Metal-Free Ring-Expansion Reaction of Six-membered Sulfonylimines with Diazomethanes: An Approach toward Seven-Membered Enesulfonamides

Article abstract of DOI:10.1002/anie.201508804

A new metal-free, ring-expansion reaction of six-membered N-sulfonylimines with unstable diazomethanes, generated in situ from the N-tosylhydrazones, has been developed. This reaction delivers valuable seven-membered enesulfonamides by a Tiffeneau-Demjanov rearrangement and intramolecular proton transfer tautomerization process. Moreover, this ring-expansion reaction can be carried out in a one-pot fashion and scaled up to the gram scale by using aryl aldehydes, without the need to isolate the N-tosylhydrazone. A diazo thing: The title reaction between cyclic N-sulfonylimines and diazo compounds generated in situ from the N-tosylhydrazones is simple and functional-group tolerant. It thus delivers valuable seven-membered sulfonamides in up to 95 % yield. Moreover, this reaction can be carried out in one-pot starting from the aryl aldehydes, without the need to isolate the N-tosylhydrazone (right).

Full text of DOI:10.1002/anie.201508804

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201508804
German Edition: DOI: 10.1002/ange.201508804
Diazo Compounds
Metal-Free Ring-Expansion Reaction of Six-membered Sulfonylimines
with Diazomethanes: An Approach toward Seven-Membered
Enesulfonamides
An-Jie Xia+, Tai-Ran Kang,* Long He,* Lian-Mei Chen, Wen-Ting Li+, Jin-Liang Yang,* and
Quan-Zhong Liu*
Abstract: A new metal-free, ring-expansion reaction of six-
membered N-sulfonylimines with unstable diazomethanes,
generated in situ from the N-tosylhydrazones, has been
developed. This reaction delivers valuable seven-membered
enesulfonamides by a Tiffeneau–Demjanov rearrangement
and intramolecular proton transfer tautomerization process.
Moreover, this ring-expansion reaction can be carried out in
a one-pot fashion and scaled up to the gram scale by using aryl
aldehydes, without the need to isolate the N-tosylhydrazone.
has been made in the past years.[6,8–10] The metal-free coupling
reactions of diazo compounds generated in situ from N-
tosylhydrazones under basic reaction conditions (Bamford–
Stevens reaction)[7] have appeared in the recent literature.[8]
In pioneering studies, Barluenga, ValdØs, and co-workers
discovered metal-free reductive cross-coupling of boronic
acids,[9a] phenols, and alcohols[9b] with N-tosylhydrazones. The
group of Wang also reported a metal-free reaction to convert
N-tosylhydrazones into pinacol boronates.[10]
À
The diazo carbon insertion into either a keto C C bond or
[11,12]
À
S
even-membered sulfonamides or sulfamates are found to
formyl C H bond is a valuable tool in organic synthesis.
possess prominent biological activities,[1] such as, calcium
sensing receptor agonists,[1c] HIV-1 protease inhibiters,[1d] and
ASBT inhibitors.[1e] In addition, they are also used as synthetic
intermediates for the synthesis of biologically active mole-
cules.[1c,2–5] Despite being appealing structural motifs, only few
metal-catalyzed methods for the synthesis of these com-
pounds have been reported.[1f, 2–5] Major synthetic methods
consist of: 1) Rhodium- or iron-catalyzed intramolecular
For example, the Lewis acid catalyzed ring-expansion reac-
tion of cyclohexanones with diazo compounds have become
a classical strategy for synthesis of seven-membered rings
through the Tiffeneau–Demjanov rearrangement (Sche-
me 1a).[13,14] Although it is clear that the reaction between
allylic C H amination;[2] 2) Rhodium-catalyzed intramolecu-
À
lar alkyne or allene amination;[3,4] 3) Copper-catalyzed intra-
molecular nucleophilic ring-opening of sulfamate-derived
aziridines;[5] 4) Scandium- or lutetium-catalyzed haloamino-
cyclization of primary sulfamate ester derivatives.[1f] Despite
great achievements in metal-catalyzed reactions, the discov-
ery of efficient metal-free reactions will also be of great
importance because of the reduced toxicity and elimination of
the cost of the metal.[9a] For these reasons, the metal-free
reaction is highly desirable, and indeed, significant progress
[*] Dr. A.-J. Xia,[+] Prof. Dr. T.-R. Kang, Prof. Dr. L. He,
Prof. Dr. L.-M. Chen, Prof. Dr. Q.-Z. Liu
Scheme 1. The ring-expansion reaction of cyclohexanone or cyclic
N-sulfonylimine. Ts =4-toluenesulfonyl.
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan
Province/College of Chemistry & Chemical Engineering, Collabora-
tive Innovation Center of Tissue Repair Material of Sichuan Province,
China West Normal University
Nanchong, 637009 (China)
E-mail: kangtairan@sina.com
longhe@cwnu.edu.cn
quanzhongliu@sohu.com
Prof. Dr. T.-R. Kang, Dr. W.-T. Li,[+] Prof. Dr. J.-L. Yang
State Key Laboratory of Biotherapy/Collaborative Innovation Center
of Biotherapy, Cancer Center, West China Hospital
Sichuan University, Chengdu (P.R. China)
acyclic N-tosylimines and acyldiazomethanes could afford N-
tosyldiazoketamines[15a] or N-tosylaziridines[15b] under various
reaction conditions (Scheme 1b), we reasoned that if the ring-
expansion reaction were conducted with a six-membered
imine, the resulting product might form a seven-membered
imine, based on a similar Tiffeneau–Demjanov rearrange-
ment mechanism under certain reaction conditions (Sche-
me 1c).
The ring-expansion reactions between cyclic ketones and
diazo compounds have been widely used in organic syn-
thesis.[16] However, to the best of our knowledge, there has
been no systematic study on the ring-expansion reaction of
E-mail: jlyang01@163.com
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201508804.
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cyclic imines with diazo compounds so far. Herein, we report
a metal-free ring-expansion reaction of six-membered imines
with diazomethanes, thus providing a new and promising
route to seven-membered enesulfonamides.
To test our hypothesis, we employed the N-tosylhydra-
zone 1a and benzoxathiazine 2,2-dioxide 2a[17] as model
substrates (for structures see Table ; see Table S1 in the
Supporting Information). After some optmization work
(entries 1–12), it was found that the best yield of the expected
seven-membered sulfonamide 3a was achieved by employing
Cs2CO3 as a base in 1,4-dioxane at 608C (entry 2). It should be
noted that the diazoketamine and aziridine products were not
found.
With the optimal reaction conditions established, a variety
of N-tosylhydrazones (1) derived from aldehydes and ben-
zoxathiazine 2,2-dioxides (2) were subjected to the ring-
expansion reaction (Table 1). The electronic nature of
substituents on the aryl ring attached on the a-position of
N-tosylhydrazone had no apparent effects on the reaction.
Aromatic groups bearing electron-donating and electron-
withdrawing substituents were tolerated. The higher reactiv-
ity of the substrates containing an electron-withdrawing
group at the 4-position of the aryl ring could lead to
formation of the products in higher yields (3b–g). Steric
hindrance had a slight effect on this transformation, both
ortho- and meta-substituted phenyl N-tosylhydrazones pre-
sented lower reactivity and led to the formation of the
products in moderate yields (3j–o). Notably, 1-naphthyl N-
tosylhydrazone participated in the reaction to give the
corresponding product 3p in 81% yield. The heteroaromatic
3-thiophenyl N-tosylhydrazone provided the expected prod-
ucts 3q in 45% yields (entry 17), but the 2-furanyl or 2-
thiophenyl N-tosylhydrazones failed (entries 18–19). To our
delight, when R2 = methyl, the corresponding products 3r–
t were afforded in moderate yield (entries 20–22). Using an N-
tosylhydrazone derived from an aliphatic aldehyde as a sub-
strate resulted in no new products (entry 23). Considering
that the alkyl diazomethane generated in situ from the
corresponding N-tosylhydrazones at 608C are highly unsta-
ble, we turned to the direct utilization of alkyl diazomethanes.
By using diazomethane as a substrate, the same seven-
membered product 3u was afforded at 08C in excellent yield,
irrespective of R2 being a hydrogen or methyl group
(entries 24 and 25). The use of diazoethane gave the product
3v at room temperature in 90% yield (entry 26).
Table 1: Reaction scope of the N-tosylhydrazones.[a]
This reaction was not significantly affected by the
substituents on the aromatic ring of the benzoxathiazine
2,2-dioxides 2 (Table 2). Although a slightly lower yield was
observed when the substituent was 8-Me or 6,8-tBu (4h, 4i),
both electron-donor and electron-withdrawing substituents
were effective, thus giving the corresponding products 4 in
moderate to good yield (4a–j). The reaction also worked well
with a 1-naphthyl N-sulfonylimine (4k).
Entry
R1
R2
3
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24[e]
25[e]
26[f]
Ph
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Me
H
H
Me
Me
3a
3b
3c
3d
3e
3 f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
–
87
95
94
92
89
90
88
70
64
78
62
60
68
65
63
81
45
4-FC6H4
4-ClC6H4
4-BrC6H4
4-CF3C6H4
4-CNC6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
3-BrC6H4
3-MeC6H4
3-MeOC6H4
2-ClC6H4
2-BrC6H4
2-MeOC6H4
1-naphthyl
3-thienyl
2-thienyl
2-furanyl
Ph
Table 2: Scope of the cyclic N-sulfonylimines.[a]
[c]
–
[c]
–
–
3r
3s
3t
–
3u
3u
3v
64
70
67
4-BrC6H4
3-BrC6H4
nBu
CH2N2
CH2N2
[d]
–
99
98
90
CH3CHN2
[a] Reaction conditions: N-tosylhydrazone (1; 0.21 mmol), cyclic N-
sulfonylimine (2; 0.2 mmol), and Cs2CO3 (75 mol%) in 0.5 mL of 1,4-
dioxane at 608C for 8–16 h under argon. [b] Yield of isolated product.
[c] Other products were obtained; see the Supporting Information.
[d] No new products were detected. [e] The CH2N2 was used. See the
Supporting Information for details. [f] The CH3CHN2 was used. See the
Supporting Information for details.
[a] Reaction conditions: N-tosylhydrazone 1a (0.21 mmol), cyclic
N-sulfonylimines 2 (0.2 mmol), Cs2CO3 (75 mol%) in 0.5 mL of 1,4-
dioxane at 608C for 8–16 h in argon. [b] Yield of isolated product.
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This ring-expansion reac-
tion could be carried out in
a one-pot fashion and scaled-
up to a gram scale from the
aryl aldehydes 5 without the
need to isolate the tosylhy-
drazone, thus affording the
enesulfonamides 3 in similar
yield (see the Supporting
Information for details; Scheme 2. Proposed mechanism for the ring-expansion reaction.
selected examples are
shown in Table 3).
Table 3: One-pot reaction of the aryl aldehydes 5 with cyclic
N-sulfonylimine 2a.[a]
Entry
Ar
3
Yield [%][b]
1
2
3
4
Ph
4-FC6H4
3a
3b
3j
3m
3o
3p
86
90
75
65
60
75
80
3-BrC6H4
2-ClC6H4
2-MeOC6H4
1-naphthyl
Ph (10.5 mmol)
5
6
Scheme 3. Transformations of 3a. Boc=tert-butoxycarbonyl, dba=di-
7[c]
3a (2.18 g)
benzylideneacetone, DCC=dicyclohexylcarbodiimide, DCM=dichloro-
methane, THF=tetrahydrofuran.
[a] Reaction conditions: 1) aryl aldehyde 5 (0.21 mmol), tosylhydrazide
(0.22 mmol) in MeOH (1 mL), at 608C for 1–2 h; 2) cyclic N-sulfonyl-
imine 2a (0.2 mmol) and Cs2CO3 (75 mol%) in 1,4-dioxane (1 mL), at
608C for 8–16 h under argon. [b] Yield of isolated product. [c] 10 mmol
scale; see the Supporting Information for the reaction conditions.
skeleton. Finally, intramolecular proton transfer tautomeri-
zation of F leads to the expected product 3a.
The synthetic versatility of the product 3a is demonstrated
by a series of transformations (Scheme 3). Hydrogenation of
3a using Pd/C gave the cyclic sulfamate 6 in 90% yield. 2-(2-
Amino-1-phenylethyl)phenol (7), which is an important
structural unit in the agricultural and pharmaceutical
agents,[19] was easily derived from the cyclic sulfonamide 6
in 85% yield. Acidic hydrolysis of 3a produced the valuable
3-phenylbenzofuran (8) in 70% yield. Palladium-catalyzed
hydroamination reaction between dimethyl 2-vinylcyclo-pro-
pane-1,1-dicarboxylate and 3a produced the allylic sulfon-
amide 9 in 95% yield. This approach is an effective and
valuable hydroamination protocol. The N-Boc-(S)-2-amino-
2-phenylacetic acid reacting with 3a afforded 10 in 95% yield.
The diazo carbon atom could be selectively inserted into the
Figure 1. X-ray structure of 3o; thermal ellipsoids shown at 30%
probability.
The structure of 3o was confirmed by X-ray crystal
structure analysis (Figure 1).[18] Based on the Bamford–
Stevens reaction[7] and the mechanistic study reported by
the groups of Barluenga[9a] and Maruoka,[15] the formation of
3a is rationalized by a ring-expansion reaction as outlined in
Scheme 2. The compound 1a undergoes deprotonation to
form the tosylhydrazone salt A. And the diazo compound B is
generated by decomposition of A. From B, two pathways are
possible: a) B could react with 2a via a similar Tiffeneau–
Demjanov-type intermediate C, and a rearrangement of the
carbon skeleton with release of N2, subsequently affords F.
b) The carbene D, generated by thermally induced N2 release,
reacts with 2a via a zwitterionic intermediate E, thus
smoothly affording F by a rearrangement of the carbon
À
N H bond of 3a, thus giving 11 in 99% yield.
In conclusion, we developed a new metal-free ring-
expansion reaction of cyclic N-sulfonylimines with diazo-
methanes by a tandem reaction similar to a Tiffeneau–
Demjanov rearrangement/proton-transfer tautomerization
process. This transformation represents an extremely simple
way to afford seven-membered enesulfonamides. Moreover,
the reaction can be conducted in one pot and on gram scale
using aryl aldehydes without isolation of the tosylhydrazones.
We believe that this new ring-expansion reaction could
become a widely used transformation in organic synthesis.
Angew. Chem. Int. Ed. 2016, 55, 1441 –1444
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Acknowledgments
We thank Science & Technology Department of Sichuan
Province (2013JY0095), Education Department of Sichuan
Province (15CZ0016), the Innovative Research Team in
College of Sichuan Province (14TD0016), and NSFC
(21572183) for financial support.
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Received: September 19, 2015
Revised: November 13, 2015
Published online: December 14, 2015
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1441 –1444