Metal-free C-H amination of unactivated hydrocarbons with sulfonylimino-λ3-bromanes generated in situ from (diacetoxybromo)benzene

Article abstract of DOI:10.1039/c4ob02160f

A simple method for direct metal-free C-H amination of unactivated hydrocarbons using easy-handling diacetoxy-λ³-bromane and triflylamide or sulfamate esters was developed. The high 2°/3° regioselectivities and deuterium isotope effects suggest a concerted organonitrenoid transition state, analogous to C-H amination with N-triflylimino-λ³-bromane. This journal is

Full text of DOI:10.1039/c4ob02160f

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Metal-free C–H amination of unactivated
3
hydrocarbons with sulfonylimino-λ -bromanes
generated in situ from (diacetoxybromo)benzene†
Cite this: DOI: 10.1039/c4ob02160f
a,b
c
c
c
Kazunori Miyamoto,* Taiga Ota, Md. Mahbubul Hoque and Masahito Ochiai
Received 9th October 2014,
Accepted 5th December 2014
A simple method for direct metal-free C–H amination of unactivated hydrocarbons using easy-handling
3
diacetoxy-λ -bromane and triflylamide or sulfamate esters was developed. The high 2°/3° regio-
DOI: 10.1039/c4ob02160f
selectivities and deuterium isotope effects suggest a concerted organonitrenoid transition state, analo-
3
www.rsc.org/obc
gous to C–H amination with N-triflylimino-λ -bromane.
Highly selective C–H amination of ubiquitous alkanes under
metal-free conditions has been an area of great interest over
the past decade, because of its environmentally friendly nature
1
,2
and economic advantage. These approaches use a combi-
nation of a suitable oxidant and a nitrogen source to generate
3
active amination species such as PhI(OAc)
2
/I
2
/amines, PhI =
4
5
2c
NTs/I
2
,
diiodohydantoin/TsNH
2
,
2
and chloramine-T/I .
Scheme 1 Regioselective metal-free C–H amination of alkane with
imino-λ -bromane 1.
Although these reactions serve as excellent amination tools for
relatively active benzylic C–H bonds, only limited success has
been reported in unactivated simple alkyl C–H bonds. In
contrast, thermally or photochemically generated free nitrenes
insert into various hydrocarbons but they are generally non-
3
Recently, we reported the stereoselective aziridination of
olefins with diacetoxybromane 2 in the presence of triflylamide,
6
selective and, thus, are of little synthetic value. We have
3
8
where N-triflylimino-λ -bromane 1 was generated in situ. The
one-pot procedure makes it possible to dispel the limitations of
original aziridination methods: thus, only the highly electron
3
reported that N-triflylimino-λ -bromane 1 undergoes regio-
and stereoselective amination of aliphatic unactivated C–H
bonds at ambient temperature in the absence of transition
9
3
deficient N-triflylimino group is available. Other imino-λ -
7
metal catalysts. A remarkable regioselectivity for methine over
bromane with the less electron deficient sulfonyl group, for
the methylene group was observed, while amination of the
methyl group has never been observed. The high regioselec-
tivity is probably because of a concerted bimolecular transition
state with some hydride-transfer character (not a nitrene mech-
3
example, N-(2,2,2-trichloroethoxysulfonyl)imino-λ -bromane is
1
0
2 2
highly labile and decomposes rapidly, even at 0 °C in CD Cl .
Although neither diacetoxybromane 2 nor triflylamide are
soluble in alkanes, ligand exchange and the following C–H
amination process occurs at ambient temperature without
requiring a transition metal catalyst. To a stirred suspension of
diacetoxybromane 2 (1.2 equiv., 0.01 M) in cyclohexane (925
equiv.) was added triflylamide at 0 °C under argon. After
warming the mixture to room temperature, the formed white
3
anism), for the C–H amination event with imino-λ -bromane 1
(
Scheme 1). We report herein inter- and intramolecular metal-
3
free C–H amination of aliphatic hydrocarbons with imino-λ -
bromanes generated in situ from (diacetoxybromo)arene 2 and
sulfonamides.
3
precipitate of λ -bromane gradually disappeared within 3 h,
yielding cyclohexyl(triflyl)amide 3 in 87% yield (Table 1, entry
a
Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-12
1). However, the conditions showed poor reproducibility
Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan. E-mail: kmiya@mol.f.u-tokyo.ac.jp
b
throughout five runs. The yields varied irregularly from 29% to
87%, and were accompanied by the formation of a small
amount of cyclohexanone 4 (7–27%). Reproducible results
were obtained when the reaction temperatures were set to
Advanced Elements Chemistry Research Team, RIKEN Center for Sustainable
Resource Science, and Elements Chemistry Laboratory, RIKEN, 2-1 Hirosawa,
Wako-shi, Saitama 351-0198, Japan
c
Graduate School of Pharmaceutical Sciences, University of Tokushima,
1
†
-78 Shomachi, Tokushima 770-8505, Japan
Electronic supplementary information (ESI) available: Schemes S1 and S2. See
7
°C, 15 °C, 25 °C, and 35 °C (entries 2–6). It is noteworthy
DOI: 10.1039/c4ob02160f
that a much lower yield of 3 was obtained at ≥25 °C (entries 2,
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a
Table 1 Amination of C
6
H
12 with diacetoxybromane 2 and triflylamide
carried out below 15 °C result in much higher yields of 3, but
the rate slowed considerably at cooler temperature (entries 4
and 5). These reactions were carried out at least two times and
3
reproducible results were obtained. Imino-λ -bromane 1 shows
very poor solubility in cyclohexane at 15 °C (≤0.005 M);
however, a reduced amount of cyclohexane was found to slow
down the reaction rates (entries 7 and 8). From our preliminary
experiments, the formation of cyclohexanone 4 probably
involves the generation of a cyclohexyl radical (Scheme S2†).
To prevent the formation of cyclohexanone, TEMPO, a free
radical scavenger, was used because this reagent immediately
traps carbon radicals. The attempt, however, was found to be
fruitless, probably due to the unwanted oxidation of TEMPO to
b
b
Entry
CyH (equiv.)
Temp. (°C)
Time (h)
Yield (%) 3
4
1
2
925
925
925
925
925
925
372
184
925
925
925
925
rt
25
25
15
7
35
15
15
15
15
15
15
7
7
6
87
27
6
3
6
4
4
6
4
7
c
c
29
45
d
c
c
c
3
d
c
4
26
144
1
67
73
23
27
24
24
94 (73)
d
5
93
50
98
76
65
98
5
d
6
d
7
the corresponding oxoammonium ion by diacetoxybromane 2
d
8
12
(
entry 9). Weakly acidic protic additives effectively stabilized
d,e
9
3
d, f
imino-λ -bromane 1 and dramatically improved the C–H amin-
ation efficiencies. However, in the present reaction, they were
1
1
1
0
1
2
6
—
—
d,g
d,h
7
0
not effective (entries 10 and 11). The low efficiency observed in
a
Unless otherwise noted, reactions were carried out by mixing the reaction with hexafluoroisopropanol (HFIP) is probably
diacetoxybromane 2 (1.2 equiv.) and TfNH
2
(1 equiv.) in cyclohexane at
due to the occurrence of a competing oxidation of this additive
by diacetoxy-λ -bromane 2. In fact, 2 promotes oxidation of
b
0
°C, and then they were warmed to the desired temperature. GC
3
c
yields, isolated yield in parenthesis. Values for two runs were
d
e
averaged. Degassed CyH was used. TEMPO (0.1 equiv.) was used. HFIP yielding hexafluoroacetone monohydrate at 15 °C in
f
g
13
AcOH (5 equiv.) was used.
HFIP (20 equiv.) was used.
dichloromethane in the absence of triflylamide. Notably, the
h
(Diacetoxyiodo)benzene (1.2 equiv.) was used.
use of (diacetoxyiodo)benzene, instead of 2, afforded neither
the desired product 3 nor cyclohexanone 4 under similar reac-
tion conditions (entry 12).
3
, and 6). In a nonpolar alkane, such as 2,2,4,4-tetramethyl-
To extend the applications of the present method, we exam-
3
pentane, imino-λ -bromane 1 was highly unstable with a half- ined C–H amination of various alkanes and the results are
life (t1/2) of about 3.6 min and degraded to triflylamide and summarized in Table 2. Both cyclic and acyclic alkanes were
bromoarene quantitatively, which partially accounts for the efficiently transformed into N-triflylamides 5–10 under metal-
7
lower yield of 3. The unexpected by-product, cyclohexanone 4, free conditions. Five-, seven-, and eight-membered cyclic
seemed to be produced by the reaction with diacetoxybromane alkanes similarly afforded good to high yields of N-triflyl-
1
1
2
in the presence of molecular oxygen. In fact, when the reac- amides at 15 °C under metal-free conditions. Similar yields
tion was carried out in degassed cyclohexane, a slight increase were obtained at 0 °C, but these reactions required prolonged
in the yield of 3 was observed (entry 3). Interestingly, reactions reaction time (entries 2 and 4). It is worth mentioning that the
a
Table 2 Amination of alkanes with diacetoxybromane 2 and triflylamide
b
Entry
Alkane (equiv.)
Temp. (°C)
Time (h)
Product
Yield (%)
1
2
15
0
25
120
91
93
3
4
15
0
11
78
60
58
5
6
15
15
19
30
68
57
e
7
15
26
61
8
9
15
15
23
24
78
44
a
Unless otherwise noted, reactions were carried out by mixing diacetoxybromane 2 (1.2 equiv., 0.01–0.05 M) and TfNH (1 equiv.) in degassed
2
b
c
d
cyclohexane (0.01 M) at 0 °C, and then they were warmed to the desired temperature. GC yields. Bromane 2 (0.05 M). N-Triflylaminoalkanes
were obtained as a mixture of regioisomers: for entry 6, 3°/2° = 88 : 12; for entry 7, 3°/2° = 91 : 9. Values for two runs were averaged.
e
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3
yields of N-triflylamides were comparable to that of imino-λ -
7
bromane 1. Acyclic alkanes afforded moderate to good yields
of amides 8–10 (entries 7–9). These reactions showed marked
preference for tertiary C–H bonds over secondary C–H bonds,
and the ratios were in fair agreement with the values observed
3
in the reaction of imino-λ -bromane 1. We did not observe for- Scheme 4 C–H amination of sulfamate ester 14.
mation of any primary (methyl) C–H insertion products with
any of the substrates examined. These regioselectivities
suggest that the reaction mechanism probably involves a con-
certed asynchronous transition state, where a C–H σ bonding
Conclusions
In conclusion, we have developed a simple and easy method
electron attacks the N–Br σ* orbital with some hydride transfer
for direct C–H amination of unactivated hydrocarbons utiliz-
7
,14
character.
We evaluated the deuterium kinetic isotope
3
ing diacetoxy-λ -bromane 2 and triflylamide or sulfamate
effect (KIE) by the competitive reaction of 2 and triflylamide
with a 1 : 1 mixture of cyclohexane and cyclohexane-d12 at
esters. The method provides a direct route for the regioselec-
tive synthesis of alkylamines.
1
H D
5 °C, which afforded the primary deuterium KIE ratio (k /k )
of 4.07 for C–H amination, as determined by GC. The large
isotope effects are very close to the previously observed KIE
value (3.72) obtained with iminobromane 1, supporting the
concerted mechanism (Scheme 2).
Experimental
General information
Direct C–H amination using (2,2,2-trichloroethoxy)-sulfon-
amide 11 is a fascinating process, because the product can be
readily deprotected under mild reaction conditions, which
may enable easy access to ubiquitous alkylamines from the
parent alkanes. The one-pot C–H amination procedure can
be applied to the C–H amination using 11 (Scheme 3). Thus,
amination of cyclohexane afforded N-(cyclohexyl)sulfonamide
IR spectra were recorded on JASCO FT/IR-420 spectrometers.
H NMR and C NMR spectra were obtained on either a JEOL
JNM-AL300, JNM-AL400, or Bruker AV400 spectrometers.
Chemical shifts (δ) are reported in parts per million (ppm)
1
13
1
5
downfield from internal Me Si. Mass spectra (MS) were
4
obtained on a Waters LCT Premier, or a SHIMADZU Model
GCMS-QP 505 spectrometer. Preparative thin-layer chromato-
graphy (TLC) was carried out on precoated plates of silica gel
1
2 in moderate yield. Interestingly, introduction of a sulfamate
ester to cyclohexane is faster than the comparable reaction
with the triflylamide, possibly reflecting the high lability, and
hence, the higher reactivity of N-(2,2,2-trichloroethoxysulfonyl)-
(
MERCK, silica gel F-254). Kieselgel 60 (Merck, 230–400 mesh)
was used for column chromatography.
3
10
imino-λ -bromane.
Substrates
Recently, Du Bois et al. and some other research groups
3
[
p-(Trifluoromethyl)phenyl](diacetoxy)-λ -bromane (2) was
have extended efficient methods for oxidative intramolecular
3
16
synthesized by the reaction of p-(trifluoromethyl)phenyl-
cyclization of sulfamate esters using diacetoxy-λ -iodanes. In
their reactions, Rh(II) catalyst plays an essential role, thus, the
Rh nitrenoid generated in situ acts as an active intermediate.
3
17
(
difluoro)-λ -bromane, with acetic anhydride and acetic acid
8
3
in a Teflon PFA vessel. p-(Trifluoromethyl)phenyl(difluoro)-λ -
3
bromane was prepared from bromine trifluoride according to
In contrast, diacetoxy-λ -bromane 2 promotes intramolecular
1
7
a literature method. A Teflon PFA vessel was used because of
the liberation of hydrogen fluoride in the reaction. Diacetoxy-
cyclization of the sulfamate ester in the absence of a transition
metal catalyst. For example, 3-phenylpropylsulfamate ester 14
could be converted into the 6-membered sultam 15 in moder-
ate yield (Scheme 4).
3
λ -bromane 2 is fairly stable in the solid state and can be
stored for more than two months without any decomposition
at room temperature and under argon. 2,2,2-Trichloroethyl-
sulfamate and 14 were prepared by sulfamoylation of the
1
8
corresponding alcohols according to the reported procedure.
General procedure for C–H amination of alkanes with
3
diacetoxy-λ -bromane 2 and triflylamide: a typical example
(
Table 1, entry 4)
To suspension of diacetoxy-λ -bromane
.086 mmol) in degassed cyclohexane (8.6 mL) in a glass tube
under argon at 0 °C was added triflylamide (10.7 mg,
.071 mmol) and the mixture was warmed to 15 °C and vigor-
Scheme 2 Deuterium kinetic isotope effect for C–H amination reaction.
3
a
2 (29.4 mg,
0
0
ously stirred for 26 h. GC yield (94%) of N-(cyclohexyl)trifluoro-
methanesulfonamide (3) and (6%) cyclohexanone (4) were
determined by capillary GC (FFS ULBON HR-1, 0.25 mm ×
50 m, 60 °C and 120 °C) of the reaction mixture using
Scheme 3 C–H amination with 2,2,2-trichloroethylsulfonylamide.
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n-nonane and n-tridecane as an internal standard. After fil- 2.12–2.04 (m, 2H), 1.79–1.71 (m, 2H), 1.64–1.56 (m, 1H),
+
tration, the reaction mixture was evaporated under vacuum 1.40–1.15 (m, 5H); ESIMS (positive) m/z 309 (M ). Spectral data
2
0
using an aspirator to give a solid residue which was recrystal- are in agreement with the literature.
lized from dichloromethane–hexane at −30 °C to give N-(cyclo- 4-Phenyl-[1,2,3]oxathiazinane-2,2-dioxide (15). (22.3 mg of 2
hexyl)trifluoromethanesulfonamide (3) (11.8 mg, 73%) as was used): White solids (2.7 mg, 24%); IR (KBr) 3280–3260,
colorless prisms; IR (KBr) 3350–3250 (br), 2933, 1454, 1373, 3067, 2967, 1418, 1357, 1186, 1015, 913, 781 cm− ; H NMR
1
1
−
1
1
3
221, 1066, 1007, 931, 613 cm ; δ 4.62 (br s, 1H), 3.58 (m, (400 MHz, CDCl ) δ 7.45–7.32 (m, 5H), 4.92–4.83 (m, 2H), 4.67
1
H), 2.07–1.97 (m, 2H), 1.80–1.70 (m, 2H), 1.67–1.57 (m, 1H), (ddd, J = 10.7, 4.3, 2.2 Hz, 1H), 4.26–4.18 (m, 1H), 2.31–2.18
+
1
.44–1.10 (m, 5H). Spectral data are in agreement with the (m, 1H), 2.07–2.00 (m, 1H); ESIMS m/z 236 [(M + Na) ]. Spectral
7
21
literature.
data are in agreement with the literature.
N-(Cyclopentyl)trifluoromethanesulfonamide (5). (32.2 mg
of 2 was used): A colorless oil; IR (neat) 3330–3270 (br), 2971,
−
1 1
1
446, 1375, 1232, 1192, 1146, 1022, 924, 609 cm ; H NMR
Acknowledgements
(400 MHz, CDCl ) δ 4.74 (br s, 1H), 3.97 (sext, J = 7.4 Hz, 1H),
3
2
.14–1.99 (m, 2H), 1.79–1.48 (m, 2H). Sulfonamide 5 shows a This work was supported by a Grant-in-Aid for Scientific
highly volatile nature which makes its isolation difficult. Thus, Research (B) (Japan Society for the Promotion of Science, JSPS)
1
5
was characterized by comparison of the H NMR and GCMS and a Grant-in-Aid for Young Scientist (B) (JSPS).
spectra with those of the authentic sample, prepared according
1
9
to a reported procedure.
N-(Cycloheptyl)trifluoromethanesulfonamide (6). (20.7 mg
of 2 was used): A colorless oil (6.3 mg, 51%); IR (neat)
Notes and references
3
6
330–3280 (br), 2932, 1435, 1377, 1230, 1192, 1147, 1039,
1 For a review, see: R. Samanta and A. P. Antonchick, Synlett,
2012, 809.
13 cm− ; H NMR (400 MHz, CDCl ) δ 4.79 (br s, 1H), 3.70
1
1
3
(
m, 1H), 2.11–1.97 (m, 2H), 1.69–1.40 (m, 10H). Spectral data
2 (a) Y. Yan, Y. Zhang, Z. Zha and Z. Wang, Org. Lett., 2013,
15, 2274; (b) Q. Xue, J. Xie, H. Li, Y. Cheng and C. Zhu,
Chem. Commun., 2013, 49, 3700; (c) Y. Takeda, J. Hayakawa,
K. Yano and S. Minakata, Chem. Lett., 2012, 41, 1672;
(d) M. Ochiai, S. Yamane, M. M. Hoque, M. Saito and
K. Miyamoto, Chem. Commun., 2012, 48, 5280.
7
are in agreement with the literature.
N-(Cyclooctyl)trifluoromethanesulfonamide (7). (24.8 mg of
2
was used): A colorless oil (9.8 mg, 63%); IR (neat) 3300–3270
br), 2925, 1435, 1378, 1230, 1194, 1149, 1054, 1018, 615 cm−
1
;
(
1
H NMR (400 MHz, CDCl ) δ 4.78 (br d, J = 8.6 Hz, 1H), 3.79
3
(
m, 1H), 2.00–1.90 (m, 2H), 1.75–1.44 (m, 12H). Spectral data
3 (a) M. Koag and S. Lee, Org. Lett., 2011, 13, 4766; (b) R. Fan,
W. Li, D. Pu and L. Zhang, Org. Lett., 2009, 11, 1425;
(c) R. Fan, D. Pu, F. Wen and J. Wu, J. Org. Chem., 2007, 72,
8994; (d) H. Togo, Y. Harada and M. Yokoyama, J. Org.
Chem., 2000, 65, 926; (e) H. Togo, Y. Hoshina, T. Muraki,
H. Nakayama and M. Yokoyama, J. Org. Chem., 1998, 63,
5193.
7
are in agreement with the literature.
N-(1,1,4-Trimethyl-1-pentyl)trifluoromethanesulfonamide (8).
(31.0 mg of 2 was used): A colorless oil (12.7 mg, 54%); IR
(neat) 3300–3290 (br), 2960, 1427, 1373, 1196, 1144, 1000,
27 cm− ; H NMR (400 MHz, CDCl ) δ 4.51 (br s, 1H), 1.78
1
1
6
3
(nonet, J = 6.6 Hz, 1H), 1.55 (d, J = 6.6 Hz, 2H), 1.43 (s, 6H),
0
.99 (d, J = 6.6 Hz, 6H). Spectral data are in agreement with the
4 A. A. Lamar and K. M. Nicholas, J. Org. Chem., 2010, 75,
7644.
7
literature.
N-(1-Ethyl-1-methyl-1-propyl)trifluoromethanesulfonamide
9). (17.9 mg of 2 was used): A colorless oil (6.5 mg, 64%); IR
5 H. Baba and H. Togo, Tetrahedron Lett., 2010, 51, 2063.
6 (a) D. S. Breslow, E. I. Edward, R. Leone and
P. v. R. Shleyer, J. Am. Chem. Soc., 1968, 90, 7097;
(b) N. Torimoto, T. Shingaki and T. Nagai, J. Org. Chem.,
1978, 43, 631; (c) P. Maslak, J. Am. Chem. Soc., 1989, 111,
8201.
(
(
1
1
neat) 3300–3280 (br), 2918, 1431, 1367, 1228, 1192, 1140,
014, 624 cm− ; H NMR (400 MHz, CDCl
1
1
) δ 4.45 (br s, 1H),
.66 (q, J = 7.0 Hz, 4H), 1.36 (s, 3H), 0.94 (t, J = 6.9 Hz, 6H).
3
Contaminated with a small amount of regioisomer. Spectral
7
data are in agreement with the literature.
7 M. Ochiai, K. Miyamoto, T. Kaneaki, S. Hayashi and
W. Nakanishi, Science, 2011, 332, 448.
N-(1,1-Dimethyl-1-propyl)trifluoromethanesulfonamide (10).
(
19.1 mg of 2 was used): A colorless oil (4.0 mg, 40%); IR (neat)
8 M. M. Hoque, K. Miyamoto, N. Tada, M. Shiro and
M. Ochiai, Org. Lett., 2011, 13, 5428.
9 For example, tosylamides readily undergo Hofmann type
rearrangement to give sulfamoyl fluoride, see: M. Ochiai,
T. Okada, N. Tada, A. Yoshimura, K. Miyamoto and
M. Shiro, J. Am. Chem. Soc., 2009, 131, 8392.
3
1
1
310–3290 (br), 2979, 1431, 1366, 1228, 1196, 1141, 1068,
003, 624 cm− ; H NMR (400 MHz, CDCl
1 1
) δ 4.54 (br s, 1H),
3
.67 (q, J = 7.1 Hz, 2H), 1.39 (s, 6H), 0.97 (t, J = 7.1 Hz, 3H).
7
Spectral data are in agreement with the literature.
N-(Cyclohexyl)-2,2,2-trichloroethoxysulfonamide
(12).
(
3
1
24.6 mg of 2 was used): White solids (3.4 mg, 18%); IR (KBr) 10 We could only detect N-(2,2,2-trichloroethoxysulfonyl)-
3
310–3290 (br), 2932, 2857, 1452, 1360, 1182, 1080, 1048,
imino-λ -bromane in the presence of cis-4-octene by low
−
1
1
1
022, 998, 933, 890, 855, 757 cm ; H NMR (400 MHz, CDCl
3
)
temperature H NMR measurement. See also Fig. S1 in
δ 4.62 (s, 2H), 4.45 (br d, J = 8.9 Hz, 1H), 3.49–3.39 (m, 1H),
ESI.†
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1
1 K. Miyamoto, M. M. Hoque and M. Ochiai, unpublished 16 C. G. Espino and J. Du Bois, in Modern Rhodium-Catalyzed
result. See also Scheme S1.†
Organic Reactions, ed. P. A. Evans, Wiley-VCH, Weinheim,
1
2 TEMPO is used as a catalyst in the presence of a stoichio-
2005, p. 379 and references therein.
metric amount of (diacetoxyiodo)benzene in the conversion 17 H. J. Frohn and M. Giesen, J. Fluorine Chem., 1998, 89,
of alcohols to carbonyl compounds. See: A. De Mico, 59.
R. Margarita, L. Parlanti, A. Vescovi and G. Piancatelli, 18 E. M. Harvey, G. D. Musaev and J. Du Bois, J. Am. Chem.
J. Org. Chem., 1997, 62, 6974.
Soc., 2011, 133, 17207.
1
1
3 Reaction conditions: bromane 2 (1.2 equiv.)/CH Cl /1 h/Ar.
4 R. Mello, M. Fiorentino, C. Fusco and R. Curci, J. Am.
Chem. Soc., 1989, 111, 6749.
19 A. Greenfield and C. Grosanu, Tetrahedron Lett., 2008, 49,
6300.
20 L. Ingram, A. Desokym, A. M. Ali and S. D. Taylor, J. Org.
Chem., 2009, 74, 6479.
2
2
1
5 For deprotection of 2,2,2-trichloroethoxysulfonylamide,
see: A. G. M. Barrett, A. Fenwick and M. J. Betts, J. Chem. 21 G. C. Espino, P. M. Wehn, J. Chow and J. Du Bois, J. Am.
Soc., Chem. Commun., 1983, 299. Chem. Soc., 2001, 123, 6935.
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