Transition metal-free aroylation of NH-sulfoximines with methyl arenes

Article abstract of DOI:10.1039/c5cc05483d

A novel protocol towards N-aroylated sulfoximines from NH-sulfoximines and methyl arenes was herein demonstrated. The reaction took place in the presence of elemental iodine, requiring no external organic solvents, transition metal-catalysts or ligands. The aroylated products were obtained from the oxidative transformation in moderate to excellent yields (up to 94% yield) with a broad substrate scope (35 examples) through a radical pathway.

Full text of DOI:10.1039/c5cc05483d

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Transition Metal-free Aroylation of NH-Sulfoximines with Methyl
Arenes
Received 00th January 20xx,
Accepted 00th January 20xx
Ya Zou,† Jing Xiao,† Zhihong Peng† Wanrong Dong†,*and Delie An†,*
DOI: 10.1039/x0xx00000x
www.rsc.org/chemcomm
A novel protocol towards N-aroylated sulfoximines from NH- necessary to the transformations.[12] However, to rule out the
sulfoximines and methyl arenes was herein demonstrated. The transition metal-catalysts, contributions have been made to seek
reaction took place in the presence of elemental iodine, requiring the possibilities for utilization of methyl arenes as aroylation
for no external organic solvents, transition metal-catalysts or coupling partners towards N-aroylated sulfoximines in the presence
ligands. The aroylated products were obtained from the oxidative of non-metal-catalysts. Thus, we wish to demonstrate a novel
transformation in moderate to excellent yields (up to 94% yields) protocol for the combination of the two nucleophilic reagents
with a broad substrate scope (up to 35 examples) through a catalysed by elemental iodine howbeit the inertness of the benzylic
radical pathway.
C(sp3)-H bonds on methyl arenes.[13]
Recently, sulfoximine chemistry has attracted more and more
attention due to the extensive utilizations in the pharmaceutical
and agricultural applications,[1] as well as for being chiral precursors
or ligands in asymmetric synthesis.[2] What’s more, sulfoximines
also served as pivotal intermediates for the construction of other
heterocyclic compounds.[3] NH-sulfoximines undertook various
transformations such as arylation,[4] alkylation,[5] vinylation,[6]
alkynylation[7] etc al.[8] easily due to the fickleness of the NH group.
Amongst, aroylation of NH-sulfoximines has been well-established
with benzoyl chlorides, aromatic carboxylic acids.[9] However, the
traditional methods for the N-aroylated sulfoximines still suffer
from the limitations like toxic reagents, harsh conditions and low
conversions. To solve the above-mentioned issues, great attempt
has been devoted over the topic. For example, Bolm has disclosed a
copper(I)-catalyzed N-aroylation method from NH-sulfoximines and
Scheme 1 N-Aroylation of Sulfoximines
benzaldehydes under the oxidative conditions through a dual C- With this in mind, reactions were embarked for the optimal
H/N-H activations pathway.[10] Then, another aroylation protocol of conditions with toluene (1a) and NH-sulfoximine (2a) as model
N-chloro sulfoximines with methyl arenes was described from the substrates (Table 1). In the presence of a catalytic amount of I2 (20
same group, using MnO2 as the catalyst.[11] Meanwhile, it is mol%) and tert-butyl hydroperoxide (TBHP), N-benzoyl sulfoximine
noteworthy that methyl arenes have been applied successfully for 3aa was obtained in moderate yield (58% for entry 1).
the formation of carbon-heteroatom bonds through the C-H Disappointingly, other oxidants like DTBP (Di-tert-butyl peroxide),
activation and successive oxidative functionalization pathway.[12] oxone, K2S2O8 and H2O2 were proved totally ineffective to the
The metallic catalysts like Pd, Cu and Mn salts were proved transformation for no product was detected after 6 h (entries 2 - 5).
However, the participation of the oxidant TBHP was significant to
the reaction. The yield decreased dramatically to 28% when the
†
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of
Chemistry and Chemical Engineering, Hunan University, Changsha, 410082, P. R.
China.
reaction took place in the absence of TBHP (entry 6). Surprisingly,
the addition of Na2CO3 (50 mol%) improved the yield greatly up to
91% under the air atmosphere, and 3aa was obtained in 89% yield
when the reaction was conducted under the nitrogen atmosphere
(entry 7). However, no reaction was detected by replacement of
Na2CO3 with triethyl amine (TEA) (entry 8). Other iodine sources,
Email-Address for the correspondence authors: wanrongdong@hnu.edu.cn,
deliean@hnu.edu.cn.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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which were able to offer elemental iodine when combined with due to the steric hindrance (entry 20). It is noteworthy that 2-
external oxidant,[13] were also checked. Pleasingly, KI, tBu4NI and methyl naphthalene (1u) reacted with NH-sulfoximine (2a) towards
NIS afforded the desired product 3aa successfully, but in lower the corresponding product 3ua in 85% yield (entry 21). Howbeit,
yields, from 38% to 68% (entries 9 – 11).
methyl-(hetero)arenes 1v – 1x failed to react with NH-sulfoximine
2a (entries 22 – 24) for unclarified reasons.
Table 1 Selected results for optimization of conditionsa
Table 2 Evaluation of scope of methylarenesa
Entry
1
catalysts
additives
oxidants
TBHP
DTBP
oxone
K2S2O8
H2O2
Yields (%)b
58
Entry
1
Ar
Ph
3
Yield (%)b
91
I2
--
--
2
I2
n.d.c
3aa
3ba
3ca
3da
3ea
3fa
2
4-CH3C6H4
4-tBuC6H4
4-MeOC6H4
4-FC6H4
79
3
I2
--
n.d.
3
81
4
I2
--
n.d.
4
82
5
I2
I2
--
n.d.
28d
5
74
6
--
--
91 (89 e)
6
4-ClC6H4
94
7
I2
Na2CO3
Et3N
Na2CO3
Na2CO3
Na2CO3
TBHP
TBHP
TBHP
TBHP
TBHP
7
4-BrC6H4
4-IC6H4
3ga
3ha
3ia
88
8
I2
n.d.
8
68
9
KI
42
n.d. (38f)
9
4-MeO(O)CC6H4
4-NCC6H4
4-CF3C6H4
4-NO2C6H4
3-MeC6H4
3-FC6H4
86
10
11
nBu4NI
NIS
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
3ja
87
68
a
3ka
3la
58
Reaction conditions: 1a (6 mmol, 20 equiv.), 2a (0.3 mmol),
69
catalyst (0.06 mmol, 20 mol%), additive (0.15 mmol, 50 mol%),
oxidant (1.2 mmol, 4.0 equiv.) at 80 oC for 6 h. b Isolated yields. c
n.d. for not detected. d I2 (0.3 mmol) was used instead of I2 (0.06
3ma
3na
3oa
3pa
3qa
3ra
3sa
3ta
3ua
3va
3wa
3xa
80
63
e
3-ClC6H4
68
mmol)/TBHP (0.6 mmol). N2 (1 atm) atmosphere was used
instead of air (1 atm). f The yield was obtained in the absence of
Na2CO3.
3-BrC6H4
3-IC6H4
68
60
3-NO2C6H4
3,5-Me2C6H3
2-MeC6H4
2-Naphthyl
2-Furyl
59
91
With the optimal conditions in hand, the limitations and scope of
the substrates were evaluated (Table 2). Firstly, the functional
groups on the para- position of the methyl arenes were tested.
Both electron-donating and electron-withdrawing functional groups
were well-tolerated in the system. For example, 4-methyl- (1b), 4-n-
butyl- (1c) and 4-methoxy- (1d) toluenes exhibited negative effect
to the reaction for the desired products 3ba – 3da were obtained in
lower yields, 79%, 81% and 82%, respectively (entries 2 – 4). While
4-fluoro- (1e), 4-chloro- (1f), 4-bromo- (1g) and 4-iodo- (1h)
toluenes reacted with 2a smoothly, furnishing the desired products
3ea – 3ha in yields ranging from 68% to 94% (entries 5 – 8). Other
electron-withdrawing groups as ester (1i), cyano (1j),
trifluoromethyl (1k) and nitro (1l) on the para- positions of the
substrates were surprisingly compatible in the transformation,
producing the expected compounds 3ia – 3la in 58% to 89% yields
(entries 9 – 12). In a similar manner, various functional groups on
the meta- position of toluenes were also checked in the protocol. N-
58
85
n.d.c
n.d. c
n.d. c
2-Thienyl
2-Pyridinyl
a
Note: Reaction conditions: 1 (10 mmol, 20 equiv.), 2a (0.5
mmol), I2 (0.1 mmol), Na2CO3 (0.25 mmol), TBHP (2.0 mmol) at
80 oC for 6 h. b Isolated yields. c n.d. for not detected.
In the same manner, the limitations and scope of the substrates on
NH-sulfoximines were checked in the reaction (Table 3). S-methyl-S-
(4-methylphenyl)- (2b) and S-methyl-S-(4-methoxyphenyl)- (2c) NH-
sulfoximines underwent the aroylation reaction with toluene (1a)
smoothly, furnishing the corresponding products 3ab and 3ac in
85% and 89% yields, respectively (entries 1 and 2). Gratifyingly, S-
methyl-S-halophenyl NH-sulfoximines such as S-methyl-S-(4-
fluorophenyl)- (2d), S-methyl-S-(4-chlorophenyl)- (2e), S-methyl-S-
(4-bromophenyl)- (2f) NH-sulfoximines reacted with toluene (1a)
successfully, offering the desired products 3ad – 3af in moderate to
good yields, from 67% to 82% (entries 3 - 5). Meantime, the
activities of S-(3-substituted phenyl) or S-(2-substituted phenyl) like
S-methyl-S-(3-methylphenyl)- (2g), S-methyl-S-(2-methylphenyl)-
(2h) and S-methyl-S-(2-chlorophenyl)- (2i) NH-sulfoximines were
transformed into the corresponding compounds 3ag – 3ai in yields
ranging from 69% to 84% (entries 6 – 8). In contrast, hetero-
(3-methylbenzoyl)
sulfoximine
(3ma),
N-(3-fluorobenzoyl)
sulfoximine (3na), N-(3-chlorobenzoyl) sulfoximine (3oa), N-(3-
bromobenzoyl) sulfoximine (3pa), N-(3-iodobenzoyl) sulfoximine
(3qa) and N-(3-nitrobenzoyl) sulfoximine (3ra) were successfully
obtained, however, generally in lower yields, ranging from 59% to
80% (entries 13 -18). But N-(3,5-dimethylbenzoyl) sulfoximine (3sa)
was smoothly produced in good yield (91% for entry 19). When 1,2-
dimethylbenzene (1t) reacted with NH-sulfoximine (2a), offering the
N-(2-methylbenzoyl) sulfoximine 3ta in a moderate yield probably
2 | J. Name., 2012, 00, 1-3
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aromatic bearing NH-sulfoximine such as S-pyridinyl-S-methyl NH- and 2a, the yield of 3fa decreased sharply to 18%, and benzyl-
sulfoximine (2j) furnished the corresponding N-benzoyl-S-pyridinyl- TEMPO adduct other than the acyl-TEMPO adduct was
4
S-methyl sulfoximine (3aj) in a medium yield under the optimal successfully isolated in 28% yield.[14] The result proved that the
conditions (62% for entry 9). Moreover, S-ethyl-S-phenyl (2k), S- reaction likely took place via a benzyl radical intermediate.
isopropyl-S-phenyl (2l), S,S-diphenyl (2m) NH-sulfoximines exhibited
good compatibility in the approach, affording the N-aroylated
products 3ak – 3am in 78% to 92% yields (entries 10 - 12). Similarly,
N-benzoyl-S,S-dimethyl sulfoximine (3an) and N-benzoyl-S,S-
tetramethylene sulfoximine (3ao) were successfully produced in
78% and 80% yields, respectively (entries 13 and 14).
Table 3 Evaluation of scope of NH-sulfoximinesa
Entry
1
R1
4-CH3C6H4
4-CH3OC6H4
4-FC6H4
4-ClC6H4
4-BrC6H4
3-CH3C6H4
2-CH3C6H4
2-ClC6H4
Pyridinyl
Ph
R2
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
3
Yield (%)b
85
3ab
3ac
3ad
3ae
3af
2
89
3
67
4
78
5
82
Figure 2 Proposed mechanism
6
3ag
3ah
3ai
84
7
79
Thus, possible mechanism of the transition metal-free protocol was
proposed as shown in Figure 2. Firstly, iodine radical particle was
generated from elemental iodine with the assistance of the oxidant
TBHP. Then, another key radical intermediate I was formed in the
presence of in-situ generated iodine radical, releasing a molecular
of HI. Successively, the newly-formed intermediate I coupled with
the substrate 2a with a release of an H radical, forming another key
intermediate N-benzyl sulfoximine II. The H radical was captured by
another iodine radical to form a HI, which was easily neutralized
with Na2CO3. Meanwhile, the newly-generated intermediate II
8
69
9
3aj
62
10
11
12
13
14
3ak
3al
78
Ph
i-Pr
Ph
88
Ph
3am
3an
3ao
92
Me
Me
(R1R2)
78
80
a
Note: Reaction conditions: 1a (10 mmol, 20 equiv.), 2 (0.5
mmol), I2 (0.1 mmol), Na2CO3 (0.25 mmol), TBHP (2.0 mmol) at
80 oC for 6 h. b Isolated yields.
underwent another fast oxidation step to furnish
a diol
intermediate III in the presence of TBHP, which afforded the
desired product 3aa after dehydration.
Nevertheless, the mechanism of the newly developed aroylation
protocol remained blurry. According to the report from Bolm[10], it
was considered the reaction might take place via the acyl-radical
intermediate. Therefore, control reactions were conducted for
clarification (Figure 1). When benzaldehyde was applied as the
aroylation reagent, 3aa was obtained in 62% yield from the iodine-
catalysed protocol.
Scheme 2 Reactions between acetopheones 5 and 2a (The yields in
the parentheses were obtained with the addition of TEMPO)
CHO
I2/Na2CO3
+
2a
3aa
TBHP, 80 oC, 6 h
62%
Me
Me
I2/Na2CO3
N
+
+
1f
2a
3fa
O
TBHP, 80 oC, 6 h
Me Me
TEMPO
Cl
18% yield
4, 28% yield
Figure 1 Control reactions with benzaldehyde and addition of
TEMPO
However, with the addition of the radical scavenger TEMPO
It is noteworthy that 4-methyl acetopheone (5a) reacted with NH-
sulfoximine 2a under the metal-free conditions smoothly (scheme
(2,2,6,6-tetramethylpiperidinooxy) into the reaction between 1f
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2). Different products 3ya, 6a were isolated successfully, in 38% and
42% yields, respectively. The product 3ya was formed by the radical
procedure, while the compound 6a was generated through a C-
H/N-H dual activations pathway.[15] As expected, with the addition
of TEMPO, the yield of 3ya was depressed significantly and only
trace was isolated while the yield of the product 6a arose to 48%
(shown in the parentheses). Furthermore, the compatibilities of the
substituents on the acetophenone were checked in the system, and
the corresponding N-(2-oxo-2-arylacetyl)-sulfoximines 6b – 6g were
furnished in yields ranging from 41% - 55% as shown in scheme 2.
Harmata, N. L. Calkins, R. G. Banghman and C. L. Barnes, J.
Org. Chem., 2006, 71, 3650; d)M. Harmata and X. Hong, J.
Am. Chem. Soc., 2003, 125, 5754; e) W. Dong, L. Wang, K.
Parthasarathy, F. Pan and C. Bolm, Angew. Chem. Int. Ed.
2013, 52, 11573; f) W. Dong, K. Parthasarathy, Y. Cheng, F.
Pan and C. Bolm, Chem. Eur. J. , 2014, 20, 15732; g) D. G. Yu,
F. de Azambuja and F. Glorius, Angew. Chem. Int. Ed., 2014,
53, 2754.
4
a) C. Bolm and J. P. Hildebrand, Tetrahedron Lett., 1998, 39
5731; b) C. Bolm and J. P. Hildebrand, J. Org. Chem., 2000, 65
169; c) J. Sedelmeier and C. Bolm, J. Org. Chem., 2005, 70
6904; d) G. Y. Cho, P. Remy, J. Jansson, C. Moessner and C.
Bolm, Org. Lett., 2004, , 3293; e) J. Sedelmeier and C. Bolm,
J. Org. Chem., 2005, 70, 6904; f) C. Moessner and C. Bolm,
Org. Lett., 2005, , 2667; g) M. Harmata, X. Hong and S. K.
Ghosh, Tetrahedron Lett., 2004, 45, 5233; h) N. Yongpruksa,
N. L. Calkins and M. Harmata, Chem. Commun., 2011, 47
,
,
,
Conclusions
6
In summary, a new protocol towards N-aroylated sulfoximines
from methyl arenes and NH-sulfoximines was disclosed. The
simple and benign method feathers for free of transition metal
-catalysts, and no extra organic solvents are required. The
transformation offers a practical and facile synthetic tool for
the useful compounds.
7
,
7665; i) M. Miyasaka, K. Hirano, T. Satoh, R. Kowalczyk, C.
Bolm and M. Miura, Org. Lett., 2011, 13, 359; j) L. Wang, D. L.
Priebbenow, W. Dong and C. Bolm, Org. Lett., 2014, 16, 2661.
a) C. R. Johnson and O. M. Lavergne, J. Org. Chem., 1993, 58
5
,
1922; b) Y. Cheng, W. Dong, L. Wang, K. Parthasarathy and C.
Bolm, Org. Lett., 2014, 16, 2000 and references therein; c) C.
M. M. Hendriks, R. A. Bohmann, M. Bohlem and C. Bolm, Adv.
Synth. Catal., 2014, 356, 1847.
J. R. Dehli and C. Bolm, J. Org. Chem., 2004, 69, 8518 and
references therein.
a) L. Wang, H. Huang, D. L. Priebbenow, F. F. Pan and C. Bolm,
Angew. Chem. Int. Ed., 2013, 52, 3478; b) D. L. Priebbenow, P.
Becker and C. Bolm, Org. Lett., 2013, 15, 6155; c) X. Y. Chen,
L. Wang, M. Frings and C. Bolm, Org. Lett. , 2014, 16, 3796.
a) Rit, R. K.; Yadav, M. R.; Sahoo, A. K. Org. Lett. 2012, 14,
Acknowledgement
The authors are grateful for the financial support from the
National Natural Science Foundation of China (NSFC) (grant
number 21072052), the National Basic Research Program of
China (grant number 2009CB421601), and the Hunan Provincial
Science and Technology Department Program (grant number
2011WK4007, 06FJ4115) and The Fundamental Research Funds
for the Central Universities, Hunan University (grant number
531107040840).
6
7
8
3724; b) Yadav, M. R.; Rit, R. K.; Sahoo, A. K. Org. Lett. 2013
,
15, 1638; c) Yadav, M. R.; Rit, R. K.; Shankar, M.; Sahoo, A. K.
J. Org. Chem. 2014, 79, 6123; d) Rit, R. K.; Yadav, M. R.;
Ghosh, K.; Shankar, M.; Sahoo, A. K. Org. Lett. 2014, 16, 5258;
e) F. Teng, J. Cheng and C. Bolm, Org. Lett., 2015, 17, 3166
and references therein; f) C. Bohnen and C. Bolm, Org. Lett.,
2015, 17, 3011 and references therein; g) Chen, X. Y.;
Bohmann, R. A.; Wang, L.; Dong, S.; Rauber, C.; Bolm, C.
Chem. Eur. J. 2015, 21, 10330 and references therein.
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