Noncatalytic electrophilic alkylation of 1H-indole with 2-trifluoroacetyl-1,3-heterazoles

Article abstract of DOI:10.1055/s-0029-1219219

A set of highly electrophilic 2-trifluoroacetyl-1,3-heterazoles demonstrated excellent activity in the C-hydroxyalkylation of 1H-indole. The reaction conditions and yields of the corresponding trifluoromethyl-substituted alcohols depend strongly on the electron-withdrawing nature of the 1,3-heterazole unit. Georg Thieme Verlag Stuttgart ? New York.

Full text of DOI:10.1055/s-0029-1219219

PAPER
967
Noncatalytic Electrophilic Alkylation of 1H-Indole with 2-Trifluoroacetyl-1,3-
heterazoles
Noncatalytic
E
a
lectrophilic
v
Alkylation
e
of
1
H
-Indo
l
le
w
ith2-Trif
V
luoroacetyl-1,3-he
.
terazoles Khodakovskiy,a,b Pavel K. Mykhailiuk,*a,b Dmitriy M. Volochnyuk,a,c Andrey A. Tolmacheva,b
a
Enamine Ltd., Oleksandra Matrosova Street 23, Kyiv 01103, Ukraine
Fax +380(44)2351273; E-mail: Pashamk@gmx.de
b
c
Department of Chemistry, Kyiv National Taras Shevchenko University, Volodymyrska Street 64, Kyiv 01033, Ukraine
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Street 5, 02660 Kyiv-94, Ukraine
Received 27 October 2009; revised 3 November 2009
The starting 2-trifluoroacetyl-1,3-heterazoles 3–13
(Figure 2) were easily prepared by trifluoroacetylation of
the corresponding 1,3-heterazoles with trifluoroacetic an-
hydride in the presence of triethylamine as described pre-
viously.5 Recently, we have shown that the nucleophilic
addition of compounds with an activated methylene group
to the carbonyl group in ketones 3–13 provides the corre-
sponding trifluoromethyl-substituted alcohols.6a We have
extended this strategy to electron-rich heterocycles.
Abstract: A set of highly electrophilic 2-trifluoroacetyl-1,3-hetera-
zoles demonstrated excellent activity in the C-hydroxyalkylation of
1H-indole. The reaction conditions and yields of the corresponding
trifluoromethyl-substituted alcohols depend strongly on the elec-
tron-withdrawing nature of the 1,3-heterazole unit.
Key words: 1,3-heterazoles, alkylations, trifluoromethyl alcohols,
indoles, electrophilic additions
The trifluoromethyl group is one of the most attractive
functional groups in organic chemistry because trifluo-
romethyl-containing molecules often possess intriguing
physical and biological properties. Therefore, the incor-
poration of the trifluoromethyl group into organic com-
pounds is a topic of growing interest in fluoroorganic
chemistry, and many corresponding synthetic strategies
have been elaborated.1 Commercially available trifluo-
romethyl ketones hexafluoroacetone (1) and trifluoropy-
ruvates 2 are highly valuable building blocks commonly
used as sources of the trifluoromethyl group to prepare tri-
fluoromethyl-containing compounds (Figure 1).2 Howev-
er, although the chemical reactivity of both compounds 1
and 2 has been thoroughly studied,3 little is known of the
chemistry of other trifluoromethyl ketones.4
N
N
N
CF3
CF3
N
CF3
Ph
N
O
O
O
O
Me
O
3
4
5
N
N
N
N
CF3
CF3
CF3
Ph
S
S
S
N
O
O
O
6
7
8
N
N
N
CF3
CF3
CF3
Cl
N
N
O
O
O
Me
Me
9
10
11
O
CF3
F3C
CF3
N
N
RO
O
CF3
O
CF3
N
N
1
2
O
O
n-Bu
12
Figure 1 Common and highly usable trifluoromethyl ketones:
hexafluoroacetone (1) and trifluoropyruvates 2
13
Figure 2 Trifluoromethyl ketones 3–13
Recently, we started a project aimed at the preparation and
application of various (trifluoroacetyl)hetarene-type ke-
tones in the synthesis of trifluoromethyl-containing build-
ing blocks.5,6 As a part of this program, we wish to report
herein a very simple and practical one-step procedure for
the preparation of new trifluoromethyl-substituted indole
derivatives from 1H-indole and 2-trifluoroacetyl-1,3-het-
erazoles.
Unsubstituted 1H-indole was chosen as a model com-
pound because it is known to react smoothly with both ke-
tones 1 and 2.7 Indeed, substrates 3–12 showed excellent
reactivity towards 1H-indole to provide trifluoromethyl-
substituted alcohols 3a–12a (Scheme 1 and Table 1, en-
tries 1–10). As shown in Table 1, the yield of alcohols 3a–
13a depends strongly on the electron-withdrawing nature
of the heterocyclic moiety in starting ketones 3–13. For
example, the addition of 1H-indole to ketones 3–8, con-
taining electron-deficient heterocyclic moieties, occurred
smoothly on heating the reaction mixture at 60–80 °C in
SYNTHESIS 2010, No. 6, pp 0967–0970
x
x
.
x
x
.2
0
1
0
Advanced online publication: 04.01.2010
DOI: 10.1055/s-0029-1219219; Art ID: Z22709SS
© Georg Thieme Verlag Stuttgart · New York

968
P. V. Khodakovskiy et al.
PAPER
Table 1 Reaction Conditions for the Synthesis of Trifluoromethyl-
Substituted Alcohols 3a–13aa (continued)
toluene for 30–60 minutes. The corresponding products
3a–8a were obtained in 86–95% yield (entries 1–6).
Entry Ketone Conditions
Product
Yield
(%)
A1
A2
N
F3C
A1
A2
N
heating
0–95%
F3C
O
X
N
OH
+
F3C
X
N
H
toluene,
100 °C, 1 h
N
8
9
10
11
12
13
57
52
49
0
OH
N
H
3–13
3a–13a
N
H
10a
Scheme 1 Synthesis of trifluoromethyl-substituted alcohols 3a–13a
from 1H-indole and the corresponding ketones 3–13
N
F3C
toluene,
100 °C, 1 h
Cl
N
Table 1 Reaction Conditions for the Synthesis of Trifluoromethyl-
Substituted Alcohols 3a–13aa
OH
Me
N
H
11a
Entry Ketone Conditions
Product
Yield
(%)
N
F3C
toluene,
100 °C, 2 h
N
N
10
11
OH
F3C
toluene,
60 °C, 0.5 h
O
1
3
95
OH
N
H
12a
3a
N
N
F3C
H
neat,
160 °C, 2 h
N
N
OH
F3C
toluene,
60 °C, 0.5 h
O
Ph
2
3
4
5
93
87
OH
N
H
13a
4a
a Compounds 4, 6, and 8 were used in the form of hydrates.
N
H
N
F3C
In contrast, the reaction of 1H-indole with ketones 9–12,
which are 1H-imidazole derivatives containing electron-
donating alkyl groups, required harsher conditions
(toluene, 100 °C, 1–2 h). The corresponding products 9a–
12a were isolated in 49–85% yield (Table 1, entries 7–
10). The only exception to the above results was imida-
zo[1,5-a]pyridine derivative 13, which did not react with
1H-indole even after heating the mixture of reactants
without any solvent at 160 °C (entry 11). The behavior of
compound 13, in our opinion, can be explained by the
poor electron-withdrawing nature of the imidazo[1,5-
a]pyridine ring system.
N
toluene,
80 °C, 0.5 h
N
OH
Me
5a
N
H
N
F3C
toluene,
80 °C, 0.5 h
S
4
5
6
7
87
90
OH
6a
N
H
N
F3C
toluene,
80 °C, 1 h
S
It should be noted that the reaction of compounds 3–12
with 1H-indole does not require the use of an anhydrous
solvent, as it could be efficiently performed in wet tolu-
ene, despite the starting ketones tending to react with wa-
ter under these conditions.5 Moreover, ketones 4, 6, and 8
form stable hydrates, which were used in the synthesis.
OH
OH
OH
7a
N
H
N
N
F3C
toluene,
80 °C, 1 h
Ph
S
6
7
8
9
86
85
In summary, we have developed a very simple and effi-
cient one-step procedure for the preparation of new tri-
fluoromethyl-substituted alcohols 3a–12a from 1H-
indole and 2-trifluoroacetyl-1,3-heterazoles 3–12. The
yield of the target alcohols depends strongly on the
electron-withdrawing nature of the 1,3-heterazole unit.
8a
N
H
N
F3C
toluene,
100 °C, 1 h
N
Me
9a
N
H
Ketones 3–13 were synthesized as previously reported.5 Melting
points were measured on a Thiele tube apparatus. The 1H, 13C, and
19F NMR spectra were recorded on a Bruker Avance 500 spectrom-
eter (at 499.9, 124.9, and 470.3 MHz, respectively). Chemical shifts
Synthesis 2010, No. 6, 967–970 © Thieme Stuttgart · New York

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Noncatalytic Electrophilic Alkylation of 1H-Indole with 2-Trifluoroacetyl-1,3-heterazoles
969
are reported in ppm downfield from TMS (1H and 13C NMR spec-
tra) or CFCl3 (19F NMR spectra) as internal standards. Mass spectra
were recorded on an Agilent 1100 LCMSD SL instrument by atmo-
spheric pressure chemical ionization (APCI).
7.56 (s, 1 H), 8.02 (d, J = 7.5 Hz, 1 H), 8.14 (d, J = 7.5 Hz, 1 H),
8.23 (s, 1 H), 11.36 (s, 1 H).
2
13C NMR (125 MHz, DMSO-d6): d = 77.05 (q, JCF = 30.2 Hz),
111.11, 112.32, 119.77, 120.91, 122.00, 122.77, 123.73, 125.27 (q,
1JCF = 286.7 Hz), 125.40, 125.75, 126.07, 126.76, 135.32, 136.89,
153.45, 172.88.
1-(1,3-Heterazol-2-yl)-Substituted 2,2,2-Trifluoro-1-(1H-indol-
3-yl)ethanol; General Procedure
19F NMR (470 MHz, DMSO-d6): d = –76.44.
A mixture of the appropriate trifluoromethyl ketone (1 mmol), or its
corresponding hydrate in the case of compounds 4, 6, and 8, 1H-in-
dole (1 mmol), and toluene (2 mL) was stirred under the conditions
given in Table 1. The mixture was cooled to r.t., and the formed
crystalline solid was collected by filtration. The product was
washed with CCl4 (0.5 mL) on the filter and then was recrystallized
(i-PrOH). Reaction scale was 0.1–2.0 g of the starting trifluoro-
methyl ketone.
MS (APCI): m/z = 349 [M + 1].
2,2,2-Trifluoro-1-(1H-indol-3-yl)-1-(4-methyl-1,3-thiazol-2-
yl)ethanol (7a)
Colorless solid. Yield: 90%; mp 131–133 °C.
1H NMR (500 MHz, DMSO-d6): d = 2.35 (s, 3 H), 6.94 (dd, J = 8.0,
6.8 Hz, 1 H), 7.08 (dd, J = 8.0, 6.8 Hz, 1 H), 7.33 (s, 1 H), 7.39 (d,
J = 8.0 Hz, 1 H), 7.46 (d, J = 8.0 Hz, 1 H), 7.50 (s, 1 H), 7.90 (s, 1
H), 11.30 (s, 1 H).
1-(1,3-Benzoxazol-2-yl)-2,2,2-trifluoro-1-(1H-indol-3-yl)eth-
anol (3a)
Colorless solid. Yield: 95%; mp 197–198 °C.
1H NMR (500 MHz, DMSO-d6): d = 6.90 (dd, J = 8.4, 6.8 Hz, 1 H),
7.07 (dd, J = 8.0, 6.8 Hz, 1 H), 7.30 (d, J = 8.0 Hz, 1 H), 7.41 (d,
J = 8.4 Hz, 1 H), 7.43–7.47 (m, 2 H), 7.50 (s, 1 H), 7.71–7.75 (m, 1
H), 7.88–7.92 (m, 1 H), 8.04 (s, 1 H), 11.43 (s, 1 H).
2
13C NMR (125 MHz, DMSO-d6): d = 17.46, 76.72 (q, JCF = 29.7
Hz), 111.78, 112.17, 116.20, 119.58, 121.27, 121.85, 125.32 (q,
1JCF = 286.7 Hz), 125.35, 125.93, 136.90, 152.80, 170.46.
19F NMR (470 MHz, DMSO-d6): d = –76.86.
MS (APCI): m/z = 313 [M + 1].
2
13C NMR (125 MHz, DMSO-d6): d = 74.71 (q, JCF = 31.0 Hz),
2,2,2-Trifluoro-1-(1H-indol-3-yl)-1-(5-phenyl-1,3,4-thiadiazol-
2-yl)ethanol (8a)
Colorless solid. Yield: 86%; mp 218–219 °C.
109.97, 111.67, 112.40, 119.91, 120.10, 121.10, 121.92, 125.03 (q,
1JCF = 286.7 Hz), 125.48, 125.49, 125.83, 126.64, 136.92, 140.43,
150.47, 162.75.
1H NMR (500 MHz, DMSO-d6): d = 6.98 (dd, J = 8.0, 7.0 Hz, 1 H),
7.11 (dd, J = 8.0, 7.0 Hz, 1 H), 7.43 (d, J = 8.0 Hz, 1 H), 7.49 (d,
J = 8.0 Hz, 1 H), 7.55–7.65 (m, 4 H), 8.01 (d, J = 7.0 Hz, 2 H), 8.43
(s, 1 H), 11.44 (s, 1 H).
19F NMR (470 MHz, DMSO-d6): d = –76.46.
MS (APCI): m/z = 333 [M + 1].
2,2,2-Trifluoro-1-(1H-indol-3-yl)-1-(5-phenyl-1,3-oxazol-2-
yl)ethanol (4a)
Colorless solid. Yield: 93%; mp 153–154 °C.
2
13C NMR (125 MHz, DMSO-d6): d = 75.95 (q, JCF = 31.0 Hz),
1
110.77, 112.42, 119.97, 120.81, 122.13, 125.07 (q, JCF = 287.6
Hz), 125.57, 125.67, 128.22, 129.78, 129.96, 132.06, 136.99,
169.91, 172.53.
19F NMR (470 MHz, DMSO-d6): d = –76.95.
1H NMR (500 MHz, DMSO-d6): d = 6.93 (t, J = 7.5 Hz, 1 H), 7.07
(t, J = 7.5 Hz, 1 H), 7.32–7.41 (m, 3 H), 7.42–7.47 (m, 3 H), 7.65
(d, J = 7.5 Hz, 2 H), 7.77 (s, 1 H), 7.83 (s, 1 H), 11.35 (s, 1 H).
2
13C NMR (125 MHz, DMSO-d6): d = 74.31 (q, JCF = 31.0 Hz),
MS (APCI): m/z = 376 [M + 1].
110.46, 112.32, 119.79, 120.44, 121.86, 122.98, 124.58, 125.07 (q,
1JCF = 286.7 Hz), 125.60, 125.79, 127.52, 129.37, 129.62, 136.84,
151.72, 160.24.
19F NMR (470 MHz, DMSO-d6): d = –76.70.
2,2,2-Trifluoro-1-(1H-indol-3-yl)-1-(1-methyl-1H-imidazol-2-
yl)ethanol (9a)
Colorless solid. Yield: 85%; mp 210–212 °C.
1H NMR (500 MHz, DMSO-d6): d = 3.21 (s, 3 H), 6.73 (d, J = 8.0
Hz, 1 H), 6.81 (dd, J = 8.0, 6.8 Hz, 1 H), 6.95 (s, 1 H), 7.03 (dd, J =
8.0, 6.8 Hz, 1 H), 7.06 (s, 1 H), 7.29 (s, 1 H), 7.37 (d, J = 8.0 Hz, 1
H), 7.40 (s, 1 H), 11.30 (s, 1 H).
MS (APCI): m/z = 359 [M + 1].
2,2,2-Trifluoro-1-(1H-indol-3-yl)-1-(1-methyl-1H-1,2,4-triazol-
5-yl)ethanol (5a)
Colorless solid. Yield: 87%; mp 213–215 °C.
1H NMR (500 MHz, DMSO-d6): d = 3.51 (s, 3 H), 6.86 (dd, J = 7.5,
7.0 Hz, 1 H), 6.91 (d, J = 7.5 Hz, 1 H), 7.05 (dd, J = 8.0, 7.0 Hz, 1
H), 7.38 (d, J = 8.0 Hz, 1 H), 7.43 (d, J = 2.5 Hz, 1 H), 7.74 (s, 1 H),
8.01 (s, 1 H), 11.40 (s, 1 H).
2
13C NMR (125 MHz, DMSO-d6): d = 34.15, 74.00 (q, JCF = 29.8
Hz), 111.54, 112.18, 119.63, 119.72, 121.66, 124.13, 125.55,
125.60, 125.64 (q, 1JCF = 286.7 Hz), 125.80, 136.78, 144.18.
19F NMR (470 MHz, DMSO-d6): d = –75.81.
MS (APCI): m/z = 296 [M + 1].
2
13C NMR (125 MHz, DMSO-d6): d = 37.29, 73.50 (q, JCF = 31.0
1-(1-Allyl-1H-imidazol-2-yl)-2,2,2-trifluoro-1-(1H-indol-3-
yl)ethanol (10a)
Hz), 110.06, 112.39, 119.49, 119.92, 121.89, 125.13, 125.26 (q,
1JCF = 286.7 Hz), 125.80, 136.90, 149.51, 152.39.
Colorless solid. Yield: 57%; mp 155–156 °C.
19F NMR (470 MHz, DMSO-d6): d = –76.74.
1H NMR (500 MHz, DMSO-d6): d = 4.22–4.40 (m, 2 H), 4.82–4.94
(m, 2 H), 5.26–5.38 (m, 1 H), 6.75 (d, J = 8.0 Hz, 1 H), 6.81 (dd,
J = 8.0, 7.0 Hz, 1 H), 6.99 (s, 1 H), 7.02 (dd, J = 8.0, 7.0 Hz, 1 H),
7.06 (s, 1 H), 7.35 (d, J = 8.0 Hz, 1 H), 7.38–7.42 (m, 2 H), 11.29
(s, 1 H).
MS (APCI): m/z = 297 [M + 1].
1-(1,3-Benzothiazol-2-yl)-2,2,2-trifluoro-1-(1H-indol-3-yl)eth-
anol (6a)
Colorless solid. Yield: 87%; mp 159–160 °C.
1H NMR (500 MHz, DMSO-d6): d = 6.91 (t, J = 7.5 Hz, 1 H), 7.07
(t, J = 7.5 Hz, 1 H), 7.40 (d, J = 7.5 Hz, 1 H), 7.43–7.54 (m, 3 H),
13C NMR (125 MHz, DMSO-d6): d = 49.06, 74.11 (q, JCF = 29.8
2
Hz), 112.03, 112.12, 118.34, 119.64, 119.80, 121.63, 122.08,
1
125.33, 125.58 (q, JCF = 286.7 Hz), 125.72, 126.51, 133.88,
136.78, 144.09.
Synthesis 2010, No. 6, 967–970 © Thieme Stuttgart · New York

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P. V. Khodakovskiy et al.
PAPER
19F NMR (470 MHz, DMSO-d6): d = –75.93.
MS (APCI): m/z = 322 [M + 1].
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Colorless solid. Yield: 52%; mp 173 °C.
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1-(1-Butyl-1H-imidazol-2-yl)-2,2,2-trifluoro-1-(1H-indol-3-
yl)ethanol (12a)
Colorless solid. Yield: 49%; mp 168–169 °C.
1H NMR (500 MHz, DMSO-d6): d = 0.51 (t, J = 6.5 Hz, 3 H), 0.86–
0.89 (m, 3 H), 1.28–1.31 (m, 1 H), 3.55–3.58 (m, 1 H), 3.80–3.83
(m, 1 H), 6.76 (d, J = 8.0 Hz, 1 H), 6.81 (dd, J = 8.0, 7.0 Hz, 1 H),
6.98 (s, 1 H), 7.02 (dd, J = 8.0, 7.0 Hz, 1 H), 7.17 (s, 1 H), 7.33
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13C NMR (125 MHz, DMSO-d6): d = 13.64, 19.59, 31.99, 46.09,
74.11 (q, 2JCF = 29.3 Hz), 112.02, 112.17, 119.56, 119.75, 121.56,
1
122.20, 125.18, 125.63 (q, JCF = 286.7 Hz), 125.78, 126.18,
136.75, 144.04.
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19F NMR (470 MHz, DMSO-d6): d = –75.96.
MS (APCI): m/z = 338 [M + 1].
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Synthesis 2010, No. 6, 967–970 © Thieme Stuttgart · New York