Molecular addition compounds. 18. Borane adducts with hydroxydialkyl sulfide borates for hydroboration. New, essentially odorless, water-soluble sulfide borane acceptors for hydroboration

Article abstract of DOI:10.1021/jo010051u

Hydroxydialkyl sulfides of general formula RS(CH₂CH₂)_nH (R = Et, t-Bu, i-Am; n = 1-3) and thiodiethanol monomethyl ether (9) have been synthesized and used as borane carriers. The compounds 3 and 6 (R = Et, n = 2, 3), 7 (R = t-Bu, n = 3), and 9 are completely miscible with water and exhibit only very mild odor. The sulfides were transformed into the corresponding borates by treatment either with boric acid or with diborane. The borates complex 3 mol of borane per 1 mol of borate to give highly reactive, stable, liquid adducts, hydroborating 1-octene in 15 min at room temperature. The adducts derived from water soluble sulfides 3 and 9, selected for the hydroboration of more hindered olefins, reacted readily with (-)-β-pinene, 1-methyleyclohexene, and 2,3-dimethyl-2-butene. The carrier borates liberated from the adducts during hydroboration are readily hydrolyzed to give 3 and 9, which can be washed off with water from trialkylboranes or oxidation products. Consequently, hydroxydialkyl sulfides 3 and 9 are the first completely water-soluble sulfide borane carriers that can be washed off in the workup of hydroboration products. The adducts derived from 3 and 9 are new, highly promising reagents suitable for large scale hydroborations and reductions.

Full text of DOI:10.1021/jo010051u

J . Org. Chem. 2001, 66, 4795-4798
4795
Molecu la r Ad d ition Com p ou n d s. 18. Bor a n e Ad d u cts w ith
Hyd r oxyd ia lk yl Su lfid e Bor a tes for Hyd r obor a tion . New ,
Essen tia lly Od or less, Wa ter -Solu ble Su lfid e Bor a n e Accep tor s for
Hyd r obor a tion †
Herbert C. Brown,* Marek Zaidlewicz,1 Pramod V. Dalvi,2 and Goutam K. Biswas2
H. C. Brown Center for Borane Research, Department of Chemistry, Purdue University,
West Lafayette, Indiana 47907
hcbrown@purdue.edu
Received J anuary 17, 2001
Hydroxydialkyl sulfides of general formula RS(CH2CH2)nH (R ) Et, t-Bu, i-Am; n ) 1-3) and
thiodiethanol monomethyl ether (9) have been synthesized and used as borane carriers. The
compounds 3 and 6 (R ) Et, n ) 2, 3), 7 (R ) t-Bu, n ) 3), and 9 are completely miscible with
water and exhibit only very mild odor. The sulfides were transformed into the corresponding borates
by treatment either with boric acid or with diborane. The borates complex 3 mol of borane per 1
mol of borate to give highly reactive, stable, liquid adducts, hydroborating 1-octene in 15 min at
room temperature. The adducts derived from water soluble sulfides 3 and 9, selected for the
hydroboration of more hindered olefins, reacted readily with (-)-â-pinene, 1-methylcyclohexene,
and 2,3-dimethyl-2-butene. The carrier borates liberated from the adducts during hydroboration
are readily hydrolyzed to give 3 and 9, which can be washed off with water from trialkylboranes
or oxidation products. Consequently, hydroxydialkyl sulfides 3 and 9 are the first completely water-
soluble sulfide borane carriers that can be washed off in the workup of hydroboration products.
The adducts derived from 3 and 9 are new, highly promising reagents suitable for large scale
hydroborations and reductions.
Borane carriers are of increasing importance with the
growing applications of diborane in the synthesis of
pharmaceuticals and other compounds.3,4 Borane-
tetrahydrofuran and borane-dimethyl sulfide (BMS), the
two most widely used borane adducts, are excellent
reagents for laboratory use; however, they have certain
limitations for larger scale applications. Thus, the com-
mercially available borane-tetrahydrofuran is a dilute
solution (1 M in BH3), unstable over prolonged periods
and, hence, inconvenient for transportation and storage,
and its use is limited to one solvent. Borane dimethyl
sulfide, a neat adduct, 10 M in borane, stable indefinitely,
and soluble in various solvents, is free from these
inconveniences. Unfortunately, dimethyl sulfide has an
obnoxious odor and is water-insoluble, highly volatile,
and flammable, creating environmental and safety prob-
lems. To circumvent some of these limitations, borane
adducts with 1,4-thioxane5 and bis-sulfides3 have been
introduced. These carriers are less volatile and odorifer-
ous than dimethyl sulfide. However, none of the presently
used sulfides for borane complexation is miscible with
water. A water-soluble borane carrier would facilitate
product isolation in hydroboration and reduction reac-
tions. Its volatility would also be lowered at the workup
stage when it is dissolved in the aqueous phase.
with water, and 2-(isoamylthio)ethanol has an agreeable
odor and is partially soluble in water.7 Consequently, we
decided to prepare and examine selected hydroxydialkyl
sulfides for borane complexation with the objective of
developing a borane carrier of low volatility, odorless or
of very mild odor, and completely miscible with water.
Resu lts a n d Discu ssion
First, the commercially available 2-(methylthio)ethanol
was examined as a model compound. The borane adduct
is readily prepared by passing diborane into the neat
sulfide. Hydrogen is evolved, and the borate ester formed
complexes with borane to give a liquid adduct, 7.5 M in
borane at room temperature (eq 1). The 11B NMR
spectrum shows a quartet at δ -20 (borane adduct), a
singlet at δ +18 (borate ester), and a small doublet at δ
+38 ppm, attributed to (MeSCH2CH2O)2BH. The adduct
hydroborates 1-octene quantitatively at room tempera-
ture to give trioctylborane and borate ester (eq 2).
Among lower molecular weight sulfides, certain hydroxy-
dialkyl sulfides, e.g., 2-(methylthio)ethanol, are miscible
† Communication no. 20 from H. C. Brown Center for Borane
Research.
(1) Visiting professor from Nicolaus Copernicus University, Torun,
on a grant from the Borane Research Fund.
(2) Postdoctoral research associate with support from the Borane
Research Fund.
These observations indicate that hydroxydialkyl sul-
fides can serve as borane carriers for hydroboration.
(6) Brown, H. C.; Zaidlewicz, M.; Dalvi, P. Organometallics 1998,
(3) Follet, M. Chem. Ind. 1986, 123.
(4) Renn, O.; Meatres, C. F. Bioconjugate Chem. 1992, 3, 563.
(5) Brown, H. C.; Mandal, A. K. J . Org. Chem. 1992, 57, 4970.
19, 4202.
(7) Scherlin, S. M.; J akubowitsch, A. I. J . Prakt. Chem. 1933, 138,
23.
10.1021/jo010051u CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/14/2001

4796 J . Org. Chem., Vol. 66, No. 14, 2001
Brown et al.
Ta ble 1. Od or a n d Miscibility w ith Wa ter of
droxymethyl group from δ ∼3.7 to δ ∼3.9 for the corre-
sponding esters. Alternatively, the borates 1a -9a were
simply synthesized by the reaction of borane-tetrahy-
drofuran with hydroxydialkyl sulfides 1-9 in the molar
ratio 1:3. The product formation is easily followed by
measuring the hydrogen evolved. Warming the reaction
mixture to 50 °C is necessary to complete the reaction.
On the basis of these observations, an efficient one-
pot synthesis of borane adducts 1b-9b was developed.
Thus, diborane, conveniently generated using a procedure
recently reported,6 was passed into a neat hydroxydialkyl
sulfide at 50 °C to form the corresponding borate ester,
and then it was absorbed by the ester till saturation. The
adducts 1b-9b, readily prepared by this procedure, are
liquids of high hydride content, stable at room temper-
ature (Table 2). The adducts are soluble in diethyl ether,
tetrahydrofuran, and dichloromethane. No change in
molarity after 1 week at room temperature was observed.
To examine the complexing ability of the borates as
compared to dimethyl sulfide, exchange between BMS
and the borates was followed by 11B NMR analysis. The
amount of borane taken by borates from BMS at equi-
librium for 1:3 mixtures is presented in Table 2. Borates
3a and 6a with an ethyl substituent at the sulfur atom
take 28% and 23% of borane, respectively. Substitution
of a tert-butyl group for the ethyl group decreases the
complexing ability, whereas borates containing an isoamyl
group do not undergo any significant exchange. In
general, the borates 1a -9a take less than 30% of borane
from BMS, indicating a relatively weaker complexing
ability compared to dimethyl sulfide. As follows from
Table 2, the complexing ability of the borates decreases
in the following order: 3a , 6a > 1a , 4a , 7a > 2a , 5a ,
8a , 9a .
Hyd r oxyd ia lk yl Su lfid es 1-9
miscibility
hydroxydialkyl sulfides
odor
with watera
t-BuSCH2CH2OH
i-AmSCH2CH2OH
EtS(CH2CH2O)2H
t-BuS(CH2CH2O)2H
i-AmS(CH2CH2O)2H
EtS(CH2CH2O)3H
t-BuS(CH2CH2O)3H
i-AmS(CH2CH2O)3H
CH3OCH2CH2SCH2CH2OH
1
2
3
4
5
6
7
8
9
mild
50
<100
miscible
15
agreeable;strong
very mild
mild
agreeable; weak
very mild
mild
<100
miscible
miscible
∼100
agreeable; weak
mild
miscible
a
Milliliters of water required to dissolve 1.0 g of hydroxydialkyl
sulfide.
Unfortunately, 2-(methylthio)ethanol is not useful be-
cause of its unpleasant odor. Similarly, 2-(ethylthio)-
ethanol is only partially soluble in water and possesses
an unpleasant odor. On the other hand, 3-ethylthio-1,2-
propanediol has a mild odor and low volatility and is
completely miscible with water. However, it reacts with
diborane to give a very viscous, glassy product. The
adduct formation under neat conditions is not complete,
and its high viscosity makes difficult the introduction and
absorption of diborane.
To circumvent these difficulties we decided to prepare
a series of hydroxydialkyl sulfides 1-9 (Table 1), the
corresponding borate esters 1a -9a and their borane
adducts 1b-9b (Table 2). The hydroxydialkyl sulfides
1-8 were readily prepared as shown in eq 3, and
thiodiethanol monomethyl ether (9) was obtained accord-
ing to eq 4.
For the exchange with 1 M borane-tetrahydrofuran
solution, the values can be considered only as qualitative
since the solution contains tetrahydrofuran in large
excess. As expected, the borates 1a -9a take more borane
(62-83%) from borane-tetrahydrofuran, a weaker ad-
duct than BMS (Table 2).
Hyd r obor a tion . Hydroboration of 1-octene with the
borane adducts 1b-9b under neat conditions was carried
out at room temperature. The results are shown in Table
2. As revealed by 11B NMR analysis, the adducts hy-
droborate 1-octene in 15 min to yield trioctylborane.
On the basis of simple synthesis, mild odor, water
solubility of the parent hydroxydialkyl sulfides, and high
molarity of adducts, 3b and 9b were selected for prepara-
tive scale hydroboration of terminal olefins. Thus, hy-
The yields are above 90%, and the product isolation is
simple. All of these hydroxydialkyl sulfides have a mild
or very mild odor (Table 1). Compounds 3, 6, 7, and 9
are miscible with water.
Initially, pure borates were prepared by refluxing the
sulfides with boric acid in toluene, removing the water
azeotropically. The formation of borates was confirmed
1
by 11B NMR (δ 17-18) and H NMR analysis, showing a
downfield shift of the methylene protons of the hy-
Ta ble 2. Bor a n e Ad d u cts w ith Bor a te Ester s of Hyd r oxyd ia lk yl Su lfid es
borane adducts with borate esters
exchangea (%)
11B NMRe (δ )
borate ester adduct
[BH3]d
(M)
HB of 1-octenef
(time, h)
borate ester
BMS
BH3/THF
adductb
statec
(t-BuSCH2CH2O)3B
(i-AmSCH2CH2O)3B
[EtS(CH2CH2O)2]3B
[t-BuS(CH2CH2O)2]3B
[i-AmS(CH2CH2O)2]3B
[EtS(CH2CH2O)3]3B
[t-BuS(CH2CH2O)3]3B
[i-AmS(CH2CH2O)3]3B
(CH3OCH2CH2SCH2CH2O)3B
1a
2a
3a
4a
5a
6a
7a
8a
9a
8
0
28
11
0
23
9
0
68
67
83
70
75
81
68
66
62
1b
2b
3b
4b
5b
6b
7b
8b
9b
liquid
liquid
liquid
liquid
liquid
liquid
liquid
liquid
liquid
6.4
5.9
5.7
5.5
5.0
5.2
4.2
4.0
6.0
17.67
18.05
18.16
17.94
18.09
18.07
18.28
18.13
18.50
-26.03
-22.27
-22.68
-26.21
-23.03
-23.48
-26.20
-23.22
-21.49
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0
a
b
BMS or BH3/THF and borate ester mixed at 3:1 molar ratio. Adducts contain three borane molecules per ester molecule, e.g., [H3B:
S(t-Bu)CH2CH2O]3B (1b). c At 20 °C. Estimated by hydrolysis in water/glycerol/THF, 1:1:1, and measurement of the hydrogen evolved.
d
e Neat. f Hydroboration with a neat adduct at room temperature.

Water-Soluble Sulfide Borane Carriers
J . Org. Chem., Vol. 66, No. 14, 2001 4797
and a small amount of sodium chloride was filtered off. The
product was isolated by distillation under vacuum.
Da ta for 1. Yield 22.35 g (90%); bp 46-48 °C/0.1 mmHg
(lit.8 101.5-102.5 °C/27 mmHg). 1H NMR (CDCl3) δ 1.34 (s,
9H, CH3), 2.77 (t, J ) 6.1, 2H, CH2), 3.93 (q, J ) 6.1, 2H, CH2).
13C NMR (CDCl3) δ 31.13 (CH3), 42.32 (C), 31.68 (CH2), 61.51
(CH2). MS (70 eV CI EI) 134(M+, 17), 57(100).
droboration of 1-octene with 9b was carried out in
dichloromethane at room temperature. 11B NMR analysis
showed completion of the reaction in 15 min. The
intermediate trioctylborane was oxidized with alkaline
hydrogen peroxide, and the oxidation product was stirred
with water at room temperature for 0.5 h or with warm
water for 15 min, to wash off thiodiethanol monomethyl
ether (9). GC analysis of the product showed 1-octanol
(94%) and 2-octanol (6%), free of 9.
Similarly, (-)-â-pinene (91% ee) was hydroborated with
the adducts 3b and 9b in dichloromethane. Both adducts
reacted in 0.5 h as showed by 11B NMR. The usual
oxidative workup and water wash gave (-)-cis-myrtanol
in 90% yield, free of 3 and 9, respectively.
To further test the reactivity of the borane adducts,
the hydroboration of representative tri- and tetrasubsti-
tuted olefins was also examined. Thus, 1-methylcyclo-
hexene was hydroborated under neat conditions using 3b
and 9b (olefin/borane ratio 2:1). After 0.5 h, the reaction
mixture was treated with ethanol. The 11B NMR analysis
showed a signal at δ 17 (borate ester) and at δ 53
(dialkylborinate), indicating quantitative conversion. Simi-
larly, hydroboration of 2,3-dimethyl-2-butene with 9b
(olefin/borane ratio 1:1) gave thexylborane in 0.5 h (11B
NMR δ 24). The reactivity of 3b toward 2,3-dimethyl-2-
butene was lower and only 80% of the olefin reacted in
24 h. The lower reactivity of 3b toward 2,3-dimethyl-2-
butene, as compared with 9b, reflects the higher com-
plexing ability of 3.
Da ta for 2. Yield 27.00 g (917); bp 55-56 °C/0.5 mmHg
1
(lit.7 110-111 °C/10 mmHg). H NMR (CDCl3) δ 0.90 (d, J )
6.6, 6H, CH3), 1.49 (q, J ) 6.6, 2H, CH2), 1.63 (nonet, J ) 6.6,
1H, CH), 2.52 (t, J ) 6.9, 2H, CH2), 2.73 (t, J ) 5.9, 2H, CH2),
3.72 (q, J ) 5.9, 2H, CH2). 13C NMR (CDCl3) δ 22.28 (CH3),
27.44 (CH), 29.65 (CH2), 35.21 (CH2), 38.74 (CH2), 60.26 (CH2).
MS (70 eV EI CI) 148(M+), 70(86), 61(100), 55(65), 47(21).
Da ta for 3. Yield 28.00 g (93%); bp 61-65 °C/0.1 mmHg
1
(lit.9 88 °C/3 mmHg). H NMR (CDCl3) δ 1.27 (t, J ) 7.3, 3H,
CH3), 2.59 (q, J ) 7.3, 2H, CH2), 2.74 (t, J ) 6.7, 2H, CH2),
3.59 (t, J ) 6.7, 2H, CH2), 3.67 (t, J ) 6.7, 2H, CH2), 3.73 (m,
J ) 6.7, 2H, CH2. 13C NMR (CDCl3) δ 14.81 (CH3), 26.23 (CH2),
31.06 (CH2), 61.47 (CH2), 70.40 (CH2), 72.15 (CH2). MS (70 eV
EI CI), 150(M+), 89(100), 75(57), 60(27), 47(27).
Da ta for 4. Yield 32.8 g (92%); bp 70-72 °C/0.1 mmHg. 1H
NMR (CDCl3) δ 1.34 (s, 9H, CH3), 2.66 (t, J ) 6.2, 2H, CH2),
3.58 (t, J ) 6.2, 2H, CH2), 3.68 (t, J ) 6.2, 2H, CH2), 3.74 (m,
J ) 6.2, 2H, CH2). 13C NMR (CDCl3) δ 28.07 (CH3), 42.09 (C),
30.96 (CH2), 61.54 (CH2), 70.77 (CH2), 72.11 (CH2). MS (70 eV
EI CI), 179(M+
C8H18O2S: C, 53.89; H, 10.17; S, 17.98. Found: C, 53.54; H,
10.03; S, 17.71.
+ 1), 61(20), 57(100). Anal. Calcd for
Da ta for 5. Yield 17.30 g (90%); bp 90-92 °C/0.2 mmHg.
1H NMR (CDCl3) δ 0.90 (d, J ) 6.7, 6H, CH3), 1.48 (q, J ) 6.7,
2H, CH2), 1.62 (nonet, J ) 6.7, 1H, CH), 2.54 (t, J ) 7.0, 2H,
CH2), 2.72 (t, J ) 6.7, 2H, CH2), 3.58 (t, J ) 6.2, 2H, CH2),
3.66 (t, J ) 6.2, 2H, CH2), 3.72 (m, J ) 6.2, 2H, CH2). 13C NMR
(CDCl3) δ 22.29 (CH3), 27.42 (CH), 30.55 (CH2), 31.64 (CH2),
38.73 (CH2), 61.70 (CH2), 70.52 (CH2), 72.09 (CH2). MS (70 eV
EI CI), 192(M+), 131(90), 75(20), 61(100), 55(35). Anal. Calcd
for C9H20O2S: C, 56.20; H, 10.48; S, 16.67. Found: C, 55.97;
H, 10.49; S, 16.32.
Da ta for 6. Yield 35.36 g (91%); bp 95-97 °C/0.1 mmHg
(lit.10 131 °C/4 mmHg). 1H NMR (CDCl3) δ 1.26 (t, J ) 7.0,
3H, CH3), 2.58 (q, J ) 7.0, 2H, CH2), 2.64 (t, J ) 6.8, 2H, CH2),
3.66 (m, J ) 6.8, 6H, CH2), 3.74 (m, J ) 6.8, 4H). 13C NMR
(CDCl3) δ 14.85 (CH3), 26.32 (CH2), 30.87 (CH2), 61.55 (CH2),
70.25 (CH2), 70.86 (CH2), 72.56 (CH2), (one peak overlaps and
only seven appear). MS (70 eV EI CI), 195(M++ 1), 106(23),
89(100), 75(20), 61(36).
Da ta for 7. Yield 41.35 g (93%); bp 100-105 °C/0.1 mmHg.
1H NMR (CDCl3) δ 1.34 (s, 9H, CH3), 2.75 (t, J ) 6.1, 2H, CH2),
3.64 (m, J ) 6.2, 6H, CH2), 3.74 (m, J ) 6.2, 4H, CH2). 13C
NMR (CDCl3) δ 21.87 (CH3), 30.98 (CH2), 42.09 (C), 61.65
(CH2), 70.28 (CH2), 70.32 (CH2), 71.10 (CH2), 72.56 (CH2). MS
(70 eV EI CI), 223(M++ 1), 134(20), 117(27), 61(26), 57(100).
Anal. Calcd for C10H22O3S: C, 54.01; H, 9.97; S, 14.42. Found:
C, 53.65; H, 10.27; S, 14.09.
Con clu sion s
The borane adducts derived from hydroxydialkyl sul-
fides 1-9 are liquids of high hydride content at room
temperature. The adducts 3b and 9b hydroborate ter-
minal, di-, tri-, and tetrasubstituted olefins, and the
corresponding hydroxydialkyl sulfides 3 and 9 can be
washed off easily in workup of the hydroboration-
oxidation products. Consequently, 3b and 9b are highly
promising, efficient, new hydroborating agents of high
potential for large scale applications in hydroborations
and reductions.
Exp er im en ta l Section
All manipulations and reactions with air-sensitive com-
pounds were carried out under nitrogen atmosphere. The
glassware was oven-dried for several hours, assembled while
Da ta for 8. Yield 15.51 g (92%); bp 115-117 °C/0.1 mmHg.
1H NMR (CDCl3) δ 0.91 (d, J ) 6.4, 6H, CH3), 1.45 (q, J ) 6.4,
2H, CH2), 1.63 (nonet, J ) 6.4, 1H, CH), 2.54 (t, J ) 6.9, 2H,
CH2), 2.71 (t, J ) 6.9, 2H, CH2), 3.65 (m, J ) 7.1, 6H, CH2),
3.72 (m, J ) 7.1, 4H, CH2). 13C NMR (CDCl3) δ 22.29 (CH3),
27.42 (CH), 30.55 (CH2), 31.33 (CH2), 38.73 (CH2), 61.68 (CH2),
70.30 (CH2), 70.36 (CH2), 70.94 (CH2), 72.56 (CH2). MS (70 eV
EI CI), 237(M++ 1), 71(30), 70(91), 69(21), 61(100) 55(34), 46-
(25). Anal. Calcd for C11H24O3S: C, 55.89; H, 10.23; S, 13.65.
Found: C, 55.52; H, 10.55; S, 13.31.
Th iod ieth a n ol Mon om eth yl Eth er (9). Sodium methox-
ide (10.88 g, 0.22 mol) was dissolved in methanol (100 mL),
2-mercaptoethanol (15.63 g, 0.2 mol) was added, and the
mixture was left for 1 h at room temperature. 2-Chloroethyl
hot, and cooled in
a stream of nitrogen. Syringes were
assembled and fitted with needles while hot. 1H and 11B NMR
spectra were recorded on a 300 MHz multinuclear instrument.
The 11B NMR shifts are in δ relative to BF3‚OEt2. GC analyses
were carried out on a chromatograph using a 12 ft × 0.125 in.
column packed with 10% Carbowax 20M or SE-30 on Chro-
mosorb W (100-120 mesh). Microanalyses were performed at
the Microanalytical Laboratory, Purdue University.
Ma ter ia ls. Borane-methyl sulfide (BMS), 2-mercaptoetha-
nol, chlorohydrins, and boric acid were commercial products
(Aldrich). 1-Octene and (-)-â-pinene were distilled prior to use
from a small amount of lithium aluminum hydride under
vacuum.
Syn th esis of Hyd r oxyd ia lk yl Su lfid es (1a -8a ). Gen -
er a l P r oced u r e. Sodium methoxide (10.80 g, 200 mmol) was
dissolved in methanol (100 mL), thioalcohol (200 mmol) was
added, and the mixture was left at room temperature for 1 h.
Chlorohydrin (200 mmol) was added, and the mixture was
refluxed for 1 h. Precipitated sodium chloride was filtered off
and washed with methanol. The solvent was removed from
the filtrate under vacuum. Diethyl ether (50 mL) was added,
(8) Strauss, C. R.; Guay, H. G.; Hardwood, H. J . J . Org. Chem. 1964,
29, 1945.
(9) Shostakovskii, M. F.; Atavin, A. S.; Nikitin, V. M.; Triofimov, B.
A.; Keiko, V. V.; Lavrov, V. I. Izv. Akad. Nauk SSSR. Ser. Khim. 1965,
11, 2049-2051.
(10) Atavin, A. S.; Triofimov, B. A.; Lavrov, V. I.; Orlova, S. E. Zh.
Org. Khim. 1966, 2, 14.

4798 J . Org. Chem., Vol. 66, No. 14, 2001
Brown et al.
methyl ether (20.80 g, 0.22 mol) was added, and the mixture
was refluxed for 1 h. Sodium chloride was filtered off, and the
product was isolated by distillation: 25.06 g, (92%); bp 64-65
°C/0.1 mmHg (lit.11 104-107 °C/6 mmHg). 1H NMR (CDCl3) δ
2.76 (m, J ) 6.0, 4H, CH2), 3.38 (s, 3H, CH3), 3.57 (t, J ) 6.1,
2H, CH2), 3.74 (t, J ) 6.0, 2H, CH2). 13C NMR (CDCl3) δ 31.53
(CH2), 35.84 (CH2), 58.76 (CH2), 61.04 (CH2), 72.30 (CH3). MS
(70 eV EI CI), 136(M+), 118(27), 75(32), 58(100), 47(37), 46-
(34).
Syn th esis of Bor a te Ester s. Typ ica l P r oced u r e for 1a .
Meth od A. tert-Butyl 2-hydroxyethyl sulfide (4.02 g, 30 mmol)
and boric acid (0.6183 g, 10 mmol) were added to toluene (40
mL). The reaction mixture was refluxed for 6 h with azeotropic
removal of water. Toluene was removed by distillation under
vacuum. The borate ester was dried over anhydrous magne-
sium sulfate and decanted. Magnesium sulfate was washed
with dichloromethane, and the organic solutions were com-
bined with the borate ester. Dichloromethane was distilled off
to give the pure borate ester: 3.73 g (91%).
(t, J ) 6.6, 2H, CH2), 2.71 (t, J ) 6.6, 2H, CH2), 3.64 (m, J )
6.6, 8H, CH2), 3.91 (t, J ) 6.6, 2H, CH2). 13C NMR (CDCl3) δ
22.29 (CH3), 27.38 (CH), 30.52 (CH2), 31.31 (CH2), 38.76 (CH2),
62.68 (CH2), 70.35 (CH2), 70.47 (CH2), 71.06 (CH2), 71.65 (CH2).
MS (70 eV EI CI) 717(M + 1), 482(22), 481(100), 131(85).
Da ta for 9a . 1H NMR (CDCl3) δ 2.71 (m, J ) 6.2, 4H, CH2),
3.38 (s, 3H), 3.56 (t, J ) 6.2, 2H, CH2), 3.92 (t, J ) 6.2, 2H,
CH2). 13C NMR (CDCl3) δ 31.58 (CH2), 33.55 (CH2), 58.68
(CH2), 62.83 (CH2), 72.19 (CH3). MS (70 eV EI CI) 417(M + 1,
14), 385(15), 281(33), 137(24), 119(20).
Bor a n e Ad d u cts w ith Bor a te Ester s of Hyd r oxyd ia lk yl
Su lfid es (1b-9b). Typ ica l P r oced u r e for Bor a n e Ad d u ct
of Bor a te Ester of ter t-Bu tyl 2-Hyd r oxyeth yl Su lfid e
(1b). A 100-mL one-neck, round-bottom flask equipped with
a septum inlet, magnetic stirring bar, and an adapter with a
stopcock was charged with boron trifluoride-diglyme (20
mmol). A 2 M solution of sodium borohydride in triglyme (7.5
mL, 15 mmol) was added dropwise by means of a hypodermic
syringe. Generation of diborane is smooth, and the reaction is
not exothermic. Diborane was absorbed in neat tert-butyl
2-hydroxyethyl sulfide (7.94 g, 60 mmol) at room temperature.
After the addition was completed, the reaction mixture was
stirred at 50 °C for 15 min under a slow stream of nitrogen.
11B NMR analysis, δ 17.67, indicated the formation of borate
ester. Diborane was then passed into the borate ester at room
temperature till saturation. The borane adduct thus obtained
was a colorless liquid, 6.4 M in borane, estimated by a standard
procedure for active hydride analysis using a water/glycerol/
THF 1:1:1 hydrolyzing mixture:12 11B NMR δ -26.03.
Tr ioctylbor a n e. A 6.9 M borane adduct 9b (3 mL, 18
mmol) was dissolved in dichloromethane (18 mL), and 1-octene
(6.0 g, 54 mmol) was added dropwise with cooling to keep the
temperature at 20-25 °C. The reaction was complete in 15
min, as indicated by 11B NMR. The reaction mixture was
oxidized with 3 M sodium hydroxide (6 mL, 18 mmol) and 30%
hydrogen peroxide (3 mL, 28 mmol) and stirred at room
temperature overnight. The organic layer was separated,
stirred with water for 0.5 h, and dried over anhydrous
magnesium sulfate, and octanol was isolated by distillation:
6.24 g (89%), bp 99-100 °C/20 mmHg. GC analysis (Carbowax
20M) showed 1-octanol 94% and 2-octanol 6%.
Meth od B. A round-bottom flask (25 mL) was charged with
tert-butyl 2-hydroxyethyl sulfide (4.82 g, 36 mmol). A 1 M
borane-tetrahydrofuran (12 mL, 12 mmol) was added with
stirring at room temperature. The reaction mixture was
refluxed for 0.5 h. Tetrahydrofuran was pumped off, and pure
borate ester was obtained: 11B NMR δ 18.26, in tetrahydro-
furan.
Meth od C. Diborane (12 mmol), generated as described
earlier,6 was absorbed in neat tert-butyl 2-hydroxyethyl sulfide
(4.70 g, 35 mmol) at room temperature. After the addition was
completed, the reaction mixture was stirred at 50 °C for 0.5 h
under a slow stream of nitrogen to obtain the borate ester:
11B NMR δ 17.67.
1
Da ta for 1a . H NMR (CDCl3) δ 1.32 (s, 9H, CH3), 2.69 (t,
J ) 6.9, 2H, CH2), 3.89 (t, J ) 6.9, 2H, CH2). 13C NMR (CDCl3)
δ 29.80 (CH3), 31.12 (CH2), 42.02 (C), 63.41 (CH2). MS (70 eV
EI CI) 411(M + 1, 25), 277(58), 221(54), 135(64).
Da ta for 2a . 1H NMR (CDCl3) δ 0.90 (d, J ) 6.6, 6H, CH3),
1.48 (q, J ) 6.6, 2H, CH2), 1.62 (nonet, J ) 6.6, 1H, CH), 2.55
(t, J ) 6.8, 2H, CH2), 2.70 (t, J ) 6.8, 2H, CH2), 3.92 (t, J )
6.8, 2H, CH2). 13C NMR (CDCl3) δ 22.32 (CH3), 27.41 (CH),
30.28 (CH2), 33.19 (CH2), 38.78 (CH2), 62.84 (CH2). MS (70 eV
EI CI) 453(M + 1, 28), 305(100), 131(52).
(-)-cis-Myr ta n ol. A 6.0 M borane adduct 9b (2.0 mL, 12
1
mmol) was dissolved in dichloromethane (12 mL), and (-)-â-
Da ta for 3a . H NMR (CDCl3) δ 1.25 (t, J ) 7.1, 3H, CH3),
pinene (5.0 g, 36 mmol), [R]23 -20.8° (neat), 91% ee, was
D
2.59 (q, J ) 7.1, 2H, CH2), 2.72 (t, J ) 6.8, 2H, CH2), 3.57 (t,
J ) 6.8, 2H, CH2), 3.65 (t, J ) 6.8, 2H, CH2), 3.94 (t, J ) 6.8,
2H, CH2). 13C NMR (CDCl3) δ 14.89 (CH3), 26.35 (CH2), 31.03
(CH2), 62.71 (CH2), 70.93 (CH2), 71.27 (CH2). MS (70 eV EI
CI) 459(M + 1), 309(60), 89(100).
added at 0 °C. The reaction was completed in 0.5 h, as
indicated by 11B NMR. The mixture was kept at room tem-
perature for 1 h and oxidized by the addition of 3 M sodium
hydroxide (5.6 mL, 17 mmol) and 30% hydrogen peroxide (4.0
mL, 40 mmol), keeping the temperature during the addition
below 30 °C, and then stirring at room temperature overnight.
The dichloromethane layer was separated, stirred with water
(20 mL) for 0.5 h, and distilled to give 5.05 g (91%) of pure
product: bp 116-118 °C/15 mmHg (lit.12 bp 65-67 °C/0.2
1
Da ta for 4a . H NMR (CDCl3) δ 1.32 (s, 9H), 2.62 (t, J )
6.9, 2H, CH2), 3.54 (t, J ) 6.9, 2H, CH2), 3.62 (t, J ) 6.7, 2H,
CH2), 3.92 (t, J ) 6.7, 2H, CH2). 13C NMR (CDCl3) δ 28.04
(CH3), 41.03 (CH2), 32.01 (C), 62.75 (CH2), 71.01 (CH2), 71.33
(CH2). MS (70 eV EI CI) 543(M + 1), 365(24), 117(100).
Da ta for 5a . 1H NMR (CDCl3) δ 0.90 (d, J ) 6.8, 6H, CH3),
1.49 (q, J ) 6.7, 2H, CH2), 1.64 (nonet, J ) 6.7, 1H, CH), 2.54
(t, J ) 6.7, 2H, CH2), 2.70 (t, J ) 6.7, 2H, CH2), 3.54 (t, J )
6.5, 2H, CH2), 3.64 (t, J ) 6.5, 2H, CH2), 3.91 (t, J ) 6.5, 2H,
CH2). 13C NMR (CDCl3) δ 22.30 (CH3), 27.36 (CH), 30.53 (CH2),
31.44 (CH2), 38.75 (CH2), 62.73 (CH2), 70.91 (CH2), 71.29 (CH2).
MS (70 eV EI CI) 585(M + 1, 14), 393(97), 131(100).
mmHg); [R]20 -19.4°.
D
Hyd r obor a tion of 1-Meth ylcycloh exen e. A 6.0 M borane
adduct 9b (1 mL, 6 mmol) was taken in a sample vial, and
1-methylcyclohexene (1.15 g, 12 mmol) was added dropwise
with cooling to keep the temperature at 20-25 °C. The reaction
mixture was allowed to stir at room temperature for 0.5 h.
Ethanol (1 mL) was added slowly with stirring at 0 °C: 11B
NMR δ 53.
1
Da ta for 6a . H NMR (CDCl3) δ 1.25 (t, J ) 6.9, 3H, CH3),
Hyd r obor a tion of 2,3-Dim eth yl-2-bu ten e. A 6.0 M bo-
rane adduct 9b (1 mL, 6 mmol) was taken in a sample vial,
and 2,3-dimethyl-2-butene (0.504 g, 6 mmol) was added
dropwise with cooling to keep the temperature at 20-25 °C.
The reaction mixture was allowed to stir at room temperature
for 0.5 h: 11B NMR δ 24.33.
2.56 (q, J ) 6.9, 2H, CH2), 2.70 (t, J ) 6.3, 2H, CH2), 3.65 (m,
J ) 5.7, 8H, CH2), 3.93 (t, J ) 6.7, 2H, CH2). 13C NMR (CDCl3)
δ 14.90 (CH3), 26.30 (CH2), 30.90 (CH2), 62.68 (CH2), 70.34
(CH2), 70.47 (CH2), 71.02 (CH2), 71.64 (CH2). MS (70 eV EI
CI) 591(M + 1, 2), 397(100), 89(25).
1
Da ta for 7a . H NMR (CDCl3) δ 1.32 (s, 9H, CH3), 2.74 (t,
J ) 6.3, 2H, CH2), 3.64 (m, J ) 6.3, 8H, CH2), 3.91 (t, J ) 6.3,
2H, CH2). 13C NMR (CDCl3) δ 27.89 (CH3), 31.01 (CH2), 42.02
(C), 62.67 (CH2), 70.33 (CH2), 70.44 (CH2), 71.17 (CH2), 71.64
(CH2). MS (70 eV EI CI) 675(M + 1), 453(19),117(100).
Da ta for 8a . 1H NMR (CDCl3) δ 0.90 (d, J ) 6.3, 6H, CH3),
1.46 (q, J ) 6.3, 2H, CH2), 1.64 (nonet, J ) 6.3, 1H, CH), 2.52
Ack n ow led gm en t. Financial support of this study
by the Borane Research Fund is acknowledged.
J O010051U
(12) Brown, H. C.; Kramer, G. W.; Levy A. B.; Midland, M. M.
Organic Syntheses via Boranes, J . Wiley: New York, 1975. A reprinted
edition is currently available: Organic Syntheses via Boranes; Aldrich
Chemical Co., Inc.: Milwaukee, WI, 1997; Vol. 1.
(11) Stevens, J . P. Pat. Belg. 1963, 626, 797.; Chem. Abstr. 1964,
61, 8493e.