Convenient and direct azidation of sec -benzyl alcohols by trimethylsilyl azide with bismuth(III) triflate catalyst

Article abstract of DOI:10.1055/s-0034-1379967

Sec-Benzyl azides were efficiently prepared by bismuth(III)-catalyzed direct azidation of sec-benzyl alcohols. The reaction was applied to a variety of substrates to provide the desired products in up to 99% yield within a short reaction time.

Full text of DOI:10.1055/s-0034-1379967

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2015, 47, 323–329
psp
323
J. Tummatorn et al.
PSP
Synthesis
Convenient and Direct Azidation of sec-Benzyl Alcohols by
Trimethylsilyl Azide with Bismuth(III) Triflate Catalyst
Jumreang Tummatorn*a,b
Charnsak Thongsornkleeba,b
Somsak Ruchirawata,b
Phanida Thongarama
Benyapa Kaewmeea
R2
R2
Bi(OTf)3 (1 mol%), TMSN3 (1.2 equiv)
OH
N3
R1
R1
up to 99% yield
CH2Cl2, r.t.
a Laboratory of Medicinal Chemistry, Chulabhorn Research
Institute, 54 Kamphaeng Phet 6, Laksi, Bangkok 10210,
Thailand
jumreang@cri.or.th
b Program on Chemical Biology, Chulabhorn Graduate Institute,
Center of Excellence on Environmental Health and Toxicology
(EHT), Ministry of Education, 54 Kamphaeng Phet 6, Laksi,
Bangkok 10210, Thailand
Received: 08.09.2014
Accepted after revision: 12.12.2014
Published online: 12.01.2015
olium hexafluorophosphate13 as an azidation agent. How-
ever, some of these conditions are inefficient for the syn-
thesis of secondary and tertiary arylmethyl azides because
a competing elimination pathway leads to low yields of the
desired products, especially in the case of electron-rich
benzyl alcohols. Among the various methods available, the
use of a combination of a Lewis acid and trimethylsilyl
azide is one of the best methods for the conversion of alco-
hols directly into azides.14 However, combinations of sever-
al Lewis acids with trimethylsilyl azide are inefficient in di-
rect azidation of sec-benzylic alcohols because of the for-
mation of dimeric ether side products 4, whereas protected
benzyl alcohols can be successfully converted into azidation
products by treatment with trimethylsilyl azide and
iron(III) chloride or bromide, as shown in Scheme 1.15
DOI: 10.1055/s-0034-1379967; Art ID: ss-2014-z0553-psp
Abstract sec-Benzyl azides were efficiently prepared by bismuth(III)-
catalyzed direct azidation of sec-benzyl alcohols. The reaction was ap-
plied to a variety of substrates to provide the desired products in up to
99% yield within a short reaction time.
Key words azides, catalysis, bismuth, alcohols
Benzyl azide is a versatile reagent that can be used in
several methods for the synthesis of nitrogen-containing
compounds. For example, benzyl azide has been used as an
important precursor to introduce an N-benzyl moiety into
molecules in preparations of isoquinolines,1 benzylamines,2
and benzyltriazoles.3 Moreover, benzyl azide can be used in
Schmidt reactions4 and Schmidt–Mannich-type reactions5
involving an azide rearrangement process. We have studied
the use of benzyl azide in an azide rearrangement to gener-
ate N-aryliminium ions for use in the synthesis of nitrogen-
containing compounds such as N-arylmethyl arenes,6 quin-
olines,7 or phenanthridines.8 Because of the important syn-
thetic potential of benzyl azides, development of methods
for their synthesis is still an active area of research. In gen-
eral, benzyl azides can be synthesized by converting the hy-
droxy group of a benzyl alcohol into a better leaving group,
with subsequent azidation by sodium azide,9 whereas di-
rect azidation can also be performed by using sodium azide
under thermal conditions.10 Because organic azides, espe-
cially low-molecular-weight azides, are sensitive to exter-
nal factors such as heat, light, or pressure, which can cause
them to explode when handled in large quantity, several
milder synthetic methods have been established employing
diphenyl azidophosphate,11 di-4-nitrophenyl azidophos-
phate,12 or 2-azido-4,5-dihydro-1,3-dimethyl-1H-imidaz-
O
O
R3
InBr3, TMSN3
CH2Cl2, r.t.
ref. 15a
R3
R1
R1
R2
R2
OH
N3
R1, R2 = alkyl or aryl
FeCl3 or FeBr3, TMSN3
CH2Cl2 or DCE
OR2
R1
N3
R1
R
2 = TMS, Me, Bn
Scheme 1 Previously reported methods
In this work, we present a convenient method for the
synthesis of sec-benzylic azides by direct azidation with
trimethylsilyl azide and a catalytic amount of bismuth(III)
triflate at room temperature (Scheme 2).
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J. Tummatorn et al.
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Synthesis
R2
Table 1 Reaction Optimization
R2
Bi(OTf)3 (1 mol%)
TMSN3 (1.2 equiv)
OH
N3
Lewis
acid
R1
R1
CH2Cl2, r.t.
OH
O
X
+
+
1a
solvent
Scheme 2 Bi(OTf)3-catalyzed direct azidation of sec-benzyl alcohols for
the preparation of sec-benzyl azides
1a
4a
2a: X = N3
3a: X = OTMS
Because metal triflates are well-established activators
of benzyl alcohols to give carbocation,16 we decided to
screen optimal conditions for the conversion of 1-phenyl-
ethanol (1a) into the corresponding azide 2a by using a
combination of a metal triflate and trimethylsilyl azide. The
ratio of the products was determined by 1H NMR spectros-
copy (Table 1). The reaction using 1 mol% of indium(III) tri-
flate in dichloromethane gave the product 2a in 52% yield at
room temperature, together with the recovered starting
material and the dimeric ether 4a as a byproduct (Table 1,
entry 1). Switching the solvent to acetonitrile gave none of
the desired product (entry 2). When we conducted the re-
action at 0 °C in dichloromethane, we obtained the azida-
tion product 2a in only 9% yield (entry 3). When scandi-
um(III) or ytterbium(III) triflate was used, we obtained only
trace amount of the desired product 2a, and the silyl-pro-
tected compound 3a was the major product in both cases
(entries 4 and 5). The yield of azidation product 2a was im-
proved to 69% when 1% of bismuth(III) triflate was used in
the reaction (entry 6). On increasing the amount of bis-
muth(III) triflate to 2 mol%, the yield of the desired azide
was slightly lowered (entry 7). The azidation product was
also obtained in a lower yield when 1,2-dichloroethane was
used as the solvent (entry 8). Bismuth(III) triflate was
therefore selected as the optimal catalyst because of the
very low loading and mild reaction conditions required,
even though starting material 1a remained and the ether
byproduct 4a was also formed. Therefore, the use of 1 mol%
bismuth(III) triflate and 1.2 equivalents of trimethylsilyl
azide in dichloromethane was selected as the protocol of
choice.
Having determined the optimal conditions, we investi-
gated the scope and limitations of the method. 1-Phenyl-
ethanol (1a), when subjected to the optimal conditions,
gave the desired product in 58% isolated yield (Table 2, en-
try 1); 1-(4-fluorophenyl)ethanol and 1-(4-chlorophe-
nyl)ethanol also gave the corresponding azidation products
in good yields (entries 2 and 3). With 1-(4-bromophe-
nyl)ethanol (1d), the reaction required a longer time (6 h)
and gave the desired product in 70% yield (entry 4). The re-
actions of 1-(4-methoxyphenyl)ethanol (1e) and 1-(3,4-di-
methoxyphenyl)ethanol (1f) proceeded to completion
within 5 min and gave the desired products in excellent
yields (entries 5 and 6). This method was also found to be
applicable to the bulkier substrate 1-(4-methoxyphe-
nyl)pentan-1-ol (1g), which gave the corresponding prod-
Entry Conditions
Solvent
Product ratio
1/2a/3a/4aa
1
2
3
4
5
6
7
8
In(OTf)3 (1 mol%), TMSN3 (1.2 equiv), r.t.
In(OTf)3 (1 mol%), TMSN3 (1.2 equiv), r.t.
In(OTf)3 (1 mol%), TMSN3 (1.2 equiv), 0 °C
Sc(OTf)3 (1 mol%), TMSN3 (1.2 equiv), r.t.
Yb(OTf)3 (1 mol%), TMSN3 (1.2 equiv), r.t.
Bi(OTf)3 (1 mol%), TMSN3 (1.2 equiv), r.t.
Bi(OTf)3 (2 mol%), TMSN3 (1.2 equiv), r.t.
Bi(OTf)3 (1 mol%), TMSN3 (1.2 equiv), r.t.
CH2Cl2
MeCN
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
28:52:0:20
no reaction
89:9:0:2
b
–
b
–
19:69:0:12
19:67:0:14
32:54:0:14
a By 1H NMR spectroscopy.
b The ratio of products could not be determined.
uct 2g in 98% yield (entry 7). Diphenylmethanol (1h) was
smoothly converted into the corresponding product in 83%
yield, and (4-methoxyphenyl)(phenyl)methanol (1i) gave
the corresponding product 2i in excellent yield. These re-
sults showed that, in comparison with electronically neu-
tral or electron-withdrawing groups, the presence of an
electron-donating group on the substrate facilitates the azi-
dation reaction. 1-(2-Naphthyl)ethanol, indan-1-ol, and
1,2,3,4-tetrahydronaphthalen-1-ol were all compatible
with our conditions and gave the corresponding azidation
products in good to excellent yields (entries 10–12). How-
ever, this method was not applicable to the azidation of eth-
yl 3-hydroxy-3-phenylpropanoate (1m), which gave the
trimethylsilyl-protected product 3m in 34% yield, together
with the unreacted starting material as the major compo-
nent (entry 13). We also examined the azidation of the pri-
mary and tertiary benzyl alcohols 1n–p (entries 14–16);
azidation of benzyl alcohol (1n) failed to give benzyl azide
(2n), whereas 4-methoxybenzyl alcohol (1o) gave only a
trace of the corresponding azide 2o; the starting materials
were recovered in both cases. These results suggested that
primary benzyl alcohols do not generate the corresponding
carbocation efficiently in the presence of bismuth(III) tri-
flate as a catalyst. In case of the tertiary benzyl alcohol 1p,
the reaction proceeded uneventfully to give the desired
product 2p with high efficiency. Similarly, 2-methyl-4-
phenylbut-3-yn-2-ol (1q) also underwent rapid conversion
into the desired azide 2q in good yield (entry 17). Unfortu-
nately, the sec-allylic benzyl alcohol 1r could not be suc-
cessfully converted into the corresponding azide but gave a
complex mixture instead.
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Table 2 Scope of Substrates
R2
R2
Bi(OTf)3 (1 mol%)
TMSN3 (1.2 equiv)
N3
OH
R1
R1
CH2Cl2, r.t.
Entry
1
Substrate
Product
Time (min)
60
Yielda (%)
58
OH
N3
1a
2a
2b
OH
N3
2
3
4
5
6
1b
1c
1d
1e
1f
60
60
360
5
64
60
70
98
98
F
F
OH
N3
2c
2d
2e
2f
Cl
Br
Cl
Br
OH
N3
OH
N3
MeO
MeO
N3
OH
OH
MeO
MeO
MeO
MeO
5
N3
7
1g
1h
1i
2g
2h
2i
5
20
5
98
83
98
80
Bu
Bu
MeO
MeO
N3
OH
8
N3
OH
9
Ph
Ph
MeO
MeO
N3
OH
10
1j
2j
60
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Table 2 (continued)
Entry
Substrate
Product
Time (min)
10
Yielda (%)
99
OH
N3
11
1k
1l
2k
OH
N3
12
13
2l
10
83
34
OH
O
TMSO
O
1m
3m
180
OEt
OEt
OH
N3
14
15
1n
1o
2n
2o
180
180
n.r.b
OH
N3
trace
MeO
MeO
N3
OH
16
17
1p
1q
2p
2q
180
30
90
87
OH
N3
OH
N3
18
1r
2r
30
–
Ph
Ph
MeO
MeO
a Isolated yield.
b No reaction.
To demonstrate the utility of our method in scalable
syntheses, the reactions of alcohols 1f and 1k were con-
ducted on a gram scale to give the corresponding azides 2f
and 2k in excellent yields (Scheme 3).
In conclusion, we have developed a convenient method
for the direct azidation of unprotected sec-benzyl alcohols
using only a 1 mol% loading of bismuth(III) triflate as a cata-
lyst. This method can be applied to a wide scope of sub-
strates, providing the desired products in good to excellent
yields and within short reaction times. The scalability and
convenience of this protocol make it a highly practical pro-
cedure for the preparation of sec-benzyl azides.
N3
OH
MeO
MeO
MeO
MeO
Bi(OTf)3 (1 mol%)
TMSN3 (1.2 equiv)
CH2Cl2, r.t., 99%
2f
1f
2.38 g (11.56 mmol)
All reagents and solvents were of commercial grade and were used as
received from the suppliers. 1H and 13C NMR spectra were recorded in
CDCl3 with a Bruker Avance 300 MHz NMR spectrometer; chemical
shifts are reported in ppm relative to TMS. IR spectra were recorded
using a PerkinElmer Spectrum One FT-IR spectrophotometer. High-
resolution mass spectra (HRMS) and electron-impact mass spectra
(EI-MS) were recorded on a Bruker Daltonics microTOF mass spec-
trometer.
OH
N3
Bi(OTf)3 (1 mol%)
TMSN3 (1.2 equiv)
CH2Cl2, r.t., 97%
2k
1k
2.53 g (16.44 mmol)
Scheme 3 Gram-scale syntheses of benzyl azides 2g and 2k
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Synthesis
sec-Benzyl Azides 2: General Procedure
13C NMR (75 MHz, CDCl3): δ = 159.4, 132.8, 127.6, 114.0, 60.6, 55.2,
21.4.
Bi(OTf)3 (1.0 mol%) was added to a solution of the appropriate sec-
benzyl alcohol (1.0 equiv) and TMSN3 (1.2 equiv) in CH2Cl2 (4.0
mL/mmol) at r.t. When the reaction was complete (TLC), the solvent
was removed and the crude material was purified by column chroma-
tography.
EI-MS: m/z (%) = 177 (14) [M+], 149 (60), 111 (61).
4-(1-Azidoethyl)-1,2-dimethoxybenzene (2f)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
90:10) to give the product as a colorless oil; yield: 115.4 mg (98%),
2.38 g (99%, gram-scale synthesis).
(1-Azidoethyl)benzene (2a)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 95:5) to give the product as a colorless oil; yield: 234.8 mg
(58%).
IR (neat): 2096, 1515, 1235, 1025 cm–1
1H NMR (300 MHz, CDCl3): δ = 6.85–6.83 (m, 3 H), 4.56 (q, J = 6.9 Hz, 1
H), 3.90 (s, 3 H), 3.87 (s, 3 H), 1.51 (d, J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 149.0, 148.7, 133.2, 118.6, 110.9, 109.3,
60.8, 55.7, 21.4.
.
IR (neat): 2926, 2111, 700 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.38–7.27 (m, 5 H), 4.48 (q, J = 6.9 Hz, 1
H), 1.51 (d, J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 140.8, 128.7, 128.0, 126.3, 61.0, 21.5.
TOF-HRMS: m/z [M + Na]+ calcd for C10H13N3NaO2: 230.0900; found:
230.0911.
1-(1-Azidoethyl)-4-fluorobenzene (2b)
1-(1-Azidopentyl)-4-methoxybenzene (2g)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 95:5) to give the product as a colorless oil; yield: 164.8 mg
(64%).
The crude product was purified on silica gel (eluent: hexane–EtOAc,
95:5) to give the product as a colorless oil; yield: 324.4 mg (98%).
IR (neat): 2091, 1611, 1513, 1247 cm–1
.
IR (neat): 2101, 1604, 1509, 1223 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.22 (d, J = 8.7 Hz, 2 H), 6.90 (d, J = 8.7
Hz, 2 H), 4.34 (t, J = 7.2 Hz, 1 H), 3.80 (s, 3 H), 1.89–1.59 (m, 2 H),
1.40–1.24 (m, 4 H), 0.88 (t, J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 159.4, 131.9, 128.1, 114.0, 65.9, 55.2,
35.7, 28.4, 22.3, 13.9.
1H NMR (300 MHz, CDCl3): δ = 7.33–7.25 (m, 2 H), 7.10–7.02 (m, 2 H),
4.60 (q, J = 6.9 Hz, 1 H), 1.51 (d, J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 162.4 (d, JCF = 245 Hz), 136.7, 128.1 (d,
JCF = 8 Hz), 115.6 (d, JCF = 21 Hz), 60.3, 21.6.
TOF-HRMS: m/z [M + H – N2]+ calcd for C8H9FN: 138.0708; found:
138.0713.
EI-MS: m/z (%) = 219 (0.5) [M+], 127 (40), 104 (92), 97 (60), 73 (100).
1,1′-(Azidomethylene)dibenzene (2h)
1-(1-Azidoethyl)-4-chlorobenzene (2c)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
95:5) to give the product as a colorless oil; yield: 311.3 mg (83%).
The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 95:5) to give the product as a colorless oil; yield: 169.6 mg
(60%).
IR (neat): 2094, 1237, 695 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.38–7.26 (m, 10 H), 5.70 (s, 1 H).
13C NMR (75 MHz, CDCl3): δ = 139.6, 128.7, 128.0, 127.4, 68.5.
EI-MS: m/z (%) = 209 (3) [M+], 167 (100), 152 (15), 77 (21).
IR (neat): 2092, 1493, 1242, 1092 cm–1
1H NMR (300 MHz, CDCl3): δ = 7.39–7.35 (m, 2 H), 7.30–7.27 (m, 2 H),
4.62 (q, J = 6.9 Hz, 1 H), 1.53 (d, J = 6.9 Hz, 3 H).
.
13C NMR (75 MHz, CDCl3): δ = 139.4, 133.8, 128.9, 127.7, 60.3, 21.5.
EI-MS: m/z (%) = 181 (10) [M+], 129 (59), 111 (42), 73 (100).
1-[Azido(phenyl)methyl]-4-methoxybenzene (2i)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
90:10) to give the product as a colorless oil; yield: 777.3 mg (98%).
1-(1-Azidoethyl)-4-bromobenzene (2d)
IR (neat): 2094, 1610, 1510, 1245, 1031 cm–1
.
The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 95:5) to give the product as a colorless oil; yield: 533.0 mg
(70%).
1H NMR (300 MHz, CDCl3): δ = 7.37–7.25 (m, 5 H), 7.24–7.19 (m, 2 H),
6.90–6.86 (m, 2 H), 5.67 (s, 1 H), 3.78 (s, 3 H).
IR (neat): 2101, 1489, 1244, 823 cm–1
.
13C NMR (75 MHz, CDCl3): δ = 159.4, 139.9, 131.7, 128.8, 128.7, 127.9,
127.3, 114.1, 68.1, 55.3.
EI-MS: m/z (%) = 239 (4) [M+], 197 (100), 167 (11).
1H NMR (300 MHz, CDCl3): δ = 7.49 (dd, J =8.7, 1.8 Hz, 2 H), 7.18 (dd,
J = 10.8, 2.4 Hz, 2 H), 4.58 (q, J = 6.6 Hz, 1 H), 1.50 (d, J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 139.9, 131.9, 128.0, 122.0, 60.4, 21.5.
EI-MS: m/z (%) = 226 (5) [M+], 129 (60), 98 (62), 73 (100).
2-(1-Azidoethyl)naphthalene (2j)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 95:5) to give the product as a colorless oil; yield: 438.5 mg
(80%).
1-(1-Azidoethyl)-4-methoxybenzene (2e)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
95:5) to give the product as a colorless oil; yield: 345.3 mg (98%).
IR (neat): 2098, 1242, 747 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.88–7.76 (m, 4 H), 7.53–7.43 (m, 3 H),
4.78 (q, J = 6.6 Hz, 1 H), 1.61 (d, J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 138.2, 133.2, 133.1, 128.7, 128.0, 127.7,
IR (neat): 2094, 1610, 1510, 1245 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.28–7.23 (m, 2 H), 6.93–6.88 (m, 2 H),
4.56 (q, J = 6.6 Hz, 1 H), 3.80 (s, 3 H), 1.50 (d, J = 6.9 Hz, 3 H).
126.4, 126.2, 125.3, 124.2, 61.3, 21.6.
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EI-MS: m/z (%) = 197 (7) [M+], 149 (60), 111 (28).
13C NMR (75 MHz, CDCl3): δ = 131.8, 128.6, 128.3, 122.1, 88.9, 84.7,
56.8, 29.1.
TOF-HRMS: m/z [M + H]+ calcd for C11H12N3: 186.1026; found:
1-Azidoindane (2k)
186.1027.
The crude product was purified on silica gel (eluent: hexane–EtOAc,
90:10) to give the product as a colorless oil; yield: 129.7 mg (99%),
2.53 g (97%, gram-scale synthesis).
IR (neat): 2922, 2093, 749 cm–1
.
Acknowledgment
1H NMR (300 MHz, CDCl3): δ = 7.39 (d, J = 6.6 Hz), 1 H, 7.31–7.21 (m, 3
H), 4.85 (q, J = 4.8 Hz, 1 H), 3.12–3.02 (m, 1 H), 2.91–2.81 (m, 1 H),
2.49–2.37 (m, 1 H), 2.16–2.06 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 143.6, 140.6, 128.8, 126.8, 125.0, 124.5,
65.8, 32.5, 30.4.
This research work was supported in part by grants from the Center
of Excellence on Environmental Health and Toxicology, Science &
Technology Postgraduate Education and Research Development Office
(PERDO), Ministry of Education, and from the Chulabhorn Research
Institute and Thailand Toray Science Foundation.
EI-MS: m/z (%) = 159 (5) [M+], 149 (90), 112 (39), 57 (100).
Supporting Information
1-Azido-1,2,3,4-tetrahydronaphthalene (2l)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
90:10) to give the product as a colorless oil; yield: 470.2 mg (83%).
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1379967.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
o
nrtogI
f
rmoaitn
IR (neat): 2090, 1232, 740 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.31–7.12 (m, 4 H), 4.56 (t, J = 3.9 Hz, 1
H), 2.89–2.69 (m, 2 H), 2.06–1.90 (m, 3 H), 1.87–1.77 (m, 1 H).
References
13C NMR (75 MHz, CDCl3): δ = 137.3, 133.7, 129.4, 129.1, 128.1, 126.1,
59.5, 29.1, 28.7, 18.9.
EI-MS: m/z (%) = 173 (14) [M+], 167 (44), 149 (80), 57 (100).
(1) (a) Nui, Y.-N.; Yan, Z.-Y.; Gao, G.-L.; Wang, H.-L.; Shu, X.-Z.; Ji, K.-
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Ethyl 3-Phenyl-3-(trimethylsiloxy)propanoate (2m)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 95:5) to give the product as a colorless oil; yield: 46.0 mg
(34%).
IR (neat): 1737, 1250, 1049, 839 cm–1
.
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11260. (b) Treece, J. L.; Goodell, J. R.; Velde, D. V.; Porco, J. A. Jr.;
Aubé, J. J. Org. Chem. 2010, 75, 2028.
1H NMR (300 MHz, CDCl3): δ = 7.35–7.19 (m, 5 H), 5.14 (dd, J = 9.3, 4.2
Hz, 1 H), 4.20–4.04 (m, 2 H), 2.70 (dd, J = 14.7, 9.0 Hz, 1 H), 2.55 (dd,
J = 14.7, 4.2 Hz, 1 H), 1.23 (td, J = 7.2, 1.2 Hz, 3 H), 0.00 (s, 9 H).
13C NMR (75 MHz, CDCl3): δ = 171.2, 143.9, 128.3, 127.5, 125.8, 72.0,
60.5, 46.2, 14.3, 14.2.
EI-MS: m/z (%) = 266 (5) [M+], 178 (99), 149 (58), 97 (77), 57 (100).
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(1-Azido-1-methylethyl)benzene (2p)
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The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 90:10) to give the product as a colorless oil; yield: 334.1 mg
(90%).
IR (neat): 2100, 1462, 1260 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.46–7.42 (m, 2 H), 7.38–7.33 (m, 2 H),
7.30–7.23 (m, 1 H), 1.63 (s, 6 H).
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1335.
13C NMR (75 MHz, CDCl3): δ = 144.6, 128.5, 127.4, 125.1, 63.8, 28.3.
EI-MS: m/z (%) = 161 (15) [M+], 149 (57), 97 (32), 57 (100).
(3-Azido-3-methylbut-1-yn-1-yl)benzene (2q)
The crude product was purified on silica gel (eluent: hexane–EtOAc,
100:0 to 95:5) to give the product as a colorless oil; yield: 442.4 mg
(87%).
IR (neat): 2096, 1159, 698 cm–1
.
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1H NMR (300 MHz, CDCl3): δ = 7.47–7.44 (m, 2 H), 7.32–7.30 (m, 3 H),
1.58 (s, 6 H).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 323–329

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PSP
Synthesis
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 323–329