O-Arylsulfonyl hydroxylamines via a decarboxylative rearrangement

Article abstract of DOI:10.1016/j.tet.2009.05.016

(E)-O-Arylsulfonyl-N-(2-nitroalk-2-enyl)hydroxylamines were easily obtained in good yields starting from (E)-nitro allylic alcohols, the crucial step being an inorganic base-catalyzed decarboxylative rearrangement of proposed labile unsaturated carbamates

Full text of DOI:10.1016/j.tet.2009.05.016

Tetrahedron 65 (2009) 5747–5751
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O-Arylsulfonyl hydroxylamines via a decarboxylative rearrangement
*
*
*
Stefania Fioravanti , Lucio Pellacani , Paolo A. Tardella
`
Dipartimento di Chimica, Universita degli Studi di Roma ‘‘La Sapienza’’, P.le Aldo Moro 2, I-00185 Roma, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
(E)-O-Arylsulfonyl-N-(2-nitroalk-2-enyl)hydroxylamines were easily obtained in good yields starting
from (E)-nitro allylic alcohols, the crucial step being an inorganic base-catalyzed decarboxylative re-
arrangement of proposed labile unsaturated carbamates. A possible mechanism for the outcome of the
reaction, characterized by the unusual retention of the sulfonyloxy group, is proposed.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 4 March 2009
Received in revised form 21 April 2009
Accepted 7 May 2009
Available online 13 May 2009
Keywords:
Nitro allylic alcohols
Hydroxylamines
Inorganic bases
Decarboxylation reaction
B
1. Introduction
H
N
ArSO3
- HB+
O
Hydroxylamines (RO–NR1R2) represent an interesting class of
electrophilic aminating agents, especially those carrying a good
leaving group that can be easily displaced by a nucleophile, leading
to the introduction of an amino residue into carbon chains. Among
these compounds, O-arylsulfonyl hydroxylamines (ArSO3–NHR)
have been considered as useful reagents for the electrophilic ami-
nation process.1
RO
N C O
OR
- ArSO3
deprotonation
Lossen-type
reaction
rearrangement
O
N
ArSO3
OR
Similarly, arylsulfonyloxy carbamates (ArSO3–NHCO2R)2 have
been used in organic synthesis as aminating reagents, due to the
ability of the nitrogen center to act either as an electrophile or as
a nucleophile as well as being able to provide in situ a source of
other chemical aminating species such as isocyanates (Scheme 1).
The reaction outcome can be controlled by the reaction condi-
tions, namely by the organic or the inorganic base used to promote
the deprotonation step, by the R group as well as by the substrate
electronic features. While a highly stereoselective aza-MIRC (Mi-
chael Initiated Ring Closure) reaction (path a) on EWG substituted
olefins led to the synthesis of different functionalized aziridines in
very good yields,3 the electrophilic amination (path b) most fre-
quently led to different amination products, depending on the na-
ture of the substrates.4 The Lossen-type rearrangement was
- ArSO3
O
a
b
nucleophilic
amination
electrophilic
amination
N
OR
Scheme 1.
2. Results and discussion
Continuing our studies on the synthesis and the reactivity of
such carbamates, a different rearrangement characterized by the
retention of the arylsulfonyloxy group coupled with a deacylation
reaction giving O-arylsulfonyl hydroxylamines was found.
In order to obtain bicyclic aziridines by an intramolecular version of
the aza-MIRC reaction, a possible synthesis of unsaturated nitro carba-
mates 1 (Ns¼4-NO2C6H4SO2)7 was considered, starting from suitable
(E)-nitroallylicalcohols2, following standardprocedures(Scheme 2).4b,8
2-Nitroethanol was chosen as the starting alcohol for the con-
densation reactions with some aliphatic or aromatic aldehydes. The
synthesis of (E)-nitro alkenes was performed by using the
observed for R¼t-Bu, leading to cyclization5 or acylation6 of
b-
dicarbonyl compounds. Anyway, the arylsulfonyloxy group is a good
leaving group, according to the chemical behavior of sulfonyl-acti-
vated hydroxy carbamates.
* Corresponding authors. Tel.: þ39 06 49913673; fax: þ39 06 490631.
E-mail address: lucio.pellacani@uniroma1.it (L. Pellacani).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.05.016

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S. Fioravanti et al. / Tetrahedron 65 (2009) 5747–5751
Table 2
NsOHN
RCHO
+
Synthesis of nitro allylic (E)-O-nosyl hydroxylamines 4a–c
R
OH
NO2
O
R
O
Entry Product
R
Base
Solvent T (ꢀC) Reaction time (h) Yielda (%)
HO
NO2
1
2
3
4
4a
i-Pr
CaO
CaO
NaH
K2CO3 Et2O
d
Et2O
Et2O
THF
25
ꢁ40
25
25
25
25
25
25
24
100
6
6
100
6
63
39
61
65
29
d
NO2
1
2
Scheme 2.
5
Et2O
CH2Cl2
Et2O
THF
6b
7
Et3N
CaO
NaH
NaH
Table 1
Synthesis of (E)-nitro allylic alcohols 2
4b
4c
i-Bu
24
6
65
67
23
63
60
8
9
10
11
THF
Et2O
THF
ꢁ40
100
24
6
Entry
2
R
Yield of 2a (%)
Pentyl CaO
NaH
25
1
2
3
4
5
a
b
i-Pr
i-Bu
Pentyl
Phenyl
2-Furyl
91
89
92
70
90
25
a
After flash chromatography on silica gel.
Standard reaction conditions using NH2OH (Ref. 8a).
c
b
db
eb
This last result seems to be in disagreement with that recently
a
After filtration of the crude on Celite using CH2Cl2 as eluent.
See Ref. 10.
b
reported in literature for the decarboxylative [1,3]-sigmatropic
rearrangement reactions found for similar carbamates. Allylic
amine derivatives were in fact obtained also with high enantiose-
lectivity starting from stable unsaturated carbamates by a domino
SN20–SN20 mechanism involving a tertiary organic base.11
With the aim of rationalizing these results, we turned our at-
tention toward the relationship between the reagents (chloro-
formates and hydroxylamines) and the reaction outcome.
First of all, two different chloroformates, the commercially
available allyl chloroformate 5 and the saturated chloroformate 6,12
obtained by reaction of nitroethanol with triphosgene, were con-
sidered in the reaction with NsONH2 (Scheme 5).
stereoselective one-pot method we recently reported for the
unfunctionalized nitro alkenes.9 Thus, (E)-2a–e were obtained in
good yields (Table 1) by performing the reaction on activated 4 Å
molecular sieves at toluene reflux, under an atmosphere of argon,
and using piperidine as catalyst (Scheme 3).
In all cases, the nitro allylic alcohols were obtained in very high
purity (E/Z ratio>99:1), as confirmed by 1H NMR spectra performed
on the crude, and then quantitatively converted by standard pro-
cedures4b to the corresponding unsaturated chloroformates (E)-3a–e
(Scheme 3).
NsONH2
OCOCl
OCONHONs
7 (80-82%)
Cl
O
base, solvent
5
RCHO
+
R
OH
R
O
o
NsONH2
triphosgene
pyridine
4A MS, piperidine
triphosgene, pyridine
O2N
O2N
complex reaction
mixture
OH
OCOCl
NO2
2a-e
NO2
3a-e
base, solvent
PhCH3, reflux, 4 h
PhCH3, 0 °C, 4 h
6
HO
NO2
Scheme 5.
E/Z ratio > 99/1
Scheme 3.
While the reaction between allyl chloroformate and O-nosyl
hydroxylamine in the presence of CaO or K2CO3 gave the allyl
nosyloxycarbamate 7 in good yield, a complex reaction mixture was
once again obtained starting from 6. The last result is consistent
with the observed reactivity of the chloroformates 3d–e, where the
aromatic ring influences the reactivity. On the other hand, the data
reported in literature7 and the formation of 7 suggest that the re-
action outcome might be sensitive to the presence of the nitro
group.
Then, to test the possible influence of the nosyl group, we
decided to replace it with the tosyl group. Again, the reaction of
O-tosyl hydroxylamine13 with (E)-3b performed in the presence of
CaO or K2CO3 gave (E)-8 as the only characterizable product in 65%
and 71% yields, respectively (Scheme 6).
Surprisingly these chloroformates did not react with hydroxyl-
amine under standard conditions8a (Et3N in CH2Cl2) giving expec-
ted unsaturated nitro carbamates 1.
Therefore, a different procedure involving the synthesis of O-
nosyl hydroxylamine (NsONH2) followed by the reaction with 3 was
attempted (Scheme 4).
NsCl + HONH2 HCl
NaHCO3
Cl
THF/H2O
O
H
NsONH2
R
O
R
N
ONs
base, solvent
NO2
3a-c
NO2
4a-c
TsCl + HONH2 HCl
NaHCO3
Scheme 4.
THF/H2O
Cl
While chloroformates 3d–e led to complex reaction mixtures,
aliphatic 3a–c led to unsaturated O-nosyl hydroxylamines (E)-4a–c
in all tested conditions. The results are reported in Table 2.
As shown in Table 2, nitro allylic O-nosyl hydroxylamines (E)-4
were obtained as the only isolable products with variable yields
while the desired carbamates 1 were not observed even as by-
products, even under other conditions, using different inorganic
bases, solvent, and/or reaction temperatures. On the other hand,
while the reaction occurred even without a base albeit in a lower
yield (entry 5), no product was detected using a tertiary organic
base (entry 6).
O
H
TsONH2
base, solvent
O
N
OTs
NO2
3b
NO2
8
Scheme 6.
Finally, since some chloroformates were reported to undergo
a decarboxylation reaction leading to the corresponding halides,14
it might be possible that decarboxylation of 3 would lead to the
corresponding allylic halides (Scheme 7).

S. Fioravanti et al. / Tetrahedron 65 (2009) 5747–5751
5749
Cl
ion mode. Anhydrous toluene and CH2Cl2 were used as such. Mo-
lecular sieves (4 Å) (Fluka, beads, diameter 1.7–2.4 mm) were ac-
tivated by heating at 280 ꢀC for 2 h under vacuum. Compounds
2d,e10 and TsONH213 were reported in the literature. Caution! Nitro
alkenes are lachrymatory and allergenic. All the procedures should be
carried out in a fume hood by a gloved operator. TsONH2 in one case
was found to decompose spontaneously and vigorously.13a
O
H
R
O
R
Cl
NO2
R
N
NsONH2
base
ONs
- CO2
NO2
NO2
3
4
Scheme 7.
4.2. Synthesis of (E)-nitro allylic alcohols 2. General
However, 4a was obtained also in the reaction performed
procedure
without base, although in lower yields and longer times (Table 2,
entry 5). Nevertheless, a solution of 3b and CaO was stirred at room
temperature for 24 h but the chloroformate was quantitatively
recovered.
As shown in Scheme 8 for reactions with NsONH2, a catalyzed
rearrangement reaction of labile allylic arylsulfonyloxy carbamate I
accompanied by decarboxylation of II and characterized by the
retention of the nosyloxy group is proposed to explain the forma-
tion of 4. Decarboxylation of stable allylic carbamates were repor-
ted on heating to 200–240 ꢀC in the presence of NaH15 or in
different catalyzed conditions.16
An equimolar solution (10 mmol) of 2-nitroethanol and alde-
hyde in anhydrous toluene (25 mL) was added under Ar into
a round-bottom flask containing previously activated 4 Å molecular
sieves (10 g).
A catalytic amount of piperidine was added
(0.6 mmol). The reactions were kept at reflux and followed by 1H
NMR analysis until disappearance of the aldehyde proton signal
(4 h). The crude mixtures were filtered under Ar through plugs of
Celite using CH2Cl2 as eluent. After solvent removal, the E isomers
were obtained in the yields reported in Table 1.
4.2.1. (2E)-4-Methyl-2-nitropent-2-en-1-ol (2a)
H
Pale yellow oil, 91%. IR: 3594, 1671 cmꢁ1 1H NMR: 1.10 (d,
.
NsON
O
Cl
NsON
O
HO
N
O
O
O
O
J¼6.6 Hz, 6H), 2.64–2.78 (m, 1H), 2.97 (br, 1H), 4.50 (s, 2H), 7.01 (d,
J¼10.7 Hz, 1H). 13C NMR: 22.0 (two C), 27.7, 55.4, 146.1, 148.3. HRMS
(ES Q-TOF) calcd for C6H12NO3 (MþH)þ: 146.0817; found: 146.0820.
H+
NsONH2
base
R
R
O
R
R
R
R
base
ONs
NO2
NO2
NO2
NO
2
3
I
II
- CO2
CaO, THF
rt, 24 h
4.2.2. (2E)-5-Methyl-2-nitrohex-2-en-1-ol (2b)
Pale yellow oil, 89%. IR: 3596, 1670 cmꢁ1 1H NMR: 0.97 (d,
.
H
N
Cl
J¼6.5 Hz, 6H), 1.77–1.91 (m, 1H), 2.20–2.26 (m, 2H), 2.80 (br, 1H),
4.53 (s, 2H), 7.27 (t, J¼8.2 Hz, 1H). 13C NMR: 22.1, 22.2, 28.2, 36.4,
55.2, 139.3, 150.3. HRMS (ES Q-TOF) calcd for C7H14NO3 (MþH)þ:
160.0974; found: 160.0981.
ONs
R = i-Bu
NO2
NO2
4
Scheme 8.
4.2.3. (2E)-2-Nitrooct-2-en-1-ol (2c)
The obtained O-nosyl hydroxylamines 4 can be regarded as
Pale yellow oil, 92%. IR: 3589, 1672 cmꢁ1 1H NMR: 0.89 (t,
.
useful precursors of functionalized allylic primary and secondary
amines. The former would be obtained by a selective cleavage of the
weak N–O bond17 while the secondary amines can be synthesized
using 4 as electrophilic nitrogen sources in the copper-catalyzed
reaction with aryl or alkyl nucleophiles.18 Finally, it is well known
that O-nosyl hydroxylamines are considered as effective electro-
philes involved in different amination reactions.19
J¼7.3 Hz, 3H), 1.20–1.40 (m, 6H), 2.20–2.45 (m, 2H), 2.86 (br, 1H),
4.53 (s, 2H), 7.37 (t, J¼7.1 Hz, 1H). 13C NMR: 13.7, 22.2, 27.7, 28.0,
31.2, 55.4, 140.4, 149.9. HRMS (ES Q-TOF) calcd for C8H16NO3
(MþH)þ: 174.1130; found: 174.1122.
4.3. Synthesis of (E)-nitro allylic chloridates 3. General
procedure
3. Conclusions
(E)-Nitro allylic alcohol (10 mmol) and pyridine (15 mmol) were
added at 0 ꢀC to a solution of triphosgene (15 mmol) in anhydrous
toluene (50 mL). After stirring (4 h), the mixture was filtered and
the solvent removed in vacuo to obtain (E)-nitro allylic chloridates
3 in quantitative yields.
In conclusion we report a decarboxylative rearrangement in
which the arylsulfonyloxy group is surprisingly retained, in spite of
its well-known character of leaving group. In fact, in the presence of
a base ArSO3NHCO2R are reported to undergo either an a-elimi-
nation reaction or a Lossen-type rearrangement, the ArSOꢁ3 acting
as a good leaving group in both cases.
4.3.1. (2E)-4-Methyl-2-nitropent-2-en-1-yl carbonochloridate (3a)
Pale yellow oil, 96%. IR: 1776, 1664 cmꢁ1 1H NMR: 1.11 (d,
.
J¼6.6 Hz, 6 H), 2.71–2.80 (m, 1 H), 4.61 (s, 2 H), 7.02 (d, J¼10.6 Hz, 1
H). 13C NMR: 22.1 (two C), 27.5, 63.4, 145.3, 147.9, 149.4. HRMS (ES
Q-TOF) calcd for C7H11ClNO4 (MþH)þ: 208.0377; found: 208.0388.
4. Experimental
4.1. General methods
4.3.2. (2E)-5-Methyl-2-nitrohex-2-en-1-yl carbonochloridate (3b)
Yellow oil, 94%. IR: 1774, 1665 cmꢁ1. 1H NMR: 0.99 (d, J¼6.6 Hz,
6H), 1.83–1.97 (m, 1H), 2.25 (dd, J1¼6.8 Hz, J2¼1.2 Hz, 2H), 4.54 (s,
2H), 7.37 (t, J¼8.1 Hz, 1H). 13C NMR: 22.4 (two C), 28.1, 37.1, 65.4,
141.1, 148.0, 149.4. HRMS (ES Q-TOF) calcd for C8H13ClNO4 (MþH)þ:
222.0533; found: 222.0527.
IR spectra were recorded on a Perkin Elmer 1600 FT/IR spectro-
photometer in CHCl3 as the solvent, and reported in cmꢁ1. 1H NMR
and 13C NMR spectra were recorded at 300 and 75 MHz or at 200
and 50 MHz with a Varian XL-300 or Gemini 200 NMR spectro-
meter, respectively, and reported in
d units. CDCl3 was used as the
solvent and CHCl3 as the internal standard. HRMS analyses were
performed using a Micromass Q-TOF Micro quadrupole-time of
flight (TOF) mass spectrometer equipped with an ESI source and
a syringe pump. The experiments were conducted in the positive
4.3.3. (2E)-2-Nitrooct-2-en-1-yl carbonochloridate (3c)
Yellow oil, 97%. IR: 1774, 1659 cmꢁ1. 1H NMR: 0.90 (t, J¼7.3 Hz,
3H), 1.10–1.65 (m, 6H), 2.27–2.41 (m, 2H), 4.54 (s, 2H), 7.36 (t,

5750
S. Fioravanti et al. / Tetrahedron 65 (2009) 5747–5751
J¼8.1 Hz, 1H). 13C NMR: 13.7, 22.2, 27.7, 28.2, 31.3, 61.8, 142.2, 147.6,
150.1. HRMS (ES Q-TOF) calcd for C9H15ClNO4 (MþH)þ: 236.0690;
found: 236.0688.
129.8 (two C), 130.9, 131.1, 144.5, 151.3. HRMS (ES Q-TOF) calcd for
C
14H20N3O7S (MþH)þ: 374.1022; found: 374.1031.
4.6. Synthesis of prop-2-en-1-yl {[(4-nitrophenyl)-
sulfonyl]oxy}carbamate (7)
4.3.4. (2E)-2-Nitro-3-phenylprop-2-en-1-yl carbonochloridate (3d)
Orange oil, 91%. IR: 1770, 1655 cmꢁ1. 1H NMR: 4.73 (s, 2H), 7.45–
7.62 (m, 5H), 8.27 (s, 1H). 13C NMR: 64.5, 129.3 (two C), 130.1, 130.9
(two C), 131.3, 138.2, 146.5, 150.1. HRMS (ES Q-TOF) calcd for
C10H9ClNO4 (MþH)þ: 242.0220; found: 242.0212.
The general procedure for the synthesis of (E)-nitro allylic O-
nosyl hydroxylamines 4 was followed. White solid, 82%. Mp 73–
75 ꢀC. IR: 1751 cmꢁ1. 1H NMR: 4.74 (dd, J1¼5.9 Hz, J2¼27.1 Hz, 2H),
5.25–5.40 (m, 2H), 5.70–6.06 (m, 1H), 8.01 (br, 1H), 8.23–8–27 (m,
2H), 8.37–8.41 (m, 2H). 13C NMR: 69.0, 124.1 (two C), 129.8 (two C),
130.6, 142.0, 149.4, 151.1, 152.9. HRMS (ES Q-TOF) calcd for
C10H11N2O7S (MþH)þ: 303.0287; found: 303.0278.
4.3.5. (2E)-3-(Furan-2-yl)-2-nitroprop-2-en-1-yl
carbonochloridate (3e)
Bright-yellow oil, 94%. IR: 1770,1657 cmꢁ1. 1H NMR: 5.05 (s, 2H),
6.64–6.71 (m, 1H), 7.02–7.10 (m, 1H), 7.75–7.81 (m, 1H), 7.98 (s, 1H).
13C NMR: 63.4, 111.9, 113.6, 122.9, 123.5, 146.6, 148.3, 158.2. HRMS
(ES Q-TOF) calcd for C8H7ClNO5 (MþH)þ: 232.0013; found:
232.0021.
4.7. Synthesis of (2E)-5-methyl-N-{[(4-methylphenyl)-
sulfonyl]oxy}-2-nitrohex-2-en-1-amine (8)
Starting from 3b, the general procedure for the synthesis of 4 was
4.4. Synthesis of 1-[(aminooxy)sulfonyl]-4-nitrobenzene
(NsONH2)
followed but using 1-[(aminooxy)sulfonyl]-4-methylbenzene
(TsONH2) as reagent. Pale yellow oil, 82%. IR: 3436, 1651 cmꢁ1 1H
.
NMR: 0.97 (d, J¼6.7 Hz, 6H), 2.14–2.33 (m, 1H), 2.40–2.48 (m, 2H),
2.45 (s, 3H), 4.54 (s, 2H), 4.98 (br, 1H), 7.33–7.37 (m, 2H), 7.56 (t,
J¼7.8 Hz, 1H), 7.79–7.85 (m, 2H). 13C NMR: 21.6, 22.2 (two C), 29.2,
38.1, 54.2, 129.6 (two C), 129.8 (two C), 131.7, 140.0, 146.0, 152.0. HRMS
(ES Q-TOF) calcd for C14H21N2O5S (MþH)þ: 329.1171; found: 329.1177.
To a solution of 4-nitrophenylsulfonyl chloride (50 mmol) in
200 mL of THF
a solution of hydroxylamine hydrochloride
(20 mmol) in 30 mL of H2O was added at ꢁ10 ꢀC. Then, 160 mL of
a solution of 10 M NaHCO3 was added dropwise during 45 min.
After stirring at ꢁ10 ꢀC for additional 2 h, the aqueous phase was
extracted with CH2Cl2, dried with Na2SO4, and the solvents evap-
orated to give a stable colorless solid that was crystallized from
hexane (needles). Mp 142–143 ꢀC (hexane). 1H NMR (DMSO): 8.03–
8.06 (m, 2H), 8.36–8.39 (m, 2H), 9.95 (br, 2H). 13C NMR (DMSO):
124.8 (two C), 130.3 (two C), 143.1, 150.7. HRMS (ES Q-TOF)
C6H6N2NaO5S (MþNa)þ: 240.9895; found: 240.9897.
Acknowledgements
This research was carried out within the framework of the Na-
tional Project ‘Stereoselezione in Sintesi Organica. Metodologie ed
Applicazioni’, supported by the Italian Ministero dell’Istruzione
`
`
dell’Universita e della Ricerca (MIUR) and by the Universita degli
Studi di Roma ‘La Sapienza’. We thank Dr. Luca Ranieri for experi-
mental support.
4.5. Synthesis of (E)-nitro allylic O-nosyl hydroxylamines 4.
General procedure
Supplementary data
To a solution of 3 (20 mmol) in 40 mL of Et2O, 20 mmol of
NsONH2 and 20 mmol of base were added in quick succession. After
stirring at rt (see Table 2), the crude mixture was filtered, the sol-
vent evaporated, and the crude product was directly purified by
flash chromatography (hexane/ethyl acetate¼75:25).
1H NMR spectra of all new compounds synthesized are pro-
vided. Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2009.05.016.
References and notes
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2-en-1-amine (4a)
Colorless oil, 65%. IR: 3438, 1651 cmꢁ1 1H NMR: 1.20 (d,
.
J¼6.5 Hz, 6H), 2.75–2.87 (m, 1H), 4.61 (s, 2H), 4.71 (br, 1H), 7.41 (d,
J¼11.4 Hz, 1H), 8.10–8.11 (m, 2H), 8.39–8.42 (m, 2H). 13C NMR: 22.1
(two C), 31.1, 54.5, 124.6 (two C), 131.0 (two C), 131.4, 144.0, 146.2,
151.0. HRMS (ES Q-TOF) calcd for C12H16N3O7S (MþH)þ: 346.0709;
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2-en-1-amine (4b)
Pale yellow oil, 67%. IR: 3436, 1649 cmꢁ1 1H NMR: 1.02 (d,
.
J¼6.6 Hz, 6H), 1.85–2.02 (m, 1H), 2.37 (t, J¼7.3 Hz, 2H), 4.61 (s, 2H),
4.97 (br, 1H), 7.67 (t, J¼7.9 Hz, 1H), 8.06–8.11 (m, 2H), 8.38–8.42 (m,
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