Small molecule library synthesis using segmented flow

Article abstract of DOI:10.3390/molecules16119161

Flow chemistry has gained considerable recognition as a simple, efficient, and safe technology for the synthesis of many types of organic and inorganic molecules ranging in scope from large complex natural products to silicon nanoparticles. In this paper

Full text of DOI:10.3390/molecules16119161

Molecules 2011, 16, 9161-9177; doi:10.3390/molecules16119161
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Small Molecule Library Synthesis Using Segmented Flow
Christina M. Thompson 1,*, Jennifer L. Poole 2, Jeffrey L. Cross 1, Irini Akritopoulou-Zanze 1
and Stevan W. Djuric 1
1
Medinical Chemistry Technologies, Abbott Laboratories, Global Pharmaceutical Research and
Development, 100 Abbott Park Road, Abbott Park, IL 60064, USA
2
Department of Chemistry at KU, 1251 Wescoe hall Drive, 2010 Marlott Hall, Lawrence,
KA 66045, USA
* Author to whom correspondence should be addressed; E-Mail: Christina.m.thompson@abbott.com.
Received: 13 September 2011; in revised form: 18 October 2011 / Accepted: 21 October 2011 /
Published: 2 November 2011
Abstract: Flow chemistry has gained considerable recognition as a simple, efficient, and
safe technology for the synthesis of many types of organic and inorganic molecules ranging
in scope from large complex natural products to silicon nanoparticles. In this paper we
describe a method that adapts flow chemistry to the synthesis of libraries of compounds
using a fluorous immiscible solvent as a spacer between reactions. The methodology was
validated in the synthesis of two small heterocycle containing libraries. The reactions were
performed on a 0.2 mmol scale, enabling tens of milligrams of material to be generated in a
single 200 µL reaction plug. The methodology allowed library synthesis in half the time of
conventional microwave synthesis while maintaining similar yields. The ability to perform
multiple, potentially unrelated reactions in a single run is ideal for making small quantities
of many different compounds quickly and efficiently.
Keywords: segmented flow; library synthesis
1. Introduction
Flow chemistry reactors have received increased attention over the last decade as flexible platforms
for organic synthesis. Their modular and simple designs have been adapted to a wide range of
applications, from the synthesis of small molecules [1,2] and complex natural products [3-6], to
nanoparticle synthesis [7,8]. Among their many benefits are excellent heat and mass transfer

Molecules 2011, 16
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capabilities, allowing for concise temperature control at very high temperatures for increasing reaction
rates, and also at low temperatures for increased control when performing exothermic reactions [9-11].
The inherent closed nature of flow systems enables very high pressures under superheating conditions
and containment of noxious or toxic reagents. The small reaction volume has enabled reactions that
were once avoided, as only a small amount of reactive intermediates is present at a given time [12].
The added ability to change temperature, residence time, and relative stoichiometry quickly and easily
during a reaction through a computer control makes flow reactor systems excellent for reaction
development and library preparation.
Plug, or segmented flow, which uses either a gaseous bubble or an immiscible solvent spacer to
separate “plugs” of desired reactions within a continuous flow machine, have also found a wide range
of applications. For example, Wheeler et al. reported a plug flow approach for reaction optimization
using a range of organic solvents separated by fluorinated spacers [13,14]. Plug flow has also been
successfully applied to protein crystallization [15], measurement of reaction kinetics [16], and
high-throughput screening [17-19].
Our goal was to adapt the modular and high-throughput nature of flow synthesis technology for use
in the generation of small molecule libraries using a single generic instrument set up. We felt that this
method should be equal to or more efficient than traditional solution phase chemistry. In this context
we describe the synthesis of two different heterocyclic libraries in yields comparable to traditional
techniques. The reactions were performed on a 0.2 mmol scale and were completed in half the time of
traditional serial microwave synthesis using a continuous process. By encapsulating each individual
library member inside a single organic droplet, and separating those with a fully immiscible fluorinated
solvent, we gained the ability to spatially separate library members along the length of a reactor tube.
We have utilized the synthesis of thiazoles and pyrazoles to develop this methodology.
2. Results and Discussion
The commercially available Uniqsis mesoscale flow machine [18] was employed for the
development of this methodology. The flow reactor was composed of two HPLC pumps that were each
responsible for a solvent and a reagent stream, and a variable temperature flow coil. The two required
starting materials for a given library member were loaded into 100 µL PTFE injection loops, one per
pump (Figure 1). These injection loops served a dual purpose of metering the correct amount of reagent
for the reaction, and also as a temporary holding port. The carrier liquid for both pumps was a
commercially available fully fluorinated solvent, F-40. When switched to inject, fluorinated solvent
drove the liquid out of both reagent loops simultaneously, where they meet at a T-joint to form a single
cohesive 200 µL reaction droplet.
It was found that solvents with higher surface tension formed more cohesive droplets than did
solvents of lower surface tension. Solvents such as MeOH, DMF, and water formed the most stable
droplets, while solvents such as acetonitrile, EtOAc, and CH2Cl2 tended to form chains of small
droplets. Droplet stability was also influenced by the flow rate, with 1.3 mL/min being the minimal rate
required for reliable droplet formation. The total volume of the droplets was controlled by the size of
the injector loops and could be varied for specific applications.

Molecules 2011, 16
Figure 1. Diagram of the flow reactor set up for library synthesis.
9163
The study was conducted on a 0.2 mmol scale, with 0.2 mmol of each reagent being dissolved in
0.1 mL of DMF. These were then serially loaded into the injection loops and injected in a standard 4 × 5
matrix to yield the desired 20 member libraries shown in Tables 1 and 2. Initially, a small amount of
contamination from one reaction to the next was observed in the LCMS trace of the crude libraries. To
eliminate this problem, each injection of a library compound was followed by an injection of pure DMF.
Table 1. Twenty member thiazole library synthesized in droplets using a continuous flow syntheisizer.
DMF
O
R2
R1
S
R3
NH
S
N
80 °C, 5 min
Br
+
R3
R1
H2N
N
H
R2
Compound
1-1
1-2
R1
R2
H
H
H
H
R3
Yield (%) a
p-CNPh
p-CNPh
p-CNPh
p-CNPh
allyl
Ph
42
48
49
48
12
34
24
53
50
40
49
36
63
31
46
55
1-3
1-4
m-FPh
CH3
allyl
Ph
1-5
1-6
R1-C6H4-2-CH2-R2
R1-C6H4-2-CH2-R2
R1-C6H4-2-CH2-R2
R1-C6H4-2-CH2-R2
1-7
1-8
m-FPh
CH3
allyl
Ph
1-9
tBu
tBu
H
H
H
H
H
H
H
H
1-10
1-11
1-12
1-13
1-14
1-15
1-16
tBu
tBu
m-FPh
CH3
allyl
Ph
p-FPh
p-FPh
p-FPh
p-FPh
m-FPh
CH3

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Table 1. Cont.
Compound
R1
Ph
Ph
Ph
Ph
R2
R3
allyl
Ph
Yield (%) a
1-17
1-18
1-19
1-20
CH3
CH3
CH3
CH3
41
40
31
61
m-FPh
CH3
a Combined chemical yield after purification.
Table 2. Twenty member pyrazole library synthesized in droplets using a continuous flow
syntheisizer.
R1
DMF
R2
R1
O
O
R2
H
N
80 °C, 5 min
N
R3
N
R3
H2N
R3
R1
N
N
R2
Compound
2(a+b)-1
2(a+b)-2
2(a+b)-3
2(a+b)-4
2(a+b)-5
2(a+b)-6
2(a+b)-7
2(a+b)-8
2(a+b)-9
2(a+b)-10
2(a+b)-11
2(a+b)-12
2(a+b)-13
2(a+b)-14
2(a+b)-15
2(a+b)-16
2(a+b)-17
2(a+b)-18
2(a+b)-19
2(a+b)-20
R1
R2
R3
Yield a Regioisomers b
R1-(CH2)3-R2
m,m-ClPh
m,m-ClPh
m,m-ClPh
m,m-ClPh
(CH2)2OH
(CH2)2OH
(CH2)2OH
(CH2)2OH
Ph
9
89:11
100
-
CF3
H
CH3
H
15
26
23
50
17
37
79
32
38
33
29
43
0
CH3
Ph
60:40
93:7
100
-
R1-(CH2)3-R2
CF3
CH3
Ph
H
CH3
H
72:28
100
100
-
R1-(CH2)3-R2
CF3
CH3
Ph
H
CH3
H
Ph
Ph
Ph
Me
100
100
-
R1-(CH2)3-R2
CF3
CH3
Ph
H
CH3
H
Me
Me
44
21
40
23
34
26
-
Me
Cy
74:26
100
100
-
R1-(CH2)3-R2
CF3
CH3
Ph
H
CH3
H
Cy
Cy
Cy
100
a Combined chemical yield after purification; b Ratio of regioisomers.
The first library synthesized was a thiazole library. The reactions were performed at 80 °C and had
a residency time of 5 min. For this library, the average purified yield was 53%, with a range from
12%–63% (Table 1).
This method was then applied to a twenty member pyrazole library. The yields for this library
ranged from 9%–79%, with one library member failing to produce any of the desired product. Mixtures
of regioisomers were obtained in cases where unsymmetric diketones were employed. The major
regioisomer observed was typically the one obtained from the reaction of hydrazines with the less
hindered carbonyl group of the diketone. When R1 is CF3, a single regioisomer is obtained. Despite the

Molecules 2011, 16
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lower yields, the library produced an average of 12 milligrams of purified product per compound, more
than sufficient for primary bioassays.
To establish if the flow method provided similar chemical yields to that of established microwave
methods, several examples from both libraries representing a range of chemical yields were then
resynthesized in a microwave on the same scale and under the same temperature and time conditions as
the flow reactions. Good correlation between the two methodologies was observed (Table 3).
Table 3. Comparison between microwave and flow yields. Reactions were performed on
0.2 mmol scale. All yields are purified yields.
Compound
1-7
Microwave Yield
Flow Yield
24%
Batch Yield
28%
34%
54%
51%
54%
32%
0%
1-13
63%
59%
1-17
41%
46%
2-5
50%
48%
2-10
38%
33%
2-14
0%
0%
3. Experimental
3.1. General
All reagents and solvents were supplied from Aldrich and were used without further purification.
1H-NMR spectra were recorded at ambient temperatures at either 400 MHz or 500 MHz on Varian
400-MR, Inova or VNMRS spectrometers. Deuterated solvents were used as received from Sigma-
Aldrich and data is reported as follows; chemical shift in ppm from tetramethylsilane as an internal
standard, multiplicity (s = singlet, d = doublet, dd = doublet of doublets, ddd = doublet of doublet of
doublets, bd = broad doublet, t = triplet, dt = doublet of triplets, td = triplet of doublets, and
m = multiplet), integration value. 13C-NMR were recorded at ambient temperature at 100 MHz or
125 MHz on Varian 400-MR or Inova 500 spectrometers and data is reported as follows; chemical shift
in ppm from tetramethylsilane as an internal standard. Regioisomers were assigned based correlations
observed in 2-dimensional rotating frame Overhauser effect spectroscopy (ROESY) experiments.
Microwave experiments were conducted in a Biotage Initiator microwave, a single-mode 400 W
instrument that uses an infrared temperature sensor.
3.2. Standard Protocol for Library Synthesis
Stock solutions of each desired starting material were first created by adding 2 mmol of a given
starting material to a 20 mL scintillation vial. To each of these vials was then added 2 mL of dry DMF,
and the vials were then sonicated to form clear solutions. For each library member, 100 µL of stock
solution from each of the required building blocks was loaded into a metering loop of known volume
on a Uniqsis flow system. The machine then injected both metering loops to form a single cohesive
droplet that was then flowed at 1.3 mL/min through an 80 °C heated coil, giving a final reaction time
of 5 min. One minute after the library member was injected, a blank plug of 200 mL of DMF was
added to the machine, and both the library droplet and the wash droplet were collected into tubes. The

Molecules 2011, 16
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DMF layer was then removed, the DMF was evaporated under warm nitrogen, and the resulting residue
was purified by preparative HPLC on a Waters Symmetry C8 column (25 mm × 100 mm, 7 m particle
µ
size) using a gradient of 10% to 100% acetonitrile: 0.1% aqueous TFA over 8 min (10 min run time) at
a flow rate of 40 mL/min to give the desired compound. The pyrrazole library was repeated in
triplicate, and gave a 5.1% standard deviation in yields.
S
NH
N
NC
1
4-(2-(Allylamino)thiazol-4-yl)benzonitrile (1-1). H-NMR (500 MHz, DMSO) δ 8.00 (d, J = 8.4, 3H),
7.83 (d, J = 8.3, 2H), 7.41 (s, 1H), 5.94 (ddd, J = 22.5, 10.5, 5.4, 1H), 5.28 (d, J = 17.2, 1H), 5.14 (d,
J = 10.2, 1H), 3.93 (d, J = 19.5, 2H). 13C-NMR (101 MHz, DMSO) δ 168.36, 147.98, 138.82, 134.76,
132.41, 126.17, 119.04, 115.97, 109.33, 105.09, 46.61.MS (DCI+) m/z 242.1 [M+H]+. 42% yield.
S
NH
N
NC
1
4-(2-(Phenylamino)thiazol-4-yl)benzonitrile (1-2). H-NMR (500 MHz, DMSO) δ 10.36 (s, 1H), 8.11
(d, J = 8.4, 2H), 7.90 (d, J = 8.4, 2H), 7.72 (d, J = 7.9, 2H), 7.66 (s, 1H), 7.36 (t, J = 7.9, 2H), 6.99 (t,
J = 7.3, 1H). 13C-NMR (126 MHz, DMSO) δ 163.37, 148.33, 140.95, 138.54, 132.72, 129.03, 126.23,
121.43, 119.01, 116.91, 109.58, 106.87. MS (DCI+) m/z 278.3 [M+H]+. 48% yield.
F
S
NH
N
NC
1
4-(2-(3-Fluorophenylamino)thiazol-4-yl)benzonitrile (1-3). H-NMR (500 MHz, DMSO) δ 10.61 (s,
1H), 8.10 (d, J = 8.3, 2H), 7.92 (d, J = 8.3, 2H), 7.78 (d, J = 11.8, 1H), 7.72 (s, 1H), 7.44–7.27 (m,
13
3H), 6.80 (m, 1H). C-NMR (126 MHz, DMSO) δ 162.96, 162.54 (d, J = 241), 148.36, 142.55 (d,
J = 11), 138.39, 132.78, 130.58 (d, J = 10), 126.20, 118.98, 112.83 (d, J = 2), 109.71, 107.65 (d,
J = 21), 107.51, 103.58 (d, J = 27). MS (DCI+) m/z 296.3 [M+H]+. 49% yield.
S
NH
N
NC
1
4-(2-(Methylamino)thiazol-4-yl)benzonitrile (1-4). H-NMR (500 MHz, DMSO) δ 8.01 (d, J = 8.2,
13
2H), 7.90 (d, J = 8.2, 2H), 7.39 (s, 1H), 3.15 (s, 3H). C-NMR (101 MHz, DMSO) δ 169.48, 147.79,
138.66, 132.53, 126.22, 119.02, 109.36, 104.88, 31.01. MS (DCI+) m/z 216.3 [M+H]+. 48% yield.

Molecules 2011, 16
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N
S
NH
N-Allyl-8H-indeno[1,2-d]thiazol-2-amine (1-5). 1H-NMR (500 MHz, DMSO) δ 7.47 (dd, J = 13.3, 7.4,
2H), 7.31 (t, J = 7.5, 1H), 7.18 (t, J = 7.4, 1H), 5.95 (ddt, J = 17.0, 10.4, 5.3, 1H), 5.41–5.22 (m, 1H),
5.17 (dd, J = 10.2, 1.4, 1H), 4.02 (s, 1H). 13C-NMR (126 MHz, DMSO) δ 173.04, 145.42, 136.79,
134.33, 126.65, 124.71, 124.34, 122.51, 117.68, 116.17, 46.72, 32.48. MS (DCI+) m/z 229.1 [M+H]+.
12% yield.
N
NH
S
1
N-Phenyl-8H-indeno[1,2-d]thiazol-2-amine (1-6). H-NMR (500 MHz, DMSO) δ 10.33 (s, 1H), 7.73
(d, J = 7.9, 2H), 7.54 (dd, J = 17.7, 7.4, 2H), 7.37–7.31 (m, J = 7.5, 3.9, 3H), 7.21 (t, J = 9.5, 5.4, 1H),
13
6.97 (t, J = 7.3, 1H), 3.81 (s, 2H). C-NMR (126 MHz, DMSO) δ 167.47, 156.16, 145.40, 141.05,
137.37, 129.00, 126.71, 124.78, 124.40, 121.26, 117.76, 116.91, 32.29. MS (DCI+) m/z 265.1 [M+H]+.
34% yield.
F
N
NH
S
1
N-(3-fluorophenyl)-8H-indeno[1,2-d]thiazol-2-amine (1-7). H-NMR (500 MHz, DMSO) δ 7.81 (d,
J = 7.3, 1H), 7.58 (d, J = 7.5, 1H), 7.53 (d, J = 7.4, 1H), 7.38–7.32 (m, 3H), 7.22 (t, J = 7.5, 1H),
6.81–6.75 (m, 1H), 3.83 (s, 2H). 13C-NMR (101 MHz, DMSO) δ 166.95, 162.60 (d, J = 241), 156.14,
145.38, 142.67 (d, J = 11), 137.21, 130.51 (d, J = 10), 126.76, 125.18, 124.83, 124.53, 117.84, 112.78
(d, J = 2), 107.43 (d, J = 21), 103.57 (d, J = 27), 32.32. MS (DCI+) m/z 283.3 [M+H]+. 24% yield.
N
NH
S
1
N-methyl-8H-indeno[1,2-d]thiazol-2-amine (1-8). H-NMR (500 MHz, DMSO) δ 7.51–7.44 (m, 2H),
7.32 (t, J = 7.5, 1H), 7.19 (t, J = 7.5, 1H), 3.72 (s, J = 18.8, 2H), 2.96 (s, J = 5.4, 3H). 13C-NMR
(101 MHz, DMSO) δ 173.89, 145.39, 136.38, 126.67, 124.73, 124.47, 122.08, 117.72, 32.61, 31.19.
MS (DCI+) m/z 203.3 [M+H]+. 53% yield.
S
NH
N
1
N-Allyl-4-tert-butylthiazol-2-amine (1-9). H-NMR (500 MHz, DMSO) δ 6.46 (s, 1H), 5.88 (m, 1H),
5.31 (d, J = 17.2, 1H), 5.23 (d, J = 10.3, 1H), 3.96 (s, J = 4.1, 2H), 1.24 (s, 9H). 13C-NMR (101 MHz,
DMSO) δ 169.78, 149.34, 131.76, 117.94, 100.05, 48.11, 33.25, 28.39. MS (DCI+) m/z 197.1 [M+H]+.
50% yield.

Molecules 2011, 16
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S
N
NH
1
4-tert-Butyl-N-phenylthiazol-2-amine (1-10). H-NMR (500 MHz, DMSO) δ 10.08 (s, 1H), 7.68–7.54
13
(m, 2H), 7.30 (t, J = 7.7, 2H), 6.92 (t, J = 7.3, 1H), 6.41 (s, 1H), 1.31 (s, 9H). C-NMR (101 MHz,
DMSO) δ 162.93, 160.86, 141.29, 128.96, 121.15, 116.87, 99.21, 34.31, 29.54. MS (DCI+) m/z 233.2
[M+H]+. 40% yield.
F
S
NH
N
1
4-tert-Butyl-N-(3-fluorophenyl)thiazol-2-amine (1-11). H-NMR (500 MHz, DMSO) δ 10.33 (s, 1H),
7.82–7.65 (m, 1H), 7.41–7.16 (m, 2H), 6.71–6.65 (m, 1H), 6.57–6.38 (m, 1H), 1.27 (s, 9H). 13C-NMR
(126 MHz, DMSO) δ 162.56 (d, J = 241), 162.04, 161.53, 143.12 (d, J = 12), 130.36 (d, J = 10),
112.44, 106.95 (d, J = 21), 103.24 (d, J = 27), 99.98, 34.39, 29.59. MS (DCI+) m/z 251.1 [M+H]+.
49% yield.
S
NH
N
1
4-tert-Butyl-N-methylthiazol-2-amine (1-12). H-NMR (500 MHz, DMSO) δ 6.50 (s, 1H), 2.97
13
(s, 3H), 1.32 (s, 9H). C-NMR (101 MHz, DMSO) δ 170.27, 162.27, 148.86, 100.12, 33.19, 28.34.
MS (DCI+) m/z 171.3 [M+H]+. 36% yield.
S
NH
N
F
1
N-Allyl-4-(4-fluorophenyl)thiazol-2-amine (1-13). H-NMR (500 MHz, DMSO) δ 7.90–7.74 (m, 2H),
7.21 (t, J = 8.8, 2H), 7.06 (s, 1H), 5.93–5.85 (m, 1H), 5.28 (d, J = 8.8, 2H), 5.15 (d, J = 10.3, 2H), 3.95
(d, J = 5.2, 1H). 13C-NMR (101 MHz, DMSO) δ 168.42, 161.53 (d, J = 244), 147.87, 134.65, 130.91
(d, J = 3), 127.65 (d, J = 8), 116.05, 115.29 (d, J = 21), 100.96, 46.77. MS (DCI+) m/z 235.2 [M+H]+.
63% yield.
S
NH
N
F

Molecules 2011, 16
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1
4-(4-Fluorophenyl)-N-phenylthiazol-2-amine (1-14). H-NMR (500 MHz, DMSO) δ 10.27 (s, 1H),
8.03–7.89 (m, 2H), 7.72 (d, J = 8.3, 2H), 7.42–7.30 (m, 2H), 7.24–7.3 (t, J = 7.25, 2H), 6.98 (t,
J = 6.98, 1H). 13C-NMR (101 MHz, DMSO) δ 163.17, 161.60 (d, J = 244), 149.01, 141.14, 131.13 (d,
J = 3), 128.99, 127.62 (d, J = 8), 121.22, 116.80, 115.46 (d, J = 21), 102.63. MS (DCI+) m/z 271.3
[M+H]+. 31% yield.
F
S
NH
N
F
1
N-(3-Fluorophenyl)-4-(4-fluorophenyl)thiazol-2-amine (1-15). H-NMR (500 MHz, DMSO) δ 10.52 (s,
1H), 7.95 (dd, J = 8.4, 5.7, 2H), 7.79 (d, J = 11.0, 1H), 7.42–7.32 (m, 3H), 7.29 (t, J = 8.8, 2H), 6.78
13
(m, 1H). C-NMR (126 MHz,z DMSO) δ 162.73, 162.55 (d, J = 241), 161.65 (d, J = 244), 149.04,
142.73 (d, J = 11), 130.98 (d, J = 3), 130.52 (d, J = 10), 127.59 (d, J = 8), 115.55 (d, J = 21), 112.70
(d, J = 2), 107.41 (d, J = 21), 103.45 (d, J = 27), 103.34. MS (DCI+) m/z 289.4 [M+H]+.
46% yield.
S
NH
N
F
1
4-(4-Fluorophenyl)-N-methylthiazol-2-amine (1-16) H-NMR (500 MHz, DMSO) δ 7.90–7.80 (m,
2H), 7.28–7.18 (m, 2H), 7.23 (s, 1H), 2.91 (s, 3H). 13C-NMR (126 MHz, DMSO) δ 169.45, 161.52 (d,
J = 244), 148.07, 130.92, 127.65 (d, J = 8), 115.28 (d, J = 22), 100.72. MS (DCI+) m/z 209.2 [M+H]+.
55% yield.
S
NH
N
N-Allyl-5-methyl-4-phenylthiazol-2-amine (1-17). 1H-NMR (500 MHz, DMSO) δ 7.55 (d, J = 8.1, 2H),
7.46 (t, J = 7.6, 2H), 7.38 (t, J = 7.3, 1H), 5.91 (dtd, J = 15.8, 10.5, 5.3, 1H), 5.30 (d, J = 10.2, 1H),
5.18 (d, J = 10.3, 1H), 3.95 (s, 2H), 2.31 (s, 3H). 13C-NMR (101 MHz, DMSO) δ 166.55, 136.86,
132.60, 129.95, 128.89, 128.66, 117.39, 114.58, 114.49, 47.48, 11.66. MS (DCI+) m/z 231.2 [M+H]+.
41% yield.
S
NH
N

Molecules 2011, 16
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5-Methyl-N,4-diphenylthiazol-2-amine (1-18). 1H-NMR (500 MHz, DMSO) δ 10.05 (s, 1H), 7.66 (dd,
J = 12.6, 8.3, 4H), 7.46 (t, J = 7.6, 2H), 7.37–7.26 (m, 3H), 6.92 (td, J = 7.4, 0.9, 1H), 2.43 (s, 3H).
13C-NMR (101 MHz, DMSO) δ 159.59, 144.82, 141.21, 134.86, 129.00, 128.36, 128.05, 127.21,
121.21, 116.96, 116.30, 11.93. MS (DCI+) m/z 267.2 [M+H]+. 40% yield.
F
S
NH
N
N-(3-Fluorophenyl)-5-methyl-4-phenylthiazol-2-amine (1-19). 1H-NMR (500 MHz, DMSO) δ 10.30 (s,
1H), 7.74 (d, J = 12.2, 1H), 7.67 (d, J = 8.0, 2H), 7.47 (t, J = 7.6, 2H), 7.40–7.24 (m, 3H), 6.82–6.65
(m, 1H), 2.44 (s, 3H). 13C-NMR (126 MHz, DMSO) δ 162.54 (d, J = 241), 158.71, 145.30, 142.90 (d,
J = 12 Hz), 134.98, 130.40 (d, J = 10), 128.36, 127.92, 127.17, 117.04, 112.51 (d, J = 2), 107.02 (d,
J = 21), 103.25 (d, J = 27), 11.91.MS (DCI+) m/z 285.4 [M+H]+. 31% yield.
S
NH
N
1
N,5-Dimethyl-4-phenylthiazol-2-amine (1-20). H-NMR (500 MHz, DMSO) δ 7.55 (d, J = 7.5, 2H),
13
7.49 (t, J = 7.6, 2H), 7.43 (t, J = 7.2, 1H), 2.96 (s, 3H), 2.27 (s, 3H). C-NMR (101 MHz, DMSO) δ
166.86, 134.06, 129.42, 128.98, 128.72, 128.28, 114.50, 31.96, 11.61. MS (DCI+) m/z 205.2 [M+H]+.
61% yield.
Cl
3
4
2
N
5
N
1
Cl
2-(3,5-Dichlorophenyl)-3-methyl-2,4,5,6-tetrahydrocyclopenta[c]pyrazole (2-1a). 1H-NMR (400 MHz,
DMSO) δ 7.59 (m, 3H), 2.63 (t, J = 7.4, 2H), 2.56 (t, J = 7.1, 2H), 2.39–2.33 (m, 2H), 2.33 (s, 3H).
13C-NMR (126 MHz, DMSO) δ 149.31, 144.74, 141.60, 134.89, 129.22, 124.16, 116.20, 30.39, 26.13,
21.65, 12.50 (s). MS (DCI+) m/z 267.1 [M+H]+. 8% yield. In the ROESY spectrum an NOE
correlation was observed between the methyl protons and resonances for the aryl ringverifying the
regioisomer.
Cl
5
1
4
N
3
N
2
Cl
1
1-(3,5-Dichlorophenyl)-3-methyl-1,4,5,6-tetrahydrocyclopenta[c]pyrazole (2-1b). H-NMR (400 MHz,
DMSO) δ 7.57 (d, J = 1.8, 2H), 7.45 (t, J = 1.8, 1H), 3.05 (m, 2H), 2.59–2.49 (m, 4H), 2.16 (s, 3H).

Molecules 2011, 16
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MS (DCI+) m/z 267.1 [M+H]+. 1% yield. In the ROESY spectrum NOE correlations were observed
between methylene protons of the cyclopentyl ring and aryl protons verifying the regioisomer.
Cl
N
F
F
N
Cl
F
1
1-(3,5-Dichlorophenyl)-5-methyl-3-(trifluoromethyl)-1H-pyrazole (2-2). H-NMR (400 MHz, DMSO)
13
δ 7.84 (dt, J = 16.5, 1.8, 1H), 7.76 (d, J = 1.8, 2H), 6.81 (s, 1H), 2.40 (s, 3H). C-NMR (126 MHz,
DMSO) δ 151.34, 144.72, 133.82, 123.92 (q, J = 287), 119.10, 114.40, 92.23 (q, J = 32), 47.70, 15.31.
MS (DCI+) m/z 294.1 [M+H]+. 15% yield. In the ROESY spectrum an NOE correlation was observed
between the methyl protons and aryl protons, verifying the regioisomer.
Cl
N
N
Cl
1
1-(3,5-Dichlorophenyl)-3,4,5-trimethyl-1H-pyrazole (2-3). H-NMR (400 MHz, DMSO) δ 7.67–7.43
(m, 3H), 2.27 (s, 3H), 2.12 (s, 3H), 1.92 (s, 3H). 13C-NMR (101 MHz, DMSO) δ 148.64, 141.80,
136.25, 134.31, 125.69, 121.70, 114.16, 11.66, 10.83, 7.82. MS (DCI+) m/z 255.1 [M+H]+. 26% yield.
Cl
5
4
1
N
3
N
2
Cl
1
1-(3,5-Dichlorophenyl)-5-methyl-3-phenyl-1H-pyrazole (2-4a). H-NMR (400 MHz, DMSO) δ 7.85
(dt, J = 8.2, 1.7, 2H), 7.75 (d, J = 1.8, 2H), 7.70 (t, J = 1.8, 1H), 7.38–7.32 (m, 2H), 6.81 (d, J = 0.8,
13
1H), 2.45 (d, J = 0.5, 3H). C-NMR (126 MHz, DMSO) δ 149.74, 143.53, 141.46, 134.02, 129.64,
128.74, 128.52, 126.39, 122.90, 109.03, 13.22. MS (DCI+) m/z 303.2 [M+H]+. 14% yield. In the
ROESY spectrum an NOE correlation was observed between the methyl protons and aryl protons of
the chlorinated ring, verifying the regioisomer.
Cl
5
4
3
1
N
N
2
Cl
1-(3,5-Dichlorophenyl)-3-methyl-5-phenyl-1H-pyrazole (2-4b). 1H-NMR (400 MHz, DMSO) δ 7.57 (t,
J = 1.9, 1H), 7.47–7.36 (m, 3H), 7.32–7.25 (m, 3H), 7.26 (d, J = 0.6, 1H), 6.48 (s, 1H), 2.24 (d,
J = 34.1, 3H) MS (DCI+) m/z 303.2 [M+H]+. 9% yield. In the ROESY spectrum NOE correlations
were observed between the aryl resonances for the chlorinated ring and the phenyl ring, verifying
the regioisomer.

Molecules 2011, 16
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OH
N
N
1
2-(3-Methyl-5,6-dihydrocyclopenta[c]pyrazol-1(4H)-yl)ethanol (2-5). H-NMR (400 MHz, DMSO)
δ 3.94 (t, J = 5.6, 2H), 3.63 (t, J = 5.6, 2H), 2.70–2.65 (m, 2H), 2.48–2.40 (m, 4H), 2.07 (s, 3H).
13C-NMR (126 MHz, DMSO) δ 153.97, 139.13, 124.94, 76.27, 59.47, 52.43, 29.83, 23.75, 22.20,
11.08. MS (DCI+) m/z 167.2 [M+H]+. 50% yield. In the ROESY spectrum NOE correlations were
observed between methylene protons in the cyclopentyl ring and the methylene protons for the alcohol
substituent, verifying the regioisomer.
OH
N
F
N
F
F
2-(5-Methyl-3-(trifluoromethyl)-1H-pyrazol-1-yl)ethanol (2-6). 1H-NMR (400 MHz, DMSO) δ 6.45 (s,
1H), 4.92 (t, J = 5.4, 1H), 4.21–4.08 (m, 2H), 3.71 (q, J = 5.5, 2H), 2.30 (dd, J = 17.1, 10.9, 3H).
13C-NMR (101 MHz, DMSO) δ 141.76, 139.76 (q, J = 37), 121.99 (q, J = 268), 103.30, 60.33, 51.90,
10.78. MS (DCI+) m/z 195.1 [M+H]+. 17% yield. In the ROESY spectrum NOE correlations were
observed between methyl protons and methylene protons for the alcohol substituent, verifying
the regioisomer.
OH
N
N
1
2-(3,5-Dimethyl-1H-pyrazol-1-yl)ethanol (2-7). H-NMR (400 MHz, DMSO) δ 4.06 (t, J = 5.6, 2H),
3.64 (t, J = 5.6, 2H), 2.18 (s, 3H), 2.11 (s, 3H), 1.90–1.82 (s, 3H). 13C-NMR (126 MHz, DMSO)
δ 143.46, 139.36, 111.58, 59.87, 50.65, 10.55, 9.19, 7.44. MS (DCI+) m/z 155.1 [M+H]+. 37% yield.
5
OH
4
1
N
3
N
2
1
2-(3-Methyl-5-phenyl-1H-pyrazol-1-yl)ethanol (2-8a). H-NMR (400 MHz, DMSO) δ 7.64–7.27 (m,
5H), 6.15 (s, 1H), 4.03 (t, J = 5.9, 2H), 3.75 (t, J = 5.9, 2H), 2.20 (s, 3H). 13C-NMR (126 MHz,
DMSO) δ 146.50, 144.43, 130.42, 128.81, 128.70, 128.38, 105.35, 59.98, 50.84, 13.28. MS (DCI+)
m/z 203.1 [M+H]+. 57% yield. In the ROESY spectrum NOE correlations were observed between
resonances for the phenyl ring and methylene protons of the alcohol substituent, verifying
the regioisomer.
5
OH
4
1
N
3
N
2

Molecules 2011, 16
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1
2-(5-Methyl-3-phenyl-1H-pyrazol-1-yl)ethanol (2-8b). H-NMR (400 MHz, DMSO) δ 7.73 (dd,
J = 8.3, 1.2, 2H), 7.44–7.31 (m, 2H), 7.25 (ddd, J = 8.6, 2.6, 1.3, 1H), 6.44 (s, 1H), 4.09 (t, J = 5.8,
2H), 3.72 (t, J = 5.8, 2H), 2.30 (s, 3H). MS (DCI+) m/z 203.1 [M+H]+. 22% yield. In the ROESY
spectrum NOE correlations were observed between methyl protons and methylene protons of the
alcohol substituent, verifying the regioisomer.
N
N
3-Methyl-1-phenyl-1,4,5,6-tetrahydrocyclopenta[c]pyrazole (2-9). 1H-NMR (400 MHz, DMSO) δ 7.59
(d, J = 8.8, 2H), 7.51–7.34 (m, 2H), 7.31–7.14 (m, 1H), 3.10–2.91 (m, 2H), 2.15 (s, 3H).
13C-NMR (126 MHz, DMSO) δ 148.68, 143.03, 139.94, 129.43, 127.94, 125.03, 118.03, 30.53, 26.25,
21.76, 12.53. MS (DCI+) m/z 199.2 [M+H]+. 32% yield. In the ROESY spectrum NOE correlations
were observed between methylene protons for the cyclopentyl ring and resonances for the phenyl ring,
verifying the regioisomer.
N
F
N
F
F
1
5-Methyl-1-phenyl-3-(trifluoromethyl)-1H-pyrazole (2-10). H-NMR (400 MHz, DMSO) δ 7.55 (m,
13
5H), 6.76 (s, 1H), 2.36 (s, 3H). C-NMR (101 MHz, DMSO) δ 141.57, 140.99 (q, J = 37), 138.42,
129.34, 128.75, 125.03, 121.56 (q, J = 268), 104.90 (q, J = 2), 11.84.MS (DCI+) m/z 227.2 [M+H]+.
38% yield. In the ROESY spectrum an NOE correlation was observed between methyl protons and
resonances for the phenyl ring verifying the regioisomer.
N
N
1
3,4,5-Trimethyl-1-phenyl-1H-pyrazole (2-11). H-NMR (400 MHz, DMSO) δ 7.53–7.40 (m, 4H),
13
7.40–7.26 (m, 1H), 2.20 (s, 3H), 2.13 (s, 3H), 1.93 (m, 3H). C-NMR (126 MHz, DMSO) δ 147.03,
139.75, 135.83, 129.05, 126.78, 124.01, 112.89, 11.65, 10.75, 7.90. MS (DCI+) m/z 187.3 [M+H]+.
33% yield.
N
N
1
5-Methyl-1,3-diphenyl-1H-pyrazole (2-12) H-NMR (400 MHz, DMSO) δ 7.46–7.26 (m, 6H),
7.27–7.13 (m, 3H), 6.45 (s, 1H), 2.25 (s, 3H). 13C-NMR (126 MHz, DMSO) δ 148.53, 143.11, 139.86,
130.29, 128.93, 128.54, 128.32, 128.19, 127.23, 124.96, 107.80, 13.27. MS (DCI+) m/z 235.3 [M+H]+.
29% yield. In the ROESY spectrum an NOE correlation was observed between the methyl protons and
resonances for the N-bound phenyl ring, verifying the regioisomer.

Molecules 2011, 16
9174
N
N
1
1,3-Dimethyl-1,4,5,6-tetrahydrocyclopenta[c]pyrazole (2-13). H-NMR (400 MHz, DMSO) δ 3.57 (s,
1H), 2.59 (m, 1H), 2.42 (m, 1H), 1.98 (m, 1H). 13C-NMR (126 MHz, DMSO) δ 150.13, 139.74,
123.91, 36.29, 30.69, 23.10, 22.51, 12.39. MS (DCI+) m/z 137.1 [M+H]+. 43% yield. In the ROESY
spectrum NOE correlations were observed between methylene resonances for the cyclopentyl ring and
the N-bound methyl group, verifying the regioisomer.
N
N
1
1,3,4,5-Tetramethyl-1H-pyrazole (2-15). H-NMR (400 MHz, DMSO) δ 3.57 (s, 3H), 2.08 (s, 3H),
1.99 (s, 3H), 1.82 (s, 3H). 13C-NMR (126 MHz, DMSO) δ 143.96, 135.34, 110.06, 35.45, 11.50, 9.05,
7.85. MS (DCI+) m/z 125.2 [M+H]+. 44% yield.
5
4
N
3
1
N
2
1,5-Dimethyl-3-phenyl-1H-pyrazole (2-16a). 1H-NMR (400 MHz, DMSO) δ 7.72 (dt, J = 8.1, 1.6, 2H),
13
7.41–7.31 (m, 2H), 7.31–7.17 (m, 1H), 6.46 (s, 1H), 3.75 (s, 3H), 2.25 (s, 3H). C-NMR (126 MHz,
DMSO) δ 146.04, 143.51, 130.31, 128.79, 128.33, 128.32, 105.28, 37.07, 13.14. MS (DCI+) m/z 173.1
[M+H]+. 15% yield. In the ROESY spectrum an NOE correlation was observed between the two
methyl groups, verifying the regioisomer.
5
4
1
N
3
N
2
1
1,3-Dimethyl-5-phenyl-1H-pyrazole (2-16b). H-NMR (400 MHz, DMSO) δ 7.61–7.27 (m, 5H), 6.18
(s, 1H), 3.76 (s, 3H), 2.20 (s, 3H). MS (DCI+) m/z 173.1 [M+H]+. 6% yield. In the ROESY spectrum
an NOE correlation was observed between resonances for the phenyl ring and the N-bound methyl
group, verifying the regioisomer.
N
N
1
1-Cyclohexyl-3-methyl-1,4,5,6-tetrahydrocyclopenta[c]pyrazole (2-17). H-NMR (500 MHz, DMSO)
δ 4.02-3.85 (m, 2H), 2.78–2.73 (m, 2H), 2.49–2.36 (m, 4H), 1.94 (s, 3H), 2.0–1.87 (m, 2H), 1.82–1.75
(m, 2H), 1.63 (qd, J = 12.5, 3.5, 3H), 1.35 (qt, J = 13.1, 3.4, 2H), 1.17 (qt, J = 13.0, 3.6, 1H).
13C-NMR (101 MHz, DMSO) δ 151.43, 138.86, 125.16, 59.77, 31.89, 29.81, 24.80, 24.60, 24.41,

Molecules 2011, 16
9175
21.64, 11.14. MS (DCI+) m/z 205.3 [M+H]+. 40% yield. In the ROESY spectrum NOE correlations
were observed between methylene resonances for the cyclopentyl ring and resonances for the
cyclohexyl substituent, verifying the regioisomer.
N
F
N
F
F
1-Cyclohexyl-5-methyl-3-(trifluoromethyl)-1H-pyrazole (2-18). 1H-NMR (400 MHz, DMSO) δ 6.43 (s,
1H), 4.18 (tt, J = 11.5, 3.9, 1H), 2.32 (s, 3H), 1.85–1.60 (m, 8H), 1.48–1.34 (m, 2H), 1.28–1.14 (m,
1H). 13C-NMR (101 MHz, DMSO) δ 139.66, 138.99 (q, J = 37), 121.81 (q, J = 268), 103.08 (q,
J = 2), 57.00, 32.26, 24.81, 24.75, 10.34. MS (DCI+) m/z 233.3 [M+H]+. 23% yield. In the ROESY
spectrum NOE correlations were observed between methyl protons and resonances for the cyclohexyl
substituent, verifying the regioisomer.
N
N
1
1-Cyclohexyl-3,4,5-trimethyl-1H-pyrazole (2-19). H-NMR (400 MHz, DMSO) δ 4.11–3.86 (m, 1H),
2.16 (s, 3H), 2.08 (s, 3H), 1.85 (s, 3H), 1.82–1.57 (m, 7H), 1.50–1.27 (m, 2H), 1.26–1.02 (m, 1H).
13C-NMR (101 MHz, DMSO) δ 143.58, 137.52, 111.25, 56.69, 32.05, 25.01, 24.81, 10.81, 9.05, 7.43.
MS (DCI+) m/z 193.2[M+H]+. 34% yield.
N
N
1
1-Cyclohexyl-3-methyl-5-phenyl-1H-pyrazole (2-20). H-NMR (400 MHz, DMSO) δ 7.57–7.27 (m,
5H), 6.06 (s, 1H), 3.98 (tt, J = 11.2, 4.2, 1H), 2.19 (s, 3H), 2.00–1.68 (m, 6H), 1.52–1.50 (m, 1H),
13
1.36 –1.01 (m, 3H). C-NMR (101 MHz, DMSO) δ 146.10, 142.90, 130.66, 128.88, 128.66, 128.42,
105.20, 56.81, 33.04, 25.15, 24.88, 13.44. MS (DCI+) m/z 241.2 [M+H]+. 26% yield. In the ROESY
spectrum an NOE correlation was observed between resonances for the phenyl ring and resonances for
the cyclohexyl substituent, verifying the regioisomer.
4. Conclusions
In this paper we have demonstrated a new method for the production of compound libraries in a
continuous flow reactor using immiscible solvent spacers. The yields for compound libraries
synthesized using this technique were consistent with that of standard microwave conditions.
Importantly, because of the continuous nature of this methodology, the 20 member libraries took 45
min to complete in flow, but would have taken 100 min to complete if synthesized sequentially in a
microwave reactor. For larger libraries the time savings using this system quickly becomes significant.
Furthermore, the continuous flow setup offers the possibility of a tandem arrangement with a variety of
analytical or biological techniques which could improve efficiency even further. Library synthesis in

Molecules 2011, 16
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this format also uses a very small amount of organic solvent, with all forty compounds discussed here
synthesized using a total of eight mL of DMF, with all of the fluorinated spacer solvent being recycled
for further library synthesis.
Future studies are directed toward automating reagent loading and injection to enable larger library
production in an automated fashion. We also intend to explore coupling the flow system directly to an
analytical device for real time library monitoring and methodology development.
Acknowledgements
The authors would like to acknowledge the analytcial and purification sciences group for their
assistance in purifying compounds for this publication, as well as the structural chemistry group for
NMR and MS support.
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© 2011 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).