Efficient Synthesis of Unsymmetrical Sulfamides via a Lossen-Like Rearrangement

Article abstract of DOI:10.1002/adsc.201501139

A convenient one-pot synthesis of unsymmetrical sulfamides via a Lossen-like rearrangement is reported. The protocol operates under simple conditions at room temperature and does not require an inert atmosphere and a dry solvent. The ability of N-hydroxy arenesulfonamide O-derivatives to generate under mild conditions N-sulfonylimine intermediates was a trigger point for developing a general synthetic strategy towards unsymmetrical sulfamides. The synthetic potential of the methodology has been investigated by preparing cyclic sulfamides and new potential chiral organocatalysts. (Figure presented.) .

Full text of DOI:10.1002/adsc.201501139

UPDATES
DOI: 10.1002/adsc.201501139
Efficient Synthesis of Unsymmetrical Sulfamides via a Lossen-
Like Rearrangement
Loïc Pantaine,a FranÅois Richard,a JØrôme Marrot,a Xavier Moreau,a,*
Vincent Coeffard,a,* and Christine Grecka
a
Institut Lavoisier Versailles, UMR CNRS 8180, UniversitØ de Versailles-St-Quentin-en-Yvelines, 45 Avenue des
États-Unis, 78035 Versailles cedex, France
E-mail: xavier.moreau@uvsq.fr or vincent.coeffard@uvsq.fr
Received: December 14, 2015; Revised: April 11, 2016; Published online: May 24, 2016
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201501139.
Abstract: A convenient one-pot synthesis of unsym-
metrical sulfamides via a Lossen-like rearrangement
is reported. The protocol operates under simple
conditions at room temperature and does not re-
quire an inert atmosphere and a dry solvent. The
ability of N-hydroxy arenesulfonamide O-deriva-
tives to generate under mild conditions N-sulfonyl-
imine intermediates was a trigger point for develop-
ing a general synthetic strategy towards unsymmet-
rical sulfamides. The synthetic potential of the
methodology has been investigated by preparing
cyclic sulfamides and new potential chiral organoca-
talysts.
Figure 1. Sulfamide-containing drugs.
À
strategies for the formation of the S N bonds in sulfa-
mides. Amongst them, the use of sulfur dioxide in
conjunction with iodine has emerged as a more con-
venient strategy to prepare symmetrical sulfamides
than the classical reaction of amines with strong elec-
trophilic reagents such as SO2Cl2 (Scheme 1, route
Keywords: amines; reactive intermediates; rear-
rangement; sulfamides; synthetic methods
The first synthesis of sulfamide was reported by V. H. a).[6,10] Nevertheless, this method did not allow the
Regnault in 1838 by reacting sulfuryl chloride with preparation of unsymmetrically substituted sulfamides
ammonia.[1] The profusion of publications that ensued which can exhibit higher biological responses than the
from this discovery relied on various aspects of sulf- symmetrical analogues.[11] One classical strategy in
amide chemistry such as synthetic strategies, physical which this demand can be achieved is through the re-
properties as well as applications of sulfamides.[2] The action of sulfamoyl chloride with an amine in the
electronic and structural nature of the sulfamide func- presence of a base (Scheme 1, route b).[12] The hazard-
tional groups make them attractive bioisosteres of ous reagents required for the preparation of sulfamoyl
amides, ureas, thioureas, carbamates and sulfon- chloride derivatives lower the synthetic appeal of this
amides.[3] Sulfamides have found interesting applica- strategy. In addition, sterically hindered or less reac-
tions in pharmaceutical research programs as depicted tive amines are less prone to form the desired sulf-
in Figure 1 with the broad-spectrum antibiotic Dori- amide targets in the presence of sulfamoyl chloride
penem and Macitentan which is used to treat pulmo- reagents. In order to develop milder and more effi-
nary arterial hypertension. Besides applications for cient approaches, new sulfuryl-containing reagents
the synthesis of therapeutic agents, the sulfamide bearing an oxazolidinone,[13] imidazolium[14] or a cate-
moiety has been incorporated in self-assembling mol- chol motif[15] have been utilized for the preparation of
ecules,[4] peptides,[5] polymers,[6] ligands,[7] chiral auxil- unsymmetrical sulfamides.[16] Despite the progress
iaries,[8] and in organocatalysts.[9] These interesting brought by these methods, most of them require
À
properties have spurred chemists to develop general a multistep approach to create the S N bonds and/or
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Table 1. Reaction optimization.[a]
Entry
Solvent
Base
Yield [%]
1
2
3
4
5
6
7
8
9
acetone
EtOAc
DMC[b]
MTBE[b]
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
NMM
NMM
NMM
NMM
NMM
n.r.
56
61
55
86
10
17
30
89
[c]
–
AcONa
Cs2CO3
Et3N
[a]
Reactions were performed on a 0.5 mmol scale using
1 equiv. of 1a, 1.2 equiv. of 2a and 1.5 equiv. of a base in
2 mL of solvent at room temperature for 16 h unless oth-
erwise noted. n.r.=no reaction.
Dimethyl carbonate (DMC), methyl tert-butyl ether
(MTBE).
[b]
[c]
Scheme 1. Main strategies towards sulfamides.
No base was added to the reaction mixture.
may be not compatible with heterocyclic amines.
Herein, we present a simple and general one-pot pro- vents (entries 1–5). The best solvent was dichlorome-
cedure to prepare unsymmetrical sulfamides via thane which produced the desired sulfamide 3 in 86%
a Lossen-like rearrangement (Scheme 1, route c). The yield (entry 5). With these conditions in hand, the in-
N-hydroxy arenesulfonamide O-derivatives 2 react fluence of the base was investigated (entries 6–9). The
akin to their N-hydroxy amide analogues and undergo presence of a base is crucial for the success of the
a Lossen rearrangement[17] to form N-sulfonylimines transformation (entry 6). Amongst the bases consid-
which can be trapped by various nucleophiles.[2,18] ered for the formation of 3, the best result was ob-
While the rearrangement of N-hydroxy amides to tained with Et3N which enables the formation of 3 in
form isocyanates has been extensively studied, a gen- 89% yield (entry 9). Switching from TsNHOTs (2a)
eral methodology devoted to the formation of N-sul- to TsNHOAc was detrimental to the formation of 3
fonylimines through a Lossen rearrangement remains which was not obtained under these conditions. With
unexplored.[19] Recently, our group reported a series the optimized conditions (Table 1, entry 9), the scope
of aminocatalytic-based methodologies involving dif- and limitations with respect to the nature of the
ferent nucleophiles such as hydrazine derivatives, in- amine 1 and the N-hydroxy arenesulfonamide O-de-
doles or sulfonamides.[20] Related to our continuing rivatives 2 were investigated (Table 2).
interest in the preparation of nitrogen-containing
Regardless of the nature of the amine 1a–o, moder-
compounds, we surmised that sulfamides could be rel- ate-to-excellent levels of yields of 3–17 were obtained
evant substrates to search for new methodologies. with 2a (Table 2, entries 1–15). Similarly to 3, the sul-
The lack of general and simple protocols towards un- famide 4 was produced in an excellent yield (entries 1
symmetrical sulfamides prompted us to investigate and 2). We then focused our attention on the nature
the possibility of achieving their preparation through and position of the halogen substituent of 1 on the ef-
a Lossen rearrangement of 2. In particular the high ficiency of the reaction. The treatment of 4-halogen-
reactivity of N-sulfonylimines would allow for the oanilines 1c–e with 2a afforded the corresponding
synthesis of sulfamides bearing heterocyclic motifs or products in excellent yields (entries 3–5). For the
bulky amino substituents which are challenging tar- bromo series, a slight decrease of the yield was ob-
gets as described above.
served when starting from 2-bromoaniline 1g (en-
We began our investigation by studying the reaction tries 5–7). This could be explained by a lower reactivi-
of para-toluidine 1a with the readily available N-hy- ty of the aniline 1g due to an increase of the steric
droxy toluenesulfonamide O-Ts 2a in the presence of hindrance and the higher deactivation role of the
various bases and solvents (Table 1). The reaction of bromo substituent at ortho position. An interesting
para-toluidine 1a with 2a in the presence of N-methyl- feature of this reaction lies in its compatibility with
morpholine (NMM) was investigated in different sol- electron-poor aromatic amines such as 1h and 1i
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Table 2. Scope and limitations.[a]
levels of yields and the desired targets 18 and 19 were
produced in 97% and 55% yields respectively (en-
tries 17 and 18). The fluoro sulfamide 5 was obtained
in an excellent yield by reaction of para-toluidine 1a
with 2e (entry 19). Nevertheless, limitations arise
from the use of the methyl derivative 2f which did
not undergo any Lossen-like rearrangement and
therefore, the compound 20 was not obtained
(entry 20). In spite of intense synthetic efforts, we
were unable to prepare a substrate 2 bearing a nitro
substituent such as N-hydroxy 4-nitrophenylsulfon-
amide O-Ns.
Entry
1
2
Product Yield [%]
In efforts to broaden the scope of potential cou-
pling partners, Lossen-like rearrangements of 2a with
chiral amines were deemed particularly worthy of in-
vestigation owing to the potential of sulfamides as
chiral organocatalysts.[9] Sulfamides act as efficient
double hydrogen-bonding donators in organocatalysis
1
2
3
4
5
6
7
8
4-MeC6H4NH2 (1a)
PhNH2 (1b)
2a
2a
2a
2a
2a
2a
2a
3
4
5
6
7
8
9
89
95
95
94
99
96
74
72
75
78
45
55
63
62
67
81
97
55
95
n.r.
4-FC6H4NH2 (1c)
4-ClC6H4NH2 (1d)
4-BrC6H4NH2 (1e)
3-BrC6H4NH2 (1f)
2-BrC6H4NH2 (1g)
4-NO2C6H4NH2 (1h)
4-EtO2CC6H4NH2 (1i) 2a 11
4-EtOC6H4NH2 (1j)
Ph2NH (1k)
2-aminopyridine (1l)
benzylamine (1m)
cyclohexylamine (1n)
1-adamantamine (1o)
4-MeC6H4NH2 (1a)
4-MeC6H4NH2 (1a)
4-MeC6H4NH2 (1a)
4-MeC6H4NH2 (1a)
4-MeC6H4NH2 (1a)
À
due to a higher acidity of the N H bonds than those
2a 10
in the corresponding (thio)ureas. The reaction of l-
phenylalanine methyl ester hydrochloride 21 with 2a
in the presence of 2.5 equiv. of triethylamine afforded
the sulfamide 22 in 84% yield (Scheme 2). HPLC
analyses did not show any racemization of the stereo-
genic center during the transformation. While chiral
amine scaffolds such 1,2-diaminocyclohexane[9a,b,d] and
pyrrolidine motifs[9c] have been used for the synthesis
of bifunctional sulfamide organocatalysts, to the best
of our knowledge, the synthesis of sulfamides derived
from 9-amino-(9-deoxy)-epi-Cinchona alkaloids has
never been reported. Therefore, the chiral sulfamide
product 24 was prepared in 53% yield by reacting 9-
amino-(9-deoxy)-epi-quinine 23 with 2a. As a further
9
10
11
12
13
14
15
16
17
18
19
20
2a 12
2a 13
2a 14
2a 15
2a 16
2a 17
2b
2c
2d 19
4
18
2e
2f
5
20
[a]
Reactions were performed on a 0.5 mmol scale using
1 equiv. of 1, 1.2 equiv. of 2 and 1.5 equiv. of Et3N in
2 mL of dichloromethane at room temperature for 16 h
unless otherwise noted; n.r.=no reaction.
which are challenging substrates in the formation of
sulfamides. The sulfamides 10 and 11 were formed in
72% and 75% yields, respectively (entries 8 and 9).
Secondary amines such as diphenylamine 1k are ame-
nable to react with 2a by producing 13 in 45% yield
and the challenging heterocyclic amine, 2-aminopyri-
dine 1l, afforded the sulfamide 14 in 55% yield (en-
tries 11 and 12). Apart from aniline derivatives, alkyl-
amines 1m–o are suitable substrates for the formation
of sulfamides (entries 13–15). In particular, the steri-
cally hindered 1-adamantamine 1o reacted with 2a to
afford the sulfamide 17 in 67% yield (entry 15). This
result confirms the synthetic interest of the reaction
which is compatible with a vast range of amines. Var-
iations to the N-hydroxy arenesulfonamide O-deriva-
tives 2 were next investigated (entries 16–20). The
Lossen-like rearrangement of 2b proceeded smoothly
and the sulfamide 4 was obtained in 81% yield
(entry 16). The introduction of electron-donating
groups on the aromatic rings did not influence the Scheme 2. Synthesis of chiral sulfamides.
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Scheme 4. Reaction of phenol with 2a.
able amines and easily accessible N-hydroxy arenesul-
fonamide O-derivatives. The reaction proceeds
through a Lossen-like rearrangement at room temper-
ature and does not require inert atmosphere and dry
solvent. Therefore, the operationally simple and high-
yielding procedure provides an efficient alternative to
previously reported strategies towards unsymmetrical
sulfamides. In particular, the synthetic potential of the
methodology has been investigated by preparing
cyclic sulfamides and new potential chiral organocata-
lysts for which their ability to promote enantioselec-
Scheme 3. Sulfamides derived from para-quinamines.
application of the methodology, we wondered wheth- tive reactions will be reported in due course.
er the reaction conditions for the formation of sulf-
amides could be applied to the hindered para-quina-
mines 25 which are prone to desymmetrization reac- Experimental Section
tion as reported by our group.[20c] We were delighted
to observe that the reaction of 25 with 2a in the pres- General Procedure
ence of N-methylmorpholine afforded the cyclic sulf-
Triethylamine (0.75 mmol, 105 mL, 1.5 equiv.) was added to
amides 26 without any traces of the acyclic sulfamides
a solution of the amine derivative 1 (0.5 mmol, 1 equiv.) in
(Scheme 3).[21]
dichloromethane (0.5 mol/L). The solution was cooled down
The formation of 26 might proceed through the for-
mation of the sulfamide moiety followed by an intra-
molecular desymmetrizing aza-Michael addition. The
reactivity decreased rapidly with an increase of the
bulkiness of the R group as observed in our previous
works.[20c] While 26a (R=Me) and 26b (R=Et) were
obtained in good yields, the butyl- and phenyl-derived
products 26c and 26d were obtained in moderate
yields.
In order to get a better understanding of the mech-
anistic pathway and to detect the N-sulfonylimine in-
termediate (Scheme 1), ESI-MS analyses were carried
out on the reaction of para-toluidine 1a with 2a by
taking samples of the reaction mixture at different
time intervals. Despite many attempts, the N-sulfonyl-
imine intermediate could not be detected which con-
firms the difficulty to observe such transient struc-
tures.[22] The trapping of N-sulfonylimine intermediate
with an alcohol has been used previously as an evi-
dence for its formation.[19a,22] Therefore, phenol was
chosen as an oxygenated nucleophile towards the for-
mation of 27 under optimized conditions (Scheme 4).
The reaction of phenol with 2a gave rise to 27 in
63% yield, confirming that the reaction conditions
allow the formation of functionalized sulfamides and
sulfamic esters.
to approximately 108C. TsONHTs 2a – or a derivative
thereof – (0.6 mmol, 1.2 equiv.) was dissolved in dichlorome-
thane (0.6 mol/L) and added dropwise to the cooled solu-
tion. The reaction was then left to warm up to room temper-
ature for 16 h. Water (2 mL) was added to the solution. The
phases were separated and the aqueous phase was extracted
with dichloromethane. The organic phases were combined,
dried on anhydrous magnesium sulfate, filtered and concen-
trated. The crude product was then purified by column chro-
matography on silica gel (petroleum ether/EtOAc) to afford
the desired sulfamides.
Acknowledgements
We thank the Fondation de CoopØration Scientifique Campus
Paris Saclay for a Ph.D. grant to LP. This work was support-
ed by the French National Research Agency under the Pro-
gram Investing in the Future Grant no. ANR-10-IDEX-0003-
02. We acknowledge financial support from CNRS and Uni-
versitØ de Versailles-St-Quentin-en-Yvelines.
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