KINETIC ANALYSIS OF ASYMMETRIC AMPLIFICATION
323
equipped with a Model P4000 pump, a Model AS3000
autosampler with a 10 ml loop and a Model UV1000 UV
detector. Gas chromatographic (GC) analyses were per-
formed on an HP 5890 gas chromatograph with flame
ionization detection. GC response factors for ꢀ-pinene
and isopinocampheol relative to the internal standard
anisole were determined.
areas were corrected for the response factors of ꢀ-pinene
(0.66) and isopinocampheol (0.63) to anisole.
General procedure for the preparation of bis(2,6,6-
trimethylbicyclo[3.1.1]hept-3-yl)borinic acid-8-quinolyl
(
Dip-Q) solutions. A 10 ml stock solution of 8-hydroxy-
quinoline (1.0 M) was prepared in anhydrous diethyl
ether; sonication was required to complete dissolution.
The stock solution (1.0 ml) was added to a clean, dry test-
tube. A 0.5 ml aliquot of Dip-Cl reaction mixture was
slowly added to the solution and a white precipitate
immediately formed and the solution turned fluorescent
green–yellow. The solution was vortex mixed to complete
mixing. The solution was filtered through a 0.2 mm filter
to give a clear fluorescent green–yellow solution which
was used for analysis by HPLC (see below).
Software. P-E Nelson (Cupertino, CA, USA) Access*
Chrom software was used for the analysis of HPLC data.
Non-linear regression analyses for the ‘Iterative curve
fitting method’ (for K and g), ‘Modeling chiral purity
over time’ and ‘Modeling ratio of Dip-Q isomers’ sec-
tions were determined with the Solver tool of the Micro-
soft Excel software package.
Preparation of B-chlorodiisopinocampheylborane (Dip-Cl)
solutions. A 100 ml, three-necked, jacketed flask was
connected to a nitrogen/vacuum manifold and equipped
with a magenetic stir bar. The flask was evacuated and
refilled with nitrogen three times. Using a plastic syringe,
anhydrous diethyl ether (5.5 ml) was added and, with
Stereochemical analysis of Dip-Q complexes. From the
above Dip-Cl solutions, 100 ml were diluted to 100 ml
with methanol to
ꢂ1
a
.15 mg ml . Analysis was performed using an HPLC
final concentration of ca
0
ꢃ
system equipped with a YMC J-sphere M-80 ODS
column (25.0 ꢁ 0.46 cm i.d.) and a UV (ꢂ¼ 265 nm).
The mobile phase consisted of 85:15 methanol–water
stirring, the vessel was cooled to ꢂ10 C. A 3.2 ml
(
20.1 mmol) aliquot of ꢀ-pinene was added. Monochlor-
oborane–methyl sulfide complex (1.0 ml, 9.6 mmol) was
added in a single addition using a plastic syringe. The
ꢂ1
and dimethyl-ꢁ-cyclodextrin (DM-ꢁ-CD) (10 mM l ) as
a chiral mobile phase additive. HPLC was performed at
ꢃ
vessel was warmed to the desired temperature of 10 C
ꢂ1
ambient temperature with a flow-rate of 0.5 ml min .
The column was allowed to equilibrate for ꢆ90 min
and allowed to stir for ca 15 h at constant temperature. A
fine white slurry was observed after several hours. Ana-
lysis (see below) indicated a concentration of 1.0 M in
Dip-Cl.
(approximately three column volumes). The total run
time was 100 min; typical retention times were (þ)(ꢂ)-
0
isomer 61.8 min (k ¼ 11.1), (þ)(þ)-isomer 67.2 min
0
0
(
k ¼ 12.1) and (ꢂ)(ꢂ) isomer 70.3 min (k ¼ 12.7).
Quantitation of Dip-Cl. The quantitation of Dip-Cl is
performed by oxidation of the isopinocampheyl ligands
to isopinocampheol and analysis by GC using anisole as
an internal standard. To a 100 ml volumetric flask was
added tetrahydrofuran (4 ml), aqueous sodium hydroxide
Stereochemical analysis of Dip-Cl via Dip-Q complexation
during conversion. Approximately 1 ml of the reduction
reaction mixture was quenched into a test-tube containing
2
ml of 1.0 M 8-hydroxyquinoline in diethyl ether. The
[
2 ml, 25% (w/v)] and a stir bar. A precisely measured
resulting slurry was filtered through a 0.45 mm syringe
filter. A 1.0 ml aliquot of the filtrate was diluted to 100 ml
aliquot (1.0 ml) of the mixture was removed from the
Dip-Cl reaction vessel. This aliquot was added to the
basic solution at the bottom of the 100 ml volumetric
flask. The solution was stirred for 30 min, then hydrogen
peroxide (2 ml, 30%) was added and the solution was
stirred for another 30 min. A solution of anisole in
methanol [3.0% (v/v), 0.28 M] was prepared for use as
an internal standard, and a 10.0 ml aliquot was added to
the volumetric flask. Water (10 ml) was added and the
solution was diluted to volume with methanol. The
resulting solution was analyzed by GC using a Stabilwax
column (30 m o.d. ꢁ 0.53 mm i.d., 1.0 mm film thickness)
ꢂ1
with methanol to a final concentration of ca 0.8 mg ml .
The resulting solution was analyzed using the conditions
described in ‘Stereochemical analysis of Dip-Q com-
plexes’ above.
Analysis of reaction conversion (all studies). To monitor
the reaction, ꢆ200 ml of the reaction mixture were remo-
ved and diluted to 100 ml with 10% water in methanol,
ꢂ1
resulting in a concentration of ca 0.05 mg ml in (S)-
(ꢂ)-1-phenylethanol. The solution was analyzed by gra-
dient HPLC with the mobile phases of 0.1% phosphoric
acid in water (mobile phase A) and acetonitrile (mobile
phase B). The gradient delivery system was programmed
to deliver a 25–75% gradient sweep of mobile phase B
over 15 min followed by a 5 min hold at 75% B. A Zorbax
ꢃ
with the following temperature program: 50 C for 2 min,
ꢃ
ꢂ1
ꢃ
ꢃ
10 C min to 200 C, 200 C for 2 mins. The injector
temperature was 170 C and the detector temperature was
30 C. A 1.0 ml injection was used and the column flow-
rate was 8 ml min with a split flow of 100:1. The fol-
lowing retention times were typical: ꢀ-pinene 3.8 min,
anisole 9.2 min and isopinocampheol 14.4 min. Peak
ꢃ
ꢃ
2
ꢂ1
Rx C column (15.0 ꢁ 0.46 cm i.d.) (MAC MOD Analy-
8
tical, Chadds Ford, PA, USA) was used at ambient
Copyright # 2004 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2004; 17: 317–324