6538
P. Gao et al. / Tetrahedron Letters 49 (2008) 6536–6538
excellent points and suggestions made before finalizing this
manuscript.
Na
OH
O
δ+
O
O
B
OH
O
B
B
B
O
δ-
O
References and notes
Na
S
H
1. (a) Luly, J. R.; Yi, N.; Soderquist, J.; Stein, H.; Cohen, J.; Perun, T. J.; Platter, J. J. J.
Med. Chem. 1987, 30, 1609; (b) Conchillo, A.; Camps, F.; Messeguer, A. J. Org.
Chem. 1990, 55, 1728.
H
O
H
Ph
2. (a) Corey, E. J.; Clark, D. A.; Goto, G.; Marfat, A.; Mioskowski, C.; Samuelsson, B.;
Hammarstroem, S. J. Am. Chem. Soc. 1980, 102, 1436; (b) Corey, E. J.; Clark, D. A.;
Goto, G. Tetrahedron Lett. 1980, 21, 3143.
Figure 1.
3. (a) Chong, J. M.; Sharpless, K. B. J. Org. Chem. 1985, 50, 1560; (b) Vougioukas, A.
E.; Kagan, H. B. Tetrahedron Lett. 1987, 28, 6065; (c) Iqbal, J.; Pandey, A.; Shukla,
A.; Srivastaca, R. R.; Tripathi, S. Tetrahedron 1990, 46, 6423; (d) Chini, M.; Crotti,
P.; Giovani, E.; Macchia, F.; Pineschi, M. Synlett 1992, 303; (e) Still, J. W. J.;
Martin, L. J. P. Synth. Commun. 1998, 28, 913; (f) Sasaki, M.; Tanino, K.;
Miyashita, M. J. Org. Chem. 2001, 66, 5388.
4. (a) Grieco, P. A. Organic Synthesis in Water; Blackie Academic and Professional:
London, 1998; (b) Tundo, P.; Ananstas, P. T. Green Chemistry: Challenging
Perspectives; Oxford University Press: Oxford, 1999; (c) Li, C.-J.; Chan, T.-H.
Comprehensive Organic Reactions in Aqueous Media, 2nd ed.; Wiley: Hoboken,
2007.
5. Fringuelli, F.; Pizzo, F.; Tortoioli, S.; Vaccaro, L. Tetrahedron Lett. 2003, 44, 6785.
6. Fringuelli, F.; Pizzo, F.; Tortoioli, S.; Vaccaro, L. Adv. Synth. Catal. 2002, 344.
7. (a) Amantini, D.; Fringuelli, F.; Pizzo, F.; Tortoioli, S.; Vaccaro, L. Synlett 2003,
2292; (b) Fringuelli, F.; Pizzo, F.; Tortoioli, S.; Vaccaro, L. J. Org. Chem. 2003, 68,
8248.
reaction time (9 h), borax-catalyzed ring opening of epoxide 1h in
water gave rise to 3ha18 in 90% yield. In contrast, replacement of
borax with Lewis bases such as DABCO or Et3N10 (PhSH (1.1 equiv),
H2O, rt, 12 h) resulted in very low yields (11–15%) of the product.
While thiolysis of trisubstituted epoxide 1j furnished 3ja in excel-
lent yield (92%) with borax as the catalyst, poor regioselectivity
and low yields were obtained when TsOH,5 ZnCl2,7 or InCl36-cata-
lyzed reactions (a/b = 43:57–55:45). For chloro epoxide 1e, the
reaction stopped at the ring opening stage (3ea); the potential tan-
dem chloride displacement failed to take place (entry 10). The
opposite regioselectivity was obtained with the spiro epoxide 1i
6
7a
(entry 14) if InCl3 or ZnCl2 was employed instead of borax.
A tentative mechanism (Fig. 1) has been postulated in order to
illustrate the present reaction rate enhancement in comparison
with other base-catalyzed ring opening reactions. Borax might
act as a bifunctional catalyst, which could bring the epoxide and
the thiol into close proximity. The capability of boron species to
coordinate to the epoxy oxygen atom, the weak basicity of the
aqueous medium, and the hydrogen bonding might be among
the most significant factors for this transformation.
In summary, a ‘green’, convenient, economical, and practical
protocol for borax-catalyzed thiolysis of 1,2-epoxides in aqueous
medium has been developed, which has expanded the utilities of
borax in organic synthesis. The products were obtained in higher
yields and with better regioselectivity when compared to the Brøn-
sted acid or Lewis acid-catalyzed reactions. In addition, under the
current conditions, the reaction proceeded faster than the Brønsted
base or Lewis base-catalyzed counterparts. Other borax-catalyzed
reactions are under investigation in our laboratory.
8. Fringuelli, F.; Pizzo, F.; Tortoioli, S.; Vaccaro, L. Green Chem. 2003, 5, 436.
9. Fan, R.-H.; Hou, X.-L. J. Org. Chem. 2003, 68, 726.
10. Wu, J.; Xia, H.-G. Green Chem. 2005, 7, 708.
11. Pironti, V.; Colonna, S. Green Chem. 2005, 7, 43.
12. Su, W.; Chen, J.; Wu, H.; Jin, C. J. Org. Chem. 2007, 72, 4524.
13. Hussain, S.; Bharadwai, S. K.; Chaudhuri, M. K.; Kalita, H. Eur. J. Org. Chem. 2007,
374.
14. Smith, B. D.; Morin, G. T. In Encyclopedia of Reagents for Organic Synthesis;
Paquette, L. A., Ed.; Wiley: Chichester, 1995; Vol. 7, p 4631 and references cited
therein.
15. General procedure: Thiol (1.1 equiv) was added to a solution of epoxide 1
(1.0 mmol) and borax (10 mol %) in water (2 mL). The reaction mixture was
stirred at rt for the time reported in Table 2. Then the mixture was extracted
with CH2Cl2 (3 Â 5 mL). The combined extracts (dried with Na2SO4) were
concentrated in vacuo and the resulting product was purified on silica gel. All
products except 3 ha are known compounds, the characterization data of
which are identical with those in literature reports.
16. Compounds 1h,16a 1i,16b and 1j16c were obtained following the literature
procedures while other substrates were commercially, available: (a)
Steinreiber, A.; Osprian, I.; Mayer, S. F.; Orru, R. V. A.; Faber, K. Eur. J. Org.
Chem. 2000, 3703; (b) Mosset, P.; Grée, R. Synth. Commun. 1985, 15, 749; (c)
Fringuelli, F.; Germani, R.; Pizzo, F.; Saveli, G. Tetrahedron Lett. 1989, 30, 1427.
17. This
is
presumably
because
the
conformationally
constrained
bicyclo[3.1.0]hexane framework exerts steric hindrance against the addition.
18. Compound 3ha, a colorless liquid: 1H NMR (CDCl3, 300 MHz) d 1.28 (s, 3H),
2.70 (s, 1H), 3.16 (d, J = 13.5 Hz, 1H), 3.23 (d, J = 13.5 Hz, 1H), 3.34 (d, J = 8.7 Hz,
1H), 3.46 (d, J = 8.7 Hz, 1H), 4.43 (s, 2H), 7.18-7.43 (m, 10H); 13C NMR (CDCl3,
75 MHz) d 23.7, 43.1, 72.5, 73.2, 75.4, 126.1, 127.6, 127.7, 128.4, 128.9, 129.4,
136.9, 137.8; MS (EI) m/z 288 (M+, 7), 167 (5), 149 (10), 124 (46), 91 (100). Anal.
Calcd. for C17H20O2S: C, 70.80; H, 6.99. Found: C, 70.72; H, 6.91.
Acknowledgments
Financial support was provided by the grants from NSFC
(90713007; 20772141; 20625204; 20632030) and MOST_863
(2006AA09Z405). We are grateful to all the reviewers for their