Studies on sulfoxide rearrangements: Regioselective synthesis of 3-(aryloxyacetyl)-2,3-dihydrothieno[3,2-c][1]benzopyran-4-ones

Article abstract of DOI:10.1016/S0040-4039(02)00200-9

Hitherto unreported 3-(aryloxyacetyl)-2,3-dihydrothieno[3,2-c][1] benzopyran-4-ones 5a-f were synthesised in 70-75% yields by the application of the sulfoxide rearrangement of 4-(4-aryloxybut-2-ynylthio)[1]benzopyran-2-ones 4a-f. The substrates 4a-f were

Full text of DOI:10.1016/S0040-4039(02)00200-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2123–2125
Studies on sulfoxide rearrangements: regioselective synthesis of
3-(aryloxyacetyl)-2,3-dihydrothieno[3,2-c][1]benzopyran-4-ones
K. C. Majumdar* and S. K. Ghosh
Department of Chemistry, University of Kalyani, Kalyani 741235, West Bengal, India
Received 19 November 2001; accepted 24 January 2002
Abstract—Hitherto unreported 3-(aryloxyacetyl)-2,3-dihydrothieno[3,2-c][1] benzopyran-4-ones 5a–f were synthesised in 70–75%
yields by the application of the sulfoxide rearrangement of 4-(4-aryloxybut-2-ynylthio)[1]benzopyran-2-ones 4a–f. The substrates
4a–f were synthesised by phase-transfer-catalysed alkylation of previously unreported 4-mercaptocoumarin. © 2002 Elsevier
Science Ltd. All rights reserved.
Some thienocoumarins are known to possess anti-
inflammatory, antipyretic and antiallergic properties.1
The construction of the five-membered heterocyclic
rings in benzo(b)thiophenes and indoles through
sulfoxide2–5 and amine oxide6–8 rearrangements, respec-
tively, was reported by Majumdar and Thyagarajan.
This protocol when applied to selenium analogues9
proceeded with different results. Application of the
amine oxide rearrangement10–12 in heterocyclic
substrates13,14 for the synthesis of a number of tricyclic
skeletons has been reported from this laboratory.
Whilst amine oxides rearrange in dichloromethane at
room temperature, the corresponding sulfoxides require
refluxing in carbon tetrachloride. Both the amine oxide
and sulfoxide rearrangement involve the intermediacy
of a [2,3] and a [3,3] sigmatropic rearrangement. Very
recently Majumdar et al. reported the regioselective
synthesis of thieno[2,3-f ]quinolin-7(6H)-one and
pyrano[3,2-f ]benzo-[b]thiophene derivatives15,16 by the
application of sulfoxide rearrangements.
phase-transfer catalysed alkylation of 4-mercaptocou-
marin 1 with 1-chloro-4-aryloxy-but-2-yne 2a–f using
benzyltriethyl ammonium chloride (BTEAC) in
aqueous NaOH and chloroform. The PTC alkylation is
faster and gives a higher yield of the S-alkylated prod-
ucts (3a–f, 70–80%) over the classical alkylation using
K2CO3 and acetone. Classical alkylation in the case of
3e gave a 55% yield but in other cases a tendency to
decompose was observed (Scheme 1).
Compounds 3a–f are all solids and were characterised
from their elemental analyses and spectroscopic data.17
This exceedingly facile and simple reaction for the
construction of five-membered heterocyclic rings moti-
vated us to undertake a study to synthesise heterocyclic
compounds from 4-(4-aryloxybut-2-ynylthio)[1]benzo-
pyran-2-ones 3a–f for the synthesis of new heterocyclic
compounds. We now report our results.
The substrates 4-(4-aryloxybut-2-ynylthio)[1]benzo-
pyran-2-ones 3a–f for this study were prepared by
* Corresponding author. Fax: 0091-33-5828282; e-mail: kcm@
klyuniv.ernet.in
Scheme 1.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00200-9

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K. C. Majumdar, S. K. Ghosh / Tetrahedron Letters 43 (2002) 2123–2125
Scheme 2.
The sulphides 3a–f were oxidised to the corresponding
sulfoxides 4a–f by slow addition of 1 equiv. of m-
chloroperoxybenzoic acid in chloroform at 0–5°C over
30 min. The formation of a new product was indicated
by a single spot (TLC monitoring) and by the disap-
pearance of the starting sulphide (Scheme 1).
Acknowledgements
We are thankful to CSIR (New Delhi) for financial
assistance. One of us (S.K.G) is grateful to CSIR for a
fellowship.
The sulfoxides 4a–f are quite unstable. They rearrange
even during work up of the reaction mixture. There-
fore, no attempt was made to characterise them. They
were directly subjected to thermal rearrangement with-
out further purification. The sulfoxide 4a was refluxed
in carbon tetrachloride to give the compound 5a in 70%
yield (Scheme 1). Compound 5a was characterised from
its elemental analysis and spectroscopic data.18
References
1. Makisumi, Y. Jpn Kokai, 73, 00,597 (cl. 16E622), 1972;
Chem. Abstr. 1973, 78, 72097.
2. Thyagarajan, B. S.; Majumdar, K. C. J. Chem. Soc.,
Chem. Commun. 1972, 83.
3. Majumdar, K. C.; Thyagarajan, B. S. Int. J. Sulfur Chem.
1972, 2A, 93.
To test the generality of the reaction five other sub-
strates 4b–f were subjected to sulfoxide rearrangement
under the same reaction conditions. All the substrates
4. Majumdar, K. C.; Thyagarajan, B. S. Int. J. Sulfur Chem.
1972, 2A, 67.
5. El-Osta, B.; Majumdar, K. C.; Thyagarajan, B. S. J.
Heterocyclic Chem. 1973, 10, 107.
1
gave similar products 5b–f in 70–75% yields. In the H
NMR spectra of 5a–f except for 5d, one of the -S-CH2-
6. Hillard, J. B.; Thyagarajan, B. S.; Reddy, K. V.; Majum-
dar, K. C. Tetrahedron Lett. 1974, 1999.
7. Hillard, J. B.; Reddy, K. V.; Majumdar, K. C.; Thyara-
gajan, B. S. J. Heterocyclic Chem. 1974, 11, 369.
8. Thyagarajan, B. S.; Majumdar, K. C. J. Heterocyclic
Chem. 1975, 12, 43.
9. Reich, H. J.; Shah, S. K. J. Am. Chem. Soc. 1977, 99,
263.
10. Majumdar, K. C.; Chattopadhyay, S. K. J. Chem. Soc.,
1
protons appeared as triplet. However, in the H NMR
spectrum of 5d these two protons appeared as two
double doublets.
The formation of products 5a–f from the sulfoxides
4a–f may be rationalised by an initial [2,3] sigmatropic
rearrangement of the sulfoxides 4 to give the intermedi-
ate allenylsulphenates 7 followed by a [3,3] sigmatropic
rearragement and enolisation leading to the intermedi-
ates 9 containing an enone moiety favourably juxta-
posed to a -SH function for an internal Michael
addition of the thiol to the enone to yield 5a–f (Scheme
2).
Chem. Commun. 1987, 524.
11. Majumdar, K. C.; Chattopadhyay, S. K.; Khan, A. T. J.
Chem. Soc., Perkin Trans. 1 1989, 1285.
12. Majumdar, K. C.; Ghosh, S. K. J. Chem. Soc., Perkin
Trans. 1 1994, 2889.
13. Majumdar, K. C.; Das, U.; Jana, N. K. J. Org. Chem.
This method is found to be general for the synthesis of
3 - (aryloxyacetyl) - 2,3 - dihydrothieno[3,2 - c][1]benzo-
pyran-4-ones (5a–f) in good yields. This is also an
example of the application of a sulfoxide rearrangement
in heterocyclic substrates to furnish polyheterocycles.
1998, 63, 3550.
14. Majumdar, K. C.; Biswas, P.; Jana, G. H. J. Chem. Res.
(S) 1997. 310; (M) 1997, 2068.
15. Majumdar, K. C.; Biswas, P. Tetrahedron 1998, 54,
11603.

K. C. Majumdar, S. K. Ghosh / Tetrahedron Letters 43 (2002) 2123–2125
2125
16. Majumdar, K. C.; Biswas, P. Tetrahedron 1999, 55, 1449.
18. Compound 5a: mp 138°C; yield 70%; UV (EtOH) umax
:
217, 270, 329 nm; IR (KBr) wmax: 1715, 1700, 1590, 1250
cm−1; 1H NMR (500 MHz): l 3.73 (dd, 1H, J=9, 12 Hz),
3.82 (dd, 1H, J=6, 12 Hz), 4.86 (dd, 1H, J=6, 9 Hz),
4.95 (d, 1H, J=15 Hz), 4.99 (d, 1H, J=15 Hz), 6.93–7.58
(m, 9H); m/z 338 (M+). Anal. calcd for C19H14O4S: C,
67.45; H, 4.14. Found: C, 67.58; H, 4.23%.
17. Compound 4a: mp 108°C; yield 75%; UV (EtOH) umax
:
218, 271 nm; IR (KBr) wmax: 1690, 1580, 1230 cm−1; H
NMR (300 MHz): l 3.82 (t, 2H, J=2 Hz), 4.71 (t, 2H,
J=2 Hz), 6.28 (s, 1H), 6.92–7.73 (m, 9H); m/z 322 (M+).
Anal. calcd for C19H14O3S: C, 70.80; H, 4.35. Found: C,
70.67; H, 4.19%.
1