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4.2. Alkenylboronic acid syntheses
5.01 (dd, J = 9.3, 6.6 Hz, 1H), 5.52 (d, J = 5.0 Hz,
OH), 7.17–7.23 (m, 10H), 7.88 (s, 1H), 8.54 (d,
J = 10 Hz, NH). 13C NMR (125 MHz, DMSO-d6): d
56.89, 74.82, 126.76, 127.00, 127.20, 127.47, 127.57,
128.17, 139.98, 142.75, 159.97.
4.2.1. (2Z)-2-Buten-2-ylboronic acid 1. A 100-mL reac-
tion flask, fitted with an addition funnel, was charged
with 2-butyne (1.6 mL, 20 mmol) in anhydrous dichlo-
romethane (8 mL) and cooled to ꢀ10 ꢁC (ice-salt bath).
HBBr2ÆSMe2 (1 M, in dichloromethane, 20 mL,
20 mmol) was transferred to the addition funnel via syr-
inge and added to the alkyne dropwise over 15 min.
After stirring for 1 h at room temperature, the reaction
was completed by 11B NMR (2.8 ppm), then cooled to
0 ꢁC and added, via cannula, to a stirred mixture of
water (50 mL) and ether (75 mL) at 0 ꢁC. After 15 min
the water layer (bottom) was separated, and the organic
layer was washed with cold water (2 · 25 mL) and brine
(2 · 25 mL), dried over MgSO4, filtered, and evaporated
under reduced pressure to yield pure (2Z)-2-buten-2-
The N-formyl compound, (1S,2R)-2-formylamino-1,2-
diphenylethanol, (1.15 g, 4.76 mmol) was suspended in
dry THF (30 mL) and cooled to ꢀ10 ꢁC. Lithium alumi-
num hydride (1 M in THF, 7 mmol) was added drop-
wise via syringe to the suspension, which turned clear
during the addition. After stirring at room temperature
for 24 h, more LiAlH4 (3 mmol) was added, and the
reaction let to stir for another 24 h. After cooling to
0 ꢁC, the reaction mixture was quenched with 3 M
NaOH and extracted with ether (3 · 20 mL). The ether
layers were dried with MgSO4 and evaporated to give
a white solid (0.98 g), which still contained 15% alde-
1
ylboronic acid as a white solid (1.65 g, 83% yield). H
1
NMR (500 MHz, CDCl3): d 1.77 (s, 3H), 1.81 (d,
J = 6.75 Hz, 3H), 6.85 (qq, J = 6.5, 1.5 Hz, 1H). 13C
NMR (125 MHz, CDCl3): d 12.76, 14.89, 143.73. 11B
NMR (80.25 MHz, CDCl3): d 28.28; HRMS (FAB)
m/z calcd for C4H8O2B (MꢀH)ꢀ: 99.0696, found
99.0618.
hyde by H NMR. Recrystallization from ethyl acetate
provided pure g (0.84 g, 77% yield) as shiny white nee-
25
D
1
dles ½aꢁ ¼ ꢀ6:8 (c 4.4, CHCl3). H NMR (500 MHz,
DMSO-d6): d 1.75 (br s, NH), 2.02 (s, 3H), 3.58 (d,
J = 5.5 Hz, 1H), 4.64 (app. t, J = 5.3 Hz, 1H), 5.23 (d,
J = 4.0 Hz, OH), 7.12–7.21 (m, 10H); 13C NMR
(125 MHz, DMSO-d6): d 34.15, 70.61, 76.19, 126.46,
126.74, 126.94, 127.35, 127.41, 128.50, 140.88, 143.23;
HRMS (ESI) m/z calcd for C15H17NO (M+H)+:
228.1391, found 228.1383.
4.2.2. (2E)-2-Buten-2-ylboronic acid 3. 2-Bromo-trans-
2-butene (1.01 mL, 10 mmol) was dissolved in THF
(10 mL), cooled to ꢀ78 ꢁC, and t-BuLi (1.7 M in pen-
tane, 12.9 mL, 22 mmol) was added dropwise. The
bright yellow solution was stirred at ꢀ78 ꢁC for 1 h,
and triisoproylborate (3.5 mL, 15 mmol) then added.
The reaction mixture was stirred at ꢀ78 ꢁC for 4 h and
then let warm to 0 ꢁC over the course of 3 h. Saturated
NH4Cl (10 mL) was added, and stirring continued at rt
for 30 min. The reaction mixture was extracted with
diethyl ether (2 · 20 mL), and the ether portions com-
bined, washed with H2O, and dried over MgSO4. After
filtration and evaporation, analytically pure 3 was ob-
tained as a white solid (0.5 g, 50% yield). 1H NMR
(500 MHz, CDCl3): d 1.84 (s, 3H), 2.04 (d, J = 7.5 Hz,
3H), 6.43 (q, J = 6.0 Hz, 1H). 13C NMR (125 MHz,
CDCl3): d 17.15, 22.56, 146.16. 11B NMR (80.25 MHz,
4.3.2. (1S,2R,10R)-2-(10-Phenylethyl)amino-1,2-diphenyl-
ethanol h. A 50-mL flask fitted with a reflux condenser
was charged with ( )-trans-stilbene oxide (1.96 g,
10 mmol),
(R)-(+)-a-methylbenzylamine
(3.87 mL,
30 mmol) and deionized water (2 mL). The mixture
was refluxed for 24 h and monitored by TLC for the dis-
appearance of starting epoxide. After cooling to room
temperature, 10 mL of water was added. Large chunks
of off-white sticky solid separated from the reaction mix-
ture. The liquid was decanted off, and the solid soni-
cated in 10 mL of ethanol. The white crystalline solid
was filtered and washed with cold ethanol to give the
title compound as a single diastereomer (1.35 g, 43%).
CDCl3):
d
28.65; HRMS (FAB) m/z calcd for
Recrystallization from ethanol gave shiny white needles
25
D
C4H8O2B (MꢀH)ꢀ: 99.0696, found 99.0618.
½aꢁ ¼ þ40 (c 4.0, CHCl3). 1H NMR (500 MHz,
CDCl3): d 1.36 (d, J = 6.5 Hz, 3H), 1.81 (br s, NH),
3.55 (d, J = 4.0 Hz, OH), 3.78 (q, J = 6.5 Hz, 1H), 4.0
(d, J = 4.5 Hz, 1H), 4.96 (t, J = 4.5 Hz, 1H), 6.98–7.00
(m, 5H), 7.17–7.34 (m, 10H); 13C NMR (125 MHz,
CDCl3): d 23.11, 54.62, 65.65, 75.41, 126.51, 126.68,
127.21, 127.37, 127.54, 127.85, 128.13, 128.22, 128.66,
139.25, 140.54, 145.56; HRMS (ESI) m/z calcd for
C22H23NO (M+H)+: 318.1877, found 318.1852.
4.3. Ligand synthesis
4.3.1. (1S,2R)-2-Methylamino-1,2-diphenylethanol g.
This procedure was derived from that of Effenberger,
who used a different but structurally similar substrate.19
Acetic anhydride (0.94 mL, 10 mmol) and formic acid
(0.38 mL, 10 mmol) were heated together at 60 ꢁC for
30 min, cooled to room temperature, and added to a sus-
pension of (+)-2-amino-1,2-diphenylethanol (1.07 g,
5 mmol) in dry diethyl ether (25 mL) at ꢀ40 ꢁC (dry
ice/CH3CN). The suspension was left to stir at ꢀ40 ꢁC
for 2 h and then at room temperature for 10 min, at
which point the reaction mixture solidified into a white
mass. More ether (10 mL) was added, and the mass bro-
ken up, filtered, and washed several times with fresh
ether. This yielded (1S,2R)-2-formyl-1,2-diphenyletha-
4.4. General procedure for the synthesis of vinyloxaza-
borolidines and vinylboronic esters
The preparation of (Z)-1-methyl-1-propenyl oxazabor-
olidine 2f is representative. An oven-dried 50 mL
round-bottom flask equipped with a side arm, con-
denser, and stir bar was charged with (2Z)-2-buten-2-
ylboronic acid (0.3 g, 3 mmol) and (ꢀ)-2-amino-1,2-
diphenylethanol (0.64 g, 3 mmol). The solids were dis-
solved in THF (10 mL), and CaH2 (0.25 g, 6 mmol) then
1
nol as a fine white solid (1.15 g, 96% yield). H NMR
(500 MHz, DMSO-d6): d 4.76 (app. t, J = 5.7 Hz, 1H),