J.S. Dhau, A. Singh / Journal of Organometallic Chemistry 749 (2014) 109e114
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1H), 7.38e7.40 (d, J ¼ 7.84 Hz,1H), 7.22e7.26 (m, J ¼ 6.80 Hz,1H), 3.76
(s, 2H), 2.00 (s, 3H). 13C NMR: DMSO-d6, 400 MHz
(ppm): 158.4,
148.9, 136.6, 122.9, 120.8, 39.5, 14.5. MS (EI): 139 (100), 107 (58), 93
(91), 66 (64), 51 (15). Anal. Calcd (%) for C7H9NS: C, 60.39, H, 6.51, N,
10.06 S, 23.02. Found: C, 60.44, H, 6.49, N, 10.05 S, 23.06.
stirred for 15e20 min at ꢁ78 ꢀC and DMDS (4.65 g, 4.44 mL,
49.5 mmol) was added to it. 5b and 7b were obtained in 10%
(0.22 g) and 71% (2.60 g) yields.
d
4.4.3.1. 3-Methyl-2-(tris(methylsulfanyl)methyl)pyridine [18] (7b).
M.p. 96e98 ꢀC. 1H NMR: DMSO-d6, 400 MHz
d (ppm): 8.29e8.31
4.2.4. 3-Methyl-2-(methylsulfanylmethyl)pyridine (5b)
(dd, J ¼ 1.12 Hz, 4.48 Hz, 1H), 7.65e7.67 (dd, J ¼ 0.88 Hz, 7.60 Hz,
Substrate:e1b, Electrophile:eDMDS (1.55 g, 1.48 mL,
1H), 7.27e7.31 (dd, J ¼ 4.68 Hz, 7.58 Hz,1H), 2.76 (s, 3H),1.80 (s, 9H).
16.5 mmol), Yield: 1.69 g (74%). 1H NMR: DMSO-d6, 400 MHz
13C NMR: DMSO-d6, 400 MHz
d (ppm): 154.3, 143.9, 140.9, 132.1,
d
(ppm): 8.24e8.25 (d, J ¼ 4.40 Hz, 1H), 7.46e7.48(d, J ¼ 7.36 Hz,
1H), 7.07e7.08 (d, J ¼ 7.00 Hz, 1H), 3.78 (s, 2H), 2.39 (s, 3H), 2.19 (s,
3H). 13C NMR: DMSO-d6, 400 MHz
(ppm): 156.5, 146.0, 136.6,
123.1, 79.2, 20.2, 12.9. MS (EI): 245 (11), 198 (100),150 (73), 136 (82),
117 (41), 92 (35), 65 (40). Anal. Calcd (%) for C10H15NS3:C, 48.94, H,
6.16, N, 5.70, S, 39.19. Found: C, 48.89, H, 6.20, N, 5.68, S, 39.23.
d
131.0, 121.1, 37.1, 22.1, 18.5. MS (EI): 153 (7), 136 (19), 107 (100), 92
(67), 77 (83), 65 (84), 51 (67). Anal. Calcd (%) for C8H11NS: C, 62.70,
H, 7.23, N, 9.13, S, 20.92. Found: C, 62.92, H, 7.12, N, 9.15, S, 20.48.
4.4.4. 1,2-Bis(6-iodopyridin-2-yl)ethane (8a)
Iodine (8.38 g, 33.0 mmol) was added to the solution containing
15.0 mmol of DL-3a (formed as in section 4.4.) at ꢁ78 ꢀC. The
temperature was slowly raised to ambience temperature with
constant stirring. The color of the solution changed from reddish
brown to dark brown and after 30 min stirring at room temperature
the reaction mixture was hydrolyzed with cold water and stirred
for 5 min. The organic layer was extracted with diethyl ether,
washed with water, sodium thiosulfate solution and then again
with water. The organic layer was dried over anhydrous sodium
sulfate. The solvent was removed and the crude product was
refrigerated. The crude product was purified by column chroma-
tography using 60e120 mesh silica gel and using hexane-ethyl
acetate as an eluent (5:1). Yield: 2.41 g (74%), m.p. 146e149 ꢀC. 1H
4.3. General procedure 2: monolithiation of 1a and 1b without
BF3.Et2O complexation
A solution of 1a (1.39 g,1.48 mL,15.0 mmol) or 1b (1.60 g,1. 64 mL,
15.0 mmol) in diethyl ether (50 mL) was cooled to ꢁ78 ꢀC in a three-
necked 100 mL RBF. LDA (16.5 mmol) was slowly added via cannula
to this solution. The color of suspension changed to pale yellow in
about 10 min. The resulting pale yellow solution containing the
carbanion was then stirred for 15e20 min at ꢁ78 ꢀC and quenched
with different electrophiles (16.5 mmol) and worked up as above.
4.4. General procedure 3: dilithiation of 1a and 1b with BF3.Et2O as
the complexing agent
NMR: DMSO-d6, 400 MHz
d
(ppm): 7.71e7.73 (dd, J ¼ 0.52 Hz,
7.68 Hz, 2H), 7.44e7.48 (t, J ¼ 7.44 Hz, 2H), 735e7.37 (dd,
J ¼ 0.52 Hz, 7.64 Hz, 2H), 3.11(s, 4H). 13C NMR: DMSO-d6, 400 MHz
A solution of 1a (1.39 g, 1.48 mL, 15.0 mmol) or 1b (1.60 g, 1.
64 mL, 15.0 mmol) in diethyl ether (50 mL) was cooled to 0 ꢀC in a
three-necked 100 mL RBF and BF3.Et2O in diethyl ether (2.34 g,
2.07 mL, 16.5 mmol) was added to it. The temperature of the RBF
was lowered to ꢁ78 ꢀC and LDA (33.0 mmol) was added slowly via
cannula. The resulting dark reddish brown solution containing the
anionic species was then stirred for 15e20 min at ꢁ78 ꢀC and was
labeled as DL-3a or DL-3b. DMDS (3.1 g, 2.96 mL, 33.0 mmol) was
added to it at ꢁ78 ꢀC and the temperature was slowly raised to the
room temperature. The reaction mixture was cooled, extracted and
purified as previously.
d (ppm): 162.6, 138.6, 132.2, 122.5, 118.1, 36.2. MS (EI): 436 (100),
309 (13), 232 (66), 181 (29), 154 (33), 127 (26), 91 (89), 77 (53), 64
(69), 51 (45). Anal. Calcd (%) for C12H10N2I2: C, 33.05, H, 2.31, N, 6.42.
Found: C, 33.08, H, 2.36, N, 6.40.
4.4.5. 1,2-Bis(6-iodo-3-methylpyridin-2-yl)ethane (8b)
Iodine (8.38 g, 33.0 mmol) was added to the solution containing
DL-3b (15.0 mmol) at ꢁ78 ꢀC and the rest of the procedure is same
as above. Yield: 3.17 g (92%), m.p. 109e111 ꢀC. 1H NMR: DMSO-d6,
400 MHz
d
(ppm): 7.44e7.46 (d, J ¼ 7.80 Hz, 2H), 7.13e7.15 (d,
J ¼ 7.92 Hz, 2H), 3.09(s, 4H) 2.24 (s, 6H). 13C NMR: DMSO-d6,
400 MHz d (ppm): 161.0, 139.3, 131.7, 130.8, 113.7, 32.1, 17.6. MS (EI):
4.4.1. Substrate:e1a
464 (100), 337 (11), 209 (13), 184 (17), 91 (17), 77 (20), 65 (12), 51
(10). Anal. Calcd (%) for C14H14N2I2: C, 36.23, H, 3.04, N, 6.03. Found:
C, 36.31, H, 2.96, N, 6.05.
5a and 6a were obtained in 26% (0.54 g) and 36% (0.99 g) yields.
4.4.1.1. 2-(Bis(methylsulfanyl)methyl)pyridine [18] (6a). M.p. 40e
43 ꢀC. 1H NMR: DMSO-d6, 400 MHz
d
(ppm): 8.48e8.50 (dd,
4.5. Dilithiation reaction and quenching with selenium and
iodomethane
J ¼ 1.04 Hz, 4.20 Hz, 1H), 8.02e8.04 (dd, J ¼ 0.92 Hz, 7.30 Hz, 1H),
7.90e7.94 (dd, J ¼ 1.76 Hz, 7.70 Hz, 1H), 7.32e7.36 (dd, J ¼ 1.24 Hz,
J ¼ 7.26 Hz, 1H), 3.30 (s, 1H), 1.89 (s, 6H) 13C NMR: DMSO-d6,
Elemental selenium (2.60 g, 33.0 mmol) was added to the so-
lution containing DL-3b (15.0 mmol) at ꢁ78 ꢀC. The temperature
was slowly raised to ambience temperature and stirring was
continued for 15 min at this temperature. The color of the reaction
mixture turns brownish red on complete dissolution of elemental
selenium. This solution was re-cooled to ꢁ78 ꢀC and iodomethane
(4.68 g, 2.04 mL, 33.0 mmol) was added to it. The reaction mixture
was slowly brought to the room temperature, hydrolyzed with
chilled water and purified by column chromatography by using
hexane-ethyl acetate as an eluent (50:1). Three products were
isolated from the reaction mixture.
400 MHz d (ppm): 159.5, 147.0, 137.4, 122.8, 122.2, 13.0. MS (EI): 184
(96), 136 (100), 122 (44), 93 (12), 78 (85), 69 (11), 51 (32). Anal.
Calcd (%) for C8H11NS: C, 51.87, H, 5.98, N, 7.56, S, 34.58. Found: C,
51.96, H, 6.02, N, 7.52, S, 34.51.
4.4.2. Substrate:e1b
5b and 7b were obtained in 29% (0.66 g) and 48% (1.75 g) yields.
4.4.3. Trilithiation of 1b with BF3.Et2O as the complexing agent
A solution of 1b (1.60 g, 1. 64 mL, 15.0 mmol) in diethyl ether
(50 mL) was cooled to 0 ꢀC in a three-necked 100 mL RBF and
BF3.Et2O in diethyl ether (2.34 g, 2.07 mL, 16.5 mmol) was added to
it. The temperature of the RBF was lowered to ꢁ78 ꢀC and LDA
(49.5 mmol) was added slowly via cannula. The resulting dark
reddish brown solution containing the anionic species was then
4.5.1. 1,2-Bis(3-methyl-6-(methylselenenyl)pyridin-2-yl)ethane
(9b)
Yield: 0.59 g (20%), 55e58 ꢀC. 1H NMR: DMSO-d6, 400 MHz
d
(ppm): 7.07e7.09 (d, J ¼ 7.84 Hz, 2H), 6.96e6.98(d, J ¼ 7.88 Hz,