Notes
J . Org. Chem., Vol. 65, No. 13, 2000 4187
tography on silica gel (hexane/EtOAc, 3:1) to give 2c as a
this compound was subjected to deprotonation with KOH,
and the generated phosphorus anion was readily oxidized
under the conditions to give compound 7.
In summary, we have shown that enantiomerically
enriched secondary phosphine-boranes are obtained from
alkyl(dimethyl)phosphine-boranes in two steps. The num-
ber of examples is limited, but this method may be
applicable for the synthesis of other alkylmethylphos-
phine-boranes in enantiomerically enriched form.
colorless oil (367 mg, 70%): [R]25 -1.9 (75% ee, c 1.6, CHCl3);
D
1H NMR (400 MHz, CDCl3) δ 0.39 (br q, J HB ) 104.4 Hz, 3 H),
1.27 (d, 2J HP ) 10.5 Hz, 3 H), 1.19-1.86 (m, 11 H), 2.18 (s, 1 H),
3.97 (s, 2 H); 13C NMR (100 MHz, CDCl3) δ 4.0 (d, J CP ) 36.1
Hz), 25.7, 26.0, 26.2, 26.3-26.4, 31.2 (d, J CP ) 33.6 Hz), 57.4 (d,
J CP ) 39.4 Hz); IR (neat) 3480, 2930, 2370, 1450, 1070 cm-1
HRMS calcd for C8H20BOP 174.1345, found 174.1351.
(R)-H yd r oxym et h yl(m et h yl)p h en ylp h osp h in e-Bor a n e
;
(2d ). This compound was prepared from 1d (3.04 g, 20 mmol)
according to the procedure described for the preparation of 2a .
After workup, the residue was purified by flash chromatography
on silica gel (hexane/EtOAc, 3:1) to give 2d as a colorless oil (2.32
g, 69%). Separation of enantiomers by chiral HPLC (Daicel
Chiralcel AS, flow rate 0.75 mL/min, 10% 2-PrOH/hexane, (R)
t1 ) 15.1 min; (S) t2 ) 17.9 min) determined the ee to be 81%:
[R]25D -7.2 (81% ee, c 1.2, CHCl3); 1H NMR (400 MHz, CDCl3) δ
Exp er im en ta l Section
Gen er a l. Diethyl ether, tetrahydrofuran (THF), and toluene
were distilled from sodium/benzophenone ketyl under argon
prior to use. 1-Adamantyl(dimethyl)phosphine-borane, tert-butyl-
(dimethyl)phosphine-borane, cyclohexyl(dimethyl)phosphine-bo-
rane, and dimethyl(phenyl)phosphine-borane (1a -d ) were pre-
pared according to the procedure described in the literature.1f,8
(R )-1-Ad a m a n t yl(h yd r oxym e t h yl)m e t h ylp h osp h in e -
Bor a n e (2a ). To a stirred, cooled (-78 °C) solution of (-)-
sparteine (8.68 g, 37 mmol) in Et2O (225 mL) was added s-BuLi
(37.0 mL of a 1.0 M cyclohexane solution, 37 mmol) under Ar
atmosphere. After 15 min, a solution of 1-adamantyl(dimethyl)-
phosphine-borane (1a ) (5.99 g, 29 mmol) in toluene (75 mL) was
added dropwise, and the mixture was stirred at the same
temperature. Three hours later, triethyl phosphite (2.38 g, 14
mmol) was added, and oxygen gas was blown through the
solution with vigorous stirring. The mixture was stirred under
O2 atmosphere at the same temperature for 1 h, and the reaction
was quenched by 1 M HCl. The organic layer was separated,
and the aqueous layer was extracted with EtOAc. The combined
organic layers were washed with brine and dried over Na2SO4.
The solvent was evaporated on a rotary evaporator, and the
residue was purified by flash chromatography on silica gel
(toluene/CHCl3, 1:1) to give 2a as a white solid (4.79 g, 74%).
An enantiomerically pure product was obtained by recrystalli-
zation from a mixed solvent of hexane/EtOAc (10:1) as colorless
2
0.35 (br q, J HB ) 104.1 Hz, 3 H), 1.63 (d, J HP ) 10.6 Hz, 3 H),
2.47 (s, 1 H), 4.06 (s, 2 H), 7.46-7.55 (m, 3 H), 7.73-7.77 (m, 2
H); 13C NMR (100 MHz, CDCl3) δ 6.9 (dq, J CP ) 38.6 Hz, 2J CB
)
ca. 10 Hz), 60.7 (d, J CP ) 41.0 Hz), 127.0 (d, J CP ) 53.3 Hz),
128.8, 131.7-131.9 (m); IR (neat) 3470, 2370, 1440, 1070, 910
cm-1; HRMS calcd for C8H14BOP 168.0875, found 168.0869.
(R)-[(1-Ad a m a n t yl(b or a n a t o)m et h ylp h osp h in o)m et h -
yloxy]d ip h en ylp h osp h in e-Bor a n e (4a ). To a stirred solution
of (R)-1-adamantyl(hydroxymethyl)methylphosphine-borane (2a )
(113 mg, 0.5 mmol) in THF (2 mL) was slowly added n-BuLi
(0.33 mL of a 1.52 M hexane solution) at 0 °C under Ar
atmosphere. After 15 min, chlorodiphenylphosphine (0.13 mL,
0.75 mmol) was added dropwise, and the mixture was gradually
warmed to room temperature during 1 h. The flask was cooled
to 0 °C again, and BH3-THF complex (1.2 mL of a 1 M THF
solution) was added. One hour later, the reaction mixture was
treated with 1 M HCl. The organic layer was separated, and
the aqueous layer was extracted with ethyl acetate three times.
The combined organic layers were washed with brine and dried
over Na2SO4. The solvent was removed on a rotary evaporator,
and the residue was purified by flash chromatography on silica
gel (hexane/EtOAc, 5:1) to give product 4a as a colorless oil that
solidified on standing (167 mg, 79%). The product was recrystal-
lized from hexane/MeOH (1:5) to give colorless needles: mp 112-
needles: mp 129-130 °C; [R]26 -4.8 (c 1.1, CHCl3); 1H NMR
D
(400 MHz, CDCl3) δ 0.35 (br q, J HB ) 105.8 Hz, 3 H), 1.22 (d,
2J HP ) 10.1 Hz, 3 H), 1.95 (s, 1 H), 1.72-2.04 (m, 15 H), 3.91 (d,
J HH ) 13.0 Hz, 1 H), 4.07 (d, J HH ) 13.0 Hz, 1 H); 13C NMR
(100 MHz, CDCl3) δ 1.5 (d, J CP ) 35.3 Hz), 27.4-27.6 (m), 30.1
(d, J CP ) 32.8 Hz), 36.1-36.4 (m), 56.0 (d, J CP ) 37.7 Hz); IR
(KBr) 3450, 2910, 2360, 1450, 1070 cm-1; FAB MS (rel intensity)
225 (M+ - H, 100), 195 (M+ - CH2OH, 91). Anal. Calcd for
114 °C; [R]27 -0.4 (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3) δ
D
2
0.0-1.4 (m, 6 H), 1.27 (d, J HP ) 9.9 Hz, 3 H), 1.57-2.00 (m, 15
2
H), 4.12 (dd, J HH ) 12.8 Hz, J HP ) 5.3 Hz, 1 H), 4.37 (dd, J HH
2
) 12.8 Hz, J HP ) 5.0 Hz, 1 H), 7.47-7.56 (m, 6 H), 7.73-7.77
(m, 4 H); 13C NMR (100 MHz, CDCl3) δ 1.6 (d, J CP ) 35.3 Hz),
27.5 (d, 2J CP ) 9.0 Hz), 30.6 (d, J CP ) 32.0 Hz), 36.2, 59.7 (d, J CP
) 36.9 Hz), 128.8-128.9 (m), 130.2 (d, J CP ) 23.0 Hz), 130.8 (d,
J CP ) 24.6 Hz), 131.3-131.5 (m), 132.4-132.5 (m); IR (KBr)
C
12H24BOP: C, 63.74; H, 10.70. Found: C, 63.53; H, 10.77.
(R )-t er t -B u t y l(h y d r o x y m e t h y l)m e t h y lp h o s p h i n e -
2900, 2390, 1440, 1030 cm-1; FAB MS (rel intensity) 423 (M+
-
Bor a n e (2b). To a stirred, cooled (-78 °C) solution of (-)-
sparteine (10.7 g, 46 mmol) in Et2O (100 mL) was added s-BuLi
(46.0 mL of a 1.0 M cyclohexane solution, 46 mmol) under Ar
atmosphere. After 15 min, a solution of tert-butyl(dimethyl)-
phosphine-borane (1b) (4.62 g, 35 mmol) in Et2O (100 mL) was
added dropwise, and the mixture was stirred at -78 °C. Three
hours later, triethyl phosphite (2.99 g, 18 mmol) was added, and
oxygen gas was blown through the solution with vigorous
stirring. The mixture was kept at -78 °C under O2 atmosphere
for 1 h, and the reaction was quenched by 1 M HCl. The organic
layer was separated, and the aqueous layer was extracted with
EtOAc. The combined organic layers were washed with brine
and dried over Na2SO4. The solvent was evaporated on a rotary
evaporator, and the residue was purified by flash chromatog-
raphy on silica gel (hexane/EtOAc, 3:1) to give 2b as a pasty
H, 42), 409 (M+ - BH3 - H, 100). Anal. Calcd for C24H36B2OP2:
C, 67.97; H, 8.56. Found: C, 68.01; H, 8.74.
(R)-[(Bor an ato(cycloh exyl)m eth ylph osph in o)m eth yloxy]-
d ip h en ylp h osp h in e-Bor a n e (4c). This compound was pre-
pared from 2c (1.22 g, 7 mmol) according to the procedure
described for the preparation of the 1-adamantyl substituted
compound. After workup, the residue was purified by flash
chromatography on silica gel (hexane/EtOAc, 5:1) to give product
(4c) as a colorless oil (2.40 g, 92%): [R]27 -7.3 (70% ee, c 1.4,
D
CHCl3); 1H NMR (400 MHz, CDCl3) δ 0.1-1.0 (m, 6 H), 1.32 (d,
2J HP ) 10.1 Hz, 3 H), 1.20-1.87 (m, 11 H), 4.13 (dd, J HH ) 13.0
Hz, 2J HP ) 5.1 Hz, 1 H), 4.30 (dd, J HH ) 13.0 Hz, 2J HP ) 5.6 Hz,
1 H), 7.47-7.59 (m, 6 H), 7.70-7.75 (m, 4 H); 13C NMR (100
MHz, CDCl3) δ 4.7 (d, J CP ) 36.1 Hz), 25.6, 26.0, 26.1, 26.2-
26.3, 31.1 (d, J CP ) 34.5 Hz), 60.4 (d, J CP ) 37.0 Hz), 128.8-
128.9 (m), 130.2 (d, J CP ) 10.6 Hz), 130.8 (d, J CP ) 10.7 Hz),
solid (3.77 g, 73%): mp 157-160 °C; [R]28 -9.8 (91% ee, c 1.0,
D
1
CHCl3); H NMR (400 MHz, CDCl3) δ 0.39 (qd, J HB ) 99.3 Hz,
2J HP ) 14.0 Hz, 3 H), 1.21 (d, 3J HP ) 13.5 Hz, 9 H), 1.27 (d, 2J HP
) 10.1 Hz, 3 H), 2.05 (s, 1 H), 3.96 (d, J HH ) 13.3 Hz, 1 H), 4.05
(d, J HH ) 13.3 Hz, 1 H); 13C NMR (100 MHz, CDCl3) δ 3.0 (d,
J CP ) 34.4 Hz), 25.4 (d, 2J CP ) 10.6 Hz), 27.2 (d, J CP ) 32.0 Hz),
57.0 (d, J CP ) 37.7 Hz); IR (KBr) 3480, 2970, 2380, 1070, 910
cm-1. Anal. Calcd for C6H18BOP: C, 48.70; H, 12.26. Found: C,
48.84; H, 12.31.
131.2-131.4 (m), 132.4; IR (neat) 2940, 2380, 1440, 1030 cm-1
HRMS calcd for C20H32B2OP2 372.2114, found 372.2124.
;
(R)-ter t-Bu tylm eth yl(p-tolu en esu lfon yloxym eth yl)p h os-
p h in e-Bor a n e (5b). To a stirred, cooled (0 °C) solution of (R)-
tert-butyl(hydroxymethyl)methylphosphine-borane (2b) (444 mg,
3 mmol) in triethylamine (4.5 mL) was added p-toluenesulfonyl
chloride (1.14 g, 6 mmol) in one portion, and the mixture was
vigorously stirred at room temperature. One hour later, the
reaction mixture was treated with 1 M HCl. The organic layer
was separated, and the aqueous layer was extracted with ethyl
acetate three times. The combined organic layers were washed
(R )-C y c lo h e x y l(h y d r o x y m e t h y l)m e t h y lp h o s p h in e -
Bor a n e (2c). This compound was prepared from 1c (474 mg, 3
mmol) according to the procedure described for the preparation
of 2a . After workup, the residue was purified by flash chroma-