33a–i, and
this led us to investigate what happens in the transposed case,
ꢀ
that is, ArN C. An amine nitrogen atom directly attached to
the arene should make electron transfer to the arene more
difficult, but the accessibility of the LUMO for electron
transfer should depend upon the third group attached to the
nitrogen atom. With the simple N-methyl-N-allylaniline 39a,
very little cleavage occurred, but the product that was
isolated, 40a (6%), showed cleavage of the N-allyl bond
(Table 3). To better facilitate the cleavage reaction, the N-Me
Substrate
R
35
36
37
Yield [%][a]
Yield [%][b]
Yield [%][b]
35a
35b
35c
35d
35e
C6H5CH2
C6H5(CH2)2
C6H5(CH2)3
C12H25
35a: 15
35b: 57
35c: 47
35d: 32
35e: 38
36a: 10
36b: 41
36c: 42
36d: 63[c]
36e: 50
62
0
0
0
0
i-pentyl
[a] Recovered starting material. [b] Yield of isolated product. We
recognize that 36a=34e, 36d=34d, and 36e=34b. [c] When addi-
tional donor 3 (6 equiv) was added after 72 h, and the reaction continued
for a further 72 h, 36d (81%) was isolated.
Table 3: Reductive deprotection of allylanilines with electron donor 3.
with expectations since the LUMO of this substrate (and the
SOMO of its radical anion) were associated with the arene
ring, rather than with the allyl group or with the sulfonyl
group. However, the presence of some product resulting from
allyl cleavage, that is, 36a (10%), encouraged us to think that
substrates which did not feature an N-benzyl group might
undergo cleavage of the allyl group. This selectivity in 35a for
benzyl cleavage over allyl cleavage contrasts with that seen in
palladium-induced reduction of benzyl allylamines where the
affinity of Pd0 for olefins dominates the reactivity.[11] It also
surprisingly contrasts with the selectivity in favor of deal-
lylation seen in the reductive deprotection of sugars with SmI2
reported by Hilmersson et al.[12]
Substrate
R
39
40
Yield [%][a]
Yield [%][b]
39a
39b
39c
39d
39e
Me
allyl
COMe
COtBu
CO2Et
39a: 62
39b: 81
39c: 59
39d: 8
40a: 6
40b: 7
40c: 33
40d: 83
40e: 58
39e: 37
[a] Recovered starting material. [b] Yield of isolated product.
group was replaced by an N-acyl group. The electron-with-
drawing acyl group can lower the LUMO energy and hence
make electron transfer to the LUMO easier. In the event,
protection of the nitrogen atom as an acetamide (39c),
a pivalamide (39d), and a urethane (39e), all enhanced the
cleavage of the allyl group.[13] A blank experiment was also
conducted on 39c (in the absence of photoactivation) and this
When the allyl alkyl methanesulfonamides 35b–e were
treated under photoactivation conditions with 3, cleavage of
the allyl group was exclusively seen, with moderate to good
yields of the products 36 being isolated. Taking the substrates
35d and 35e as examples, the LUMO of the substrates (and
476
www.angewandte.org
ꢀ 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 474 –478

Angewandte
Chemie
showed no conversion into the product, but rather quantita-
tive recovery of 39c, thus illustrating the essential role of the
photoactivation of the donor. The pivalamide was most
successful, thus affording the product 40d in 83% yield. The
significant difference in efficiency between 39c and 39d led us
to investigate whether deprotonation of the acetyl group by
the basic donors might be occurring. When a repeat of the
experiment with 39c was subjected to addition to D2O, as
opposed to H2O, prior to acidification and extraction, both
the product 40c and the recovered starting material 39c
showed incorporation of a single deuterium atom by mass
spectrometry. For further thoughts on the role of deprotona-
tion, see discussion of reactivity of substrate 44.
Since the ease of bond cleavage in the radical anion seems
to correlate with the stabilization given to the radical and
anion products, then replacing the alkene of the allyl group in
39 by a carbonyl group, as in 41, (Table 4) might additionally
Table 4: Reductive deprotection of N-(acylmethyl)anilines with electron
donor 3.
ꢀ
Scheme 3. Substrates for ArN C cleavage.
ꢀ
Finally, we prepared the modified ArN C substrate 44
ꢀ
where cleavage of the ArN C bond at the radical anion stage
Substrate
R
41
Product
Yield [%][a]
Yield [%][b]
(46) would leave the radical and anion tethered together in 47
(Scheme 3). In this case, an intriguing rearrangement of the
pyrrolidine into a piperidone product 45 (30%) occurred.
Efforts to improve the conversion by adding more equivalents
of 3 were not successful, and this is consistent with the
representation in Scheme 3. The initial radical anion 46
undergoes fragmentation to 47. In the presence of excess 3,
further reduction to the amidyl anion 48 should occur rapidly.
The dianion 48 is unlikely to cyclize, but cyclization could
occur after proton transfer from another molecule of 44,
thereby forming the enolate 49 which will not undergo any
reduction. Finally, cyclization of the anion 50 would afford the
piperidone 45. If this proposal is correct, it would also be
relevant for the closest analogue of 44, that is, 41a. The lower
yield in these two substrates could therefore be explained
both by this proton transfer from substrate and by the
inherent difficulty of electron transfer to an N,N-dialkylani-
line.
41a
41b
41c
41d
Me
41a: 58
41b: 25
41c: 0
40a: 34
40c: 74
40e: 92
42: 89
COMe
CO2Et
Ts
41d: 0
[a] Recovered starting material. [b] Yield of isolated product.
facilitate the cleavage reactions, since the anionic leaving
group would be an enolate, in place of an allyl anion.
Accordingly, the substrates 41a–c were prepared. Encourag-
ingly, the N-methyl substrate 41a showed a higher yield of
cleavage product [here 40a (34%)] than had been seen for the
corresponding allyl case, 39a (6%). The N-acetyl and the N-
carbethoxy cases, 41b and 41c, respectively, underwent very
efficient reaction (74% and 92% yield of products respec-
tively) with loss of the CH2CO2Et side chain. This outcome
ꢀ
shows that ArN C bonds are also subject to reductive
cleavage, and that the efficiency of cleavage correlates with
stabilization of the radical and anion produced. A repeat
reaction was carried out for 41b, but in the absence of
photoactivation. This reaction gave no 40c, but gave recov-
ered starting material (41b, 91%). A final example of this
series, 41d, was reacted to give a comparison with other
sulfonamide substrates reported herein, and this afforded 42
(89%), the expected product of fragmentation of the
arenesulfonamide radical anion.
To conclude, electron transfer from the photoactivated
ꢀ
ꢀ
neutral electron donor 3 delivers high yields of S N and C N
cleavage products for a range of nitrogen-containing species
including anilines, sulfonamides, and amides. These reactions
proceed at room temperature and under mild reaction
conditions in the absence of any metal reagents, thus
illustrating challenging reactions which can be achieved by
photoactivated neutral organic electron donors.
Received: July 26, 2013
Revised: September 25, 2013
Published online: December 6, 2013
To verify the importance of the aryl group, the substrate
43 was next prepared (Scheme 3). If electron transfer to the
ꢀ
ester group occurred, then cleavage of the N CH2CO2Et
bond might have been expected, but none was seen. Accord-
ꢀ
ingly, the N-aryl group is crucial for the N C cleavage to
occur.
Keywords: electron transfer · cleavage reactions ·
photochemistry · radical ions · reduction
.
Angew. Chem. Int. Ed. 2014, 53, 474 –478
ꢀ 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
477

.
Angewandte
Communications
2013, 135, 10934 – 10937; u) S. Zhou, G. M. Anderson, B.
Mondal, E. Doni, V. Ironmonger, M. Kranz, T. Tuttle, J. A.
Murphy, Chem. Sci. 2013, DOI: 10.1039/C3SC52315B; v) H. S.
Farwaha, G. Bucher, J. A. Murphy Org. Biomol. Chem. 2013, 11,
8073 – 8081.
[1] a) J. A. Murphy, T. A. Khan, S. Z. Zhou, D. W. Thomson, M.
Mahesh, Angew. Chem. 2005, 117, 1380 – 1384; Angew. Chem.
Int. Ed. 2005, 44, 1356 – 1360; b) J. A. Murphy, S.-Z. Zhou, D. W.
Thomson, F. Schoenebeck, M. Mohan, S. R. Park, T. Tuttle,
L. E. A. Berlouis, Angew. Chem. 2007, 119, 5270 – 5275; Angew.
Chem. Int. Ed. 2007, 46, 5178 – 5183; c) J. A. Murphy, F.
Schoenebeck, S.-Z. Zhou, Y. Uenoyama, Y. Miclo, T. Tuttle, J.
Am. Chem. Soc. 2007, 129, 13368 – 13369; d) J. A. Murphy, J.
Garnier, S. R. Park, F. Schoenebeck, S.-Z. Zhou, A. T. Turner,
Org. Lett. 2008, 10, 1227 – 1230; e) J. Garnier, J. A. Murphy, S. Z.
Zhou, A. T. Turner, Synlett 2008, 2127 – 2131; f) S. P. Y. Cutulic,
J.A. Murphy, H. Farwaha, S.-Z. Zhou, E. Chrystal, Synlett 2008,
2132 – 2136; g) M. Mohan, J. A. Murphy, F. LeStrat, H. P. Wessel,
Beilstein J. Org. Chem. 2009, 5, 1; h) S. P. Y. Cutulic, N. J. Findlay,
S. Z. Zhou, E. J. T. Chrystal, J. A. Murphy, J. Org. Chem. 2009,
74, 8713 – 8718; i) J. A. Murphy, F. Schoenebeck, N. J. Findlay,
D. W. Thomson, S. Z. Zhou, J. Garnier, J. Am. Chem. Soc. 2009,
131, 6475 – 6479; j) J. Garnier, A. R. Kennedy, L. E. A. Berlouis,
A. T. Turner, J. A. Murphy, Beilstein J. Org. Chem. 2010, 6, 73;
k) R. Sword, L. A. Baldwin, J. A. Murphy, Org. Biomol. Chem.
2011, 9, 3560 – 3570; l) P. I. Jolly, S. Zhou, D. W. Thomson, J.
Garnier, J. A. Parkinson, T. Tuttle, J. A. Murphy, Chem. Sci.
2012, 3, 1675 – 1679; m) E. Cahard, F. Schoenebeck, J. Garnier,
S. P. Y. Cutulic, S. Zhou, J. A. Murphy, Angew. Chem. 2012, 124,
3733 – 3736; Angew. Chem. Int. Ed. 2012, 51, 3673 – 3676; n) P. I.
Jolly, N. Fleary-Roberts, S. OꢁSullivan, E. Doni, S. Zhou, J. A.
Murphy, Org. Biomol. Chem. 2012, 10, 5807 – 5810; o) S. Zhou,
H. Farwaha, J. A. Murphy, Chimia 2012, 66, 418 – 425; p) J.
Garnier, D. W. Thomson, S. Zhou, P. I. Jolly, L. E. A. Berlouis,
J. A. Murphy, Beilstein J. Org. Chem. 2012, 8, 994 – 1002; q) E.
Cahard, F. Schoenebeck, J. Garnier, S. P. Y. Cutulic, S. Zhou,
J. A. Murphy, Angew. Chem. 2012, 124, 3733 – 3736; Angew.
Chem. Int. Ed. 2012, 51, 3673 – 3676; r) R. Sword, S. OꢁSullivan,
J. A. Murphy, Aust. J. Chem. 2013, 66, 314 – 322; s) E. Doni, S.
OꢁSullivan, J. A. Murphy, Angew. Chem. 2013, 125, 2295 – 2298;
Angew. Chem. Int. Ed. 2013, 52, 2239 – 2242; t) E. Doni, B.
Mondal, S. OꢁSullivan, T. Tuttle, J. A. Murphy, J. Am. Chem. Soc.
[2] a) Greeneꢀs Protective Groups in Organic Synthesis, 4th ed. (Eds.:
P. G. M. Wuts, T. W. Greene), Wiley, Hoboken, 2006, ISBN-10:
0471697540
j
ISBN-13: 978-0471697541; b) P. J. Kocienski,
Protecting Groups, 3rd ed., Georg Thieme, New York, 2005,
ISBN-10: 1588903761 j ISBN-13: 978 – 158890376; c) S. Searles,
N. Nukina, Chem. Rev. 1959, 59, 1077 – 1103; d) T. Kan, T.
Fukuyama, Chem. Commun. 2004, 353 – 359; T. Fukuyama, C. K.
Jow, M. Cheung, Tetrahedron Lett. 1995, 36, 6373 – 6374.
[3] a) S. D. Bull, S. G. Davies, G. Fenton, A. W. Mulvaney, R. S.
Prasad, A. D. Smith, J. Chem. Soc. Perkin Trans. 1 2000, 3765 –
3774; b) B. D. Gray, P. W. Jeffs, J. Chem. Soc. Chem. Commun.
1987, 1329 – 1330.
[4] For fragmentations of other arene radical anions, see a) P.
Maslak, R. D. Guthrie, J. Am. Chem. Soc. 1986, 108, 2628 – 2636;
b) P. Maslak, R. D. Guthrie, J. Am. Chem. Soc. 1986, 108, 2637 –
2640.
[5] W. Kohn, L. J. Sham, Phys. Rev. 1965, 140, A1133.
[6] R. G. Parr, W. T. Yang, Density Functional Theory of Atoms and
Molecules, Oxford University Press, New York, 1989.
[7] S. Grimme, J. Comput. Chem. 2006, 27, 1787 – 1799.
[8] R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem. Phys.
1980, 72, 650 – 654.
[9] A. D. McLean, G. S. Chandler, J. Chem. Phys. 1980, 72, 5639 –
5648.
[10] J. Tomasi, B. Mennucci, R. Cammi, Chem. Rev. 2005, 105, 2999 –
3093.
[11] S. Chandrasekhar, C. R. Reddy, R. J. Rao, Tetrahedron 2001, 57,
3435 – 3438.
[12] A. Dahlꢂn, A. Sundgren, M. Lahmann, S. Oscarson, G.
Hilmersson, Org. Lett. 2003, 5, 4085 – 4088.
[13] For recent remarkable reductive cleavage of amides, see M.
Szostak, M. Spain, D. J. Procter, Angew. Chem. 2013, 125, 7378 –
7382; Angew. Chem. Int. Ed. 2013, 52, 7237 – 7241.
478
www.angewandte.org
ꢀ 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 474 –478