Simple strategy for sulfonyl ethynylogs of coumarins

Article abstract of DOI:10.1080/00397911.2010.515344

Synthesis of 3-(2-(phenylsulfonyl) ethynyl)-2H-chromen-2-one is described. Reaction of β-ketosulfones with semicarbazide hydrochloride in ethanol at reflux temperature gave the corresponding semicarbazones, which on oxidative cyclization with selenium dioxide resulted in the formation of the corresponding 1,2,3-selenodiazole derivatives. These on pyrolysis gave the titled compounds. Taylor & Francis Group, LLC.

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Simple Strategy for Sulfonyl Ethynylogs
of Coumarins
Nalajam Guravaiah a & Vedula Rajeswar Rao a
a Department of Chemistry, National Institute of Technology,
Warangal, India
Published online: 29 Jun 2011.
To cite this article: Nalajam Guravaiah & Vedula Rajeswar Rao (2011) Simple Strategy
for Sulfonyl Ethynylogs of Coumarins, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 41:18, 2693-2700, DOI:
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Synthetic Communications1, 41: 2693–2700, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.515344
SIMPLE STRATEGY FOR SULFONYL ETHYNYLOGS
OF COUMARINS
Nalajam Guravaiah and Vedula Rajeswar Rao
Department of Chemistry, National Institute of Technology, Warangal, India
GRAPHICAL ABSTRACT
Abstract Synthesis of 3-(2-(phenylsulfonyl) ethynyl)-2H-chromen-2-one is described.
Reaction of b-ketosulfones with semicarbazide hydrochloride in ethanol at reflux tempera-
ture gave the corresponding semicarbazones, which on oxidative cyclization with selenium
dioxide resulted in the formation of the corresponding 1,2,3-selenodiazole derivatives. These
on pyrolysis gave the titled compounds.
Keywords Alkynes; b-ketosulfones; 1,2,3-selenodiazoles; semicarbazones; SeO2
INTRODUCTION
1,2,3-Selenadiazoles and their derivatives are well known and have attracted
attention as versatile synthetic intermediates.[1,2] Substituted 1,2,3-selenadiazole
and many of its derivatives have been prepared to date, and some of them show high
antibacterial activity.[3–6] The antifungal activity of other substituted 1,2,3-selenadia-
zoles has also been determined.[6–8] It has been found that the introduction of a
1,2,3-selenadiazole ring to molecules of known biological activity changes their
activities and in some cases leads to an increase in their biological activity.[9] 4-
Methyl-1,2,3-selenadiazole-5-carboxamides inhibit tumor cell colony formation.[10,11]
In the area of antibacterial therapeutics, resistance to currently available drugs is
progressively limiting their utility in treating bacterial infections. This problem can
be solved by discovering novel pharmaceutical drugs that inhibit novel targets.
Advances in molecular microbiology and genomics have led to the identification of
Received April 1, 2010.
Address correspondence to Vedula Rajeswar Rao, Department of Chemistry, National Institute of
Technology, Warangal, AP 506 004, India. E-mail: vrajesw@yahoo.com
2693

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N. GURAVAIAH AND V. R. RAO
numerous bacterial genes that are encoding for novel proteins, which could poten-
tially serve as novel targets for antibacterial compounds. Regulatory proteins such
as the two-component histidine kinases, involved in bacterial signal transduction,
have recently gained considerable attention as one such class of potential targets.[12]
The long-standing but modest use of selenium reagents by organic synthetic
chemists received new impetus because of the numerous organoselenium reagents,
catalysts, and intermediates employed in synthesis. Nevertheless, their role in some
synthetically useful reactions for preparation of nonselenium organic compounds
is prominent and worthy of note. The reactions can be divided into two groups:
(i) those that proceed through extrusion of the selenium in thermal or reductive
conditions, or under treatment with a nucleophile (photochemical extrusion of the
selenium is of minor importance for use in synthesis), and (ii) those in which sel-
enium plays a role as oxygen-transfer agent. The ready thermal and photochemical
decomposition of 1,2,3-selenadiazoles resulting in extrusion of nitrogen and selenium
or nitrogen only has been exploited widely in synthesis for more than 30 years. Their
thermolysis or decomposition with butyllithium gave the alkynes. More recently,
thermolysis of 1,2,3-selenadiazoles fused them to carbocyclic rings.[13–15]
Novobiocin is a coumarin-derived antibiotic used as a competitive inhibitor of
the bacterial ATP binding gyrase B subunit, blocking the negative supercoiling of
relaxed DNA.[16–19] Lamellarin is utilized as a selective inhibitor of HIV-I integrase.[20]
The discovery of promising lead antivirus compounds and their moderate activity war-
ranted the development of efficient and rapid synthesis and evaluation of analogous
structures in the search for better inhibitors. Thus, we initiated a program to develop
efficient methods for the synthesis of diversified coumarin molecules, with the hope of
finding more active hits or leads for our particular biological assays.
Our work on the synthesis of heterocyclic compounds containing sulfone-
linked 1,2,3-thiadiazoles, b-ketosulfones, and heteryl styryl sulfones at the 3-position
of coumarin[21–23] and our sustained interest in this field led us to develop a simple
and elegant methodology for a new class of compounds, ethynesulfones, through
a facile route. Literature search shows not only the compounds involving alkene
and alkyne moieties but also chalone ethynylogs are relatively few.[24] One such
method involves the Pd coupling reaction of vinyl halides with terminal alkynes
and alkynyl metals. Moreover, the carbonyl activated enyne systems have also been
obtained by the direct condensation of phenyl acetylenes with a stoichiometric
amount of triethyl amine and dichlorobis(triphenyl phosphine)palladium and copper
iodide as catalyst.[25] However, there have been no reports to date about ethynologs
of coumarins.
The synthetic scheme is based on the reactivity of the 1,2,3-selenadiazolyl ring,
which on pyrolysis affords alkynes as major products. This paves the way for the
synthesis of phenyl sulfonyl ethynylogs of coumarin derivatives. To achieve the tar-
gets species, 3-[2-(phenylsulfonyl)acetyl-2H-chromen-2-ones[22] (3) have been chosen
in which the a-halo methylene group is exploited for developing a selenodiazole ring.
The former on reaction with semicarbazide hydrochloride gave corresponding semi-
carbazones[21] (4), which on oxidative cyclization with selenium dioxide results in
3-(5-(phenylsulfonyl)-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one (5). The reactivity of
5 has been assessed by pyrolysis, leading to the formation of 3-(2-(phenylsulfonyl)
ethynyl)-2H-chromen-2-one (Scheme 1). The method described in the present

SULFONYL ETHYNYLOGS OF COUMARINS
2695
Scheme 1. Synthesis of 3-(2-(arylsulfonyl)ethynyl)-2H-chromen-2-ones.
instance is a facile route. Indeed, the sulfonyl ethylene analogs are valuable synthons
in a number of organic reactions, and a study related to them is in progress.
EXPERIMENTAL
All the reagents and solvents were pure, purchased from commercial sources,
and used without further purification unless otherwise stated. 3-(2-Bromoacetyl)
coumarins[26,27] are prepared by literature procedures. Melting points were determ-
ined in open capillaries with a Cintex melting-point apparatus (Mumbai, India)
and were uncorrected. CHNS analysis was done on a Carlo Erba EA 1108 automatic
elemental analyzer. The purity of the compounds was checked by thin-layer chroma-
tographic (TLC) plates (E. Merek, Mumbai, India), and infrared (IR) spectra (KBr)
1
were recorded on a Bruker WM-4(X) spectrometer (577 model). H NMR spectra
were recorded on a Bruker WM-300 spectometer in d ppm using tetramethylsilane

2696
N. GURAVAIAH AND V. R. RAO
(TMS) as internal standard. Mass spectra (EI-MS) were determined on a Perkin-
Elmer (SCIEX API-2000, ESI) instrument at 12.5 eV.
3-(5-(Phenylsulfonyl)-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one:
General Procedure
Semicarbazone 4 (0.001 mol) was dissolved in acetic acid, and selenium dioxide
(0.001 mol) was added. Then the reaction mixture was heated at reflux temperature
for more than 6 h. The reaction was followed by TLC until completion. After
cooling, the selenium metal deposited was filtered, and the reaction mixture was
poured into ice-cold water and neutralized with saturated sodium carbonate. The
solid separated was filtered, washed with water, dried, and purified by column chro-
matography (silica gel 60–120 mesh, hexane–ethylacetate, 9:1).
Spectral Data of 5a–h
3-(5-(Phenylsulfonyl)-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one (5a).
Yellow solid, yield 92%, mp 198–200 ꢀC. IR (KBr, cmax cmꢁ1): 1150, 1320 (SO2),
1420 (N N), 1610 (C C), 1710 (C O of lactone); 1H NMR (CDCl3, d ppm):
6.90–6.95 (m, 2H, Ar-H), 7.22–7.40 (m, 5H, Ar-H), 7.55–7.61 (m, 2H, Ar-H), 8.15 (s,
1H, C4 of coumarin proton). EI-MS 419 (M þ H)þ. Anal. calcd. for C17H10N2O4SSe:
C, 48.93; H, 2.42; N, 6.71; S, 7.68. Found: C, 48.90; H, 2.47; N, 6.74; S, 7.71%.
=
=
=
6-Bromo-3-(5-(phenylsulfonyl)-1,2,3-selenadiazol-4-yl)-2H-chromen-2-
one (5b). Yellow solid, yield 87%, mp 208–210 ꢀC. IR (KBr, cmax cmꢁ1): 1170, 1330
1
=
=
=
(SO2), 1440 (N N), 1610 (C C), 1730 (C O of lactone). H NMR (CDCl3, d ppm):
7.36–7.40 (m, 3H, Ar-H), 7.53–7.55 (m, 2H, Ar-H), 7.84–7.86 (m, 3H, Ar-H), 8.12 (s,
1H, C4 of coumarin proton). Anal. calcd. for C17H9BrN2O4SSe: C, 41.15; H, 1.83;
N, 5.65; S, 6.46. Found: C, 41.18; H, 1.87; N, 5.69; S, 6.49%.
6,8-Dibromo-3-(5-(phenylsulfonyl)-1,2,3-selenadiazol-4-yl)-2H-chromen-
2-one (5c). Yellow solid, yield 78%, mp 228–230 ꢀC. IR (KBr, cmax cmꢁ1): 1150,
1
=
=
=
1315 (SO2), 1460 (N N), 1612 (C C), 1715 (C O of lactone). H NMR (CDCl3,
d ppm): 7.38–7.97 (m, 7H, Ar-H), 8.12 (s, 1H, C4 of coumarin proton). Anal. calcd.
for C17H8Br2N2O4SSe: C, 35.50; H, 1.40; N, 4.87; S, 5.58. Found: C, 35.58; H, 1.44;
N, 4.91; S, 5.60%.
6,8-Dichloro-3-(5-(phenylsulfonyl)-1,2,3-selenadiazol-4-yl)-2H-chromen-
2-one (5d). Yellow solid, yield 83%, mp 188–190 ꢀC. IR (KBr, cmax cmꢁ1): 1150,
1
=
=
=
1350 (SO2), 1430 (N N), 1612 (C C), 1720 (C O of lactone). H NMR (CDCl3,
d ppm): 7.15–7.55 (m, 7H, Ar-H), 8.50 (s, 1H, C4 of coumarin proton). Anal. calcd.
for C17H8Cl2N2O4SSe: C, 42.00; H, 1.66; N, 5.76; S, 6.60. Found: C, 42.10; H, 1.70;
N, 5.79; S, 6.64%.
3-(5-Tosyl-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one (5e). Yellow solid,
yield 91%, mp 192–194 ꢀC. IR (KBr, cmax cmꢁ1): 1150, 1340 (SO2), 1430 (N N),
=
1620 (C C), 1720 (C O of lactone). 1H NMR (CDCl3, d ppm): 2.35 (S, 3H,
CH3), 7.52–7.70 (m, 4H, Ar-H), 7.80–8.10 (m, 4H, Ar-H), 8.5 (s, 1H, C4 of coumarin
proton). EI-MS 433 (M þ H)þ. Anal. calcd. for C18H12N2O4SSe: C, 50.12; H, 2.80;
N, 6.49; S, 7.43. Found: C, 50.16; H, 2.84; N, 6.52; S, 7.46%.
=
=

SULFONYL ETHYNYLOGS OF COUMARINS
2697
6-Bromo-3-(5-tosyl-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one
(5f).
Yellow solid, yield 82%, mp 200–202 ꢀC. IR (KBr, cmax cmꢁ1): 1130, 1355 (SO2),
1480 (N N), 1616 (C C), 1726 (C O of lactone). 1H NMR (CDCl3, d ppm):
2.40 (S, 3H, CH3), 7.36–7.41 (m, 5H, Ar-H), 7.65–7.83 (m, 2H, Ar-H), 8.11 (s,
1H, C4 of coumarin proton). Anal. calcd. for C18H11BrN2O4SSe: C, 42.37; H,
2.17; N, 5.49; S, 6.28. Found: C, 42.32; H, 2.19; N, 5.52; S, 6.32%.
=
=
=
6,8-Dibromo-3-(5-tosyl-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one (5g).
Yellow solid, yield 75%, mp 221–223 ꢀC. IR (KBr, cmax cmꢁ1): 1150, 1365 (SO2),
1
=
=
=
1425 (N N), 1605 (C C), 1715 (C O of lactone); H NMR (CDCl3, d ppm) 2.44
(S, 3H, CH3), 7.36–7.41 (m, 4H, Ar-H), 7.63–7.72 (m, 2H, Ar-H), 8.11 (s, 1H, C4
of coumarin proton). Anal. calcd. for C18H10Br2N2O4SSe: C, 36.70; H, 1.71; N,
4.76; S, 5.44. Found: C, 36.74; H,1.76; N, 4.79; S, 5.49%.
6,8-Dichloro-3-(5-tosyl-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one (5h).
1
Yellow solid, yield 79%, mp 205–207 ꢀC. H NMR (CDCl3, d ppm) 2.40 (s, 3H,
CH3), 7.70–7.90 (m, 6H, Ar-H), 8.35 (s, 1H, C4 of coumarin proton). Anal. calcd.
for C18H10Cl2N2O4SSe: C, 43.22; H, 2.02; N, 5.60; S, 6.41. Found: C, 43.25; H,
2.00; N, 5.63; S, 6.44%.
3-(2-(Phenylsulfonyl)ethynyl)-2H-chromen-2-one: General Procedure
3-(5-(Phenylsulfonyl)-1,2,3-selenadiazol-4-yl)-2H-chromen-2-one 4 (0.001 mol)
was heated for 15 min above its melting point. After completion of the reaction,
as monitored by TLC, the reaction mass was poured into water, stirred for 10 min,
filtered, and dried. The crude product was purified by column chromatography
(ethyl acetate=hexane, 1:9). All the other compounds were prepared similarly.
Spectral Data of 6a–h
3-(2-(Phenylsulfonyl)ethynyl)-2H-chromen-2-one (6a). Red solid, yield
90%, mp 180–182 ꢀC. IR (KBr, cmax cmꢁ1): 1156, 1346 (SO2), 1746 (C O of lactone),
=
2210 (CꢂC). 1H NMR (CDCl3, d ppm): 7.25–7.40 (m, 2H, Ar-H), 7.50–7.60 (m, 2H,
Ar-H), 7.63–7.80 (m, 5H, Ar-H), 8.61 (s, 1H, C4 of coumarin proton). EI-MS 311
(M þ H)þ. Anal. calcd. for C17H10O4S: C, 65.80; H, 3.25; S, 10.33. Found: C,
65.83; H, 3.27; S, 10.35%.
6-Bromo-3-(2-(phenylsulfonyl)ethynyl)-2H-chromen-2-one
(6b). Red
solid, yield 85%, mp 168–170 ꢀC. IR (KBr, cmax cmꢁ1): 1152, 1331 (SO2), 1723
(C O of lactone), 2192 (CꢂC). 1H NMR (CDCl3, d ppm): 7.25–7.60 (m, 8H,
=
Ar-H), 8.55 (s, 1H, C4 of coumarin proton). Anal. calcd. for C17H9BrO4S: C,
52.46; H, 2.33; S, 8.24. Found: C, 52.49; H, 2.35; S, 8.27%.
6,8-Dibromo-3-(2-(phenylsulfonyl)ethynyl)-2H-chromen-2-one
(6c).
Red solid, yield 79%, mp 208–210 ꢀC. IR (KBr, cmax cmꢁ1): 1156, 1324 (SO2),
1
=
1725 (C O of lactone), 2270 (CꢂC). H NMR (CDCl3, d ppm): 7.25–8.10 (m,
7H, Ar-H), 8.56 (s, 1H, C4 of coumarin proton). Anal. calcd. for C17H8Br2O4S: C,
43.62; H, 1.72; S, 6.85. Found: C, 43.65; H, 1.75; S, 6.87%.

2698
N. GURAVAIAH AND V. R. RAO
6,8-Dichloro-3-(2-(phenylsulfonyl)ethynyl)-2H-chromen-2-one (6d). Red
solid, yield 88%, mp 198–200 ꢀC. IR (KBr, cmax cmꢁ1): 1179, 1367 (SO2), 1727 (C O
of lactone), 2275 (CꢂC). 1H NMR (CDCl3, d ppm): 7.22–7.55(m, 7H, Ar-H), 8.55 (s,
1H, C4 of coumarin proton). Anal. calcd. for C17H8Cl2O4S: C, 53.84; H, 2.13; S,
8.46. Found: C, 53.87; H, 2.16; S, 8.49%.
=
3-(2-Tosylethynyl)-2H-chromen-2-one (6e). Red solid, yield 93%, mp
168–170 ꢀC. IR (KBr, cmax cmꢁ1): 1150, 1331 (SO2), 1720 (C O of lactone), 2232
=
1
(CꢂC); H NMR (CDCl3, d ppm): 2.70 (s, 3H, CH3), 7.20–7.30 (m, 5H, Ar-H),
7.50–7.70 (m, 2H, Ar-H), 7.95–8.0 (m, 1H, Ar-H), 8.45 (s, 1H, C4 of coumarin pro-
ton). EI-MS 325 (M þ H)þ. Anal. calcd. for C18H12O4S: C, 66.65; H, 3.73; S, 9.89.
Found: C, 66.68; H, 3.71; S, 9.91%.
6-Bromo-3-(2-tosylethynyl)-2H-chromen-2-one (6f). Red solid, yield 88%,
mp 180–182 ꢀC. IR (KBr, cmax cmꢁ1): 1156, 1331 (SO2), 1726 (C O of lactone), 2250
=
1
(CꢂC); H NMR (CDCl3, d ppm): 2.28 (s, 3H, CH3), 7.50–7.60 (m, 2H, Ar-H),
7.62–7.80 (m, 4H, Ar-H), 8.05 (s, 1H, Ar-H), 8.55 (s, 1H, C4 of coumarin proton).
Anal. calcd. for C18H11BrO4S: C, 53.61; H, 2.75; S, 7.95. Found: C, 53.59; H,
2.73; S, 7.98%.
6,8-Dibromo-3-(2-tosylethynyl)-2H-chromen-2-one (6g). Red solid, yield
76%, mp 178–180 ꢀC. IR (KBr, cmax cmꢁ1): 1135, 1350 (SO2), 1730 (C O of lactone),
=
1
2215 (CꢂC); H NMR (CDCl3, d ppm 1.95 (s, 3H, CH3), 7.0–7.18 (m, 6H, Ar-H),
8.45 (s, 1H, C4 of coumarin proton). Anal. calcd. for C18H10Br2O4S: C, 44.84; H,
2.09; S, 6.65. Found: C, 44.87; H, 2.0; S, 6.61%.
6,8-Dichloro-3-(2-tosylethynyl)-2H-chromen-2-one (6h). Red solid, yield
80%, mp 188–190 ꢀC. IR (KBr, cmax cmꢁ1): 1130, 1330 (SO2), 1725 (C O of lactone),
=
2234 (CꢂC); 1H NMR (CDCl3, d ppm) 2.65 (s, 3H, CH3), 7.25–7.40 (m, 2H, Ar-H),
7.60–7.75 (m, 4H, Ar-H), 8.50 (s, 1H, C4 of coumarin proton). Anal. calcd. for
C18H10Cl2O4S: C, 54.98; H, 2.56; S, 8.15. Found: C, 54.94; H, 2.58; S, 8.19%.
CONCLUSIONS
In conclusion, we have developed a simple, inexpensive, and efficient strategy
for phenyl sulfonyl ethynylogs of coumarins without using any catalyst.
ACKNOWLEDGMENT
Financial support from the Council of Scientific and Industrial Research,
New Delhi, for the project (No. 01 (2062) 06=EMR-II) is gratefully acknowledged.
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