R. Shankar et al. / Tetrahedron Letters 47 (2006) 3077–3079
3079
ketones including tetralone, benzosuberone, benzoin
and acetylacetone. The mildness of the reaction condi-
tions prompted us to explore different nucleophiles like
indole, imidazole, benzenethiol and piperidine (Table
1) and found the reaction to be equally efficient. Among
different phase-transfer catalysts such as TBAF, TBAC,
TBAB, TBAI and benzyltrimethylammoniun hydroxide
solution (Triton B, 40% in water) that were used, tetra-
n-butylammonium iodide was found to give the best
results.
In conclusion, we have successfully demonstrated a very
efficient and mild conjugate addition of various nucleo-
philes to 1,3-diphenyl propenones or propynones by the
use of only catalytic amounts of 10% aqueous sodium
hydroxide in combination with TBAI in dimethyl sulf-
oxide. The ease of workup and good yields of diketone
products are significant improvements over existing
methods that chiefly employ expensive metal catalysts.
Transformation of diketones into a new class of biolog-
ical active compounds is in progress and will be pub-
lished soon.
The success with 1,3 diaryl alkenones prompted us to
explore conjugate addition to alkynones. The reaction
was carried out with 1,3-diaryl propynones under simi-
lar reaction conditions. However, with alkynones the
reaction times were longer and the yields of diketones
were also moderate ranging between 42% and 52% for
the cyclic ketones, but with acyclic ketones, thiols and
amines the yields were higher and ranged between 55%
and 72%. Further, recovery of phenylacetylene and
benzoic acid from column chromatography indicated
decomposition of alkynones under prolonged basic
conditions.
Acknowledgements
The authors Ravi Shankar and Ashok K. Jha thank
CSIR for JRF, SRF fellowships and Uma Sharan Singh
is grateful for an MOH fellowship and all are grateful to
SAIF for spectroscopic analysis of the compounds.
References and notes
1. Bergmann, E. D.; Ginsburg, D.; Pappo, R. Org. React.
1959, 10, 179.
General experimental procedure: To a solution of benzene-
thiol (110 mg, 1 mmol) dissolved in dimethyl sulfoxide
(5 ml) were added tetra-n-butylammonium iodide
(10 mg) and 10% aq NaOH solution (0.5 ml). The mix-
ture was stirred at rt for 30 min. Thereafter, 1-(4-meth-
oxyphenyl)-3-phenyl-propynone (1 mmol, 236 mg) was
added and the solution stirred for another 15 min. On
completion of the reaction (TLC), the mixture was
quenched with water (5 ml) resulting in precipitation
of the product. Filtration, washing with water and
recrystallization from benzene–hexane gave pure adduct
5A (202 mg), yield; 68%, mp 108 °C, 1H NMR
(200 MHz, CDCl3): d 8.03, (d, J = 9 Hz, 2H), 7.25–
7.03 (m, 11H), 6.92, (d, J = 9 Hz, 2H) and 3.88 (s, 3H,
OCH3). 13C NMR (50 MHz, CDCl3): d 187.8, 163.5,
161.1, 139.3, 134.6, 133.3, 131.8, 130.8, 129.3, 128.7,
120.5, 114.2, 110.0, 55.8. IR (KBr) cmÀ1 1632, 1594,
1536, 1507–1440, 2843. HRMS: Calcd for C22H18O2S:
346.1028, measured mass 346.1018. Reaction with 1,3-
diphenyl propenone and benzenethiol gave adduct 5B
2. Periasamy, M. ARKIVOC 2002, VIII, 151–166.
3. (a) Loh, T. P.; Wei, L. I. Synlett 1998, 975–976; (b) Ranu,
B.; Dey, S. S.; Samanta, S. ARKIVOC 2005, III, 44–50.
4. (a) Christoffers, J. Synlett 2001, 6, 723–732; (b) Pelzer, S.;
Kauf, T.; Willen, C. V.; Christoffers, J. J. Organomet.
Chem. 2003, 684, 308–314.
5. (a) Kobyashi, S.; Ogawa, C.; Kawamura, M.; Sugiura, M.
Synlett 2001, 983–985; (b) Zhan, Z. P.; Yang, R. F.; Lang,
K. Tetrahedron Lett. 2005, 46, 3859–3862.
6. Srivastava, N.; Banik, B. K. J. Org. Chem. 2003, 68, 2109–
2114.
7. (a) Varala, R.; Alam, M. M.; Adapa, S. R. Synlett 2003,
720–722; (b) Alam, M. M.; Varala, R.; Adapa, S.
Tetrahedron Lett. 2003, 44, 5115–5119.
8. Garg, S. K.; Kumar, R.; Chakraborti, A. K. Tetrahedron
Lett. 2005, 46, 1721–1724.
9. (a) Bartoli, G.; Bartolacci, M.; Giuliani, A.; Marcantoni,
E.; Massaccesi, M.; Torregiani, E. J. Org. Chem. 2005, 70,
169–174; (b) Yang, L.; Xu, L. W.; Xia, C. G. Tetrahedron
Lett. 2005, 46, 3279–3282; (c) Arcadi, A.; Bianchi, G.;
Chiani, M.; Gaetano, D.; Marinelli, F. Synlett 2004, 944–
950; (d) Ji, S. J.; Wang, S. Y. Synlett 2003, 2074–2076.
10. (a) Banik, B. K.; Fernandez, M.; Alvarez, C. Tetrahedron
Lett. 2005, 46, 2479–2482; (b) Chu, C-Fa. Tetrahedron
Lett. 2005, 46, 4971–4974.
11. Genisson, Y.; Gorrichon, L. Tetrahedron Lett. 2000, 41,
4881–4884.
12. Dere, R. T.; Pal, R. R.; Patil, P. S.; Salunkhe, M. M.
Tetrahedron Lett. 2003, 44, 5351–5353.
1
(220 mg), yield; 70%, mp 120 °C, H NMR (200 MHz,
CDCl3): d 7.86 (d, J = 8.6 Hz, 2H), 7.45–7.13 (m,
13H), 4.96 (t, J = 14.2 Hz, 1H), 3.65 (m, 2H). 13C
NMR (50 MHz, CDCl3): d 187.8, 163.5, 161.1, 139.3,
134.6, 133.3, 131.8, 130.8, 129.4, 128.7, 127.9, 127.5,
120.5, 114.2, 55.8, 31.3. IR (KBr) cmÀ1 1677, 1592,
1480–1450, 2903. HRMS: Calcd for C21H18OS:
318.1078, measured mass 318.1069.