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reflux in a 1000 ml round-bottomed flask equipped with
a dropping funnel and reflux condenser. A solution of
FeCl3·6H2O (30.00 g, 111 mmol) in water (60 mL) was
added dropwise with vigorous stirring and the mixture
heated under reflux for another 30 min after completion
of the addition. Racemic 2,2%-dihydroxy-1,1%-binaphthyl
precipitated during the procedure and the hot slurry
was filtered through a preheated Buchner funnel. After
washing with boiling water until the filtrate became
colorless, the brownish residue was dried by sucking air
through the funnel for another 1.5 h. Two recrystallisa-
tion procedures were performed from refluxing toluene
(180 mL) with cooling to 40°C in a water bath of that
temperature and filtration through a preheated filtra-
tion funnel. The mother liquors were combined, the
solvent removed and the residue twice recrystallised in
the same fashion from toluene (2×80 mL). Both sets of
crystals were combined and dried under vacuum in the
desiccator (16 h at 20 mbar). The product was obtained
as colorless needles (11.81 g, 41.11 mmol, 79%; mp:
219°C, lit 218°C6).
4.4.3. Formation of (S)-BINOL-(S,S)-cyclohexanedi-
amine·toluene inclusion complex. The crude BINOL was
dissolved in toluene (50 ml) and the solution added to
(S,S)-1 (1.39 g, 12.20 mmol, 1.2 equiv.). The mixture
was stirred for 30 min at room temperature and then
heated to reflux for 5 min. Upon slow cooling to room
temperature, a precipitate was formed which was
filtered, washed with ice-cold toluene (2×10 mL) to give
colorless needles of (S)-2·(S,S)-1·toluene (4.20 g, 8.51
mmol, 43%, >99.8% ee) after removal of solvent traces
in the desiccator under reduced pressure (16 h at 20
mbar). The filtrate was kept for further manipulations.
4.4.4. Recovery of excess (S,S)-cyclohexanediamine. The
filtrate was transferred into a round-bottomed flask, the
solvent was evaporated and the residue was dissolved in
a mixture of methanol (45 mL) and water (5 mL).
DL-(+/−)-Tartaric acid (0.751 g, 5.00 mmol, ꢀ2.3
equiv. of calculated excess diamine) was added in one
portion and the mixture heated to reflux for 16 h.
During the procedure a crystalline precipitate (S,S-1·D-
(−)-tartrate: 0.302 g, 1.14 mmol, 9% of total S,S-
diamine employed, >99.8% ee [HPLC]) was formed
and, after cooling to room temperature, it was filtered,
washed with methanol (2×10 mL) and dried in the oven
(12 h at 80°C).
4.4. Resolution of racemic 2—formation of the inclu-
sion complexes
4.4.1. Formation of (R)-BINOL-(R,R)-cyclohexanedi-
amine·toluene inclusion complex. Racemic 2 (5.73 g,
20.03 mmol) was added to a solution of (R,R)-1 [2.514
g, 22.05 mmol, 2.2 equiv. with respect to (R)-2] in
toluene (60 mL) and the solution was stirred for 30 min
at room temperature, heated to 100°C for 10 min and
then slowly cooled to room temperature. A precipitate
was formed which was filtered and washed with cold
toluene (2×10 mL). The mother liquor was kept for
further manipulations (vide infra). Recrystallisation of
the precipitate from hot toluene (20 mL) afforded
enantiomerically pure (R)-2·(R,R)-1·toluene (4.47 g,
9.06 mmol, 45%, 99.8% ee [HPLC of the liberated
BINOL-vide infra]) as colorless needles which were
dried in the desiccator under vacuum (16 h at 20 mbar).
4.5. Liberation of enantiopure (R)-2 and (S)-2 from
their inclusion complexes
4.5.1. Liberation of (R)-BINOL and recovery of (R,R)-1
(+)-tartrate. The inclusion complex (R)-2·(R,R)-
1·toluene (4.47 g, 9.06 mmol) was dissolved in a mix-
ture of water (9 mL) and methanol (80 mL) and
L
-(+)-tartaric acid (1.136 g, 9.97 mmol, 1.1 equiv.) was
added in one portion. The reaction was heated under
reflux for 16 h and after cooling the precipitate {(R,R)-
1 (+)-tartrate: 2.38 g, 9.02 mmol, >99% recovery for the
reaction, 41% of total (R,R)-diamine employed, >99.8%
ee [HPLC]} was removed by filtration, washed with
methanol (2×20 mL) and dried in the oven (12 h at
80°C). Water (30 mL) was added to the filtrate and the
methanol was removed under reduced pressure afford-
ing the precipitation of the (R)-BINOL. The precipitate
was filtered, washed with water (5×20 mL) and trans-
ferred into a separatory funnel charged with CH2Cl2
(50 mL) and saturated aqueous Na2CO3 solution (20
mL). After vigorous shaking, the organic layer was
separated, dried over MgSO4 and after solvent removal
under reduced pressure (R)-2 (2.43 g, 8.50 mmol, 94%,
>99.8% ee) was obtained in enantiomerically pure form.
4.4.2. Liberation of crude (S)-BINOL and recovery of
excess (R,R)-cyclohexanediamine. The mother liquor
(vide supra) was transferred into a round-bottomed
flask, the solvent was evaporated and the pale-yellow,
gluey residue {(S)-2·(R,R)-1: 4.28 g, 96% ee [HPLC]}
was dissolved in a mixture of methanol (90 mL) and
water (10 mL). -(+)-Tartaric acid (1.875 g, 12.5 mmol,
L
1.1 equiv. of calculated excess diamine) was added in
one portion and the mixture heated to reflux for 16 h.
During the procedure a crystalline precipitate {(R,R)-1
(+)-tartrate: 1.43 g, 5.43 mmol, 25% of total (R,R)-
diamine employed, 99.8% ee [HPLC]} was formed and,
after cooling to room temperature, it was filtered,
washed with methanol (2×20 mL) and dried in the oven
(12 h at 80°C). The filtrate was transferred into a
round-bottomed flask, water (30 mL) was added and
the methanol was removed at the rotary evaporator.
During the procedure, the crude (S)-BINOL precipi-
tated almost quantitatively and was filtered, washed
with water (5×20 mL) and dried in the desiccator under
reduced pressure (16 h at 20 mbar) to give (S)-2 (2.90 g,
10.14 mmol, 51%, 96% ee [HPLC]).
4.5.2. Liberation of (S)-BINOL and recovery of (S,S)-1
(−)-tartrate. In an almost identical procedure (S)-
2·(S,S)-1·toluene (4.20 g, 8.51 mmol) was dissolved in a
mixture of water (9 mL) and methanol (80 mL) and
DL-( )-tartaric acid (2.70 g, 18.0 mmol, 2.2 equiv.) was
added in one portion. The reaction was heated under
reflux for 16 h and after cooling the precipitate {(S,S)-1
(−)-tartrate: 2.24 g, 8.48 mmol, >99% for the reaction,
70% of total (S,S)-diamine employed, >99.8% ee
[HPLC]} was removed by filtration, washed with
methanol (2×20 mL) and dried in the oven (12 h at