D. E. White, E. N. Jacobsen / Tetrahedron: Asymmetry 14 (2003) 3633–3638
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Oligomeric (salen)Co Complexes, 2: Typical procedure:
deoxygenated toluene (ca. 11.6 mL) was added to 8
(649 mg, 1.1 mmol) under N2, and deoxygenated
MeOH (ca. 11.6 mL) to Co(OAc)2·4H2O (545 mg, 2.2
mmol) under N2. N2 was bubbled through the resulting
solutions for 20 min to ensure complete deoxygenation.
The solution of Co(OAc)2·4H2O in MeOH (purple) was
added via cannula under N2 to the solution of 8 in
toluene (yellow) to give a deep red solution. The result-
ing mixture was stirred for 30 min under an N2 purge.
Trifluoromethanesulfonic acid (97 mL, 1.1 mmol) and
CH2Cl2 (16.6 mL) were added, and the resulting black
solution stirred for an additional 2 h under an air
atmosphere with vigorous stirring. Solvent was
removed under reduced pressure, and the residue dis-
solved in minimal CH2Cl2. Excess insoluble
Co(OAc)2·4H2O was removed via filtration through a
Celite® pad, washing with CH2Cl2 (200 mL). Removal
of solvent under reduced pressure provided complex 1a
as a paramagnetic black solid (892 mg, >99%). IR (thin
film) w 3476 (broad), 2947, 2869, 1750, 1644, 1610,
1547, 1417, 1340, 1258, 1231, 1171, 1030. MS (FAB)
m/z calcd for C68H85Co2N4O14 1299, found 1299
(100%) [n=1, M+H]+, calcd for C102H126Co3N6O21
1948, found 1948 (54%) [n=2, M]+, calcd for
reduced pressure (51 mm). Resolved epoxide was then
purified by vacuum distillation (bp 64°C/25 mmHg) to
give a clear liquid (5.46 g, 44%) in >99% ee as deter-
mined by chiral GC analysis (g-TA, 100°C, isothermal,
tR (minor)=1.8 min; tR (major)=2.4 min). [h]3D1=−9.8
(c 1.01, MeOH); lit.11 [h]2D0=+10.4 (c 3.6, MeOH, R
enantiomer).
(S)-Allyl glycidyl ether, 10: To a mixture of ( )-allyl
glycidyl ether (15.4 mL, 130 mmol) and 1a (2.6 mg,
0.0033 mmol) in a rt water bath was added H2O (1.4
mL, 78 mmol) in one portion. After stirring 24 h at rt,
resolved epoxide and excess H2O were vacuum trans-
ferred (0.45 mmHg, reaction pot: rt–52°C) to a −78°C
receiving flask. H2O was separated and the epoxide
dried over MgSO4. Filtration through a sand plug gave
a clear liquid (6.41 g, 43%) in >99% ee as determined by
chiral GC analysis (g-TA, 60°C, isothermal, tR
(minor)=6.1 min; tR (major)=8.5 min). [h]3D1=+11.6 (c
1.00, MeOH); lit.12 [h]2D5=+9.6 (c 0.94, EtOH).
(S)-Epichlorohydrin, 11: To a mixture of ( )-epichloro-
hydrin (10.3 mL, 130 mmol) and 1a (1.0 mg, 0.0013
mmol) in a rt water bath was added H2O (1.4 mL, 78
mmol) in one portion. After stirring 15 h at rt, resolved
epoxide and excess H2O were vacuum transferred (0.45
mmHg, reaction pot: rt) to a −78°C receiving flask. The
epoxide was then separated and dried by filtration
through neutral Brockmann Activity Grade I alumina
to give a clear liquid (5.27 g, 44%) in >99% ee as
determined by chiral GC analysis (g-TA, 40°C, isother-
mal, tR (major)=6.9 min; tR (minor)=8.6 min). [h]3D1=
+32.9 (c 0.998, MeOH); lit.13 [h]D25=+34.5 (c 1.20,
MeOH).
C
136H168Co4N8O28 2597, found 2597 (14%) [n=3, M]+.
2b: The reaction was carried out on a 0.7 mmol scale
with respect to ligand to provide complex 1b as a
paramagnetic black solid (552 mg, 88%). IR (thin film)
w 3387 (broad), 2950, 2869, 1754, 1651, 1644, 1606,
1548, 1538, 1417, 1347, 1229, 1183, 1164, 1027. MS
(FAB) m/z calcd for C68H84Co2N4O14 1298, found 1298
(100%) [n=1, M]+, calcd for C102H126Co3N6O21 1948,
found 1948 (12%) [n=2, M]+.
(R)-Propylene oxide, 12: To a mixture of ( )-propylene
oxide (105 mL, 1.5 mol) and 1a (3.6 mg, 0.0045 mmol)
in a rt water bath was added H2O (16.2 mL, 0.90 mol)
in one portion. The reaction vessel was sealed to pre-
vent substrate evaporation. (CAUTION! An initial
pressure buildup is observed due to the volatility of the
epoxide under the exothermic reaction conditions. Care
should be taken to use equipment adequate for elevated
pressures). After stirring 24 h at rt, resolved epoxide
and excess H2O were vacuum transferred (51 mmHg,
reaction pot: rt) to a −78°C receiving flask. The epoxide
was dried over MgSO4 and filtered through a sand plug
to give a clear liquid (35.2 g, 40%) in >99% ee as
determined by chiral HPLC analysis of the 2-napthyl-
sulfide derivative (obtained by ring opening with 0.8
equiv. 2-napthalenethiol and 0.8 equiv. Et3N in MeOH
at 4°C and subsequent purification of the terminal
addition product by preparative TLC, Chiracel® OD,
4% EtOH/Hexanes, 1 mL/min, 220 nm, tR (minor)=
13.2 min; tR (major)=15.6 min). [h]3D1=+13.8 (neat);
lit.14 [h]2D5=+13.9 (neat).
2c: The reaction was carried out on a 0.42 mmol scale
with respect to ligand to provide complex 1c as a
paramagnetic black solid (296 mg, 82%). IR (thin film)
w 3456 (broad), 2945, 2917, 2867, 1751, 1644, 1608,
1417, 1340, 1228, 1182, 1164. MS (FAB) m/z calcd for
C68H84Co2N4O14 1298, found 1298 (100%) [n=1, M]+,
calcd for C102H126Co3N6O21 1948, found 1948 (15%)
[n=2, M]+.
2d: The reaction was carried out on a 0.48 mmol scale
with respect to ligand to provide complex 1d as a
paramagnetic black solid (361 mg, 92%). IR (thin film)
w 3439 (broad), 2947, 2868, 1754, 1644, 1609, 1538,
1532, 1417, 1350, 1228, 1182, 1167. MS (FAB) m/z
calcd for C68H85Co2N4O14 1299, found 1299 (100%)
[n=1, M+H]+, calcd for C102H127Co3N6O21 1949, found
1949 (16%) [n=2, M+H]+.
3.3. Resolution of terminal epoxides, 9–13
(S)-Methyl glycidate, 9: To a mixture of ( )-methyl
glycidate (12.28 g, 120 mmol) and 1a (14.4 mg, 0.018
mmol) in a rt water bath was added H2O (1.3 mL, 72
mmol) in one portion. After stirring 16 h at rt, the
reaction was diluted with H2O (18 mL) and extracted
with CH2Cl2 (3×30 mL). The combined organic layers
were dried over Na2SO4 and concentrated under
(R)-Styrene oxide, 13: To a mixture of ( )-styrene oxide
(14.8 mL, 130 mmol) and 1d (42.8 mg, 0.052 mmol) in
a rt water bath was added H2O (1.4 mL, 78 mmol) in
one portion, and the reaction stirred at rt for 19 h.
Between 18 and 18.75 h, the diol product was observed
to precipitate from solution. At 19 h, resolved epoxide