[()TD$FIG]
A.H. Yu et al. / Chinese Chemical Letters 22 (2011) 687–690
689
1
R
H
ArSH
2
CsOH
SeR
ArS
H O
H O
2
2
1
+
R
Cs
-
+
ArS Cs
2
1
2
SeR
R
ArS
SeR
Scheme 2. The mechanism for the addition of thiol to alkynyl selenide.
We also compared the catalytic activity of other alkali metal hydroxides; the results are shown in Table 2. As is
apparent from Table 2, the cesium hydroxide showed the strongest catalytic activity for the reaction. The other alkali
metal hydroxides showed lower catalytic activity. The difference in the catalytic activity among the hydroxides is
ascribed to the differing sizes of the alkali metal ions [25]. The cesium ion, which has the largest ionic radius, is
anticipated to be only weakly paired with the counter-anion. Thus the in situ generated cesium aryl sulfide (ArSCs) is
considered to be more nucleophilic than the sulfide conjugated with other alkali metals.
A possible reaction mechanism for the addition reaction of thiols to alkynyl selenide is depicted in Scheme 2. First,
arylthiols reacted with cesium hydroxide to give cesium arylsulfides and H2O. Second, the cesium arylsulfides
underwent nucleophilic addition to the alkynyl selenides to form (Z)-1-organoseleno-2-arylthiovinylic anion, which
reacted with water to give product (Z)-1-organoseleno-2-arylthio-1-alkenes and catalyst cesium hydroxide.
The analysis of 1H NMR and 13C NMR spectra showed that all (Z)-1-organoseleno-2-arylthio-1-alkenes prepared
presented data in full agreement with their assigned structures. The stereochemistry of trisubstituted alkenes was
determined by NOESY experiments. The NOESY NMR experiment of compound 3a showed only a correlation
between the vinylic hydrogen and the methylene hydrogen bonded to the methoxy, indicating a cis relation between
them.
In conclusion, a mild, efficient and highly stereo-, and regioselective method for the synthesis of (Z)-1-
organoseleno-2-arylthio-1-alkenes was developed. The present method use air-stable cesium hydroxide as catalyst,
require neither the high temperature nor the use of expensive transition metals. It could provide a new and expedient
way for the preparation of (Z)-1-organoseleno-2-arylthio-1-alkenes. The hydroselenolation, hydrophosphination of
alkynyl sulfides and selenides as well as phosphines catalyzed by cesium hydroxide will be reported soon.
1. Experimental
Arylthiol (1.2 mmol) and cesium hydroxide (0.1 mmol) were added to a solution of alkynyl selenide (1.0 mmol) in
DMF (2.0 mL). The reaction mixture was stirred at room temperature under a nitrogen atmosphere for a period time
listed in Table 1. Then 20 mL of water was added to the mixture and extracted with petroleum ether (3 Â 30 mL). The
combined organic phase was dried over anhydrous Na2SO4, and concentrated under vacuum. The residue was purified
by flash chromatography on silica gel giving products. Compound 3a: 1H NMR (400 MHz, CDCl3): d 2.26 (s, 3H),
3.02 (s, 3H), 3.81 (s, 2H), 7.04 (d, 2H, J = 8.0 Hz), 7.08 (s, 1H), 7.23–7.25 (m, 5H), 7.50–7.52 (m, 2H). 13C NMR
(100 MHz, CDCl3): d 21.1, 57.9, 74.7, 127.7, 129.3, 129.4, 129.8, 130.5, 130.7, 131.8, 131.8, 133.0, 137.2. MS(EI), m/
z (%): 350 (M+, 100). Anal. Calcd. for C17H18OSSe: C 58.38, H 5.16, Found: C 58.45, H 5.13.
Acknowledgments
We are grateful to Natural Science Foundation of Hunan (No. 2009NK3162) and National Natural Science
Foundation of China (No. 21003040, 20372020) for financial support.