Synthesis of pyrrolo[1,2-a]naphthyridines by Lewis acid mediated cycloisomerization

Article abstract of DOI:10.1039/C7OB00343A

Pyrrolo[1,2-a]naphthyridines were synthesized from 3-alkynyl-2-([1H]-pyrrol-1-yl)pyridines and 3-alkynyl-4-([1H]-pyrrol-1-yl)pyridines by cycloisomerization. The reactions are performed by application of the Lewis acids PtCl₂ or Bi(OTf)₃ without the need of further additives. With the described methods a number of derivatives containing a variety of functional groups have been synthesized in up to 78% yield.

Full text of DOI:10.1039/C7OB00343A

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Synthesis of pyrrolo[1,2-a]naphthyridines by Lewis acid mediated
cycloisomerization
Anika Flader,a,b Silvio Parpart,a Peter Ehlers,a,b and Peter Langer*a,b
a
Universität Rostock, Institut für Chemie, AlbertꢀEinsteinꢀStr. 3a, 18059 Rostock
Eꢀmail: peter.langer@uniꢀrostock.de
b
LeibnizꢀInstitut für Katalyse e.V. an der Universität Rostock, AlbertꢀEinsteinꢀStr. 29a,
18059 Rostock
Abstract:
Pyrrolo[1,2ꢀa]naphthyridines
and
were
synthesized
from
3ꢀalkynylꢀ
by
2ꢀ([1H]ꢀpyrrolꢀ1ꢀyl)pyridines
3ꢀalkynylꢀ4ꢀ([1H]ꢀpyrrolꢀ1ꢀyl)pyridines
cycloisomerization. The reactions are performed by application of the Lewis acids PtCl2 or
Bi(OTf)3 without the need of further additives. With the described methods a number of
derivatives containing a variety of functional groups have been synthesized in up to 78% yield.
Graphical abstract:
Keywords: pyrrolonaphthyridine, naphthyridine, indolizine, nitrogen heterocycle, annulation,
cycloisomerization, Lewis acid, Sonogashira reaction

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Introduction
Nitrogen heterocycles are found in many natural products and exhibit not only biological
activity, but also interesting properties in the field of material science. For instance,
naphthyridines are fused heterocycles which belong to the group of diazanaphthalines and
contain one nitrogen atom in each aromatic ring (Figure 1). Their derivatives show
antibacterial, antitumor, antiviral and analgesic activity as well as anticancer potential.[1]
Furthermore, naphthyridines have been applied as ligands in transition metal complexes[2],
they have been investigated for their corrosion inhibition[3] and they were used as fluorescent
dyes[4]. Likewise, indolizines, which consist of a fused pyrrole and pyridine system, have been
proven to be interesting core structures. They have been examined for their vast biological
activity[5] and, more recently, because of their fluorescence properties[6].
The synthesis of functionalized, annulated heterocycles can be achieved through
intramolecular or intermolecular cyclization of dienyl alkynes. Accordingly, arylations have
been realized under transitionꢀmetal catalysis or by employing acids.[7] The group of Fürstner
reported the synthesis of phenanthrenes by 6ꢀendoꢀdig cyclization of orthoꢀalkynylated
biphenyls in the presence of catalytic amounts of transition metals. Later, the same group
extended their substrates to orthoꢀalkynylated Nꢀpyrrolylbenzenes and other heteroarenes.[8]
Moreover, Fürstner utilized his strategy repeatedly for the synthesis of natural products.[9]
Grätzel, on the other hand, introduced in 2013 the synthesis of ullazines applying InCl3 as a
Lewis acid and performing
a
twofold cyclization on 1ꢀ(2,6ꢀbisalkynylphenyl)ꢀ
[1H]pyrroles.[10] Recently, Das et al. developed a photocatalyzed method for the synthesis of
pyrrolo[1,2ꢀa]quinolines and ullazines. Therein, the formation of 6ꢀphenylpyrrolo[1,2ꢀa]ꢀ
[1,8]naphthyridine and 6ꢀ(paraꢀtolyl)pyrrolo[1,2ꢀa][1,8]naphthyridine has been described in
the presence of the organic dye rhodamine 6G under visible light irradiation.[11] Recent
approaches for the synthesis of pyrrolo[1,2ꢀa]naphthyridines are summarized in Figure 1.
These strategies often require complex starting materials, harsh reaction conditions or
ineconomic catalyst systems.[12]

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Figure 1. Overview of recently published results synthesizing pyrrolo[1,2ꢀa]naphthyridines
Based on the importance of fused heterocycles, we herein report the synthesis of [1,6]ꢀ and
[1,8]naphthyridine derivatives by Lewis acidꢀmediated cycloisomerization of orthoꢀalkynylꢀ
Nꢀpyrrolylpyridines (Scheme 1). This methodology is highly efficient, versatile and
operationally simple and allows the introduction of various functional groups without the
need of specific ligands, metal catalysts or other additives.
Scheme 1. Strategy for the synthesis of pyrrolo[1,2ꢀa]naphthyridines
Results & discussion
The starting material 1a was prepared by ClausonꢀKaas reaction[13] of 2ꢀaminoꢀ3ꢀ
bromopyridine (Scheme 2). Subsequently, the Sonogashira coupling[14] of 1a with phenyl
acetylene was thoroughly optimized under both standard Sonogashira conditions[14] as well as
by using different catalyst/ligandꢀsystems and different solvents (Table 1). Under the best

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conditions, the use of PdCl2(PPh3)2 (0.03 eq.) as catalyst and triethylamine (3 eq.) as the base
in acetonitrile at 50 °C (16 h), allowed the preparation of the desired product 2a in 88% yield.
Especially the solvent proved to be of great importance in this coupling reaction.
Scheme 2. Synthesis of 1a and 2a; reagents and conditions: (i) 2,5ꢀdimethoxytetrahydrofuran
(1.05 eq.), H2O/HOAc (2:1), DCE, 80 °C, 12 h; (ii) PdCl2(PPh3)2 (0.03 eq.), CuI (0.02 eq.),
Et3N (3 eq.), MeCN, 50 °C, 16 h.
Table 1. Optimization of Sonogashira reaction of 2ꢀbromo([1H]ꢀpyrrolꢀ1ꢀyl)pyridine (1a)a
catalyst
ligand
(0.06 eq.)
–
temp.
[°C]
100
time yield
entry
base eq. solvent
(0.03 eq.)
PdCl2(PPh3)2
[h]
24
24
48
48
3
[%]c
20
–
1
NEt3
NEt3
–
3
3
–
–
3
DMF
DMF
2
PdCl2(PPh3)2 P(tBu)3
100
3
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
Pd(OAc)2
–
Et2NH r.t.
63
–
4
5b
–
–
NEt3
r.t.
80
50
50
d
–
NEt3
DMF
–
6
PCy3
NEt3 1.5 THF
NEt3 1.5 THF
48
48
4
–
d
7
Pd(OAc)2
XPhos
–
8
PdCl2(PPh3)2
P(PPh3)4
–
–
–
NEt3
NEt3
NEt3
3
3
3
3
dioxane 50
dioxane 50
MeCN 50
MeCN 50
45
–
9
4
10
11
PdCl2(PPh3)2
Pd(OAc)2
16
16
88
92
CataCXium A NEt3
a Reaction conditions: 1a (0.5 mmol, 111.5 mg) and phenyl acetylene (1.5 eq., 0.75 mmol,
82 µl) react with CuI (0.02 eq., 0.01 mmol, 1.9 mg) in 2 ml of solvent in a glass tube under
b
c
d
argon. Reaction with phenyl acetylene (3 eq.). Isolated yields. Occurrence of inseparable
mixtures.

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In the following, the optimized conditions for the Sonogashira coupling were applied to the
synthesis of 2a-m (Table 2). All products were obtained in good to very good yields. With
regard to the arylꢀsubstituted alkynes, both electron withdrawing and donating functional
groups were successfully employed. Alkynes with aliphatic substituents were also
successfully employed.
Table 2. Synthesis of starting material 2-m
product
alkyne
yield [%]a product
alkyne
yield [%]a
98
88
2a
2h
81
98
2b
2i
86
78
98
94
94
87
86
2c
2d
2e
2f
2j
2k
2l
89
95
2m
2g
a Isolated yield.
The cyclization was studied next. In an initial attempt, 3ꢀphenylethynylꢀ2ꢀ([1H]ꢀpyrrolꢀ1ꢀyl)
pyridine 2a was cyclized in the presence of InCl3 (1.5 eq.) under argon in toluene at 80 °C for
24 h (entry 1 in Table 3) to give the desired [1,8]naphthyridine 3a, albeit, in only 13% yield.
The same conditions were previously employed by Grätzel and gave ullazines in an overall
yield of 55%.[10] To improve the reaction conditions different Lewis acids[8a, 15] (entries 1 to 6
in Table 3) and Brønsted acids[16] (entries 7 to 12 in Table 3) were employed. In addition, the
reaction time was prolonged. The use of PtCl2 (entry 5 & 6 in Table 3) proved to be the most

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efficient catalyst and 3a could be isolated in up to 50% when the temperature was increased to
120 °C using xylene as the solvent.
Table 3. Synthesis of 6ꢀphenylpyrrolo[1,2ꢀa][1,8]naphthyridine (2a)a
entry
1
2
3
4
5
6
7
8
acid
eq.
1.5
1.5
1.5
1.5
0.05
0.05
0.1
18
solvent
toluene
toluene
toluene
toluene
toluene
xylene
DCM
DCM
DCE
DCE
xylene
xylene
temp. [°C] time [h]
yield [%]b
InCl3
80
80
80
80
24
24
20
20
12
24
2
24
24
12
24
24
13
–
Cu(OTf)2
In(OTf)3
Bi(OTf)3
PtCl2
PtCl2
Tf2NH
TFA
20
28
33
50
–
80
120
−20
r.t.
90
–
9
TFA
6.5
14
65
15
28
28
18
10
11
12
pTSA
pTSA
pTSA
80
120
140
65
a Reaction conditions: 2a (0.205 mmol) with acid under argon in 2 ml solvent. b Isolated yield.
With these optimized conditions in hand, the scope of the reaction was examined by
employment of various substituted alkynes. Both electron poor and electron rich arylalkynes
were tested as well as alkylꢀsubstituted alkyne moieties (Table 4). Products 3a-m were
obtained in 40–66% yield. Disparity in yields for the cyclized products can be explained due
to varying capability of substituents to stabilize cationic transition states of Lewis acidꢀ
adductꢀcomplexes.[7, 8] Therefore, the cyclization afforded generally higher yields for
arylalkynes in comparison to alkylalkynes. With regard to the aromatic substituents of 3a-i,
both electron poor and electron rich systems gave equally good results. Slightly deviating
results may appear because of the poor solubility and consequently difficulties during
purification of some products. Product 3j, containing a thiophene moiety, was also prepared
(41% yield). The synthesis of 3k, containing a triisopropylsilyl protecting group, failed
probably due to steric hindrance. The alkyl substituted derivatives 3l and 3m were
successfully prepared in 37% and 62% yields, respectively.

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Table 4. Cyclization of 3ꢀalkynylꢀ2ꢀ([1H]ꢀpyrrolꢀ1ꢀyl)pyridinesa
a Reaction conditions: 3a-m (0.6 mmol) and PtCl2 (0.03 mmol) under argon in xylene (2 ml)
at 120 °C for 24 h.
The synthesis of [1,6]naphthyridines was studied next. The reaction of 4ꢀaminoꢀ3ꢀ
bromopyridine with 2,5ꢀdimethoxytetrahydrofuran afforded 3ꢀbromoꢀ4ꢀ([1H]ꢀpyrrolꢀ1ꢀ
yl)pyridine 1c (Scheme 3). The conditions of the Sonogashira coupling of 1c with phenyl
acetylene were thoroughly optimized (Table 5). The best yield of the desired product 4a
(81%) was obtained using 1.5 eq. of the acetylene, Pd(MeCN)2Cl2 (0.05 eq.) as the catalyst,
XPhos (0.1 eq.) as ligand, CuI (0.05 eq.) as coꢀcatalyst and triethylamine (3 eq.) as base in
dioxane under inert atmosphere at room temperature for 24 h (entry 7 in Table 5).

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Scheme 3. Synthesis of 1c and 4a; reagents and conditions: (i) 2,5ꢀdimethoxytetrahydrofuran
(2.5 eq.), HOAc, 120 °C, 1 h; (ii) Pd(MeCN)2Cl2 (0.05 eq.), CuI (0.05 eq.), XPhos (0.1 eq.),
Et3N (3 eq.), dioxane, r.t., 24 h.
Table 5. Optimization of Sonogashira reaction of 2ꢀbromo([1H]ꢀpyrrolꢀ1ꢀyl)pyridine (1c)a
catalyst
ligand
temp.
[°C]
140
50
yield
[%]b
59
entry
base
eq. solvent
(0.05 eq.)
(0.1 eq.)
1
2
3
4
5
6
7
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(MeCN)2Cl2
Pd(MeCN)2Cl2
Pd(MeCN)2Cl2
–
–
Et3N
Et3N
3
3
3
3
3
3
3
DMF
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
56
P(tBu)3·HBF4 Et3N
P(tBu)3·HBF4 HNiPr2
P(tBu)3·HBF4 Et3N
50
65
50
65
50
69
XPhos
XPhos
Et3N
Et3N
50
73
r.t.
81
a
Reaction conditions: 1a (0.45 mmol, 100 mg) and phenyl acetylene (1.5 eq., 0.68 mmol,
73 µl) react with CuI (0.05 eq., 0.01 mmol, 4.3 mg) in 2 ml of solvent in a glass tube under
argon for 24 h. b Isolated yields.
Subsequently, products 4a-n were prepared under the optimized conditions (Table 6).
Different aromatic alkynes bearing electron donating substituents gave the corresponding
products in good to very good yields. Moderate yields were observed for the strongly electron
withdrawing trifluoromethyl group of 4e (55%) and the aliphatic moieties of 4m (56%) and
4n (56%).
Table 6. Synthesis of starting material 4a-n
product
alkyne
yield [%]a product
alkyne
yield [%]a

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81
88
98
86
4a
4b
4h
4i
91
99
83
76
4c
4j
4d
4k
CF3
55
88
95
78
56
56
4e
4f
4l
4m
4n
4g
a Isolated yield.
Subsequently, the synthesis of [1,6]naphthyridines by cyclization was studied. The conditions
were optimized for derivate 4a (Table 7). The first test reaction using In(OTf)3 (1 eq.) in
toluene at 100 °C (24 h) afforded the desired cyclized product 5a, albeit, in only 20% yield.
The yield was improved by employing Bi(OTf)3. An increase of the temperature to 120 °C
and the use of xylene as solvent resulted in the formation of 5a in 55% yield (entry 10 in
Table 7). The application of the Brønsted acids trifluoroacetic acid (TFA) or paraꢀ
toluenesulfonic acid (pTSA) (entry 11 & 12 in Table 7) yielded the desired product only in
trace amounts.

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Table 7. Synthesis of 6ꢀphenylpyrrolo[1,2ꢀa][1,6]naphthyridine (5a)a
entry
1
2
3
4
5
6
7
8
acid
eq.
1
1
1
1
1
0.5
1
2
1
solvent
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
xylene
toluene
toluene
temp. [°C]
100
100
100
100
100
100
100
100
110
120
100
100
yield [%]b
In(OTf)3
Zn(OTf)2
AuCl3
Ag(OAc)
PtCl2
Bi(OTf)3
Bi(OTf)3
Bi(OTf)3
Bi(OTf)3
Bi(OTf)3
TFA
20
22
8
15
–
7
50
30
55
55
traces
mixtures
9
10
11
12
1
20
25
pTSA
a Reaction conditions: 4a (0.41 mmol) with acid in 3 ml solvent for 24 h. b Isolated yield.
The scope of the reaction was studied next. The cyclization of 4a–n afforded the desired
products 5a–n in 25–78% yield (Table 8). With regards to the aromatic alkynes, electron
donating substituents gave higher yields than electron withdrawing groups, due to a better
stabilization of cationic transition states. Therefore, products 5a–d and 5f–k were obtained in
moderate to good yields. The presence of the electron withdrawing trifluoromethyl group in
5e resulted in only 25% yield, possibly caused by the less stabilizing effect of electron
acceptors during charged transition states.[8] Furthermore, aliphatic alkynes gave the cyclized
products 5m and 5n only in traces, while the sterically demanding triisopropylsilyl fragment
5l could not be synthesized, again. Overall, the latter 3ꢀalkynylꢀ4ꢀpyrrolopyrodines appear to
be less active for this type of cycloisomerization requiring electron rich substituents at the
alkyne moiety. Hence, it can be considered that the pyridine moiety and specifically the
position of the Nꢀatom can similarly promote the reaction.

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Table 8. Cyclization of 3ꢀalykynlꢀ4ꢀ([1H]ꢀpyrrolꢀ1ꢀyl)pyridinesa
R
Bi(OTf)3
R
xylene
N
N
N
N
4a-n
5a-n
a Reaction conditions: 3a-o (0.4–0.7 mmol) and Bi(OTf)3 (1 eq.) under argon in xylene (2 ml)
at 120 °C for 24 h.
Conclusion
To conclude, we prepared
a
variety of pyrrolo[1,2ꢀa][1,8]naphthyridines and
pyrrolo[1,2ꢀa][1,6]naphthyridines. The reactivity of alkynes 4 was lower than the reactivity of
2. Therefore, the yields of [1,6]naphthyridines were, in most cases, lower than the yields of
the isomeric [1,8]naphthyridines. Our strategy required no special catalyst/ligandꢀsystems and
was realized by the application of PtCl2 and Bi(OTf)3 as simple Lewis acids.

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Experimental Section
General
For NMR spectra the substrates were dissolved in CDCl3, DMSOꢀd6 or C6D6 and the spectra
recorded on a Bruker AVANCE 300 III, 250 II or 500. The IR spectra were measured as ATR
experiments with a Nicolet 6700 FTꢀIR spectrometer and a Nicolet 550 FTꢀIR spectrometer.
MS and HRMS were measured by an Agilent 6890 N/5973 GCꢀMS and an Agilent 1200/6210
TimeꢀofꢀFlight LCꢀMS. Melting points were determined by a MicroꢀHotꢀStage GalenTM III
Cambridge Instruments.
Synthesis of starting materials
3-Bromo-2-([1H]-pyrrol-1-yl)pyridine[11] 1a. To a solution of 2ꢀaminoꢀ3ꢀbromopyridine
(5.8 mmol, 1.0 g) in 1.5 ml DCE at 80 °C 2,5ꢀdimethoxytetrahydrofuran (1.05 eq., 6.1 mmol,
0.79 ml) was added. A mixture of H2O/HOAc (2:1, 2 ml) was poured into the solution. The
reaction was stirred at 80 °C for 12 h. Thereafter, the crude product was washed with distilled
water and extracted with DCM. Following the evaporation of the organic solvent the product
1a was obtained after column chromatography (heptane/DCM, 5:1) as a white solid
(76% yield, 978.1 mg); mp 36–39 °C. 1H NMR (300 MHz, CDCl3): δ = 8.45 (dd, 3J = 4.6 Hz,
3
4
4J = 1.6 Hz, 1H, CHpyridine), 8.03 (dd, J = 7.9 Hz, J = 1.6 Hz, 1H, CHpyridine), 7.41–7.32 (m,
2H, CHpyrrole), 7.11 (dd, 3J = 7.9 Hz, 3J = 4.6 Hz, 1H, CHpyridine), 6.39–6.32 (m, 2H,
CHpyrrole) ppm. 13C NMR (75 MHz, CDCl3): δ = 150.1 (Cpyridine), 147.6, 143.7, 122.7
(CHpyridine), 121.5 (CHpyrrole), 112.5 (Cpyridine), 110.2 (CHpyrrole) ppm. MS (EI, 70 eV): m/z
(%) = 224 ([C9H781BrN2]+, 98), 222 ([C9H779BrN2]+, 100), 198 (16), 197 (42), 196 (17), 195
(41), 158 (12), 156 (12), 143 (20), 142 (18), 117 (12), 116 (60), 89 (20), 78 (12), 76 (25), 63
(12), 51 (18), 50 (17), 39 (18). HRMS (ESI-TOF): m/z = calcd. for C9H779BrN2 ([M+H]+)
222.98654, found 222.98668. Calcd. for C9H781BrN2 ([M+H]+) 224.98453, found 224.98458.
4-Amino-3-bromopyridine 1b. NꢀBromosuccinimide (1.1 eq., 29.2 mmol, 5.2 g) was added
slowly to a stirred solution of 4ꢀaminopyridine (26.6 mmol, 2.5 g) in 140 ml acetonitrile. The
mixture was stirred for 48 h at room temperature. Afterwards the solvent was removed under
reduced pressure and the product was purified by column chromatography (heptane/ethyl
acetate, 2:1 → 1:2) to yield 4ꢀaminoꢀ3ꢀbromopyridine 1b as a white solid (86% yield, 3.95 g).
1H NMR (300 MHz, DMSO): δ = 11.11 (bs, 2H, NH2), 8.23 (s, 1H, CHpyridine), 7.96 (d,

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3
3J = 5.5 Hz, 1H, CHpyridine), 6.68 (d, J = 5.5 Hz, 1H, CHpyridine) ppm. 13C NMR (75 MHz,
DMSO): δ = 151.4 (CꢀNH2), 150.8, 148.2, 109.9 (CHAr), 105.5 (CꢀBr) ppm. IR (ATR):
ṽ = 3440 (w), 3342 (w), 3217 (w), 2946 (w), 2545 (br, w), 1700 (s), 1632 (s), 1501 (m), 1199
(s), 1074 (w), 1014 (m), 815 (s), 633 (s), 562 (s) cm−1. MS (EI, 70 eV): m/z (%) = 174
([C9H781BrN2]+, 100), 172 ([C9H779BrN2]+, 99), 145 (2), 119 (8), 117 (6), 93 (53). HRMS (EI,
70 eV): m/z = calcd. for C5H5N279Br (M+) 171.96306, found 171.96313; calcd. for
C5H5N281Br (M+) 173.96102, found 173.96131.
3-Bromo-4-([1H]-pyrrol-1-yl)pyridine
1c.
2,5ꢀdimethoxytetrahydrofuran
(2.5 eq.,
28.9 mmol, 3.75 ml) was added to a stirred solution of 1b (17.3 mmol, 3.0 g) in 12 ml HOAc.
The mixture was then refluxed (120 °C) for 1 h. Afterwards, the reaction mixture was diluted
with DCM and washed with distilled water and NaHCO3 solution subsequently. The aqueous
phase was extracted with DCM. The organic fractions were combined and the solvent
removed under vacuum. Finally, the crude product was purified from reagent residues through
column chromatography (heptane/ethyl acetate, 4:1) to obtain 1c as a white solid (79% yield,
2.03 g). 1H NMR (300 MHz, DMSO-d6): δ = 8.87 (s, 1H, CHpyridine), 8.60 (d, 3J = 5.2 Hz, 1H,
3
3
CHpyridine), 7.48 (d, J = 5.2 Hz, 1H, CHpyridine), 7.19 (t, J = 2.2 Hz, 2H, CHpyrrole), 6.33 (t,
3J = 2.2 Hz, 2H, CHpyrrole) ppm. 13C NMR (75 MHz, DMSO-d6): δ = 153.4, 149.8 (CHpyridine),
145.7 (Cqpyridine), 121.8 (CHpyridine), 121.6 (CHpyrrole), 114.5 (CꢀBr), 110.5 (CHpyrrole) ppm. IR
(ATR): ṽ = 3118 (br, w), 1737 (w), 1574 (s), 1497 (s), 1339 (s), 1180 (w), 1069 (s), 1017 (s),
834 (s), 726 (s), 667 (s), 619 (s), 570 (s) cm−1. MS (EI, 70 eV): m/z (%) = 222 ([M]+, 100),
196 (7), 183 (3), 156 (4), 143 (27), 142 (18), 116 (67). HRMS (EI, 70 eV): m/z = calcd. for
C9H7N279Br (M+) 221.97871, found 221.97828. Calcd. for C9H7N281Br (M+) 223.97667,
found 223.97663.
General procedure for Sonogashira reaction to synthesize 3-alykynl-2-([1H]-
pyrrol-1-yl)pyridines 2.
1a was dissolved in 3 ml MeCN under an argon atmosphere. After the addition of
PdCl2(PPh3)2 (0.03 eq.), CuI (0.02 eq.) and Et3N (3 eq.) in advance of the corresponding
acetylene (1.2 eq.) the reaction is stirred at 50 °C for 24 h. The reaction mixture was
subsequently cooled to room temperature and washed with distilled water and extracted with
DCM. The organic layers were collected and the solvent evaporated. The crude product was
thereafter purified by column chromatography (heptane/DCM, 5:1) to give the alkynylated

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products 2a-m. Thereby, 1–2 ml Et3N were added to 250 ml eluent mixture to deactivate the
acidic silica.
3-(Phenylethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2a. The reaction of 1a (0.9 mmol, 200 mg)
with phenylacetylene (1.08 mmol, 118.3 µl) gave 2a as a pale brown solid (382 mg, 88%);
1
3
4
mp 82–84 °C. H NMR (300 MHz, CDCl3): δ = 8.43 (dd, J = 4.8 Hz, J = 1.9 Hz, 1H,
3
4
CHpyridine), 7.96 (dd, J = 7.7 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.85–7.80 (m, 2H, CHpyrrole),
3
3
7.57–7.50 (m, 2H, CHPh), 7.42–7.34 (m, 3H, CHPh), 7.16 (dd, J = 7.7 Hz, J = 4.8 Hz, 1H,
CHpyridine), 6.39–6.35 (m, 2H, CHpyrrole) ppm. 13C NMR (75 MHz, CDCl3): δ = 151.3
(Cpyridine), 147.9, 143.4 (CHpyridine), 131.6, 129.1, 128.6 (CHPh), 122.6 (CPh), 120.8 (CHpyrrole),
120.2 (CHpyridine), 110.5 (CHpyrrole), 110.4 (Cpyridine), 96.1, 85.7 (Calkyne) ppm. IR (ATR):
ṽ = 3052 (w), 1562 (w), 1469 (w), 1437 (m), 1336 (w), 1060 (w), 800 (w), 728 (m), 687 (m),
624 (w), 553 (w) cm−1. MS (EI, 70 eV): m/z (%) = 244 ([M]+, 100), 243 (77), 242 (43), 241
(5), 218 (11), 216 (8), 215 (5), 214 (6), 190 (6), 189 (5), 177 (6), 151 (6), 150 (9), 121 (11),
109 (6), 77 (5), 75 (5), 51 (5), 39 (5). HRMS (EI): m/z = calcd. for C17H12N2 (M+) 244.09950,
found 244.09919.
3-((2-Fluorophenyl)ethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2b. 2ꢀethynylꢀ1ꢀfluorobenzene
(0.6 mmol, 78 µl) reacted with 1a (0.5 mmol, 111.5 mg) to 2b as a pale brown oil (106 mg,
1
81%); Rf 0.39 (heptane/ethyl acetate 5:1). H NMR (250 MHz, CDCl3): δ = 8.44 (dd,
4
3
4
3J = 4.8 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.97 (dd, J = 7.7 Hz, J = 1.9 Hz, 1H, CHpyridine),
3
3
4
7.88–7.83 (m, 2H, CHpyrrole), 7.50 (ddd, J = 7.7 Hz, J = 7.1 Hz, J = 2.0 Hz, 1H, CHAr),
7.39–7.33 (m, 1H, CHAr), 7.15 (dd, 3J = 7.6 Hz, 3J = 4.8 Hz, 1H, CHpyridine), 7.21–7.11 (m, 2H,
CHAr), 6.40–6.35 (m, 2H, CHpyrrole) ppm. 19F NMR (235 MHz, CDCl3): δ = −109.1 ppm.
1
13C NMR (63 MHz, CDCl3): δ = 162.92 (d, JC,F = 252.7 Hz, CꢀF), 151.2 (Cpyridine), 148.4,
143.6 (CHpyridine), 133.32 (d, 4JC,F = 1.3 Hz, CHAr), 130.87 (d, 3JC,F = 8.0 Hz, CHAr), 124.24 (d,
2
3JC,F = 3.7 Hz, CHAr), 120.7 (CHpyrrole), 120.1 (CHpyridine), 115.80 (d, JC,F = 20.6 Hz, CHAr),
2
3
111.31 (d, JC,F = 15.6 Hz, CAr), 110.5 (CHpyrrole), 110.2 (Cpyridine), 90.54 (d, JC,F = 3.2 Hz,
Calkyne), 89.6 (Calkyne) ppm. IR (ATR): ṽ = 3065 (br, w), 2921 (w), 1708 (br, w), 1560 (m),
1472 (m), 1434 (m), 1224 (m), 1095 (m), 1058 (m), 797 (m), 754 (s), 728 (s), 544 (m), 470
(m) cm−1. MS (EI, 70 eV): m/z (%) = 262 ([M]+, 100), 261 (61), 260 (33), 243 (6), 242 (8),
236 (10), 234 (5), 168 (5), 130 (5), 118 (5). HRMS (ESI-TOF): m/z = calculated for
C17H11FN2 ([M+H]+) 263.09790, found 263.09786.

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15
3-((4-Fluorophenyl)ethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2c. 1a (0.5 mmol, 111.5 mg) and
4ꢀethynylꢀ1ꢀfluorobenzene (0.6 mmol, 68.8 µl) achieved 2c as a yellow solid (113 mg, 86%);
1
3
4
mp 78–82 °C. H NMR (250 MHz, CDCl3): δ = 8.43 (dd, J = 4.8 Hz, J = 1.9 Hz, 1H,
3
4
CHpyridine), 7.93 (dd, J = 7.7 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.83–7.72 (m, 2H, CHpyrrole),
7.56–7.46 (m, 2H, CHAr), 7.15 (dd, 3J = 7.7 Hz, 3J = 4.8 Hz, 1H, CHpyrrole), 7.12–7.02 (m, 2H,
3
4
CHAr), 6.38 (dt, J = 3.8 Hz, J = 2.3 Hz, 2H, CHpyrrole) ppm. 19F NMR (235 MHz, CDCl3):
1
δ = −109.4 ppm. 13C NMR (63 MHz, CDCl3): δ = 162.98 (d, JC,F = 250.9 Hz, CꢀF), 151.3
3
(Cpyridine), 148.0, 143.1 (CHpyridine), 133.50 (d, JC,F = 8.5 Hz, CHAr), 120.7 (CHpyrrole), 120.2
(CHpyridine), 118.67 (d, 4JC,F = 3.5 Hz, CAr), 115.97 (d, 2JC,F = 22.2 Hz, CHAr), 110.4 (CHpyrrole),
110.1 (Cpyridine), 94.9 (Calkyne), 85.40 (d, 5JC,F = 1.6 Hz, Calkyne) ppm. IR (ATR): ṽ = 3049 (w),
1600 (w), 1562 (w), 1505 (w), 1472 (w), 1439 (w), 1216 (w), 1056 (w), 833 (w), 806 (w), 728
(m), 640 (w), 620 (w), 532 (w), 522 (w) cm−1. MS (EI, 70 eV): m/z (%) = 262 ([M]+, 100),
261 (75), 260 (39), 236 (12), 234 (7), 232 (5), 208 (5), 195 (5), 169 (5), 168 (7), 130 (5), 118
(5), 39 (5). HRMS (EI): m/z = calcd. for C17H11FN2 (M+) 262.09008, found 262.08955.
3-((4-Methylphenyl)ethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2d. 4ꢀEthynyltoluene (0.6 mmol,
76 µl) and 1a (0.5 mmol, 111.5 mg) gave 2d as a yellow solid (101 mg,78%); mp 71–75 °C.
1H NMR (250 MHz, CDCl3): δ = 8.42 (dd, 3J = 4.8 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.94 (dd,
3J = 7.7 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.89–7.79 (m, 2H, CHpyrrole), 7.43 (d, 3J = 8.1 Hz, 2H,
3
3
3
CHAr), 7.18 (d, J = 8.6 Hz, 2H, CHAr), 7.14 (dd, J = 7.7 Hz, J = 4.7 Hz, 1H, CHpyridine),
6.43–6.33 (m, 2H, CHpyrrole), 2.39 (s, 3H, Me) ppm. 13C NMR (63 MHz, CDCl3): δ = 151.2
(Cpyridine), 147.7, 143.2 (CHpyridine), 139.4 (CꢀMe), 131.4, 129.4 (CHAr), 120.7 (CHpyrrole),
120.2 (CHpyridine), 119.5 (CAr), 110.5 (Cpyridine), 110.3 (CHpyrrole), 96.3, 85.1 (Calkyne), 21.7
(Me) ppm. IR (ATR): ṽ = 3030 (w), 2916 (w), 1703 (br, w), 1565 (w), 1474 (w), 1439 (w),
1339 (w), 1311 (w), 1099 (w), 1060 (w), 1017 (w), 818 (w), 733 (m), 529 (w) cm−1.MS (EI,
70 eV): m/z (%) = 258 ([M]+, 100), 257 (47), 256 (12), 255 (17), 243 (15), 242 (36), 232 (7),
231 (6), 128 (6), 39 (5). HRMS (ESI-TOF): m/z = calcd. for C18H14N2 ([M+H]+) 259.12297,
found 259.12281.
3-((4-tert-Butylphenyl)ethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2e. The reaction of 1a
(0.5 mmol, 111.5 mg) with 4ꢀtertꢀbutylphenylacetylene (0.6 mmol, 108 µl) resulted in the
1
product 2e as a pale brown oil (155 mg, 98%); Rf 0.45 (heptane/ethyl acetate 5:1). H NMR
(300 MHz, CDCl3): δ = 8.42 (dd, 3J = 4.8 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.94 (dd,
3J = 7.7 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.86–7.79 (m, 2H, CHpyrrole), 7.48 (d, 3J = 8.6 Hz, 2H,

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3
3
3
CHAr), 7.40 (d, J = 8.7 Hz, 2H, CHAr), 7.15 (dd, J = 7.7 Hz, J = 4.8 Hz, 1H, CHpyridine),
6.43–6.35 (m, 2H, CHpyrrole), 1.34 (s, 9H, CH3tBu) ppm. 13C NMR (63 MHz, CDCl3):
δ = 152.5 (Cpyridine), 147.8, 143.2 (CHpyridine), 131.3, 125.7 (CHAr), 120.7(CHpyrrole), 120.2
(CHpyridine), 119.6 (CAr), 110.5 (Cpyridine), 110.3 (CHpyrrole), 110.2 (CꢀtBu), 96.3, 85.1 (Calkyne),
35.0 (CtBu), 31.3 (CH3tBu) ppm. IR (ATR): ṽ = 2953 (w), 1562 (w), 1469 (w), 1437 (w), 1338
(w), 1059 (w), 926 (w), 833 (w), 724 (m), 625 (w), 561 (w) cm−1. MS (EI, 70 eV): m/z
(%) = 300 ([M]+, 67), 286 (23), 285 (100), 284 (8), 283 (8), 270 (23), 269 (18), 268 (10), 267
(5), 258 (6), 257 (27), 255 (18), 244 (13), 243 (20), 242 (21), 241 (5), 128 (26), 121 (6), 115
(6), 41 (7), 39 (5). HRMS (EI): m/z = calcd. for C21H20N2 (M+) 300.16210, found 300.16165.
3-((4-Methoxyphenyl)ethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2f. 1a (0.25 mmol, 56 mg) and
1
4ꢀethynylanisole (0.3 mmol, 40 µl) gave 2f as a solid (61 mg, 89%); mp 61–64 °C. H NMR
(300 MHz, CDCl3): δ = 8.40 (dd, 3J = 4.8 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.92 (dd,
4
3J = 7.7 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.85–7.79 (m, 2H, CHpyrrole), 7.48–7.45 (m, 2H,
CHAr), 7.14 (dd, 3J = 7.7 Hz, 3J = 4.8 Hz, 1H, CHpyridine), 6.94–6.86 (m, 2H, CHAr), 6.42–6.31
(m, 2H, CHpyrrole), 3.83 (s, 3H, OMe) ppm. 13C NMR (75 MHz, CDCl3): δ = 160.3 (CꢀOMe),
151.1 (Cpyridine), 147.6, 143.0 (CHpyridine), 133.1 (CHAr), 120.7 (CHpyrrole), 120.2 (CHpyridine),
114.7 (CAr), 114.3 (CHAr), 110.7 (Cpyridine), 110.3 (CHpyrrole), 96.2, 84.5 (Calkyne), 55.5
(OMe) ppm. IR (ATR): ṽ = 3011 (br, w), 2215 (w), 1604 (w), 1508 (m), 1435 (w), 1245 (m),
1173 (w), 1028 (w), 833 (w), 725 (m), 699 (w), 536 (m) cm−1. MS (EI, 70 eV): m/z (%) = 274
([M]+, 100), 260 (6), 259 (33), 258 (7), 242 (5), 232 (7), 231 (41), 230 (25), 229 (29), 205
(13), 203 (11), 177 (5), 176 (5), 164 (7), 137 (6), 115 (7), 39 (5). HRMS (ESI-TOF):
m/z = calcd. for C18H14N2O ([M+H]+) 275.11789, found 275.11784.
3-((3-Methylphenyl)ethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2g. 3ꢀethynyltoluene (0.6 mmol,
77 µl) and 1a (0.5 mmol, 111.5 mg) gave 2g as a yellow oil (123 mg, 95%); Rf 0.44
(heptane/ethyl acetate 5:1). 1H NMR (250 MHz, CDCl3): δ = 8.43 (dd, 3J = 4.8 Hz,
3
4
4J = 1.9 Hz, 1H, CHpyridine), 7.94 (dd, J = 7.7 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.90–7.86 (m,
3
2H, CHpyrrole), 7.40–7.35 (m, 2H, CHAr), 7.29 (t, J = 7.7 Hz, 1H, CHAr), 7.24–7.18 (m, 1H,
CHAr), 7.14 (dd, 3J = 7.7 Hz, 3J = 4.8 Hz, 1H, CHpyridine), 6.45–6.41 (m, 2H, CHpyrrole), 2.39 (s,
3H, Me) ppm. 13C NMR (63 MHz, CDCl3): δ = 151.2 (Cpyridine), 147.8, 143.1 (CHpyridine),
138.2 (CꢀMe), 132.0, 129.9, 128.6, 128.4 (CHAr), 122.3 (CAr), 120.6 (CHpyrrole), 120.1
(CHpyridine), 110.3 (CHpyrrole), 110.2 (Cpyridine), 96.2, 85.3 (Calkyne), 21.3 (Me) ppm. IR (ATR):
ṽ = 2915 (w), 1705 (br, w), 1558 (w), 1474 (w), 1433 (w), 1308 (w), 1165 (w), 1057 (w), 782

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(w), 728 (w), 687 (w), 442 (w), 406 (w) cm−1. MS (EI, 70 eV): m/z (%) = 258 ([M]+, 100),
257 (42), 256 (11), 255 (17), 243 (16), 242 (36), 231 (8), 128 (5). HRMS (ESI-TOF):
m/z = calcd. for C18H14N2 ([M+H]+) 259.12297, found 259.12289.
3-((3-Methoxyphenyl)ethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2h. Substrate 1a (0.5 mmol,
111.5 mg) reacted with 3ꢀethynylanisole (0.6 mmol, 78 µl) to give 2h as a brown oil (152 mg,
1
98%); Rf 0.38 (heptane/ethyl acetate 5:1). H NMR (300 MHz, CDCl3): δ = 8.43 (dd,
4
3
4
3J = 4.8 Hz, J = 1.8 Hz, 1H, CHpyridine), 7.95 (dd, J = 7.7 Hz, J = 1.8 Hz, 1H, CHpyridine),
3
3
7.86–7.78 (m, 2H, CHpyrrole), 7.30 (d, J = 7.9 Hz, 1H, CHAr), 7.15 (dd, J = 7.8 Hz,
4
4
4J = 4.8 Hz, 1H, CHpyridine), 7.15–7.11 (m, 1H, CHAr), 7.05 (dd, J = 2.5 Hz, J = 1.4 Hz, 1H,
3
4
3
CHAr), 6.94 (ddd, J = 8.4 Hz, J = 2.7 Hz, J = 1.1 Hz, 1H, CHAr), 6.41–6.29 (m, 2H,
CHpyrrole), 3.83 (s, 3H, OMe) ppm. 13C NMR (75 MHz, CDCl3): δ = 159.5 (CAr), 151.3
(Cpyridine), 148.0, 143.3 (CHpyridine), 129.7, 124.1 (CHAr), 123.6 (CAr), 120.8 (CHpyrrole), 120.2
(CHpyridine), 116.4, 115.7 (CHAr), 110.5 (CHpyrrole), 110.3 (Cpyridine), 96.0, 85.5 (Calkyne), 55.5
(OMe) ppm. IR (ATR): ṽ = 2936 (br, w), 2833 (w), 1710 (br, w), 1573 (m), 1475 (m), 1434
(m), 1235 (m), 1038 (m), 868 (m), 708 (m), 730 (m), 684 (m), 551 (m), 461 (w) cm−1. MS (EI,
70 eV): m/z (%) =274 ([M]+, 100), 273 (23), 244 (12), 243 (17), 242 (19), 241 (7), 231 (24),
230 (18), 229 (23), 205 (8), 204 (7), 203 (10), 164 (8), 115 (6). HRMS (ESI-TOF):
m/z = calcd. for C18H14N2O ([M+H]+) 275.11789, found 275.11807.
3-((4-Methoxy-2-methylphenyl)ethynyl)-2-([1H]-pyrrol-1-yl)-pyridine 2i. The reaction of
1a (0.5 mmol, 111.5 mg) and 1ꢀethynylꢀ4ꢀmethoxyꢀ2ꢀmethylbenzene (0.6 mmol, 87.7 mg)
1
gave 2i as a yellow oil (141 mg, 98%); Rf 0.50 (heptane/ethyl acetate 5:1). H NMR
(250 MHz, CDCl3): δ = 8.40 (dd, 3J = 4.8 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.93 (dd,
3J = 7.7 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.82–7.77 (m, 2H, CHpyrrole), 7.42 (d, 3J = 8.4 Hz, 1H,
CHAr), 7.15 (dd, 3J = 7.7 Hz, 3J = 4.8 Hz, 1H, CHpyridine), 6.77 (d, 4J = 2.6 Hz, 1H, CHAr), 6.73
3
4
(dd, J = 8.4 Hz, J = 2.6 Hz, 1H, CHAr), 6.38–6.31 (m, 2H, CHpyrrole)), 3.82 (s, 3H, OMe),
2.45 (s, 3H, Me) ppm. 13C NMR (63 MHz, CDCl3): δ = 160.3 (CꢀOMe), 151.0 (Cpyridine),
147.6, 143.2 (CHpyridine), 142.4 (CꢀMe), 133.6 (CHAr), 120.7 (CHpyrrole), 120.2 (CHpyridine),
115.4 (CHAr), 114.7 (CAr), 111.6 (CHAr), 111.1 (Cpyridine), 110.3 (CHpyrrole), 95.5, 88.0 (Calkyne),
55.4 (OMe), 21.2 (Me) ppm. IR (ATR): ṽ = 2916 (br, w), 2205 (w), 1706 (br, w), 1602 (m),
1560 (m), 1472 (m), 1433 (m), 1294 (m), 1236 (s), 1036 (m), 797 (m), 727 (m), 561 (m) cm−1.
MS (EI, 70 eV): m/z (%) = 288 ([M]+, 58), 287 (100), 273 (19), 272 (17), 271 (8), 261 (8),
256 (7), 255 (10), 245 (14), 244 (21), 243 (42), 242 (18), 230 (7), 229 (8), 218 (10), 205 (9),

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151 (6), 128 (6), 122 (7), 39 (7). HRMS (ESI-TOF): m/z = calcd. for C19H16N2O ([M+H]+)
289.13354, found 289.13364.
2-([1H]-pyrrol-1-yl)-3-(thiophen-3-ylethynyl)pyridine 2j. The starting material 1a
(0.5 mmol, 111.5 mg) and 1ꢀethynylꢀ4ꢀmethoxyꢀ2ꢀmethylbenzene (0.6 mmol, 59 µl) delivered
1
2j as a yellow oil (117 mg, 94%); Rf 0.48 (heptane/ethyl acetate 5:1). H NMR (250 MHz,
CDCl3): δ = 8.42 (dd, 3J = 4.8 Hz, 4J = 1.9 Hz, 1H, CHpyridine), 7.92 (dd, 3J = 7.7 Hz,
4
4
4J = 1.9 Hz, 1H, CHpyridine), 7.87–7.81 (m, 2H, CHpyrrole), 7.57 (dd, J = 3.0 Hz, J = 1.2 Hz,
1H,CHthioph.), 7.32 (dd, 3J = 5.0 Hz, 4J = 3.0 Hz, 1H, CHthioph.), 7.21 (dd, 3J = 5.0 Hz,
3
3
4J = 1.2 Hz, 1H, CHthioph.), 7.12 (dd, J = 7.7 Hz, J = 4.8 Hz, 1H, CHpyridine), 6.44–6.38 (m,
2H, CHpyrrole) ppm. 13C NMR (63 MHz, CDCl3): δ = 151.1 (Cpyridine), 147.8, 143.0 (CHpyridine),
129.5, 129.4, 125.8 (CHthioph.), 121.5 (Cthioph.), 120.6 (CHpyrrole), 120.1 (CHpyridine), 110.3
(CHpyrrole), 110.0 (Cpyridine), 91.4, 85.2 (Calkyne) ppm. IR (ATR): ṽ = 3107 (w), 3050 (w), 1561
(w), 1473 (w), 1438 (w), 1335 (w), 1058 (w), 1017 (w), 869 (w), 781 (w), 726 (m), 625
(w) cm−1. MS (EI, 70 eV): m/z (%) = 250 ([M]+,100), 249 (62), 248 (24), 224 (11), 223 (5),
222 (6), 205 (18), 140 (5), 113 (5), 45 (5), 39 (5). HRMS (ESI-TOF): m/z = calcd. for
C15H10N2S ([M+H]+) 251.06375, found 251.06395.
2-([1H]-pyrrol-1-yl)-3-((triisopropylsilyl)ethynyl)pyridine 2k. The reaction of 1a (1 mmol,
223 mg) with ethynyltriisopropylsilane (1.2 mmol, 269 µl) achieved product 2k as a pale
1
yellow oil (295 mg, 94%); Rf 0.60 (heptane/ethyl acetate 5:1). H NMR (300 MHz, CDCl3):
3
4
3
4
δ = 8.40 (dd, J = 4.8 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.90 (dd, J = 7.7 Hz, J = 1.9 Hz, 1H,
3
3
CHpyridine), 7.88–7.85 (m, 2H, CHpyrrole), 7.09 (dd, J = 7.7 Hz, J = 4.7 Hz, 1H, CHpyridine),
6.33–6.27 (m, 2H, CHpyrrole), 1.16–1.09 (m, 21H, iPr3) ppm. 29Si INEPT NMR (60 MHz,
CDCl3): δ = −1.4 ppm. 13C NMR (75 MHz, CDCl3): δ = 151.2 (Cpyridine), 148.0, 144.5
(CHpyridine), 120.6 (CHpyrrole), 119.9 (CHpyridine), 110.3 (CHpyrrole), 110.0 (Cpyridine), 102.8, 99.7
(Calkyne), 18.8 (CH3iPr), 11.5 (CHiPr) ppm. IR (ATR): ṽ = 2942 (w), 2864 (m), 2153 (w), 1720
(br, w), 1531 (m), 1476 (m), 1436 (s), 1070 (m), 881 (m), 727 (m), 674 (m), 629 (m), 557 (w),
412 (w) cm−1.MS (EI, 70 eV): m/z (%) = 324 ([M]+, 12), 282 (32), 281 (100), 253 (23), 240
(12), 239 (30), 225 (14), 223 (10), 211 (18), 209 (11), 195 (35), 181 (15), 169 (12), 168 (12),
43 (10). HRMS (ESI-TOF): m/z = calcd. for C20H28N2Si ([M+H]+) 325.20945, found
325.20938.

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3-(n-Hex-1-yn-1-yl)-2-([1H]-pyrrol-1-yl)pyridine 2l. 1ꢀHexyne (0.6 mmol, 69 µl) and 1a
(0.5 mmol, 111.5 mg) gave the desired product 2l as a yellow oil (98 mg,87%); Rf 0.43
(heptane/ethyl acetate 5:1). 1H NMR (300 MHz, CDCl3): δ = 8.36 (dd, 3J = 4.8 Hz,
3
3
3J = 1.9 Hz, 1H, CHpyridine), 7.81 (dd, J = 7.7 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.79–7.74 (m,
3
2H, CHpyrrole), 7.08 (dd, 3J = 7.7 Hz, J = 4.7 Hz, 1H, CHpyridine), 6.36–6.32 (m, 2H, CHpyrrole),
3
2.45 (t, J = 7.0 Hz, 2H, CH2), 1.70–1.53 (m, 2H, CH2), 1.54–1.40 (m, 2H, CH2), 0.96 (t,
3J = 7.2 Hz, 3H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 151.3 (Cpyridine), 147.2, 143.6
(CHpyridine), 120.6 (CHpyrrole), 120.0 (CHpyridine), 110.9 (Cpyridine), 110.0 (CHpyrrole), 98.0, 76.9
(Calkyne), 30.4, 22.2, 19.5 (CH2), 13.7 (CH3) ppm. IR (ATR): ṽ = 2930 (w), 2870 (w), 2230
(w), 1530 (m), 1474 (m), 1434 (s), 1336 (m), 1073 (m), 1068 (m), 925 (m), 797 (m), 725 (s),
517 (m), 545 (w) cm−1. MS (EI, 70 eV): m/z (%) = 224 ([M]+, 5), 223 (8), 209 (5), 196 (5),
195 (22), 194 (6), 193 (7), 183 (13), 182 (100), 181 (67), 179 (14), 169 (5), 168 (14), 155 (12),
154 (9), 153 (6), 128 (5), 127 (7), 63 (5), 51 (5), 43 (7), 41 (14), 39 (12), 29 (5). HRMS
(ESI-TOF): m/z = calcd. for C15H16N2 ([M+H]+) 225.13862, found 225.13859. Calcd. for
C15H16N2 ([M+Na]+) 247.12057, found 247.12030.
3-(Cyclohexylethynyl)-2-([1H]-pyrrol-1-yl)pyridine 2m. The reaction of 1a (1 mmol,
223 mg) with ethynylcyclohexane (1.2 mmol, 157 µl) provided 2m as a yellow oil (214 mg,
1
86%); Rf 0.56 (heptane/ethyl acetate 5:1). H NMR (250 MHz, CDCl3): δ = 8.35 (dd,
4
3
4
3J = 4.8 Hz, J = 1.9 Hz, 1H, CHpyridine), 7.81 (dd, J = 7.7 Hz, J = 1.9 Hz, 1H, CHpyridine),
3
7.81–7.77 (m, 2H, CHpyrrole), 7.07 (dd, J = 7.7 Hz, 3J = 4.8 Hz, 1H, CHpyridine), 6.36–6.29 (m,
3
3
2H, CHpyrrole), 2.64 (tt, Ja,a = 9.2 Hz, Ja,e = 3.8 Hz, 1H, CHa), 1.96–1.84 (m, 2H, CH2),
1.81–1.67 (m,2H, CH2), 1.63–1.48 (m, 3H, CH2), 1.45–1.30 (m, 3H, CH2) ppm. 13C NMR
(63 MHz, CDCl3): δ = 151.2 (Cpyridine), 147.2, 143.6 (CHpyridine), 120.6 (CHpyrrole), 120.0
(CHpyridine), 110.9 (Cpyridine), 109.9 (CHpyrrole), 101.7, 76.9 (Calkyne), 32.2 (CH2), 30.1 (CH),
25.9, 25.0 (CH2) ppm. IR (ATR): ṽ = 2926 (m), 2852 (w), 2223 (w), 1717 (br, w), 1451 (m),
1434 (s), 1336 (m), 1074 (m), 926 (m), 796 (m), 726 (s), 617 (w) cm−1.MS (EI, 70 eV): m/z
(%) = 250 ([M]+, 28), 249 (20), 221 (18), 209 (13), 207 (23), 206 (13), 205 (17), 196 (17),
195 (100), 193 (20), 192 (12), 182 (24), 181 (16), 169 (17), 168 (22), 155 (14). HRMS
(ESI-TOF): m/z = calcd. for C17H18N2 ([M+H]+) 251.15428, found 251.15414
General
method
for
cycloisomerization
to
achieve
6-substituted
pyrrolo[1,2-a][1,8]naphthyridines 3.

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In a pressure tube the Sonogashira products 2 were dissolved in xylene (3 ml, isomeric
mixture) under an argon atmosphere. The catalyst PtCl2 (0.05 eq.) was added to the mixture.
The solution was stirred at 120 °C for 24 h.
After cooling to room temperature the crude product was treated with water and extracted
with DCM. For further purification the organic solvent was evaporated and column
chromatography (heptane/DCM, 5:1 → 3:1) was performed. Thereby, 1–2 ml Et3N were
added to 250 ml eluent mixture to deactivate the acidic silica.
6-Phenylpyrrolo[1,2-a][1,8]naphthyridine 3a. 2a (0.2 mmol, 50 mg) cyclized in the
presence of PtCl2 (0.01 mmol, 2.7 mg) to give 3a as a pale yellow solid (25 mg, 50%);
1
3
4
mp 102–105 °C. H NMR (300 MHz, CDCl3): δ = 8.54 (dd, J = 4.7 Hz, J = 1.7 Hz, 1H,
CHnaphtyr.), 8.46 (dd, 3J = 2.9 Hz, 4J = 1.5 Hz, 1H, CHpyrrole), 7.97 (dd, 3J = 7.8 Hz, 4J = 1.7 Hz,
3
4
1H, CHnaphtyr.), 7.72 (dd, J = 8.0 Hz, J = 1.6 Hz, 2H, CHPh), 7.55–7.44 (m, 3H, CHPh), 7.30
3
3
3
(dd, J = 7.7 Hz, J = 4.7 Hz, 1H, CHnaphtyr.), 6.91 (s, 1H, CHnaphtyr.), 6.84 (dd, J = 3.8 Hz,
3
4
3J = 2.9 Hz, 1H, CHpyrrole), 6.68 (dd, J = 3.8 Hz, J = 1.5 Hz, 1H, CHpyrrole) ppm. 13C NMR
(75 MHz, CDCl3): δ = 146.6 (CHnaphtyr.), 144.0 (Cnaphtyr.), 138.5 (CPh), 136.3 (CHnaphtyr.),
134.2 (Cnaphtyr.), 131.5 (Cpyrrole), 128.8, 128.5, 128.5 (CHPh), 120.1 (CHnaphtyr.), 119.2 (Cnaphtyr.),
116.2 (CHnaphtyr.), 114.5 (CHnaphtyr.), 113.3, 105.3 (CHpyrrole) ppm. IR (ATR): ṽ = 3119 (w),
3094 (w), 2921 (w), 2851 (w), 1726 (w), 1595 (w), 1531 (w), 1493 (w), 1442 (w), 1370 (w),
1297 (w), 1143 (w), 1074 (w), 958 (w), 848 (w), 761 (m), 740 (m), 701 (m), 663 (w), 583 (w),
446 (w) cm−1. MS (EI, 70 eV): m/z (%) = 244 ([M]+, 100), 243 (81), 242 (43), 218 (13), 216
(8), 214 (7), 190 (7), 151 (7), 150 (10), 122 (5), 121 (7), 77 (6), 51 (7), 39 (8). HRMS (EI,
70 eV): m/z = calcd. for C17H12N2 244.09950, found 244.09919.
6-(2-Fluorophenyl)pyrrolo[1,2-a][1,8]naphthyridine 3b. 2b (0.36 mmol, 95 mg) gave 3b
under the influence of PtCl2 (0.02 mmol, 5.3 mg) as a pale green solid (58 mg, 61%);
1
3
4
mp 96–99 °C. H NMR (300 MHz, CDCl3): δ = 8.56 (dd, J = 4.7 Hz, J = 1.8 Hz, 1H,
CHnaphtyr.), 8.43 (dd, 3J = 2.9 Hz, 4J = 1.5 Hz, 1H, CHpyrrole), 7.96 (dd, 3J = 7.8 Hz, 4J = 1.8 Hz,
3
3
4
1H, CHnaphtyr.), 7.62 (td, J = 7.5 Hz, J = 7.5 Hz, J = 1.9 Hz, 1H, CHAr), 7.43 (dddd,
4
3J = 9.2 Hz, 3J = 8.1 Hz, JH,F = 5.1 Hz, 4J = 1.8 Hz, 1H, CHAr), 7.31 (dd, 3J = 7.7 Hz,
3J = 4.7 Hz, 1H, CHnaphtyr.), 7.29–7.23 (m, 1H, CHAr), 7.23–7.20 (m, 1H, CHAr) 6.95 (d,
3
3
5JH,F = 1.2 Hz, 1H, CHnaphtyr.), 6.82 (dd, J = 3.8 Hz, J = 2.9 Hz, 1H, CHpyrrole), 6.47 (dt,
3
5
3J = 3.8 Hz, J = 1.4 Hz, JH,F = 1.4 Hz 1H, CHpyrrole) ppm. 19F NMR (235 MHz, CDCl3):
1
δ = −114.3 ppm. 13C NMR (75 MHz, CDCl3): δ = 160.14 (d, JC,F = 248.5 Hz, CꢀF), 147.1

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4
(CHnaphtyr.), 144.1 (Cnaphtyr.), 136.4 (CHnaphtyr.), 131.4 (CAr), 131.22 (d, JC,F = 3.3 Hz, CHAr),
3
2
130.12 (d, JC,F = 8.2 Hz, CHAr), 128.0 (Cpyrrole), 125.76 (d, JC,F = 14.9 Hz, CAr), 124.27 (d,
4
3JC,F = 3.7 Hz, CHAr), 120.1 (CHnaphtyr.), 118.8 (Cnaphtyr.), 117.96 (d, JC,F = 2.1 Hz, CHnaphtyr.),
2
5
116.30 (d, JC,F = 22.3 Hz, CHAr), 114.3, 113.3 (CHpyrrole), 105.07 (d, JC,F = 1.8 Hz,
CHpyrrole) ppm. IR (ATR): ṽ = 3033 (w), 2921 (w), 2851 (w), 1724 (br, w), 1571 (m), 1433
(m), 1370 (m), 1259 (m), 1216 (m), 1087 (m), 1037 (m), 863 (m), 781 (m), 757 (m), 720 (s),
651 (m), 525 (m), 434 (m) cm−1. MS (EI, 70 eV): m/z (%) = 262 ([M]+, 100), 261 (26), 260
(14), 242 (5), 118 (6). HRMS (ESI-TOF): m/z = calcd. for C17H11FN2 ([M+H]+) 263.09790,
found 263.09795.
6-(4-Fluorophenyl)pyrrolo[1,2-a][1,8]naphthyridine 3c. 2c (0.2 mmol, 45 mg) reacted with
PtCl2 (0.01 mmol, 2.3 mg) to give 3c as a pale green solid (19 mg, 42%); mp 128–131 °C.
1H NMR (250 MHz, CDCl3): δ = 8.55 (dd, 3J = 4.7 Hz, 4J = 1.7 Hz, 1H, CHnaphtyr.), 8.43 (dd,
4
3
4
3J = 2.9 Hz, J = 1.5 Hz, 1H, CHpyrrole), 7.95 (dd, J = 7.8 Hz, J = 1.8 Hz, 1H, CHnaphtyr.),
7.73–7.64 (m, 2H, CHAr), 7.30 (dd, 3J = 7.7 Hz, 3J = 4.7 Hz, 1H, CHnaphtyr.), 7.24–7.12 (m, 2H,
3
3
CHAr), 6.87 (s, 1H, CHnaphtyr.), 6.83 (dd, J = 3.8 Hz, J = 2.9 Hz, 1H, CHpyrrole), 6.62 (dd,
4
3J = 3.8 Hz, J = 1.5 Hz, 1H, CHpyrrole) ppm. 19F NMR (235 MHz, CDCl3): δ = −113.4 ppm.
1
13C NMR (63 MHz, CDCl3): δ = 162.95 (d, JC,F = 247.6 Hz, CꢀF), 147.0 (CHnaphtyr.), 144.1
4
(Cnaphtyr.), 136.1 (CHnaphtyr.), 134.60 (d, JC,F = 3.4 Hz, CAr), 133.1 (Cnaphtyr.), 131.4 (Cpyrrole),
3
130.13 (d, JC,F = 8.1 Hz, CHAr), 120.2 (CHnaphtyr.), 119.1 (Cnaphtyr.), 116.3 (CHpyrrole), 115.73
2
(d, JC,F = 21.4 Hz, CHAr), 114.5 (CHnaphtyr.), 113.3, 105.0 (CHpyrrole) ppm. IR (ATR):
ṽ = 3041 (w), 2921 (w), 1724 (w), 1601 (w), 1508 (m), 1454 (m), 1438 (m), 1368 (w), 1298
(w), 1223 (m), 1160 (m), 1092 (m), 1036 (w), 857 (m), 831 (m), 794 (m), 725 (m), 623 (m),
556 (m), 510 (m), 497 (m), 448 (m) cm−1. MS (EI, 70 eV): m/z (%) = 262 ([M]+, 100), 261
(36), 260 (19), 118 (6). HRMS (ESI-TOF): m/z = calcd. for C17H11FN2 ([M+H]+) 263.09790,
found 263.09759.
6-(4-Tolyl)pyrrolo[1,2-a][1,8]naphthyridine 3d. The reaction of 2d (0.3 mmol, 78 mg)
with PtCl2 (0.015 mmol, 4 mg) gave 3d as a yellow solid (34 mg, 68%); mp 86–91 °C.
1H NMR (300 MHz, CDCl3): δ = 8.53 (dd, 3J = 4.7 Hz, 4J = 1.7 Hz, 1H, CHnaphtyr.), 8.47 (dd,
4
3
4
3J = 2.9 Hz, J = 1.5 Hz, 1H, CHpyrrole), 7.96 (dd, J = 7.8 Hz, J = 1.7 Hz, 1H, CHnaphtyr.),
7.64–7.57 (m, 2H, CHAr), 7.35–7.25 (m, 3H, CHnaphtyr./Ar), 6.89 (s, 1H, CHnaphtyr.), 6.84 (dd,
3
3J = 3.8 Hz, 3J = 2.9 Hz, 1H, CHpyrrole), 6.69 (dd, J = 3.8 Hz, 4J = 1.5 Hz, 1H, CHpyrrole), 2.45
(s, 3H, Me) ppm. 13C NMR (75 MHz, CDCl3): δ = 146.3 (CHnaphtyr.), 143.8 (Cnaphtyr.), 138.4

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(CꢀMe), 136.3 (CHnaphtyr.), 135.6 (CAr), 134.2 (Cnaphtyr.), 131.6 (Cpyrrole), 129.5, 128.3 (CHAr),
120.0 (CHnaphtyr.), 119.4 (Cnaphtyr.), 115.8, 114.5 (CHnaphtyr.), 113.4, 105.3 (CHpyrrole), 21.5
(Me) ppm. IR(ATR): ṽ = 3120 (m), 2917 (m), 2851 (m), 1723 (m), 1665 (w), 1604 (m), 1571
(m), 1510 (m), 1436 (s), 1369 (m), 1299 (m), 1282 (m), 1180 (m), 1145 (m), 1095 (m), 1060
(m), 1033 (m), 927 (m), 850 (m), 816 (s), 761 (s), 735 (vs), 722 (vs), 624 (m), 557 (m), 496
(m) cm−1. MS (EI, 70 eV): m/z (%) = 258 ([M]+, 100), 257 (21), 256 (6), 255 (10), 243 (6),
242 (14), 128 (8). HRMS (ESI-TOF): m/z = calcd. for C18H14N2 ([M+H]+) 259.12297, found
259.12293.
6-(4-tert-Butylphenyl)pyrrolo[1,2-a][1,8]naphthyridine 3e. Starting material 2e (0.3 mmol,
90.1 mg) reacted with PtCl2 (0.015 mmol, 4 mg) giving 3e as a brown oil (59 mg, 66%);
1
3
Rf 0.58 (heptane/ethyl acetate 5:1). H NMR (300 MHz, CDCl3): δ = 8.53 (dd, J = 4.7 Hz,
3
4
4J = 1.7 Hz, 1H, CHnaphtyr.), 8.45 (dd, J = 2.9 Hz, J = 1.5 Hz, 1H, CHpyrrole), 7.94 (dd,
4
3J = 7.8 Hz, J = 1.7 Hz, 1H, CHnaphtyr.), 7.70–7.65 (m, 2H, CHAr), 7.55–7.50 (m, 2H, CHAr),
7.29 (dd, 3J = 7.8 Hz, 3J = 4.7 Hz, 1H, CHnaphtyr.), 6.90 (s, 1H, CHnaphtyr.), 6.84 (dd, 3J = 3.8 Hz,
3
4
3J = 2.9 Hz, 1H, CHpyrrole), 6.73 (dd, J = 3.8 Hz, J = 1.5 Hz, 1H, CHpyrrole), 1.41 (s, 9H,
CH3tBu) ppm. 13C NMR (75 MHz, CDCl3): δ = 151.6 (CꢀtBu), 146.6 (CHnaphtyr.), 144.0
(Cnaphtyr.), 136.0 (CHnaphtyr.), 135.6 (CAr), 134.1 (Cnaphtyr.), 131.6 (Cpyrrole), 128.1, 125.7 (CHAr),
120.0 (CHnaphtyr.), 119.3 (Cnaphtyr.), 116.0 (CHpyrrole), 114.3 (CHnaphtyr.), 113.2, 105.3 (CHpyrrole),
34.9 (CtBu), 31.5 (CH3tBu) ppm. IR (ATR): ṽ = 2957 (w), 1721 (w), 1589 (w), 1512 (w), 1434
(m), 1362 (m), 1268 (m), 1146 (w), 1092 (m), 1018 (w), 831 (m), 787 (m), 768 (m), 722 (m),
610 (m), 542 (m), 448 (w) cm−1. MS (EI, 70 eV): m/z (%) = 300 ([M]+, 100), 286 (13), 285
(64), 270 (12), 269 (8), 268 (7), 257 (13), 255 (9), 244 (7), 243 (9), 242 (12), 128 (15).
HRMS (ESI-TOF): m/z = calcd. for C21H20N2 ([M+H]+) 301.16993, found 301.16950.
6-(4-Methoxyphenyl)pyrrolo[1,2-a][1,8]naphthyridine 3f. 2f (0.15 mmol, 42 mg) cyclized
under influence of PtCl2 (0.01 mmol, 2 mg) giving 3f as a pale yellow solid (17 mg, 40%);
1
3
4
mp 123–128 °C. H NMR (300 MHz, CDCl3): δ = 8.53 (dd, J = 4.7 Hz, J = 1.7 Hz, 1H,
CHnaphtyr.), 8.44 (dd, 3J = 2.9 Hz, 4J = 1.5 Hz, 1H, CHpyrrole), 7.96 (dd, 3J = 7.8 Hz, 4J = 1.7 Hz,
3
3
1H, CHnaphtyr.), 7.69–7.62 (m, 2H, CHAr), 7.30 (dd, J = 7.7 Hz, J = 4.7 Hz, 1H, CHnaphtyr.),
3
3
7.06–7.00 (m, 2H, CHAr), 6.87 (s, 1H, CHnaphtyr.), 6.83 (dd, J = 3.8 Hz, J = 2.9 Hz, 1H,
CHpyrrole), 6.68 (dd, 3J = 3.8 Hz, 4J = 1.5 Hz, 1H, CHpyrrole), 3.89 (s, 3H, OMe) ppm. 13C NMR
(75 MHz, CDCl3): δ = 160.0 (CꢀOMe), 146.3 (CHnaphtyr.), 143.7 (Cnaphtyr.), 136.1 (CHnaphtyr.),
133.9 (CAr), 131.7 (Cnaphtyr.), 131.0 (Cpyrrole), 129.6 (CHAr), 120.1 (CHnaphtyr.), 119.4 (Cnaphtyr.),

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115.6 (CHpyrrole), 114.4 (CHnaphtyr.), 114.2 (CHAr), 113.3, 105.2 (CHpyrrole), 55.5 (OMe) ppm.
IR (ATR): ṽ = 2919 (w), 2849 (w), 1720 (w), 1601 (w), 1509 (w), 1436 (w), 1367 (w), 1280
(w), 1239 (w), 1175 (w), 1111 (w), 1032 (w), 834 (w), 782 (w), 768 (w), 732 (w), 621 (w),
563 (w), 523 (w), 445 (w) cm−1. MS (EI, 70 eV): m/z (%) = 274 ([M]+, 100), 259 (18), 242
(5), 231 (21), 230 (13), 229 (19), 205 (15), 204 (7), 203 (6), 115 (6). HRMS (ESI-TOF):
m/z = calcd. for C18H14N2O ([M+H]+) 275.11789, found 275.11788. Calcd. for C18H14N2O
([M+Na]+) 297.09983, found 297.10014.
6-(3-Tolyl)pyrrolo[1,2-a][1,8]naphthyridine 3g. 2g (0.32 mmol, 82 mg) and PtCl2 (0.016
1
mmol, 4 mg) gave the product 3g as a yellow oil (21 mg, 25%); mp 86–89 °C. H NMR
(300 MHz, CDCl3): δ = 8.54 (dd, 3J = 4.8 Hz, 4J = 1.7 Hz, 1H, CHnaphtyr.), 8.47 (dd,
4
3
4
3J = 3.0 Hz, J = 1.5 Hz, 1H, CHpyrrole), 7.98 (dd, J = 7.8 Hz, J = 1.7 Hz, 1H, CHnaphtyr.),
3
3
7.57–7.47 (m, 2H, CHAr), 7.42–7.36 (m, 1H, CHAr), 7.32 (dd, J = 7.8 Hz, J = 4.8 Hz, 1H,
CHnaphtyr.), 7.29–7.27 (m, 1H, CHAr), 6.90 (s, 1H, CHnaphtyr.), 6.84 (dd, 3J = 3.8 Hz, 3J = 2.9 Hz,
3
4
1H, CHpyrrole), 6.69 (dd, J = 3.8 Hz, J = 1.5 Hz, 1H, CHpyrrole), 2.45 (s, 3H, Me) ppm.
13C NMR (75 MHz, CDCl3): δ = 146.4 (CHnaphtyr.), 143.8 (Cnaphtyr.), 138.5 (CꢀMe), 136.4
(CHnaphtyr.), 134.5 (CAr), 131.6 (Cnaphtyr.), 129.3, 129.1, 128.7, 125.6 (CHAr), 120.1 (CHnaphtyr.),
119.4 (Cnaphtyr.), 116.0 (CHpyrrole), 114.6 (CHnaphtyr.), 113.4, 105.4 (CHpyrrole), 21.7 (Me) ppm.
IR (ATR): ṽ = 3142 (w), 2917 (w), 1722 (w), 1603 (w), 1571 (w), 1531 (w), 1436 (m), 1366
(w), 1304 (w), 1283 (w), 1091 (w), 1038 (w), 1019 (w), 860 (m), 782 (m), 728 (m), 708 (m),
665 (w), 589 (w), 447 (w), 436 (w) cm−1. MS (EI, 70 eV): m/z (%) = 258 ([M]+, 100), 257
(20), 256 (5), 255 (11), 243 (6), 242 (16), 128 (8). HRMS (ESI-TOF): m/z = calcd. for
C18H14N2 ([M+H]+) 259.12297, found 259.12314.
6-(3-Methoxyphenyl)pyrrolo[1,2-a][1,8]naphthyridine 3h. Substrate 2h (0.6 mmol,
166 mg) and PtCl2 (0.03 mmol, 8 mg) reacted to 3h as a pale brown oil (99 mg, 60%); Rf 0.36
(heptane/ethyl acetate 5:1). 1H NMR (300 MHz, CDCl3): δ = 8.54 (dd, 3J = 4.7 Hz,
3
4
4J = 1.7 Hz, 1H, CHnaphtyr.), 8.45 (dd, J = 2.9 Hz, J = 1.5 Hz, 1H, CHpyrrole), 7.96 (dd,
4
3
3
3J = 7.8 Hz, J = 1.7 Hz, 1H, CHnaphtyr.), 7.41 (dd, J = 8.1 Hz, J = 7.5 Hz, 1H, CHAr),
3
4
4
7.34–7.26 (m, 3H, CHnaphtyr./Ar), 7.00 (ddd, J = 8.2 Hz, J = 2.6 Hz, J = 1.1 Hz, 1H, CHAr),
6.92 (s, 1H, CHnaphtyr.), 6.84 (dd, 3J = 3.8 Hz, 4J = 2.9 Hz, 1H, CHpyrrole), 6.71 (dd, 3J = 3.8 Hz,
3J = 1.5 Hz, 1H, CHpyrrole), 3.88 (s, 3H, OMe) ppm. 13C-NMR (75 MHz, CDCl3): δ = 159.9
(CꢀOMe), 146.8 (CHnaphtyr.), 144.0 (Cnaphtyr.), 139.9 (CAr), 136.2 (CHnaphtyr.), 134.0 (Cnaphtyr.),
131.4 (Cpyrrole), 129.8, 120.9 (CHAr), 120.1 (CHnaphtyr.), 119.1 (Cnaphtyr.), 116.2 (CHpyrrole), 114.4

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(CHnaphtyr.), 114.1, 114.0 (CHAr), 113.3, 105.2 (CHpyrrole), 55.5 (OMe) ppm. IR (ATR):
ṽ = 2933 (w), 2832 (w), 1574 (m), 1434 (m), 1239 (m), 1169 (m), 1038 (m), 851 (m), 785 (m),
725 (m), 694 (m), 555 (m), 447 (m) cm−1. MS (EI, 70 eV): m/z (%) = 274 ([M]+, 100), 259
(9), 258 (9), 242 (6), 231 (9), 230 (7), 229 (13), 205 (5), 203 (5). HRMS (ESI-TOF):
m/z = calcd. for C18H14N2O ([M+H]+) 275.11789, found 275.11795.
6-(4-Methoxy-2-methylphenyl)pyrrolo[1,2-a][1,8]naphthyridine 3i. 2i (0.5 mmol, 149 mg)
and PtCl2 (0.03 mmol, 7 mg) achieved 3i as a pale brown oil (92 mg, 62%); Rf 0.40
(heptane/ethyl acetate 5:1). 1H NMR (300 MHz, CDCl3): δ = 8.57 (dd, 3J = 4.7 Hz,
3
4
4J = 1.7 Hz, 1H, CHnaphtyr.), 8.45 (dd, J = 2.9 Hz, J = 1.5 Hz, 1H, CHpyrrole), 7.93 (dd,
3J = 7.8 Hz, 4J = 1.7 Hz, 1H, CHnaphtyr.), 7.33 (d, 3J = 8.4 Hz, 1H, CHAr), 7.30 (dd, 3J = 7.8 Hz,
4J = 4.8 Hz, 1H, CHnaphtyr.), 6.93 (d, 4J = 2.6 Hz, 1H, CHAr), 6.87 (dd, 3J = 8.4 Hz, 4J = 2.7 Hz,
1H, CHAr), 6.82 (dd, 3J = 3.7 Hz, 3J = 2.9 Hz, 1H, CHpyrrole), 6.78 (s, 1H, CHnaphtyr.), 6.29 (dd,
4
3J = 3.9 Hz, J = 1.6 Hz, 1H, CHpyrrole), 3.90 (s, 3H, OMe), 2.29 (s, 3H, Me) ppm. 13C NMR
(75 MHz, CDCl3): δ = 159.4 (CꢀOMe), 146.6 (CHnaphtyr.), 144.0 (Cnaphtyr.), 137.9 (CꢀMe),
135.8 (CHnaphtyr.), 133.6 (CAr), 132.5 (Cnaphtyr.), 130.7 (CHAr), 130.2 (Cpyrrole), 119.9 (CHnaphtyr.),
119.0 (Cnaphtyr.), 117.0 (CHAr), 115.8 (CHpyrrole), 113.9 (CHnaphtyr.), 113.1 (CHpyrrole), 111.1
(CHAr), 105.1 (CHpyrrole), 55.3 (OMe), 20.2 (Me) ppm. IR (ATR): ṽ = 2919 (w), 2833 (w),
1722 (w), 1604 (w), 1560 (w), 1499 (w), 1455 (m), 1434 (m), 1368 (w), 1291 (m), 1237 (m),
1161 (w), 1042 (m), 940 (w), 856 (w), 788 (m), 725 (m), 626 (w), 557 (w), 446 (w) cm−1. MS
(EI, 70 eV): m/z (%) = 288 ([M]+, 86), 287 (100), 273 (10), 272 (10), 271 (5), 256 (5), 255 (8),
245 (8), 244 (13), 243 (30), 242 (15), 229 (7), 218 (5), 205 (5), 128 (6), 122 (7), 109 (5).
HRMS (ESI-TOF): m/z = calcd. for C19H16N2O ([M+H]+) 289.13354, found 289.13338.
6-(Thiophen-3-yl)pyrrolo[1,2-a][1,8]naphthyridine 3j. 2j (0.3 mmol, 86 mg) reacted with
PtCl2 (0.015 mmol, 4 mg) giving 3j as a yellow solid (35 mg, 41%); Rf 0.55 (heptane/ethyl
1
3
4
acetate 5:1). H NMR (300 MHz, CDCl3): δ = 8.54 (dd, J = 4.8 Hz, J = 1.7 Hz, 1H,
CHnaphtyr.), 8.47 (dd, 3J = 2.9 Hz, 4J = 1.5 Hz, 1H, CHpyrrole), 7.97 (dd, 3J = 7.8 Hz, 4J = 1.8 Hz,
4
4
3
1H, CHnaphtyr.), 7.70 (dd, J = 2.9 Hz, J = 1.4 Hz, 1H, CHthioph.), 7.50 (dd, J = 5.0 Hz,
3
4
4J = 1.4 Hz, 1H, CHthioph.), 7.46 (dd, J = 5.0 Hz, J = 2.9 Hz, 1H, CHthioph.), 7.31 (dd,
3
3
3J = 7.8 Hz, J = 4.8 Hz, 1H, CHnaphtyr.), 7.00 (s, 1H. CHnaphtyr.), 6.85 (dd, J = 3.8 Hz,
3
4
3J = 2.9 Hz, 1H, CHpyrrole), 6.81 (dd, J = 3.8 Hz, J = 1.5 Hz, 1H, CHpyrrole) ppm. 13C NMR
(75 MHz, CDCl3): δ = 146.3 (CHnaphtyr.), 143.7 (Cnaphtyr.), 138.9 (Cthioph.), 136.4 (CHnaphtyr.),
131.2 (Cnaphtyr.), 128.9 (Cpyrrole), 127.8, 126.1, 123.5 (CHthioph.), 120.1 (CHnaphtyr.), 119.2

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(Cnaphtyr.), 115.6 (CHpyrrole), 114.7 (CHnaphtyr.), 113.5, 105.3 (CHpyrrole) ppm. IR (ATR):
ṽ = 3091 (w), 2921 (w), 1717 (br, w), 1570 (m), 1469 (m), 1435 (s), 1136 (m), 1080 (m), 859
(m), 836 (m), 777 (m), 715 (s), 633 (m), 448 (m) cm−1. MS (EI, 70 eV): m/z (%) = 250 ([M]+,
100), 249 (22), 248 (9), 205 (10). HRMS (EI): m/z = calcd. for C15H10N2S ([M]+) 250.05592,
found 250.05591.
6-(n-Butyl)pyrrolo[1,2-a][1,8]naphthyridine 3l. Substrate 2l (0.2 mmol, 50 mg) and PtCl2
(0.01 mmol, 2.6 mg) resulted in product 3l as an oil (19 mg, 37%); Rf 0.63 (heptane/ethyl
1
3
4
acetate 5:1). H NMR (300 MHz, CDCl3): δ = 8.48 (dd, J = 4.7 Hz, J = 1.7 Hz, 1H,
CHnaphtyr.), 8.33 (dd, 3J = 2.9 Hz, 4J = 1.5 Hz, 1H, CHpyrrole), 7.87 (dd, 3J = 7.8 Hz, 4J = 1.8 Hz,
3
3
3
1H, CHnaphtyr.), 7.25 (dd, J = 7.7 Hz, J = 4.7 Hz, 1H, CHnaphtyr.), 6.80 (dd, J = 3.7 Hz,
3
4
3J = 2.9 Hz, 1H, CHpyrrole), 6.73 (s, 1H, CHnaphtyr.), 6.62 (dd, J = 3.7 Hz, J = 1.5 Hz, 1H,
3
3
CHpyrrole), 2.79 (t, J = 7.7 Hz, 2H, CH2), 1.78 (p, J = 7.5 Hz, 2H, CH2), 1.45 (hept,
3
3J = 7.4 Hz, 2H, CH2), 0.98 (t, J = 7.3 Hz, 3H, CH3) ppm. 13C NMR (75 MHz, CDCl3):
δ = 146.1 (CHnaphtyr.), 144.0 (Cnaphtyr.), 135.4 (CHnaphtyr.), 134.0 (Cnaphtyr.), 132.6 (Cpyrrole), 119.8
(CHnaphtyr.), 119.3 (Cnaphtyr.), 114.7 (CHpyrrole), 113.8 (CHnaphtyr.), 112.7, 102.7 (CHpyrrole), 32.2,
31.1, 22.9 (CH2), 14.1 (CH3) ppm. IR (ATR): ṽ = 2855 (w), 2927 (w), 2858 (w), 1723 (w),
1612 (w), 1592 (w), 1559 (w), 1537 (w), 1459 (w), 1436 (w), 1377 (w), 1289 (w), 1171 (w),
1090 (w), 1033 (w), 849 (w), 783 (w), 726 (w) cm−1. MS (EI, 70 eV): m/z (%) = 224 ([M]+,
40), 195 (12), 194 (5), 193 (7), 183 (13), 182 (100), 181 (42), 179 (5), 168 (7), 154 (5), 127
(6). HRMS (ESI-TOF): m/z = calcd. for C15H16N2 ([M+H]+) 225.13862, found 225.13887.
6-(Cyclohexyl)pyrrolo[1,2-a][1,8]naphthyridine 3m. Starting material 2m (0.8 mmol,
204 mg) and PtCl2 (0.04 mmol, 10.6 mg) gave 3m as an oil (127 mg, 62%); Rf 0.58
(heptane/ethyl acetate 5:1). 1H NMR (250 MHz, CDCl3): δ = 8.47 (dd, 3J = 4.7 Hz,
3
4
4J = 1.7 Hz, 1H, CHnaphtyr.), 8.37 (dd, J = 3.0 Hz, J = 1.5 Hz, 1H, CHpyrrole), 7.86 (dd,
3
3
3
3J = 7.8 Hz, J = 1.8 Hz, 1H, CHnaphtyr.), 7.23 (dd, J = 7.7 Hz, J = 4.7 Hz, 1H, CHnaphtyr.),
6.82 (dd, 3J = 3.7 Hz, 3J = 2.9 Hz, 1H, CHpyrrole), 6.74 (s, 1H, CHnaphtyr.), 6.67 (dd, 3J = 3.8 Hz,
3J = 1.5 Hz, 1H, CHpyrrole), 2.86 (tt, 3Ja,a = 8.2 Hz, 3Ja,e = 3.2 Hz, 1H, CHa), 2.22–2.05 (m, 2H,
CH2), 1.98–1.79 (m, 3H, CH2), 1.62–1.44 (m, 3H, CH2), 1.47–1.24 (m, 2H, CH2) ppm.
13C NMR (63 MHz, CDCl3): δ = 146.1 (CHnaphtyr.), 143.8 (Cnaphtyr.), 139.2 (Cnaphtyr.), 135.5
(CHnaphtyr.), 132.3 (Cpyrrole), 119.8 (CHnaphtyr.), 119.3 (Cnaphtyr.), 113.7 (CHpyrrole), 112.6
(CHnaphtyr.), 112.2, 102.4 (CHpyrrole), 40.4 (CH), 33.1, 27.0, 26.5 (CH2) ppm. IR (ATR):
ṽ = 2924 (m), 2850 (m), 1720 (br, w), 1560 (w), 1434 (s), 1336 (m), 1289 (m), 1073 (m),

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1059 (m), 845 (m), 783 (m), 721 (s), 615 (m), 554 (m), 448 (m) cm−1. MS (EI, 70 eV): m/z
(%) = 250 ([M]+, 100), 249 (23), 235 (6), 221 (18), 219 (6), 209 (12), 207 (23), 206 (13), 205
(22), 196 (13), 195 (70), 194 (19), 193 (27), 192 (11), 182 (26), 181 (17), 169 (6), 168 (22),
140 (6), 56 (6), 41 (13), 39 (8). HRMS (EI): m/z = calcd. for C17H18N2 ([M]+) 250.14645,
found 250.14577.
General procedure for the Sonogashira reaction to synthesize 3-alykynl-4-([1H]-
pyrrol-1-yl)pyridines 4.
1c was dissolved in 2 ml dioxane under an argon atmosphere. After the addition of
Pd(MeCN)2Cl2 (0.05 eq.), CuI (0.05 eq.), XPhos (0.1 eq.) and Et3N (3 eq.) in advance of the
corresponding acetylene (1.5 eq.) the reaction was stirred at room temperature for 24 h. The
reaction mixture was subsequently cooled to room temperature and washed with distilled
water and ethyl acetate. The organic layers were collected and the solvent evaporated. The
crude product was thereafter purified by column chromatography (heptane/ethyl acetate, 10:1
→ 2:1) to give the alkynylated products 4a–n1.
3-(Phenylethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4a. Reaction of 1c (0.45 mmol, 100 mg)
and phenylacetylene (0.07 mmol, 73 µl gave 4a as a white solid (88 mg, 81%); mp 68–69 ˚C.
1H NMR (250 MHz, CDCl3): δ = 8.77 (bs, 1H, CHpyridine), 8.51 (bs, 1H, CHpyridine), 7.43–7.39
3
(m, 2H, Ph), 7.31 (t, J = 2.2 Hz, 2H, CHpyrrole), 7.27–7.25 (m, 3H, Ph), 7.18–7.13 (m, 1H,
CHpyridine), 6.32 (t, 3J = 2.2 Hz, 2H, CHpyrrole) ppm. 13C NMR2 (62.9 MHz, CDCl3): δ = 155.0,
149.5 (CHpyridine), 147.2 (Cpyridine), 131.6, 129.1, 128.6 (CHPh), 122.4 (CPh), 120.8 (CHpyrrole),
111.3 (CHpyrrole), 96.8, 84.2 (Calkyne) ppm. IR (ATR): ṽ = 3130 (w), 3055 (w), 2220 (w), 1562
(m), 1589 (m), 1393 (m), 1344 (m), 1185 (w), 1062 (m), 1018 (m), 920 (w), 836 (s), 749 (s),
722 (s), 685 (s), 621 (m), 562 (s) cm−1. MS (EI, 70 eV): m/z (%) = 244 ([M+], 100), 243 (69),
242 (36), 218 (8), 216 (7), 215 (5), 214 (5), 189 (6), 150 (8), 122 (5). HRMS (EI, 70 eV):
calcd. for C17H12N2 ([M]+) 244.09950, found 244.09904.
3-((3-Methylphenyl)ethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4b. Reaction of 1c (1.35 mmol,
300 mg) and tolylacetylene (2.02 mmol, 234.3 mg) gave 4b as a white solid (304 mg, 88%);
1
3
mp 99–100 ˚C. H NMR (250 MHz, C6D6): δ = 8.91 (s, 1H, CHpyridine), 8.21 (d, J = 5.5 Hz,
1
1 The pyridine fragment provides very broad signals in H and 13C NMR spectra. Therefore, it was not possible
to detect all pyridine signals of some substrates. Known effects that can lead to broad or undetecTable NMR
signals are exchange broadening due to changes in the spin and rotational states of the observed atom or
aggregation with the solvent. However, all signals reappear in the cyclized products 5a–n.
2 metaꢀCpyridine and metaꢀCHpyridine are undetectable.

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1H, CHpyridine), 7.27 (d, 3J = 7.6 Hz, 1H, CHAr), 7.22 (t, 3J = 2.2 Hz, 2H, CHpyrrole), 7.23 (s, 1H,
3
3
3
CHAr), 6.94 (t, J = 7.6 Hz, 1H, CHAr), 6.82 (d, J = 7.6 Hz, 1H, CHAr), 6.52 (d, J = 5.5 Hz,
3
1H, CHpyridine), 6.36 (t, J = 2.2 Hz, 2H, CHpyrrole), 1.96 (s, 3H, Me) ppm. 13C NMR
(62.9 MHz, C6D6): δ = 155.5, 150.1 (CHpyridine), 147.1 (Cpyridine), 138.4 (CAr), 132.4, 130.1,
129.1, 128.6 (CHAr), 122.8 (CAr), 121.0 (CHpyrrole), 117.1 (CHpyridine), 113.0 (Cpyridine), 111.5
(CHpyrrole), 97.2, 84.6 (Calkyne), 21.0 (Me) ppm. IR (ATR): ṽ = 3034 (w), 2919 (w), 2207 (w),
1720 (w), 1577 (w), 1558 (m), 1498 (s), 1392 (w), 1339 (s), 1180 (w), 1062 (m), 1018 (m),
827 (w), 782 (m), 722 (s), 687 (m), 569 (m) cm−1. MS (EI, 70 eV): m/z (%) = 258 ([M+], 100),
257 (38), 256 (12), 255 (16), 243 (22), 242 (32), 241 (4), 231 (6), 229 (4), 214 (4), 202 (3),
164 (3), 163 (6). HRMS (EI, 70 eV): calcd. for C18H14N2 ([M]+) 258.11515, found 258.11562.
3-((4-Methoxy-2-methylphenyl)ethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4c. Reaction of 1c
(1.35 mmol, 300 mg) and 4ꢀmethoxyꢀ2ꢀmethylphenylacetylene (294.9 mg, 2.017 mmol) gave
1
4c as a yellow solid (356 mg, 91%); mp 77–78 ˚C. H NMR (250 MHz, C6D6): δ = 8.90 (bs,
1H, CHpyridine), 8.20 (bs, 1H, CHpyridine), 7.35–7.15 (m, 3H, CHAr), 6.54–6.31 (m, 5H, CHAr),
3.20 (s, 3H, OMe), 2.23 (s, 3H, Me) ppm. 13C NMR (62.9 MHz, C6D6): δ = 160.7 (CAr),
155.5, 149.7 (CHpyridine), 146.6 (Cpyridine), 142.6 (CAr), 133.9 (CHAr), 121.0 (CHpyrrole), 117.3
(CHpyridine), 115.7 (CHAr), 115.0 (CAr), 113.8 (Cpyridine), 111.8 (CHAr), 111.3 (CHpyrrole), 96.4,
87.2 (Calkyne), 54.8 (OMe), 21.0 (Me) ppm. IR (ATR): ṽ = 2957 (w), 2202 (w), 1725 (w),
1602 (w), 1560 (m), 1491 (m), 1341 (w), 1276 (w), 1237 (s), 1022 (w), 846 (w), 815 (s), 726
(s), 688 (m), 576 (m) cm−1. MS (EI, 70 eV): m/z (%) = 288 ([M+], 100), 287 (77), 273 (9),
272 (15), 271 (8), 257 (6), 256 (9), 255 (10), 246 (7), 245 (40), 244 (23), 243 (39), 242 (15),
230 (10), 229 (10), 218 (7), 217 (6), 216 (5), 205 (5), 151 (6). HRMS (EI, 70 eV): calcd. for
C19H16ON2 ([M]+) 288.12571, found 288.12528.
3-(Naphtalen-1-ylethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4d. Reaction of 1c (1.57 mmol,
350 mg) and 1ꢀnaphthylacetylene (2.35 mmol, 364 µl) gave 4d as a white solid (458 mg,
1
99%); mp 121–122 ˚C. H NMR (250 MHz, CDCl3): δ = 9.00 (bs, 2H, CHpyridine), 8.27–8.23
(m, 1H, CHnaphthyl.), 7.90–7.85 (m, 2H, CHnaphthyl.), 7.78–7.74 (m, 1H, CHnaphthyl.), 7.58–7.50
3
(m, 2H, CHnaphthyl.), 7.47–7.44 (m, 1H, CHnaphthyl.), 7.45 (t, J = 2.2 Hz, 2H, CHpyrrole),
3
7.18–7.05 (m, 1H, CHpyridine), 6.46 (t, J = 2.2 Hz, 2H, CHpyrrole) ppm. 13C NMR3 (62.9 MHz,
CDCl3): δ = 133.2, 133.2 (Cnaphthyl.), 131.1, 129.8, 128.5, 127.2, 126.8, 126.2, 125.3
(CHnaphthyl.), 121.0 (CHpyrrole), 120.0 (Cnaphthyl.), 111.6 (CHpyrrole), 95.6, 88.7 (Calkyne) ppm. IR
3 All carbon signals of the pyridine moiety were undetectable.

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(ATR): ṽ = 3043 (w), 2206 (w), 1556 (w), 1494 (m), 1388 (w), 1340 (m), 1179 (w), 1063 (m),
1019 (w), 832 (m), 803 (s), 777 (s), 728 (s), 672 (m), 620 (m), 560 (s) cm−1. MS (EI, 70 eV):
m/z (%) = 293 ([M+], 100), 292 (50), 291 (11), 266 (6), 265 (8), 264 (7), 238 (3), 200 (6), 174
(2), 146 (6), 132 (5). HRMS (EI, 70 eV): calcd. for C21H13N2 ([M]+) 293.10732, found
293.10668.
3-((4-Trifluoromethylphenyl)ethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4e. Reaction of 1c
(2.02 mmol, 450 mg,) and 4ꢀ(trifluoromethyl)ꢀphenylacetylene (2.80 mmol, 494 µl) gave 4e
as a yellow solid (343 mg, 55%); mp 75–76 ˚C. 1H NMR (300 MHz, C6D6): δ = 8.92 (bs, 1H,
CHpyridine), 8.32 (bs, 1H, CHpyridine), 7.22–7.13 (m, 6H, CHAr), 6.58 (bs, 1H, CHpyridine), 6.40 (t,
3J = 2.2 Hz, 2H, CHpyrrole) ppm. 13C NMR (75 MHz, C6D6): δ = 155.5, 150.7 (CHpyridine),
2
4
147.3 (Cpyridine), 131.9 (CHAr), 130.5 (q, JC,F = 32.6 Hz, CAr), 126.3 (q, JC,F = 1.4 Hz, CAr),
3
1
125.5 (q, JC,F = 3.8 Hz, CHAr), 124.4 (q, JC,F = 272.3 Hz, CF3), 120.9 (CHpyrrole), 117.3
(CHpyridine), 111.6 (CHpyrrole), 105.2(Cpyridine), 95.1, 87.0 (Calkyne) ppm. 19F NMR (282 MHz,
C6D6) δ = −62.59 ppm. IR (ATR): ṽ = 2929 (w), 1724 (w), 1613 (w), 1583 (w), 1557 (w),
1496 (m), 1407 (w), 1324 (s), 1163 (m), 1101 (s), 1062 (s), 1016 (m), 834 (s), 729 (s), 675
(m), 577 (m) cm−1. MS (EI, 70 eV): m/z (%) = 312 ([M+], 100), 311 (37), 310 (8), 293 (5),
291 (5), 286 (7), 243 (9), 242 (20), 214 (4), 199 (4). HRMS (EI, 70 eV): calcd. for
C18H11F3N2 ([M]+) 312.28855, found 312.28849.
3-((4-Methylphenyl)ethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4f. Reaction of 1c (1.57 mmol,
350 mg) and 4ꢀmethylphenylacetylene (2.35 mmol, 274 mg) gave 4f as a white solid (355 mg,
1
88%); mp 97–98 ˚C. H NMR (250 MHz, CDCl3): δ = 8.91 (bs, 2H, CHpyridine), 7.42 (t,
3
3
3J = 2.2 Hz, 2H, CHpyrrole), 7.40 (d, J = 7.9 Hz, 2H, CHAr), 7.18 (d, J = 7.9 Hz, 2H, CHAr),
3
7.19–7.10 (m, 1H, CHpyridine), 6.42 (t, J = 2.2 Hz, 2H, CHpyrrole), 2,38 (s, 3H, Me) ppm.
13C NMR4 (62.9 MHz, CDCl3): δ = 139.6 (CꢀMe), 131.6, 129.4 (CHAr), 120.8 (CHpyrrole),
119.2 (CAr), 111.4 (CHpyrrole), 97.6, 83.7 (Calkyne), 21.7 (Me) ppm. IR (ATR): ṽ = 3128 (w),
2658 (w), 2217 (m), 1560 (m), 1494 (s), 1389 (s), 1313 (w), 1179 (m), 1115 (w), 1068 (s),
1016 (s), 821 (m), 808 (s), 732 (s), 685 (m), 623 (w), 577 (m) cm−1. MS (EI, 70 eV): m/z
(%) = 258 ([M+], 100), 257 (40), 256 (12), 255 (14), 243 (17), 242 (30), 231 (5), 163 (6), 139
(3), 128 (4). HRMS (EI, 70 eV): calcd. for C18H14N2 ([M]+) 258.11515, found 258.11472.
4 All carbon signals of the pyridine moiety were undetectable.

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3-((4-Methoxyphenyl)ethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4g. Reaction of 1c (1.57 mmol,
350 mg) and 4ꢀmethoxyphenylacetylene (2.35 mmol, 311 mg) gave 4g as a yellow solid
1
(408 mg, 95%); mp 89–90 ˚C. H NMR (250 MHz, CDCl3): δ = 8.72 (bs, 2H, CHpyridine),
3
3
7.45 (d, J = 8.9 Hz, 2H, CHAr), 7.45 (t, J = 2.0 Hz, 2H, CHpyrrole), 7.31 (bs, 1H, CHpyridine),
3
3
6.89 (d, J = 8.9 Hz, 2H, CHAr), 6.41 (t, J = 2.0 Hz, 2H, CHpyrrole), 3.83 (s, 3H, OMe) ppm.
13C NMR5 (62.9 MHz, CDCl3): δ = 160.5 (CꢀOMe), 133.3 (CHAr), 120.9 (CHpyrrole), 114.5
(CAr), 114.4 (CHAr), 111.5 (CHpyrrole), 97.5, 82.9 (Calkyne), 55.5 (OMe) ppm. IR (ATR):
ṽ = 3035 (w), 2933 (w), 2218 (m), 1559 (m), 1504 (s), 1338 (m), 1290 (m), 1247 (s), 1174
(m), 1067 (m), 1020 (s), 826 (s), 732 (s), 686 (s), 326 (m), 542 (m) cm−1. MS (EI, 70 eV): m/z
(%) = 274 ([M+], 100), 273 (8), 259 (36), 232 (8), 231 (46), 230 (38), 229 (34), 205 (10), 204
(9), 203 (12), 151 (7), 137 (12). HRMS (EI, 70 eV): calcd. for C18H14N2O ([M]+) 274.11006,
found 274.10990.
3-((4-tert-Butylphenyl)ethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4h. Reaction of 1c
(1.57 mmol, 350 mg) and 4ꢀtertꢀbutylphenylacetylene (2.35 mmol, 425 µl) gave 4h as a
brown oil (463 mg, 98%). 1H NMR (250 MHz, CDCl3): δ = 8.99 (bs, 2H, CHpyridine), 7.46 (d,
3
3
3J = 8.6 Hz, 2H, CHAr), 7.42 (t, J = 2.2 Hz, 2H, CHpyrrole), 7.39 (d, J = 8.6 Hz, 2H, CHAr),
3
7.20–7.09 (m, 1H, CHpyridine), 6.41 (t, J = 2.2 Hz, 2H, CHpyrrole), 1.33 (s, 9H, CH3tBu) ppm.
13C6 NMR (62.9 MHz, CDCl3): δ = 152.6 (CꢀtBu), 131.4, 125.6 (CHAr), 120.8 (CHpyrrole),
119.3 (CAr), 111.3 (CHpyrrole), 97.3, 83.7 (Calkyne), 35.0 (CtBu), 31.2 (CH3tBu) ppm. IR (ATR):
ṽ = 2960 (m), 2866 (w), 2217 (w), 1724 (w), 1559 (m), 1494 (s), 1394 (m), 1340 (s), 1266 (w),
1180 (w), 1063 (m), 1018 (m), 926 (w), 831 (s), 724 (s), 677 (m), 617 (w), 562 (m) cm−1. MS
(EI, 70 eV): m/z (%) = 300 ([M+], 64), 286 (22), 285 (100), 270 (11), 269 (17), 257 (22), 256
(7), 255 (16), 244 (10), 243 (17), 242 (13), 128 (12). HRMS (EI, 70 eV): calcd. for C21H20N2
([M]+) 300.16210, found 300.16172.
3-((4-n-Propylphenly)ethynyl)-4-([1H]-pyrrol-1-yl)pyridine 4i. Reaction of 1c (1.35 mmol,
300 mg,) and 4ꢀnꢀpropylphenylacetylene (2.02 mmol, 291 mg) gave 4i as a white solid
1
(332 mg, 86%), mp 74–75 ˚C. H NMR (300 MHz, C6D6): δ = 8.93 (bs, 1H, CHpyridine), 8.22
(bs, 1H, CHpyridine), 7.38 (d, 3J = 8.3 Hz, 2H, CHAr) 7.23 (t, 3J = 2.2 Hz, 2H, CHpyrrole), 6.85 (d,
3J = 8.3 Hz, 2H, CHAr), 6.52 (d, 3J = 5.0 Hz, 1H, CHpyridine), 6.37 (t, 3J = 2.2 Hz, 2H, CHpyrrole),
3
3
3
2.29 (t, J = 7.6 Hz, 2H, CH2), 1.40 (tq, J = 7.6 Hz, J = 7.3 Hz, 2H, CH2), 0.77 (t,
5 All carbon signals of the pyridine moiety were undetectable.
6 All carbon signals of the pyridine moiety were undetectable.