Synthesis of Diarylacetylenes Bearing Electron-Withdrawing Groups via the Smiles Rearrangement

Article abstract of DOI:10.1055/s-0037-1612423

Nitrobenzyl benzothiazol-2-yl sulfones and nitrobenzyl 1-phenyl-1 H -tetrazol-5-yl sulfones react with chlorides of aromatic acids to form β-acyl derivatives. These products undergo the Smiles rearrangement resulting in the formation of the corresponding nitrophenyl arylacetylenes in 50-60% overall yields (approx. 75% per step). Sulfones bearing CF ₃ or CN groups instead of a NO ₂ substituent form mixtures of the acetylenes in moderate yields and benzyl aryl ketones in yields above 40%.

Full text of DOI:10.1055/s-0037-1612423

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2019, 51, A–H
paper
A
de
R. Bujok, M. Mąkosza
Paper
Synthesis
Synthesis of Diarylacetylenes Bearing Electron-Withdrawing
Groups via the Smiles Rearrangement
R1
Robert Bujok
R1
R1
1) LHMDS,
THF, –70 °C, 4 min
Mieczysław Mąkosza*
Cs2CO3
R2
acetone, reflux, 1d
O
Institute of Organic Chemistry, Polish Academy of Sciences,
ul. Kasprzaka 44/52, 01-224 Warsaw, Poland
robert.bujok@icho.edu.pl
O
2
2)
R
Het SO2
16 examples
overall yields usually 55%
Het SO2 R2
Cl
THF, –70–0 °C, 1 d
mieczyslaw.makosza@icho.edu.pl
Het = benzothiazol-2-yl
or 1-phenyl-1H-tetrazol-5-yl
R1 = NO2, CF3, CN
R
2 = 4-F3CC6H4, 3-F3CC6H4, 4-ClC6H4, 2-BrC6H4, Ph, 4-MeOC6H4, 2-naphthyl, 2-furyl
Received: 30.01.2019
Accepted after revision: 05.03.2019
Published online: 24.04.2019
to the low nucleophilicity of the acetylenic carbanion,
ONSH proceeds efficiently only in highly active nitroarenes
such as dinitrobenzenes or nitropyridines.
DOI: 10.1055/s-0037-1612423; Art ID: ss-2019-t0060-op
Recently, an interesting synthesis of dinitroaryl acety-
Abstract Nitrobenzyl benzothiazol-2-yl sulfones and nitrobenzyl 1-
phenyl-1H-tetrazol-5-yl sulfones react with chlorides of aromatic acids
to form -acyl derivatives. These products undergo the Smiles rear-
rangement resulting in the formation of the corresponding nitrophenyl
arylacetylenes in 50–60% overall yields (approx. 75% per step). Sulfones
bearing CF3 or CN groups instead of a NO2 substituent form mixtures of
the acetylenes in moderate yields and benzyl aryl ketones in yields
above 40%.
lenes via Smiles rearrangement of the enolates of benzothi-
azolyl dinitroarylketones, in a similar manner to the Julia–
Kocienski olefination,7 was described by Jorgensen (Scheme
1).8 The starting dinitroaryl ketosulfones II were prepared
via reaction of chloromethylketones with 2-mercaptoben-
zothiazole, followed by oxidation of the formed sulfides to
give ketosulfones I. Subsequent nitroarylation of the keto-
sulfones I gave dinitroaryl ketosulfones II. The carbanions
of the ketosulfones I are weak nucleophiles, so this method
is limited to highly electrophilic fluorodinitroarenes. Treat-
ment of the formed ketonitroaryl sulfones II with a base re-
sults in the Smiles rearrangement of the generated enolates
and the formation of dinitroaryl acetylenes III (Scheme 1).
The Jorgensen synthesis inspired us to extend this ap-
proach and test the generality of the methodology (Scheme
1). In particular, we expected that changing the order of
events and synthesizing the key intermediate ketosulfones
2 via acylation of benzothiazolylsulfones 1 would offer a
more general approach. Subsequent Smiles rearrangement
of the ketosulfones 2 produced via acylation should give ex-
pected diarylacetylenes 3 (see mechanism in Scheme 1).
As a model compound we chose sulfone 1a (Scheme 2),
which is readily available via benzylation of 2-mercapto-
benzothiazole and oxidation of the formed sulfide. Acyla-
tion of 1a with benzoyl chloride was carried out according
to the procedure described by Pospisil9 to give the expected
ketosulfone 2a in high yield (84% after chromatographic pu-
rification).
Key words acetylenes, sulfones, Smiles rearrangement, Julia–Ko-
cienski olefination, benzyl ketones
Substituted acetylenes are widely used as versatile
starting materials in modern organic synthesis. Of particu-
lar value is the synthesis of different heterocycles: indoles,1
anthranils,2 quinolines,3 etc., via transition-metal-catalyzed
addition of nitrogen nucleophiles to carbon–carbon triple
bonds. The common way to synthesize aryl acetylenes is by
way of the Sonogashira reaction, which involves the transi-
tion-metal-catalyzed replacement of halogens on aromatic
rings by acetylenic moieties.4 This reaction is presently the
most common and widely used tool for the preparation of
diarylacetylenes. The coupling usually proceeds with high
yield, however, the high cost of transition metals can be a
problem for large-scale synthesis. Moreover, if the products
have potential pharmaceutical applications, they should be
meticulously purified to remove the transition metals.5
Nitroaryl acetylenes can also be prepared by substitu-
tion of fluorine6a or hydrogen6b in nitroarenes via nucleop-
hilic aromatic substitution (SNAr) or by oxidative substitu-
tion of hydrogen (ONSH) via reactions with acetylenic car-
banions. The latter method is the simplest way to introduce
an acetylenic moiety into nitroaromatic rings, however, due
Unfortunately, all attempts to perform the Smiles rear-
rangement of the enolate of 2a gave negative results. Re-
gardless of the tested conditions: Cs2CO3/boiling acetone;
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H

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R. Bujok, M. Mąkosza
Paper
Synthesis
R1
JORGENSEN METHOD
R1
O2N
O2N
F
O
O
1) LHMDS,
THF, –70 °C, 4 min
N
S
O
N
S
Het SO2 R3
NO2
O2N
SO2
SO2
O
Het SO2 R3
(I)
2)
(II)
Het = benzothiazol-2-yl
Cl
2a, 84%
2b, 53%
1a, R = H
1b, R = 2-NO2
THF, –70 to 0 °C, 1 d
O2N
R3
R1
NO2
(III)
Cs2CO3
acetone, reflux, 1 d
THIS WORK
3a, 0%
3b, 72% (38% overal yield
based on 1b)
R1
R1
1) base
Scheme 2 Attempted synthesis of acetylenes 3a,b from purified mod-
el sulfones 2a,b. Yields of isolated products are given.
O
O
R2
2)
Het SO2
Het SO2
R2
Cl
1
2
crucial factor for the reaction. We therefore tested the pos-
sibility to perform such a sequence of reactions with 2-ni-
trobenzyl benzothiazol-2-yl sulfone (1b) (Scheme 2). Ben-
zoylation of 1b proceeded smoothly (TLC analysis), howev-
er, the yield of the product 2b after chromatographic
purification was moderate (53%), leading to the assumption
that product 2b partially decomposes on silica gel.
R1
Cs2CO3
acetone, reflux, 1 d
R2
3
Het = benzothiazol-2-yl
or 1-phenyl-1H-tetrazol-5-yl
R1 = NO2, CF3, CN
R2 = 4-F3CC6H4, 3-F3CC6H4, 4-ClC6H4, 2-BrC6H4, Ph,
4-MeOC6H4, 2-naphthyl, 2-furyl
To our satisfaction, ketosulfone 2b underwent the
Smiles rearrangement in the presence of Cs2CO3 in boiling
acetone to afford the desired product, 2-nitrophenyl phenyl
acetylene (3b), in a good yield of 72%. However, the overall
yield (38%) of acetylene 3b based on sulfone 1b was unsat-
isfactory, mostly due to loss of ketosulfone 2b during purifi-
cation.
Since the acylation of sulfone 1b is carried out in the
presence of an excess of the base, we tried to perform the
acylation and rearrangement steps as a one-pot process
(Scheme 3), however, under such conditions, the yield of
acetylene 3b was poor (16%).
MECHANISM OF THE REACTION
R1
R1
Smiles
base
rearrangement
R2
O–
R2
O
O2S
O2S
Het
Het
R1
R1
R2
R2
– HetO–
– SO2
–O2S
O
On the other hand, when crude sulfone 2b was used in
the rearrangement step, a much better result was obtained.
On this occasion, the overall yield of acetylene 3b based on
starting material 1b was 54% (Scheme 3).
Het
Scheme 1 Synthesis of nitroaryl acetylenes via Smiles rearrangements
of ketoaryl sulfones
The latter result confirms that compound 2b partially
decomposes during column chromatographic purification,
therefore, all subsequently prepared sulfones 2 were used
in the rearrangement step without purification.
NaH/DMF, 45 °C; t-BuOK/DMF, 60 °C; LHMDS/THF, 45 °C
and KOH/MeOH, 45 °C, ketosulfone 2a was partially decom-
posed or was recovered unchanged, whilst no acetylene 3a
was found in the reaction mixture.
Compound 2a is a relatively strong CH-acid, so under
the tested conditions it should be completely deprotonated.
At present, it is not clear why the enolate of 2a does not un-
dergo the rearrangement. One reason might be that the
enolate is formed as the wrong geometric isomer.
As we mentioned previously, dinitroaryl ketosulfones II
(Scheme 1) undergo the Smiles rearrangement to produce
dinitrophenyl aryl acetylenes III, hence it appears that the
presence of a nitro group on the benzylic substituent is a
In order to clarify whether the presence of the 2-nitro
group in compound 2b favors the Smiles rearrangement
due to steric or electronic effects, we prepared 4-nitroben-
zyl benzothiazol-2-yl sulfone (1c) in a similar manner to
that used to prepare 1b. The benzoylation of 1c and the
Smiles rearrangement of crude 2c proceeded similarly to
sulfone 2b and gave 4-nitrophenyl phenyl acetylene (3f) in
a good overall yield of 62% (Scheme 4). Thus, the beneficial
influence of the nitro groups in compounds 1b and 1c on
the Smiles rearrangement is due to their electronic effects.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H

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R. Bujok, M. Mąkosza
Paper
Synthesis
NO2
ONE-POT EXPERIMENT
NO2
1) LHMDS,
NO2
1) LHMDS,
THF, –70 °C, 4 min
N
S
N
THF, –70 °C, 4 min
SO2
SO2
O
O
S
2
2)
R
3b, 16%
1b–c
2)
1b
Cl
Cl
THF, –70 to 0 °C, 1 d
THF, –70 to 0 °C, 5 h
NO2
3) 60 °C, overnight
NO2
Cs2CO3
O
EXPERIMENT WITH CRUDE 2b
acetone, reflux, 1 d
N
S
SO2 R2
R2
NO2
NO2
O
1) LHMDS,
N
N
S
NO2
THF, -70 °C, 4 min
NO2
SO2
SO2
O
S
CF3
2)
1b
crude 2b
3b, 54%
Cl
3c, 67%
NO2
THF, –70 to 0 °C, 1 d
NO2
Cl
NO2
Cs2CO3
3d, 59%
3e, 53%
acetone, reflux, 1 d
3b, 54% overal yield
based on 1b
O2N
CF3
O2N
3g, 59%
3i, 51%
3f, 62%
3h, 56%
Scheme 3 One-pot synthesis of the acetylene 3b and the synthesis
from the crude sulfone 2b. Yields of isolated products are given.
O2N
Cl
F
O2N
Conversion of 2- and 4-nitrobenzyl benzothiazol-2-yl
sulfones (1b) and (1c) into nitrophenyl aryl acetylenes 3 via
acylation with aroyl chlorides and the Smiles rearrange-
ment is a general process exemplified by the results shown
in Scheme 4. Good overall yields (50–60%; approx. 75% per
step) were obtained for benzoyl chlorides bearing both
electron-withdrawing and electron-donating substituents
on the phenyl ring. Also, the use of 2-naphthoyl chloride
gave good results.
O2N
O2N
OMe
O
3l, 27%
3j, 53%
O2N
3k, 56%
Scheme 4 Synthesis of nitrophenyl aryl acetylenes 3 from the benzo-
thiazol-2-yl sulfones 1b,c. Yields of isolated products are given.
The furan ring is probably less stable under the condi-
tions of both steps. TLC analysis indicated that the acylation
and the Smiles rearrangement were less selective and prod-
uct 3l was obtained in only moderate yield (27%; 52% per
step).
An attempt to apply the elaborated reaction sequence
for the synthesis of 4-cyanophenyl aryl acetylenes from sul-
fone 1d was unsuccessful (Scheme 5). Treatment of the
crude benzoyl ketosulfone with Cs2CO3 under standard con-
ditions resulted in elimination of the benzothiazol-2-yl sul-
fonyl group without the Smiles rearrangement, resulting in
the corresponding ketone 4o being isolated in 46% overall
yield.
NC
NC
1) LHMDS,
THF, –70 °C, 4 min
O
N
N
S
O
SO2
SO2
2)
S
Cl
1d
THF, –70 to 0 °C, 1 d
O
Cs2CO3
NC
acetone, reflux, 1 d
4o, 46% overall yield
based on 1d
For the Julia–Kocienski olefination via the Smiles rear-
rangement, the 1-phenyl-1H-tetrazol-5-yl sulfones are of-
ten used. Hence, we prepared a series of the corresponding
sulfones 1e–g bearing NO2, CN and CF3 groups at the 4-posi-
tion of the phenyl ring in order to investigate the effect of
the heterocyclic leaving group (Scheme 6).
Scheme 5 Attempted synthesis of the 4-cyanophenyl acetylene from
the 4-cyanobenzyl sulfone 1d. Yields of isolated product is given.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H

D
R. Bujok, M. Mąkosza
Paper
Synthesis
more reactive than benzothiazole sulfones, but the reac-
tions proceed less selectively. This is typical situation, i.e.,
more active reagents react with lower selectivity.
R1
R1
O
1) LHMDS,
THF, –70 °C, 4 min
In conclusion, we have described a new approach for the
synthesis of diaryl acetylenes containing electron-with-
drawing groups via the benzothiazol-2-yl and the 1-phe-
nyl-1H-tetrazol-5-yl ketosulfones, themselves prepared by
acylation of the corresponding sulfones. This methodology
is of general applicability for nitroaryl aryl acetylenes. The
products bearing electron-withdrawing and electron-do-
nating substituents were synthesized in good overall yields,
usually 50–60% (approx. 75% per step). Inferior results were
obtained for 4-cyano- and 4-trifluoromethyl groups, the
corresponding acetylenes being isolated in moderate over-
all yields (approx. 22%; 46% per step). In these cases, the
corresponding ketones were the main products of the reac-
tions.
N
N
N
N
N
N
N
SO2 R2
SO2
O
N
2
2)
R
Ph
Ph
Cl
THF, –70 to 0 °C, 1 d
R1
R1
Cs2CO3
acetone, reflux, 1 d
O
+
R2
R2
O2N
3f, 54%
O2N
O2N
3m, 40%
Br
Column chromatography was accomplished using Merck silica gel
230-400 mesh. Analytical TLC was performed on Merck 60 silica gel
plates. Melting points were determined using a Franz Kurstner Nach
KG Dresden HMK 713398 instrument. IR spectra were recorded on a
JASCO FT/IR-6200 spectrophotometer. 1H and 13C NMR spectra were
recorded on Bruker DRX 500 "Avance" 500 MHz (500 MHz for 1H and
125 MHz for 13C spectra) or Varian-NMR-VNMRS-500 (500 MHz for
1H and 125 MHz for 13C spectra) instruments. Chemical shifts () are
expressed in ppm referred to TMS (internal standard), and coupling
constants are in hertz. Multiplicities are reported as follows: singlet
(s), doublet (d), doublet of doublets (dd), triplet (t), quartet (q) and
multiplet (m). ESI mass spectra were obtained on SYNAPT G2-S
HDMS instrument. EI mass spectra were recorded on gas chromato-
graph 7890A (Agilent) coupled with magnetic sector mass spectrom-
eter AutoSpec Premier. Elemental analysis was performed using
VARIO EL III instrument.
3n, 46%
CF3
O
Cl
Cl
NC
Cl NC
4o, 52%
3o, 22%
3p, 21%
O
F3C
Cl
F3C
4p, 41%
Scheme 6 Synthesis of arylacetylenes from 1-phenyl-tetrazol-5-yl sul-
fones 1e–g. Yields of isolated products are given.
The acylation step proceeded smoothly in all cases. The
crude ketosulfones obtained from 1-phenyl-1H-tetrazol-5-
yl nitrobenzyl sulfone 1e reacted in similar manner to the
benzothiazol-2-yl analog 1c. The corresponding acetylenes
3f, 3m and 3n were isolated in satisfactory yields (40–54%).
The results were slightly worse than for the benzothiazol-
2-yl sulfone 1c, because of a drop in the selectivity of the
rearrangement step, but the desired acetylenes were still
the main products of the reactions.
Sulfones 1a–g
Sulfones 1a–g were obtained from commercial 2-mercaptobenzothi-
azole or 1-phenyl-1H-tetrazole-5-thiol via alkylation with the corre-
sponding benzyl bromide followed by oxidation with mCPBA accord-
ing to the procedure described for sulfone 1a.7a
2-(2-Nitrophenylmethanesulfonyl)benzothiazole (1b)
Under the standard rearrangement conditions acylation
products formed from the sulfones 1f,g bearing weaker
electron-withdrawing groups (CN, CF3) to give mixtures of
the corresponding acetylenes 3o,p (approx. 22%) and ke-
tones 4o,p (41–52%). The formation of ketones from a side
reaction during the rearrangement step was reported by
Jorgensen for sulfones II (see Scheme 1).8 It is noteworthy
that ketones such as 4o are also interesting compounds.8,10
In contrast to the benzothiazol-2-yl sulfone 1d, com-
The crude product was purified by column chromatography (hex-
anes/EtOAc, 2:1).
White solid (2.65 g, 72% based on 2-mercaptobenzothiazole); mp
132–135 °C; Rf = 0.38 (SiO2, hexanes/EtOAc, 2:1).
IR (KBr): 3067, 3022, 2961, 1724, 1605, 1577, 1521, 1466, 1416, 1350,
1311, 1241, 1147, 1082, 1016, 861, 859, 793, 766, 701, 632, 547, 513,
455, 432 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.22 (d, J = 7.5 Hz, 1 H), 8.03 (dd, J = 7.5
Hz, 1.5 Hz, 1 H), 7.98–7.96 (m, 1 H), 7.65–7.63 (m, 1 H), 7.61–7.50 (m,
4 H), 5.38 (s, 2 H).
pound 1f bearing
a 1-phenyl-1H-tetrazol-5-yl group
formed the desired acetylene 3o (22%), but still the corre-
sponding ketone 4o was the main product of the reaction.
Thus tetrazol-5-yl sulfone 1f reacts in a different way than
the benzothiazol-2-yl sulfone 1d. Tetrazol-5-yl sulfones are
13C NMR (125 MHz, CDCl3):  = 164.7, 152.5, 149.6, 136.9, 134.4,
133.4, 130.5, 128.4, 127.8, 125.8, 125.6, 122.3, 121.7, 57.0.
HRMS–EI: m/z [M]+ calcd for C14H10N2O4S2: 334.0082; found:
334.0084.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H

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R. Bujok, M. Mąkosza
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Synthesis
2-(4-Nitrophenylmethanesulfonyl)benzothiazole (1c)
HRMS–ESI+ (MeOH): m/z [M
+
Na]+ calcd for C15H11N5O2SNa:
348.0531; found: 348.0521.
The crude product was used in the next step without further purifica-
tion.
1-Phenyl-5-(4-trifluoromethyl-phenylmethanesulfonyl)-1H-
tetrazole (1g)
White solid (3.5 g, 95% based on 2-mercaptobenzothiazole); mp 210–
211 °C (dec.).
The crude product was used in the next step without further purifica-
tion.
IR (KBr): 3110, 3069, 2932, 1606, 1523, 1469, 1345, 1315, 1234, 1147,
1123, 1102, 1012, 864, 853, 767, 698, 651, 610, 558, 517, 504, 460,
434 cm–1
.
White solid (5.6 g, ~100% based on 1-phenyl-1H-tetrazole-5-thiol);
mp 138–140 °C.
1H NMR (500 MHz, DMSO-d6):  = 8.32–8.29 (m, 2 H), 8.22–8.20 and
7.62–7.60 (AA′XX′, 4 H), 7.77–7.69 (m, 2 H), 5.35 (s, 2 H).
13C NMR (125 MHz, DMSO-d6):  = 165.3, 152.0, 147.7, 136.4, 134.7,
132.6, 128.3, 128.0, 124.9, 123.5, 59.0.
HRMS–EI: m/z [M]+ calcd for C14H10N2O4S2: 334.0082; found:
IR (KBr): 3076, 2990, 2942, 1696, 1620, 1593, 1553, 1496, 1418, 1355,
1324, 1175, 1153, 1112, 1065, 1015, 853, 762, 731, 688, 656, 588, 520
cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.64–7.62 (m, 2 H), 7.61–7.57 (m, 1 H),
7.55–7.50 (m, 4 H), 7.44–7.42 (m, 2 H), 5.03 (s, 2 H).
13C NMR (125 MHz, CDCl3):  = 152.8, 132.7, 132.1, 131.5, 129.5,
128.8, 126.0 (q, J = 3.5 Hz), 125.1, 123.6 (q, J = 273 Hz), 61.6.
HRMS–ESI+ (MeOH): m/z [M + Na]+ calcd for C15H11N4O2SF3Na:
334.0089.
2-(4-Cyanophenylmethanesulfonyl)benzothiazole (1d)
The crude product was used in the next step without further purifica-
tion.
391.0453; found: 391.0440.
White solid (2.8 g, 89% based on 2-mercaptobenzothiazole); mp 182–
184 °C.
Ketosulfones 2a,b
To a solution of sulfone 1 (1.0 mmol) in dry THF (10 mL) cooled to –
70 °C under an argon atmosphere was added LHMDS (1.7 mL, 1.3 M in
THF, 2.2 mmol) via a microsyringe (in two portions over 30 s) and the
mixture then stirred for 3–4 min. The acyl chloride (1.5 mmol) was
added, the cooling bath removed and the reaction mixture allowed to
warm to 5 °C over 15 min and then stirred overnight at 5 °C. 2 M HCl
(1 mL) was added, the mixture was extracted with EtOAc (20 mL) and
the extract dried and evaporated. The crude product was purified by
column chromatography on silica gel (hexanes/EtOAc).
IR (KBr): 3067, 2224, 1693, 1603, 1550, 1501, 1468, 1411, 1335, 1315,
1147, 1083, 1023, 852, 767, 728, 622, 569, 544 cm–1
.
1H NMR (500 MHz, DMSO-d6):  = 8.33–8.29 (m, 2 H), 7.84–7.82 and
7.52–7.51 (AA′XX′, 4 H), 7.77–7.69 (m, 2 H), 5.28 (s, 2 H).
13C NMR (125 MHz, DMSO-d6):  = 165.3, 152.0, 136.4, 132.8, 132.3,
132.2, 128.3, 128.1, 124.9, 123.5, 118.4, 111.7, 59.3.
HRMS–EI: m/z [M]+ calcd for C15H10N2O2S2: 314.0184; found:
314.0177.
2-(Benzothiazole-2-sulfonyl)-1,2-diphenyl-ethanone (2a)
5-(4-Nitrophenylmethanesulfonyl)-1-phenyl-1H-tetrazole (1e)
White solid (0.331 g, 84%); mp 141–142 °C; Rf = 0.31 (SiO2, hex-
anes/EtOAc, 4:1).
The crude product was used in the next step without further purifica-
tion.
IR (KBr): 3435, 3060, 1676, 1594, 1468, 1450, 1340, 1279, 1207, 1148,
White solid (2.7 g, 98% based on 1-phenyl-1H-tetrazole-5-thiol); mp
173–176 °C (dec.).
1081, 1024, 991, 855, 767, 725, 697, 617, 546, 518, 501 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.15–8.13 (m, 1 H), 7.95–7.93 (m, 1 H),
7.89–7.87 (m, 2 H), 7.61–7.50 (m, 5 H), 7.42–7.31 (m, 5 H), 6.81 (s, 1
H).
13C NMR (125 MHz, CDCl3):  = 189.5, 165.8, 152.2, 137.2, 135.2,
134.2, 131.0, 130.1, 129.4, 129.0, 128.8, 128.0, 127.5, 126.5, 125.4,
122.3, 75.0.
IR (KBr): 3074, 2990, 2941, 1695, 1599, 1526, 1494, 1462, 1416, 1400,
1349, 1152, 1101, 1077, 1053, 1012, 861, 765, 688, 652, 597, 519 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.26–8.22 and 7.63–7.60 (AA′XX′, 4 H),
7.68–7.64 (m, 1 H), 7.54–7.52 (m, 4 H), 5.45 (s, 2 H).
13C NMR (125 MHz, CDCl3):  = 152.9, 148.0, 133.2, 133.0, 132.7,
131.4, 129.2, 126.1, 123.6, 60.6.
HRMS–ESI+ (MeOH): m/z [M
+
Na]+ calcd for C21H15NO3S2Na:
HRMS–ESI+ (MeOH): m/z [M
+
Na]+ calcd for C14H11N5O4SNa:
416.0391; found: 416.0382.
368.0429; found: 368.0422.
2-(Benzothiazole-2-sulfonyl)-2-(2-nitrophenyl)-1-phenyl-etha-
none (2b)
5-(4-Cyanophenylmethanesulfonyl)-1-phenyl-1H-tetrazole (1f)
The crude product was used in the next step without further purifica-
tion.
Light-brown solid (0.235 g, 53%); mp 93–95 °C; Rf = 0.17 (SiO2, hex-
anes/EtOAc, 4:1).
White solid,(4.9 g, ~100% based on 1-phenyl-1H-tetrazole-5-thiol);
mp 178–180 °C (dec.).
IR (KBr): 1670, 1595, 1577, 1528, 1466, 1346, 1216, 1148, 1002, 876,
844, 759, 698, 625, 554, 521 cm–1
.
IR (KBr): 3067, 2960, 2904, 2227, 1593, 1494, 1399, 1351, 1269, 1165,
1H NMR (500 MHz, CDCl3):  = 8.14–8.12 (m, 1 H), 8.09–8.07 (m, 4 H),
7.96–7.93 (m, 2 H), 7.68–7.65 (m, 1 H), 7.62–7.54 (m, 4 H), 7.45–7.42
(m, 2 H).
1137, 870, 849, 764, 689, 580, 523 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.68–7.66 (m, 2 H), 7.61–7.51 (m, 7 H),
5.05 (s, 2 H).
13C NMR (125 MHz, CDCl3):  = 188.8, 164.5, 152.1, 149.7, 137.0,
135.1, 134.6, 133.5, 133.1, 130.9, 129.3, 129.0, 128.3, 127.7, 125.7,
122.2, 121.2, 67.4.
13C NMR (125 MHz, CDCl3):  = 152.8, 132.6, 132.5, 131.6, 130.0,
129.7, 125.0, 117.8, 113.9, 61.6.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H

F
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Paper
Synthesis
HRMS–ESI+ (MeOH): m/z [M
461.0242; found: 461.0230.
+
Na]+ calcd for C21H14N2O5S2Na:
13C NMR (125 MHz, CDCl3):  = 149.6, 134.6, 133.3, 132.9, 132.8,
132.4, 128.5, 128.3, 128.2, 128.0, 127.8, 127.2, 126.7, 124.8, 119.7,
118.8, 97.6, 85.1.
HRMS–EI: m/z [M]+ calcd for C18H11NO2: 273.0790; found: 273.0797.
Acetylenes 3 from Sulfones 1 without Purification of Ketosulfones
2; General Procedure
The crude ketosulfones were obtained in similar manner to sulfones
2a,b. Next, Cs2CO3 (0.195 g, 0.60 mmol) and acetone (15 mL) were
added and the mixture was refluxed for 1–2 d. The solvent was evap-
orated, H2O (6 mL) was added and the mixture was extracted with
EtOAc (2 × 20 mL). The combined extracts were dried and evaporated.
The crude product was purified by column chromatography on silica
gel (hexanes/EtOAc) to afford acetylenes 3.
1-Nitro-4-(phenylethynyl)benzene (3f)
Yellow solid (0.207 g, 62%); mp 114–116 °C (Lit.4a 110–114 °C); Rf =
0.52 (SiO2, hexanes/EtOAc, 19:1).
IR (KBr): 2214, 1591, 1511, 1345, 1103, 858, 765, 688, 506 cm–1
1H NMR (500 MHz, CDCl3):  = 8.23–8.20 and 7.68–7.64 (AA′XX′, 4 H),
7.58–7.54 (m, 2 H), 7.41–7.37 (m, 3 H).
.
13C NMR (125 MHz, CDCl3):  = 147.0, 132.3, 131.8, 130.3, 129.3,
128.5, 123.6, 122.1, 94.7, 87.5.
1-Nitro-2-(phenylethynyl)benzene (3b)4a
Orange oil (0.085 g, 54%); TLC (SiO2): Rf = 0.40 (SiO2, hexanes/EtOAc,
9:1)
1-Nitro-4-{[4-(trifluoromethyl)phenyl]ethynyl}benzene (3g)
Light-yellow solid (0.168 g, 59%); mp 108–110 °C (Lit.4b 110–111 °C);
Rf = 0.46 (SiO2, hexanes/EtOAc, 19:1).
IR (film): 3053, 2220, 1608, 1568, 1523, 1495, 1442, 1343, 1293,
1143, 1070, 888, 834, 784, 757, 744, 690, 520 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.08 (dd, J = 8.2 Hz, 1.1 Hz, 1 H), 7.71
(dd, J = 7.7 Hz, 1.4 Hz, 1 H), 7.61–7.58 (m, 3 H), 7.48–7.44 (m, 1 H),
7.40–7.36 (m, 3 H).
IR (KBr): 3115, 2222, 1926, 1593, 1513, 1346, 1319, 1173, 1125, 1105,
1063, 855, 839, 749, 687, 595, 507 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.26–8.23 and 7.71–7.68 (AA′XX′, 4 H),
7.67–7.65 (m, 4 H).
13C NMR (125 MHz, CDCl3):  = 149.6, 134.6, 132.8, 132.0, 129.2,
13C NMR (125 MHz, CDCl3):  = 147.4, 132.5, 132.1, 130.9 (q, J = 33
Hz), 129.4, 125.9, 125.5 (q, J = 4 Hz), 124.3 (q, J = 272 Hz), 123.7, 92.8,
89.5.
128.5, 128.4, 124.7, 122.4, 118.8, 97.1, 84.8.
1-Nitro-2-{[4-(trifluoromethyl)phenyl]ethynyl}benzene (3c)
Orange solid (0.252 g, 67%); mp 52–54 °C (Lit.11 46–48 °C); Rf = 0.35
(SiO2, hexanes/EtOAc, 9:1).
4-(4-Chlorophenylethynyl)-1-nitrobenzene (3h)
Yellow solid (0.177 g, 56%); mp 152–155 °C (Lit.12 155–156 °C); Rf =
0.51 (SiO2, hexanes/EtOAc, 19:1).
IR (KBr): 2221, 1924, 1611, 1523, 1319, 1177, 1121, 1062, 842, 744,
688, 595, 516 cm–1
.
IR (KBr): 2210, 1586, 1535, 1343, 1088, 1010, 834, 746, 505 cm–1
1H NMR (500 MHz, CDCl3):  = 8.23–8.21 and 7.66–7.64 (AA′XX, 4 H),
7.49–7.48 and 7.37–7.36 (AA′XX, 4 H).
.
1H NMR (500 MHz, CDCl3):  = 8.11 (dd, J = 8.2 Hz, 1.1 Hz, 1 H), 7.74
(dd, J = 7.8 Hz, 1.4 Hz, 1 H), 7.70–7.68 (m, 2 H), 7.64–7.61 (m, 3 H),
7.53–7.49 (m, 1 H).
13C NMR (125 MHz, CDCl3):  = 149.7, 134.7, 132.9, 132.2, 130.8 (q, J =
33 Hz), 129.2, 126.2, 125.3 (q, J = 4 Hz), 124.8, 123.8 (q, J = 271 Hz),
118.0, 95.2, 86.8.
13C NMR (125 MHz, CDCl3):  = 147.2, 135.5, 133.0, 132.3, 129.9,
128.9, 123.7, 120.6, 93.4, 88.4.
4-(4-Fluorophenylethynyl)-1-nitrobenzene (3i)
Yellow solid (0.122 g, 51%); mp 107–109 °C (Lit.4c 111–113 °C); Rf =
0.48 (SiO2, hexanes/EtOAc, 19:1).
2-(4-Chlorophenylethynyl)-1-nitrobenzene (3d)
Orange solid (0.193 g, 59%); mp 93–95 °C; Rf = 0.39 (SiO2, hex-
anes/EtOAc, 4:1).
IR (KBr): 2209, 1589, 1516, 1343, 1232, 1179, 1105, 852, 838, 747,
685, 511 cm–1
.
IR (KBr): 2219, 1605, 1566, 1518, 1341, 1291, 1088, 1011, 825, 743,
513 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.23–8.21 and 7.66–7.64 (AA′XX, 4 H),
7.56–7.54 (m, 2 H), 7.10–7.07 (m, 2 H).
13C NMR (125 MHz, CDCl3):  = 163.1 (d, J = 250 Hz), 147.0, 133.8 (d,
J = 9 Hz), 132.2 (d, J = 7 Hz), 130.1, 123.7, 118.2, 115.9 (d, J = 22 Hz),
93.6, 87.3.
1H NMR (500 MHz, CDCl3):  = 8.09 (dd, J = 8.2 Hz, 0.9 Hz, 1 H), 7.71
(dd, J = 7.8 Hz, 1.4 Hz, 1 H), 7.62–7.59 (m, 1 H), 7.53–7.51 and 7.37–
7.34 (AA′XX, 4 H), 7.50–7.46 (m, 1 H).
13C NMR (125 MHz, CDCl3):  = 149.5, 135.4, 134.5, 133.2, 132.9,
128.8, 128.7, 124.8, 120.9, 118.5, 95.9, 85.7.
HRMS–EI: m/z [M]+ calcd for C14H8NO2Cl: 257.0244; found: 257.0234.
4-(4-Methoxyphenylethynyl)-1-nitrobenzene (3j)
Yellow solid (0.204 g, 53%); mp 113–115 °C (Lit.4a 110–111 °C); Rf =
0.38 (SiO2, hexanes/EtOAc, 9:1).
2-(2-Nitrophenylethynyl)naphthalene (3e)
Orange solid (0.195 g, 53%); mp 78–81 °C; Rf = 0.36 (SiO2, hex-
anes/EtOAc, 4:1).
IR (KBr): 2963, 2838, 2209, 1588, 1513, 1337, 1246, 1173, 1105, 1027,
858, 836, 747, 687 cm–1
.
IR (KBr): 2202, 1605, 1567, 1517, 1334, 1289, 739, 472 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.21–8.19 and 7.64–7.62 (AA′XX, 4 H),
7.51–7.49 and 6.92–6.90 (AA′XX, 4 H), 3.85 (s, 3 H).
13C NMR (125 MHz, CDCl3):  = 160.4, 146.7, 133.4, 132.0, 130.7,
1H NMR (500 MHz, CDCl3):  = 8.13 (br s, 1 H), 8.10 (dd, J = 8.2 Hz, 0.9
Hz, 1 H), 7.85–7.82 (m, 3 H), 7.76 (dd, J = 7.9 Hz, 1.3 Hz, 1 H), 7.64–
7.59 (m, 2 H), 7.54–7.50 (m, 2 H), 7.48–7.45 (m, 1 H).
123.6, 114.2, 114.1, 95.1, 86.6, 55.4.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H

G
R. Bujok, M. Mąkosza
Paper
Synthesis
2-(4-Nitrophenylethynyl)naphthalene (3k)
13C NMR (125 MHz, CDCl3):  = 135.3, 133.0, 132.1, 129.7, 128.9,
Yellow solid (0.152 g, 56%); mp 135–138 °C (Lit.4d 141–144 °C); Rf =
127.9, 120.7, 118.4, 111.7, 92.5, 88.6.
0.47 (SiO2, hexanes/EtOAc, 19:1).
4-[2-(4-Chlorophenyl)-2-oxo-ethyl]benzonitrile (4o)
Light-yellow solid (0.257 g, 52%); mp 113–114 °C (Lit.10b 119–120 °C);
Rf = 0.42 (SiO2, hexanes/EtOAc, 4:1).
IR (KBr): 2207, 1592, 1513, 1337, 1103, 850, 822, 746, 684, 472 cm–1
.
1H NMR (500 MHz, CDCl3):  = 8.25–8.22 and 7.71–7.69 (AA′XX, 4 H),
8.10 (br s, 1 H), 7.85–7.83 (m, 3 H), 7.58 (dd, J = 8.6 Hz, 1.5 Hz, 1 H),
7.54–7.52 (m, 2 H).
13C NMR (125 MHz, CDCl3):  = 147.0, 133.2, 132.9, 132.3, 132.2,
130.3, 128.3, 128.1, 127.9, 127.8, 127.3, 126.8, 123.7, 119.4, 95.2, 87.9.
IR (KBr): 2220, 1687, 1589, 1398, 1338, 1218, 1199, 1093, 994, 829,
816, 794, 567, 550, 527 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.94–7.91 and 7.63–7.61 (AA′XX, 4 H),
7.47–7.45 and 7.36–7.34 (AA′XX, 4 H), 4.32 (s, 2 H).
2-(4-Nitrophenylethynyl)furan (3l)
13C NMR (125 MHz, CDCl3):  = 194.9, 140.2, 139.5, 134.5, 132.4,
130.5, 129.8, 129.2, 118.7, 111.1, 45.2.
Yellow solid (0.080 g, 27%); mp 143–144 °C (dec.); Rf = 0.42 (SiO2, hex-
anes/EtOAc, 19:1).
4-(4-Chlorophenylethynyl)trifluoromethylbenzene (3p)
IR (KBr): 2200, 1596, 1513, 1339, 1213, 1103, 850, 822, 746, 684, 472
cm–1
.
The reaction was carried out on 2 mmol scale.
Light-yellow solid (0.120 g, 21%); mp 108–110 °C (Lit.13 109–111 °C);
Rf = 0.83 (SiO2, hexanes/EtOAc, 19:1).
1H NMR (500 MHz, CDCl3):  = 8.23–8.21 and 7.66–7.64 (AA′XX, 4 H),
7.49–7.48 (m, 1 H), 6.77 (d, J = 3.2 Hz, 1 H), 6.49–6.47 (m, 1 H).
13C NMR (125 MHz, CDCl3):  = 147.1, 144.7, 136.2, 131.9, 129.2,
123.7, 117.1, 111.4, 91.7, 84.6.
IR (KBr): 2215, 1914, 1611, 1587, 1484, 1404, 1322, 1181, 1135, 1064,
1011, 831, 632, 598, 512 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.63–7.59 (m, 4 H), 7.48–7.46 and
7.35–7.33 (AA′XX, 4 H).
HRMS–EI: m/z [M]+ calcd for C12H7NO3: 213.0413; found: 213.0418.
4-(2-Bromophenylethynyl)-1-nitrobenzene (3m)
13C NMR (125 MHz, CDCl3):  = 134.9, 132.9, 131.8, 130.1 (q, J = 32
Hz), 128.8, 126.7, 125.3, 123.9 (q, J = 270 Hz), 121.0, 90.6, 88.8.
Light-yellow solid (0.096 g, 40%); mp 115–117 °C; Rf = 0.44 (SiO2, hex-
anes/EtOAc, 19:1).
4-[2-(4-Chlorophenyl)-2-oxo-ethyl]trifluoromethylbenzene (4p)
IR (KBr): 2218, 1595, 1527, 1492, 1343, 1104, 1041, 1025, 864, 850,
762, 745, 683, 657, 443 cm–1
.
Light-yellow solid (0.247 g, 41%); mp 118–121 °C; Rf = 0.36 (SiO2, hex-
anes/EtOAc, 9:1).
1H NMR (500 MHz, CDCl3):  = 8.24–8.22 and 7.73–7.71 (AA′XX, 4 H),
7.65 (dd, J = 8.0 Hz, 1.0 Hz, 1 H), 7.58 (dd, J = 7.7 Hz, 1.6 Hz, 1 H), 7.35–
7.31 (m, 1 H), 7.27–7.23 (m, 1 H).
IR (KBr): 2908, 1927, 1691, 1586, 1488, 1422, 1403, 1325, 1201, 1165,
1113, 1065, 990, 866, 821, 796, 757, 703, 593, 563, 526 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.95–7.93 and 7.60–7.59 (AA′XX, 4 H),
7.46–7.44 and 7.37–7.35 (AA′XX, 4 H), 4.32 (s, 2 H).
13C NMR (125 MHz, CDCl3):  = 147.3, 133.5, 132.7, 132.4, 130.4,
129.8, 127.2, 125.9, 124.4, 123.7, 93.0, 91.7.
13C NMR (125 MHz, CDCl3):  = 195.4, 140.0, 138.1, 138.0, 134.6,
129.9, 129.5, 129.1, 125.6 (q, J = 4 Hz), 124.1 (q, J = 270 Hz), 45.0.
HRMS–EI: m/z [M]+ calcd for C14H8NO279Br: 300.9738; found:
300.9744.
Anal. Calcd for C15H10ClF3O: C, 60.32; H, 3.37; N, 11.87. Found: C,
60.22; H, 3.36; N, 11.70.
1-Nitro-4-{[3-(trifluoromethyl)phenyl]ethynyl}benzene (3n)
Yellow solid (0.113 g, 46%); mp 138–140 °C; Rf = 0.40 (SiO2, hex-
anes/EtOAc, 19:1).
Funding Information
IR (KBr): 2214, 1592, 1535, 1496, 1432, 1347, 1296, 1271, 1117, 1071,
901, 891, 854, 808, 747, 719, 693, 660 cm–1
.
This work was supported by the Narodowe Centrum Nauki (National
Science Centre; grant UNO 2014/15/B/ST5/0218).
1H NMR (500 MHz, CDCl3):  = 8.25–8.23 and 7.70–7.68 (AA′XX, 4 H),
7.83 (br s, 1 H), 7.73 (d, J = 7.5 Hz, 1 H), 7.65 (d, J = 8.0 Hz, 1 H), 7.54–
7.51 (m, 1 H).
N
aro
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o
w
e
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m
N
a
u
k
i(U
N
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2
0
1
4/15/B/S
T
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2
1
8)
13C NMR (125 MHz, CDCl3):  = 147.3, 134.8, 132.4, 131.2 (q, J = 33
Hz), 129.4, 129.1, 128.6 (q, J = 4 Hz), 125.7 (q, J = 4 Hz), 123.8, 123.6
(q, J = 271 Hz), 123.1, 92.7, 88.8.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1612423.
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p
p
orit
n
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o
n
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u
p
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o
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HRMS–EI: m/z [M]+ calcd for C15H8NO2F3: 291.0507; found: 291.0514.
4-(4-Chlorophenylethynyl)benzonitrile (3o)
References
The reaction was carried out on 2 mmol scale.
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.
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H

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R. Bujok, M. Mąkosza
Paper
Synthesis
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2019, 51, A–H