Debrominations of vic-Dibromides with Diorganotellurides
J . Org. Chem., Vol. 63, No. 1, 1998 175
Concentration in vacuo was performed on a Bu¨chi rotary
evaporator. Nuclear magnetic resonance (NMR) spectra were
recorded at 30.0 °C on a Varian Gemini-300 instrument with
residual solvent signal as internal standard: CDCl3 (δ 7.26
for proton, δ 77.0 for carbon).
Hz), 2.08 (m, 1 H), 1.73 (d, 3 H, J ) 6.7 Hz), 1.06 (d, 3 H, J )
6.5 Hz), 0.98 (d, 3 H, J ) 6.5 Hz); 13C NMR (CDCl3) δ 69.88,
52.23, 34.18, 25.58, 21.29, 20.71; FDMS m/z 242 (C6H1279Br2).
For erythro-1,2-dibromo-1,2-diphenylethane: mp 226-228
°C (lit15 mp 237-239 °C); 1H NMR (CDCl3) δ 7.50 (m, 4 H),7.43
79
P r ep a r a tion of Di-n -h exyl Tellu r id e (9).7b Sodium boro-
hydride (1.9 g, 0.050 mol) was added in three portions every
15 min to a refluxing slurry of tellurium powder (2.55 g, 0.020
mol) in 50 mL of 0.3 M sodium ethoxide in ethanol under an
inert atmosphere of argon. After the tellurium was consumed,
a chalky white mixture was obtained. 1-Bromohexane (6.6 g,
0.040 mol) in 20 mL of ethanol was added. The reaction
mixture was stirred for 3 h at ambient temperature. The
mixture was then poured into water, and the product was
extracted with hexanes (3 × 50 mL). The combined organic
extracts were washed with brine, filtered through Celite, dried
over MgSO4, and concentrated. The reside was purified via
short-path distillation at 100-102 °C (0.05 Torr) to give 97b
(m, 2 H), 7.38 (m, 4 H), 5.46 (s, 2 H); FDMS m/z 338 (C14H12 -
Br2).
For threo-1,2-dibromo-1,2-diphenylethane: mp 108.5-110.0
°C (lit15 mp 110-111 °C), 1H NMR (CDCl3) δ 7.15 (s, 10 H),
5.45 (s, 2 H); FDMS m/z 338 (C14H1279Br2).
For erythro-1,2-dibromo-1-phenylpropane: 1H NMR (CDCl3)
δ 7.31-7.43 (m, 5 H), 5.04 (d, 1 H, J ) 10.2 Hz), 4.61 (m, 1H),
2.04 (d, 3 H, J ) 6.2 Hz); 13C NMR (CDCl3) δ 140.60, 128.81,
79
128.67, 127.76, 59.22, 51.19, 25.86; FDMS m/z 276 (C9H10
-
Br2).
For 1,2-dibromodecane: 1H NMR (CDCl3) δ 4.14 (m, 1 H),
3.82 (dxd, 1 H, J ) 4.1, 10.0 Hz), 3.60 (t, 1 H, J ) 10.0 Hz,
2.11 (m, 1 H), 1.76 (m, 1 H), 1.55 (m, 1 H), 1.40 (m, 1 H), 1.26
(br s, 10 H), 0.86 (t, 3 H, J ) 6.7 Hz); 13C NMR (CDCl3) δ 53.10,
36.33, 36.06, 31.84, 29.37, 29.20, 28.84, 26.77, 22.66, 14.10;
FDMS m/z 298 (C10H2079Br2).
1
as a light orange oil (3.32 g, 56% yield): H NMR (CDCl3) δ
2.60 (t, 4 H, J ) 7.7 Hz), 1.71 (quintet, 4 H, J ) 7.5 Hz), 1.32
(m, 12 H), 0.88 (t, 6 H, J ) 6.9 Hz); 13C NMR (CDCl3) δ 32.19,
31.73, 31.20, 22.57, 14.03, 3.22; FDMS, m/z 300 (C12H26130Te).
For erythro-5,6-dibromodecane: 1H NMR (CDCl3) δ 4.12 (m,
2 H), 2.08 (m, 2 H), 1.92 (m, 2 H), 1.54 (m, 2 H), 1.2-1.5 (m,
6 H), 0.90 (t, 6 H, J ) 7.2 Hz); 13C NMR (CDCl3) δ 59.96, 36.64,
29.12, 22.07, 13.95; FDMS m/z 298 (C10H2079Br2).
For threo-2,3-dibromopentane: 1H NMR (CDCl3) δ 4.41 (qxd,
1 H, J ) 3, 7 Hz), 4.07 (txd, 1 H, J ) 3, 10 Hz),2.10 (m, 1 H),
1.80 (m, 1 H), 1.72 (d, 3 H, J ) 7 Hz), 1.04 (t, 3 H, J ) 7 Hz);
13C NMR (CDCl3) δ 62.22, 52.26, 27.54, 21.66, 12.72; FDMS
m/z 228 (C5H1079Br2).
For 2,3-dibromo-2-methylpentane: 1H NMR (CDCl3) δ 4.08
(d, 1 H, J ) 11 Hz), 2.43 (m, 1 H), 1.73 (m, 1 H), 1.94 (s, 3 H),
1.76 (s, 3 H), 1.10 (t, 3 H, J ) 7.1 Hz); 13C NMR (CDCl3) δ
69.18, 68.59, 35.55, 29.29, 28.19, 13.43; FDMS m/z 242
(C6H1279Br2).
For 1,2-dibromo-2-methylpentane: 1H NMR (CDCl3) δ 3.85
(d, 1 H, J ) 10.2 Hz), 3.77 (d, 1 H, J ) 10.2 Hz), 1.83 (m, 1 H),
1.82 (s, 3 H), 1.50 (m, 2 H), 1.12 (m, 1 H), 0.94 (t, 3 H, J ) 7.2
Hz); 13C NMR (CDCl3) δ 67.98, 44.40, 42.53, 30.65, 18.87,
13.90; FDMS m/z 242 (C6H1279Br2).
P r ep a r a t ion of Dib r om o Di-n -h exyl Tellu r iu m (IV)
(10).7b Dihexyl telluride (3, 596 mg, 2.00 mmol) was dissolved
in acetone (10 mL). A 2.5-mL aliquot of a 1.0 M solution of
bromine in CHCl3 was added dropwise, and the resulting
solution was stirred for 15 min at ambient temperature. The
reaction mixture was concentrated to give 10 as a dark brown
oil (0.855 g, 93.3%): 1H NMR (CDCl3) δ 3.61 (t, 4 H, J ) 7.7
Hz), 2.14 (quintet, 4 H, J ) 7.1 Hz), 1.47 (m, 4 H), 1.34 (m, 8
H), 0.88 (t, 6 H, J ) 6.7 Hz); 13C NMR (CDCl3) δ 45.29, 31.08,
30.71, 25.76, 22.40, 13.98; FDMS, m/z 458 (C12H26130Te79Br2).
P r ep a r a tion of Su bstr a tes. The known vic-dibromide
substrates were all prepared from brominations of com-
mercially available mono-, di-, and trisubstituted olefins:
erythro-1,2-dibromo-1,2-diphenylethane from trans-stilbene,13
threo-1,2-dibromo-1,2-diphenylethane from cis-stilbene,13 erythro-
1,2-dibromo-1-phenylpropane from trans-1-phenylpropene,13
1,2-dibromodecane from 1-decene,3i erythro-3,4-dibromohexane
from trans-3-hexene,15 erythro-5,6-dibromodecane from trans-
5-decene,15 threo-2,3-dibromopentane from cis-2-pentene,16
threo-2,3-dibromo-4-methylpentane from cis-4-methyl-2-pen-
tene,17 1,2-dibromo-2-methyl-1-phenylpropane from 2-methyl-
1-phenylpropene,18 2,3-dibromo-2-methylpentane from 2-methyl-
2-pentene,19 trans-1,2-dibromocyclohexane from cyclohexene,20
trans-1,2-dibromocycloheptane from cycloheptene,15 and 1,2-
dibromo-2-methylpentane from 2-methyl-1-pentene.15
Gen er a l P r oced u r e for Debr om in a tion s of vic-Dibr o-
m id es. The substrate (0.10 mmol) and diorganotelluride (0.10
mmol, 36 mg for 1, 30 mg for 9) were dissolved in 1.0 mL of
CDCl3 in a 5-mm NMR tube. The tube was sealed, and
resulting solution was placed in a thermostated bath at 90-
100 °C as indicated. The samples were examined periodically
by 1H NMR using residual CHCl3 as an internal standard until
no further change in the ratio of products was observed.
In a typical procedure, bromine (1.68 g, 10.5 mmol) in 30
mL of CHCl3 was added dropwise to a stirred solution of
substrate (10 mmol) in 30 mL of CHCl3 at ambient tempera-
ture in the dark (3 h to 7 days).15 The reaction mixture was
washed with saturated NaHSO3 solution. The organic layer
was separated, dried over MgSO4, and concentrated. The
dibromide was recrystallized (EtOAc/hexanes) for threo- and
erythro-1,2-dibromo-1,2-diphenylethane and was distilled (bulb-
to-bulb, 0.1 Torr) for the other substrates. The diastereomeric
purity of the vic-dibromides was established by 1H and 13C
NMR.
For erythro-3,4-dibromohexane: 1H NMR (CDCl3) δ 4.12 (m,
2 H), 2.08 (m, 2 H), 0.90 (t, 6 H, J ) 7.2 Hz); 13C NMR (CDCl3)
δ 59.96, 36.64, 13.95; FDMS m/z 242 (C6H1279Br2).
For threo-2,3-dibromo-4-methylpentane: 1H NMR (CDCl3)
δ 4.31 (dxq, 1 H, J ) 3.3, 6.7 Hz), 3.71 (dxd, 1 H, J ) 3.3, 6.8
The olefins were identified in the reaction mixture from
1
their H NMR and 13C NMR spectra, which were superimpos-
able on the spectra of authentic samples (Aldrich).
Gen er a l P r oced u r e for Com p etition Exp er im en ts.
The vic-dibromides (0.20 mmol each) and telluride 9 (30.0 mg,
0.10 mmol) were dissolved in 2.0 mL of CDCl3 or CD3CN. The
resulting solutions were placed in 5-mm NMR tubes (1 mL in
each) and were immersed in a constant temperature bath at
90 °C. After the indicated times, product ratios were measured
1
by H NMR spectroscopy and averaged for duplicate runs.
Gen er a l P r oced u r e for Kin etics Exp er im en ts. A stock
solution of 0.80 mmol each of dibromide and telluride 9 in 4.0
mL of CDCl3 (0.20 M in each reagent) was prepared. Dilution
(2- and 4-fold) of the stock solution gave a series with
concentrations of 0.20, 0.10, and 0.050 M in each reagent. The
solutions were immersed in a constant temperature bath at
(90 ( 1) °C and were sampled periodically over the initial
reaction. A plot of [A]t/[A0] as a function of time gave initial
slopes of -(4.89 ( 0.06) × 10-5 s-1 at 0.20 M reagents, -(2.74
( 0.04) × 10-5 s-1 at 0.10 M reagents, and -(1.56 ( 0.05) ×
10-5 s-1 at 0.05 M reagents for 2,3-dibromo-2-methylpentane
and slopes of -(7.50 ( 0.05) × 10-7 s-1 at 0.20 M reagents,
-(3.1 ( 0.1) × 10-7 s-1 at 0.10 M reagents, and -(1.86 ( 0.04)
× 10-7 s-1 at 0.05 M reagents for erythro-5,6-dibromodecane.
(15) Buckles, R. E.; Bader, J . M.; Thurmaier, R. J . J . Org. Chem.
1962, 27, 4523-4527.
(16) Zavada, J .; Krupicka, J .; Sicher, J . Collect. Czech. Chem.
Commun. 1963, 28, 1664-1674.
(17) Snyder, R. G. J . Mol. Spectrosc. 1968, 28, 273-308.
(18) Bennett, S. W.; Eaborn, C.; J ackson, R. A.; Walsingham, R. W.
J . Organomet. Chem. 1971, 27, 195-200.
(19) Snyder, E. I. J . Am. Chem. Soc. 1963, 85, 2624-2627.
(20) Lexa, D.; Save´ant, J .-M.; Scha¨ffer, H. J .; Su, K.-B.; Vering, B.;
Wang, D. L. J . Am. Chem. Soc. 1990, 112, 6162-6177.