Reduction of sulfonylimines with raney nickel

Article abstract of DOI:10.1080/00397911.2011.594974

Raney-Ni/EtOH reduction of different N-sulfonylimines provides a new entry for synthesizing sulfonamides in good yields under mild conditions. This protocol, which does not require additional hydrogen, constitutes a cheap, safe, and easy-to-handle alterna

Full text of DOI:10.1080/00397911.2011.594974

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Reduction of Sulfonylimines with Raney
Nickel
José Luis García Ruano a , José A. Fernández-Salas a , M. Carmen
Maestro a & Alejandro Parra a
a Departamento de Química Orgánica, Universidad Autónoma de
Madrid, Cantoblanco, Madrid, Spain
Accepted author version posted online: 01 Feb 2012.Version of
record first published: 18 Oct 2012.
To cite this article: José Luis García Ruano , José A. Fernández-Salas , M. Carmen Maestro &
Alejandro Parra (2013): Reduction of Sulfonylimines with Raney Nickel, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 43:2, 198-207
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Synthetic Communications1, 43: 198–207, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.594974
REDUCTION OF SULFONYLIMINES WITH RANEY
NICKEL
´
Jose Luis Garcıa Ruano, Jose A. Fernandez-Salas,
M. Carmen Maestro, and Alejandro Parra
´
´
´
´
Departamento de Quımica Organica, Universidad Autonoma de Madrid,
Cantoblanco, Madrid, Spain
´
´
GRAPHICAL ABSTRACT
Abstract Raney-Ni/EtOH reduction of different N-sulfonylimines provides a new entry for
synthesizing sulfonamides in good yields under mild conditions. This protocol, which does
not require additional hydrogen, constitutes a cheap, safe, and easy-to-handle alternative
procedure to prepare a-branched sulfonamides.
Keywords a-Branched amines; a-branched sulfonamides; C¼N reductions; Raney Ni; N-
sulfonylimines
INTRODUCTION
The use of the sulfonyl moiety to modulate the reactivity and properties of
nitrogen functions has been extensively exploited.[1] Thus, one of the most developed
methods for obtaining a-branched amines from carbonyl compounds involves the
Received May 26, 2011.
Address correspondence to Jose Luis Garcıa Ruano or M. Carmen Maestro, Departmento de
´
Quımica Organica, universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid, Spain. E-mail:
´
´
joseluis.garcia.ruano@uam.es; carmen.maestro@uam.es
´
´
198

REDUCTION OF SULFONYLIMINES
199
Scheme 1. Synthesis of sulfonamides with Raney Ni=EtOH.
reduction of N-sulfonylketimines as an intermediate step.[2] The synthetic interest of
this transformation has determined the use of a plethora of reagents such as sodium
borohydride,[3] silane derivatives,[4] borane,[5] dialkylzinc,[6] and transfer hydrogen-
ation[7] in the presence of different additives and=or catalysts. The use of hydrogen
as the reducing reagent deserves a special comment and, in this context, sulfona-
mides have been successfully prepared by transition-metal-catalyzed hydrogen-
ation.[8] Regarding the last methodology, the need of a hydrogen atmosphere,
many times demanding high gas pressure, is usually required for attaining good
conversions.
Although Raney Ni is one of the most used catalysts in the hydrogenation of
imines or in reductive amination reactions,[2,9] because it is cheap, safe, and easy to
handle, it has never been used for reducing N-sulfonylimines. During our studies on
the use of Raney Ni as a catalyst of the alkylation of amines and sulfinamides with
alcohols,[10] this reagent was useful for reduction of N-sulfonylimines without requir-
ing hydrogen gas, thus becoming safer and simpler to handling than other proce-
dures so far reported. In this article, we describe the results obtained in this study
starting from different aliphatic and aromatic N-sulfonylketimines (Scheme 1).
RESULTS AND DISCUSSION
N-Sulfonylimines used in this article were obtained by 3-chloroperbenzoic acid
(MCPBA) oxidation of the related N-sulfinylimines, easily obtained by condensation
of aldehydes or ketones with N-p-tolyl or tert-butylsulfinamides[11] (Scheme 1).
Reduction of N-p-Toluenesulfonylimines
The search of the optimal reduction conditions for sulfonylketimines with
Raney-Ni was performed using p-toluenesulfonylimine (1a) as the model substrate
(Table 1). As usual in reactions with Raney-Ni, the reagent was used in a large excess
and we tried to find the minimum amount allowing efficient transformations. A com-
plete reduction of 0.05 mmol of the sulfonylimine with 1 g of Raney Ni in ethanol at
room temperature required 3.5 h (entry 2). Reaction times were shortened to 2 h by
increasing the amount of the reagent to 1.5 g (entry 1, Table 1), whereas the conver-
sion was not complete (50% after 3.5 h) by decreasing this amount to 0.5 g (entry 3).
This low conversion could not be improved by applying longer reaction times (12 h,
entry 4) nor by increasing the temperature to 50 ꢀC (entry 5), which suggests that 1 g
of Raney Ni per 0.05 mmol of 1a is required for achieving the complete reduction of

200
J. L. G. RUANO ET AL.
Table 1. Optimization of the reduction of the N-sulfonylketimine 1a with Raney Ni=EtOH
Entry
Raney Ni (g)
Reaction time (h)
T (ꢀC)
Conversion (%)a
1
2
3
4
5
1.5
1.0
0.5
0.5
0.5
2
rt
rt
100
100
50
3.5
3.5
12
12
rt
rt
50
50
b
—
aMeasured by 1H NMR.
bOnly decomposition was observed.
the substrate. Under these conditions, an efficient reduction of different N-p-toluene-
sulfonylketimines 1a-l could be achieved. The results are shown in table 2.
We first studied the reduction of the N-sulfonylimines derived from substituted
acetophenones, which provided satisfactory results regardless of the electronic
character of the substituent at the aromatic ring (entries 1–9, Table 2). Reaction con-
ditions required for reducing 3-methoxy derivative 1b (entry 2) and 1a (entry 1) were
similar, but reaction times were slightly longer starting from 4-methyl derivative 1c
(4 h, entry 3). In all these cases, sulfonamides 2a, 2b, and 2c were obtained as pure
compounds in good isolated yields (84–88%) by simple filtration of the reagent.
Starting from the imine derived from 4-methoxyacetophenone, 1d, a clearly longer
reaction time (7 h) was required for obtaining a similarly good yield (84%, entry
4). The incorporation of electron-withdrawing groups, such as in the case of 1e
(4-CF3, entry 5), facilitated the reduction, and the reaction time for completion is
0.5 h. The moderate but clear dependence existing between the electronic density
=
at the aromatic ring and the reactivity of the C N suggests some nucleophilic
character of the reduction.
The presence at the aromatic ring of other groups able to be reduced by
Raney Ni gave interesting results. Concerning the chemoselectivity, only the alkoxy-
carbonyl group 1f (4-CO2Et, entry 6) was not affected under the conditions used in
the previous reactions, yielding 2f in good yield. As expected, reaction time required
for completion (1 h) was shorter than that of 1a. This was not the case of the halo-
derivatives 1g and 1h (entries 7 and 8). We have looked for the conditions allowing
the reduction of only one of the two groups present in these molecules, but unfortu-
nately selective reduction was not possible.[12] Although we could appreciate that
=
hydrogenolysis of C-Br was faster than reduction of C N bond (which, in its turn,
was faster than hydrogenolysis of C-Cl), mixtures of amino haloaryl sulfonamides,
=
dehalogenated tosylimines, and 2a (resulting from the reduction of C N and
hydrogenolysis of C-halogen)[13] were always obtained at the different temperatures,
reaction time, and amounts of catalyst that we have studied. However, we could

REDUCTION OF SULFONYLIMINES
201
Table 2. Reduction of the N-p-toluenesulfonylimines 1a–l with Raney Ni=EtOH
Imine
Entry
R1
R2
Time (h)
Product
Yield (%)
1
2
C6H5
Me (1a)
Me (1b)
Me (1c)
Me (1d)
Me (1e)
Me (1f)
Me (1g)
Me (1h)
Me (1i)
Me (1j)
Me (1k)
(1l)
3.5
3.5
4
2a
2b
2c
2d
2e
2f
86
84
88
84
86
85
79
71
—
83
83
82
88
78
76
3-MeOC6H4
4-MeC6H4
4-MeOC6H4
4-CF3C6H4
4-CO2EtC6H4
4-BrC6H4
4-ClC6H4
4-NO2C6H4
i-Pr
3
4
7
5
0.5
1
6
7a
8a,b
9a
10d
11d
12d
13
14
15a
3
2a
2a
7
c
—
10
5
2j
2k
2l
C7H15
4
-(CH2)4-
C6H5
C6H5
4
C6H5 (1m)
H (1n)
H (1o)
2.5
1.5
2
2m
2n
2o
i-Pr
a1.5 g of Raney Ni were used.
bReflux was necessary.
cComplex mixture (see text).
dNa2SO4 was used as water scavenger.
obtain 2a in good yield by using 1.5 g of Raney Ni from halogenated tosylimines
(entries 7 and 8).
Similarly, poor chemoselectivity was observed in the reaction of 1i, derived
from 4-nitroacetophenone (entry 9). We observed the formation of a mixture con-
taining 4-aminophenyl imine 1p,[14] along with 4-aminophenyl sulfonamide 2p and
the 4-ethylaminoarilderivative 3 (Scheme 2), resulting from the ethylation of the
NH2 group at 2p.[10] The composition of the mixture changed with the time but
we could not find conditions to attain the exclusive formation of 2p.
Scheme 2. Reduction of N-sulfonylketimine 1i with Raney Ni=EtOH.

202
J. L. G. RUANO ET AL.
Then we studied the Raney Ni = EtOH reduction of the N-sulfonylimines
derived from dialkylketones 1j–1l (entries 10–12, Table 2). The first attempts were
unsuccessful, and only decomposition products (ketone and p-toluenesulfonamide)
1
were observed by H NMR. It indicated that these imines were not stable enough
to the water present in the EtOH used as the solvent and therefore they were easily
hydrolyzed. To solve the problem, different water scavengers, such as molecular
˚
sieves (3 or 4 A) and inorganic salts, were added to the reaction mixture. To our
delight, when anhydrous Na2SO4 was added, imine 1j could be cleanly reduced to
2j in 83% yield (entry 10). The reaction time is longer (5 h) than that required for
reducing 1a, which is not surprising because of the expected lower reactivity of the
aliphatic imines. The same procedure was successfully applied to the alkylketimines
1k and 1l, yielding sulfonamides 2k (83%, entry 11) and 2l (82% yield, entry 12)
respectively. Finally, we have also used Raney Ni = EtOH for reducing the N-sulfo-
nyl diarylimine 2m (entry 13) and the aldimines 2n and 2o (entries 14 and 15) with
satisfactory results. As in the previous case, the aliphatic character of the imine 2o
=
required the addition of Na2SO4 for avoiding the hydrolysis of the C N bond.
Reduction of N-p-Toluenesulfonylimines
Taking into account that the N-tert-butanesulfonyl group (Bus) can be easily
removed to afford the free amines,[15,16] we applied our reduction protocol to the N-
tert-butanesulfonylimines, with the results indicated in Table 3. Reaction of aldimine
4n with Raney Ni under the usual conditions allowed the preparation of 5n in 4.5 h
(79% yield, entry 1, Table 3). However, when we applied the same conditions to keti-
mines, incomplete conversion was obtained, thus evidencing their expected lower reac-
tivity because of the large size of the tert-butyl group. Thus, 4a was partially transformed
(ꢁ50%) into 5a after 10 h at rt (entry 2, Table 3). To our delight, by increasing the tem-
perature to 80 ꢀC, conversion was complete and the N-tert-butanesulfonamide 5a was
obtained in 80% yield after 1 h (entry 2, Table 3). Under these same conditions, but using
Table 3. Reduction of the N-tert-butanesulfonylimines 3a–c using Raney Ni=EtOH
Imine
Entry
R1
R2
T (ꢀC)
Time (h)
Product
Yield (%)
1
C6H5
C6H5
-(CH2)4-
H(4n)
Me (4a)
(4l)
rt
4.5
1
5n
5a
5l
79
80
75
2a
3b
80
80
2
aA 50% conversion was obtained after 10 h at rt.
bNa2SO4 was used as water scavenger.

REDUCTION OF SULFONYLIMINES
203
Na2SO4 as water scavenger, ketimine derived from cyclohexanone 4l was reduced into 5l
in 75% yield (entry 3, Table 3).
In summary, we have developed an efficient method for reducing N-sulfonyl
ketimines and aldimines with Raney Ni = ethanol. The experimental method is very
simple and the reported conditions are safe (neither hydrogen atmosphere nor high
pressure are required) and mild (rt in most of the cases).
EXPERIMENTAL
1H and 13C NMR spectra were acquired at 300 MHz and 75 MHz respectively
(unless otherwise indicated). Chemical shifts (d) are reported in parts per million
(ppm) relative to CDCl3 (7.26 and 77.0 ppm respectively). Melting points were deter-
mined in open capillary tubes. All reactions were carried out in dry ethanol. Flash
column chromatography was performed using silica gel Merck-60 (230–400 mesh).
General Procedure for the Preparation of N-p-Toluenesulfonylimines
and N-Tert-Butanesulfonylimines
The N-sulfonylimines were synthesized by oxidation of the corresponding
N-toluenesulfinyl and N-tert-butanesulfinyl imines with MCPBA following our
methodology.[11]
N-[(4-Trifluoromethyl)phenyl]ethylidene-p-toluenesulfonylimine
(1e)[7a]. Yield: 86%. White solid, mp 62–64 ꢀC. 1H NMR: d 7.98 and 7.65 (AA0 BB0
system, 4H), 7.94 and 7.36 (AA0 BB0 system, 4H), 3.00 (s, 3H), 2.45 (s, 3H).19F NMR
(282 MHz, CDCl3): ꢂ63.2. 13C NMR: d 178.3, 143.9, 138.3, 134.5, 134.1, 129.6,
128.6, 127.2, 125.5 (c), 121.7, 21.6, 21.3. MS (FABþ) M=Z 342 (M þ 1, 29), 155
(38). HRMS calcd. for C16H15F3NO2S [M þ 1] 342.0787; found 342.0776.
(E)-Ethyl 4-[(p-toluenesulfonylimino)ethyl]benzoate (1f). Yield: 93%.
1H NMR: d 8.06 (d, J ¼ 8.4 Hz, 2H), 7.93–7.90 (m, 4H), 7.34 (d, J ¼ 8.0 Hz, 2H),
4.38 (q, J ¼ 7.0 Hz, 2H), 3.00 (s, 3H), 2.44 (s, 3H), 1.38 (t, 3H).13C NMR: d 178.8,
165.6, 143.7, 141.2, 138.3, 134.3, 129.6, 129.5, 128.1, 127.1, 61.4, 21.5, 21.3, 14.2.
General Procedure for Raney Nickel Reduction of N-p-
Toluenesulfonylimines and N-t-Butanesulfonylimines
To a stirred solution of the corresponding sulfonylimine (0.5 mmol) in EtOH
(3 mL) at rt, activated Raney Ni (1 g) (caution: pyrophoric) was added. Procedure
for activation: Commercially available aqueous Raney Ni (Fluka, cat. No. 83440)
was weighed as an aqueous slurry (1 g) and then washed with ethanol (3 ꢃ 20 mL)
before being directly used in the reaction. The reaction was monitored by thin-layer
chromatography (TLC). Upon completion (see tables 2 and 3), the Raney Ni was
filtered through Celite and washed with Et2O (2 ꢃ 20 mL). The organic phase was
dried (MgSO4) and concentrated under vacuum. The residue was purified by flash
chromatography on silica gel (230–400 mesh) with a 5:1 hexane = ethyl acetate
mixture.

204
J. L. G. RUANO ET AL.
N-(1-Phenylethyl)-4-methylbenzenesulfonamide (2a)[17]. Yield: 86%.
White solid, mp 62–64 ꢀC. 1H NMR: d 7.62 (d, J ¼ 8.3 Hz, 2H), 7.20–7.16 (m,
5H), 7.12–7.08 (m, 2H), 4.95 (br d, J ¼ 6.9 Hz, 1H, NH), 4.46 (quintet, J ¼ 6.9 Hz,
1H), 2.38 (s, 3H), 1.42 (d, 3H).13C NMR: d 143.1, 142.0, 137.7, 129.4, 128.5,
127.4, 127.1, 126.1, 53.6, 23.5, 21.4.
N-(1-(3-Methoxyphenyl)ethyl)-4-methylbenzenesulfonamide
(2b)[17]. Yield: 84%. Colorless oil. 1H NMR: d 7.62 and 7.18 (AA0 BB0 system, 4H),
7.11 (t, J ¼ 6.9 Hz, 1H) 6.72–6.68 (m, 2H), 6.59–6.58 (m, 1H), 4.91 (br d, 1H, NH),
4.43 (quintet, J ¼ 6.8 Hz, 1H), 2.38 (s, 3H), 1.41 (d, 3H).13C NMR: d 159.7, 143.7,
143.1, 137.7, 129.6, 129.4, 127.1, 118.4, 113.0, 111.7, 55.1, 53.6, 23.5, 21.4. MS
(FABþ) m=z 916 [(3M þ 1)þ, 1], 611 [(2M þ 1)þ, 7], 305 (Mþ, 16), 136 (35), 135
(100). HRMS calcd. for C16H19NO3S [Mþ] 305.1086; found 305.1086.
N-(1-p-Tolylethyl)-4-methylbenzenesulfonamide (2c)[18]. Yield: 88%.
1
White solid, mp 110–111 ꢀC. H NMR: d 7.62 and 7.18 (AA0 BB0 system, 4H),
7.01–6.99 (m, 4H), 4.72 (br d, 1H, NH), 4.41 (quintet, J ¼ 6.7 Hz, 1H), 2.39 (s,
3H), 2.28 (s, 3H), 1.41 (d, 3H).13C NMR: d 143.1, 139.1, 137.8, 137.2, 129.4,
129.2, 127.1, 126.1, 53.4, 23.5, 21.5, 21.0.
N-(1-(4-Methoxyphenyl)ethyl)-4-methylbenzenesulfonamide (2d)[19]. Yield:
1
84%. White solid, mp 88–89 ꢀC. H NMR: d 7.61 and 7.19 (AA0 BB0 system,
4H), 7.01 and 6.72 (AA0 BB0 system, 4H), 4.64 (br d, 1H, NH), 4.17 (quintet,
J ¼ 6.7 Hz, 1H), 3.76 (s, 3H), 2.40 (s, 3H), 1.41 (d, 3H).13C NMR: d 159.9,
143.0, 137.8, 134.2, 129.4, 127.3, 127.1, 113.9, 55.7, 53.1, 23.4, 21.5.
N-[1-(4-Trifluoromethylphenyl)ethyl]-4-methylbenzenesulfonamide
1
(2e)[17]. Yield: 86%. White solid, mp 127–129 ꢀC. H NMR: d 7.53 and 7.19 (AA0
BB0 system, 4H, 2H), 7.38 and 7.12 (AA0 BB0 system, 4H), 5.19 (br d, 1H, NH),
4.54 (quintet, J ¼ 6.9 Hz, 1H), 2.36 (s, 3H), 1.41 (d, 3H).13C NMR: d 145.9, 143.4,
137.3, 129.8, 129.4, 127.1, 126.6, 125.8, 125.4 (q), 122.2, 53.3, 23.5, 21.3. 19F
NMR (282 MHz, CDCl3): d ꢂ62.64.
Ethyl 4-[1-(4-Toluenesulfonamido)ethyl]benzoate (2f). Yield: 85%. Col-
1
orless oil. H NMR: d 7.83 and 7.16 (AA0 BB0 system, 4H), 7.58 and 7.16 (AA0
BB0 system, 4H), 5.17 (br s, 1H, NH), 4.51 (quintet, 1H), 4.35 (q, J ¼ 7.1 Hz, 2H),
2.36 (s, 3H), 1.40 (d, J ¼ 6.2 Hz, 3H), 1.37 (t, 3H).13CNMR: d 166.2, 147.0, 143.4,
137.5, 129.8, 129.6, 129.5, 127.1, 126.1, 61.0, 53.4, 23.5, 21.4, 14.3. MS (FABþ)
m=z 348 (M þ 1, 20), 177 (100). HRMS calcd. for C18H22NO4S [M þ 1] 348.1270
found 348.1276.
N-(3-Methylbutan-2-yl)-4-methylbenzenesulfonamide (2j)[20]. Na2SO4
1
(100 mg) was used as scavenger. Yield: 83%. Colorless oil. H NMR: d 7.75 and
7.29 (AA0 BB0 system, 4H), 4.39 (br s, 1H, NH), 3.17–3.14 (m, 1H), 2.41 (s, 3H),
1.64–1.61 (m, 1H), 0.92 (d, J ¼ 6.7 Hz, 3H), 0.80 (d, J ¼ 6.8 Hz, 6H).13C NMR: d
143.1, 138.2, 129.6, 127.0, 54.8, 33.4, 21.5, 18.1, 18.0, 17.9.
N-(Nonan-2-yl)-4-methylbenzenesulfonamide (2k). Na2SO4 (100 mg) was
1
used as scavenger. Yield: 83%. Colorless oil. H NMR: d 7.76 and 7.29 (AA0 BB0
system, 4H), 4.31 (br d, 1H), 3.29 (septet, J ¼ 6.5 Hz, 1H), 2.35 (s, 3H), 1.32–1.24

REDUCTION OF SULFONYLIMINES
205
(m, 12H), 1.02 (d, 3H), 0.88–0.84 (m, 3H), 1.51–1.47 (m, 2H), 13C NMR: d 143.1,
138.4, 129.6, 127.1, 50.0, 37.5, 31.7, 29.2, 29.1, 25.5, 22.6, 21.9, 21.5, 14.1. MS
(FABþ) m=z 298 (M þ 1, 100), 172 (68). HRMS calcd. for C16H28NO2S [M þ 1]
298.1841; found 298.1846.
N-Cyclopentyl-4-methylbenzenesulfonamide (2l)[21]. Na2SO4 (100 mg)
1
was used as water scavenger. Yield: 82%. Colorless oil. HNMR: d 7.76 and 7.29
(AA0 BB0 system, 4H), 4.49 (br d, 1H, NH), 3.58 (septet, J ¼ 6.7 Hz, 1H), 2.42 (s,
3H), 1.80–1.75 (m, 2H), 1.61–1.59 (m, 2H), 1.51–1.47 (m, 2H), 1.39–1.31 (m,
2H).13C NMR: d 143.2, 138.0, 129.7, 127.1, 55.2, 33.5, 23.2, 21.5.
N-Benzhydryl-4-methylbenzenesulfonamide (2m)[22]. Yield: 88%. White
1
solid, mp 140–141 ꢀC. H NMR: d 7.55 (d, J ¼ 8.2 Hz, 2H), 7.22–7.19 (m, 6H),
7.14–7.09 (m, 6H), 5.57 (br d, 1H, NH), 5.09 (d, J ¼ 7.0 Hz, 1H), 2.38 (s,
3H).13C NMR: d 143.2, 140.6, 137.4, 129.4, 128.6, 127.6, 127.4, 127.2, 61.4, 21.5.
N-Benzyl-4-methylbenzenesulfonamide (2n)[23]. Yield: 78%. White solid,
mp 116–117 ꢀC. 1H NMR: d 7.77 and 7.31 (AA0 BB0 system, 4H), 7.27–7.25 (m, 3H),
7.21–7.19 (m, 2H), 4.74 (br s, 1H, NH), 4.12 (d, J ¼ 6.2 Hz, 2H), 2.4 (s, 3H).13C
NMR: d 143.5, 136.9, 136.3, 129.7, 128.7, 127.9, 127.8, 127.2, 47.2, 21.5. MS (ESI)
m=z 284.1 (M þ Na, 100), 545.1 (2M þ Na, 54). Anal. calcd. for C14H15NO2S: C,
64.34; H, 5.79; N, 5.36; S, 12.27. Found: C, 64.64; H, 5.80; N, 5.34; S, 12.26.
N-(3-Methylbut-2-yl)-4-methylbenzenesulfonamide (2o)[24]. Yield: 76%.
1
White solid, mp 49–50 ꢀC. H NMR: d 7.74 and 7.29 (AA0 BB0 system, 4H), 4.52
(br s, 1H, NH), 2.72 (t, J ¼ 6.6 Hz, 2H), 2.42 (s, 3H), 1.68 (nonet, 1H), 0.86 (d,
6H).13C NMR: d 143.3, 137.2, 129.7, 127.1, 50.6, 28.4, 21.5, 19.6. MS (FABþ) m=z
184 (82), 155 (100). HRMS calcd. for C11H17NO2S [Mþ] 227.0980; found 227.0982.
N-(1-Phenylethyl)-2-methylpropane-2-sulfonamide (5a). Yield: 80%.
1
White solid, mp 109–111 ꢀC. H NMR: d 7.36–7.26 (m, 5H), 4.68 (dq, J ¼ 6.9 and
8.8 Hz, 1H), 4.38 (br d, J ¼ 8.8 Hz, 1H, NH), 1.58 (d, 3H), 1.32 (s, 9H).13C NMR:
d 143.5, 128.8, 127.4, 125.9, 59.7, 54.3, 25.5, 24.2. MS (ESI) m=z 264.1 (M þ Na,
100). Anal. calcd. for C12H19NO2S: C, 59.72; H, 7.93; N, 5.80; S, 13.29. Found:
C, 60.02; H, 7.79; N, 5.75; S, 13.19.
N-Cyclopentyl-2-methylpropane-2-sulfonamide (5l). Yield: 75%. White
1
solid, mp 96–97 ꢀC. H NMR: 3.77–3.72 (m, 2H), 1.98–1.92 (m, 2H), 1.71–1.65
(m, 2H), 1.60–1.45 (m, 4H), 1.39 (s, 9H).13C NMR: d 59.6, 56.7, 34.6, 24.4, 23.3.
MS (ESI) m=z 228.1 (M þ Na, 100). Anal. calcd. for C9H19NO2S: C, 52.65; H,
9.33; N, 6.82; S, 15.62. Found: C, 52.95; H, 9.17; N, 6.74; S, 15.55.
N-Benzyl-2-methylpropane-2-sulfonamide (5n). Na2SO4 (100 mg) was
1
used as scavenger. Yield: 79%. White solid, mp 116–117 ꢀC. HNMR: 7.30–7.20
(m, 5H), 4.28 (d, J ¼ 5.9 Hz, 2H), 4.12 (br s, 1H, NH), 1.35 (s, 9H).13C NMR: d
137.7, 128.8, 127.9, 127.7, 60.1, 48.6, 24.4. MS (ESI) m=z 250 (M þ Na, 100). Anal.
calcd. for C11H17NO2S: C, 58.12; H, 7.54; N, 6.16; S, 14.11. Found: C, 58.20; H,
7.43; N, 6.12; S, 14.02.

206
J. L. G. RUANO ET AL.
ACKNOWLEDGMENTS
´
We thank the DGYCT (CTQ2009-12168-BQU) and Comunidad Autonoma de
Madrid (S2009=PPQ-1634) for financial support. J. A. F.-S. thanks Comunidad
´
Autonoma de Madrid for a predoctoral contract.
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