acid (0.010 g) were allowed to react together in acetonitrile
(20 cm3) solution as in the above preparation of ( )-1,2-O-
(xanthen-9-ylidene)glycerol 17a. The products were worked up
and chromatographed in the same way to give the title com-
pound 17b (Found: C, 71.6; H, 6.2. C18H18O4ؒ0.2 H2O requires
C, 71.60: H, 6.14%) as a colourless solid (0.60 g, 67%), mp 137–
138 ЊC, Rf 0.60 (system A); λmax (EtOH)/nm 297 (ε/dm3 molϪ1
cmϪ1 3910); δH [(CD3)2SO] 2.34 (3 H, s), 2.36 (3 H, s), 3.73 (2 H,
m), 4.04 (1 H, t, J 7.9), 4.39 (1 H, dd, J 6.3 and 7.8), 4.60 (1 H,
m), 5.11 (1 H, t, J 5.6), 7.15 (2 H, dd, J 5.3 and 8.4), 7.24 (2 H,
dd, J 1.9 and 8.3), 7.48 (1 H, d, J 1.4), 7.63 (1 H, d, J 1.6);
δC [(CD3)2SO] 20.46, 20.50, 61.06, 67.47, 78.27, 100.46, 115.84,
116.09, 122.72, 123.37, 126.18, 126.72, 130.58, 130.76, 132.13,
132.23, 148.70, 149.21.
portion to a stirred, cooled (ice–water-bath) mixture of 1,2:5,6-
di-O-(xanthen-9-ylidene)--mannitol 19a (3.15 g, 5.85 mmol),
sodium hydrogen carbonate (1.96 g, 23.3 mmol) and ethyl acet-
ate (115 cm3). After 1 h, the products were filtered through a
bed of Celite (20 g) and the residue was washed with ethyl
acetate (30 cm3). The combined filtrate and washings were
added dropwise over a period of 15 min to a stirred solution of
sodium borohydride (1.75 g, 46.3 mmol) in ethanol (115 cm3) at
0 ЊC (ice–water-bath). After a further period of 1 h, sodium
hydroxide pellets (0.80 g) and then 1.0 mol dmϪ3 aq. sodium
hydroxide (50 cm3) were added with continued stirring. The
products were filtered and the layers were separated. The aque-
ous layer was extracted with dichloromethane (3 × 20 cm3) and
the combined organic layers were concentrated to dryness
(water-pump, followed by oil-pump). When petroleum spirit
(100 cm3) was added to a solution of the residue in dichloro-
methane (20 cm3), the title compound 20a (2.58 g, 81%)
[Found, in material recrystallized from ethyl acetate–petroleum
spirit: C, 70.85; H, 5.1. C16H14O4 requires C, 71.10; H, 5.22%]
was obtained as a colourless solid, mp 105–107 ЊC; Rf 0.52
1,2:5,6-Di-O-(xanthen-9-ylidene)-D-mannitol 19a
A solution of -mannitol 18 (1.82 g, 10.0 mmol) in dry pyridine
was evaporated under reduced pressure and the residue was
redissolved in dry pyridine (30 cm3). 9,9-Dichloroxanthene 14a
(see above under preparation of 9,9-dimethoxyxanthene 15a;
6.32 g, ca. 25 mmol) was added to the stirred, cooled (ice–
water-bath) solution and the reactants were allowed to warm to
room temperature. After 1 h, the products were poured into
saturated aq. sodium hydrogen carbonate (150 cm3). After the
resulting mixture had been stirred at room temperature for 1 h,
the precipitate was collected by filtration and washed with water
(340 cm3). The air-dried solid was suspended in ethyl acetate (25
cm3) for 10 min and then petroleum spirit (25 cm3) was added.
After 1 h, the mixture was filtered and the residue was washed
with ethyl acetate–petroleum spirit (1:1 v/v; 40 cm3) to give the
title compound 19a as an off-white solid (4.55 g, 84.5%) (Found,
in material recrystallized from ethyl acetate: C, 71.0; H, 4.8.
C32H26O8 requires C, 70.89: H, 4.91%), mp 222.5–224 ЊC; Rf
0.53 (system A); δH [(CD3)2SO] 3.83 (2 H, t, J 7.7), 4.13 (2 H,
m), 4.31 (2 H, dd, J 6.2 and 8.3), 4.62 (2 H, dd, J 6.9 and 13.9),
5.25 (2 H, d, J 7.7), 6.81 (2 H, m), 7.22 (6 H, m), 7.34 (2 H, m),
7.41 (2 H, m), 7.64 (4 H, dd, J 1.3 and 7.8); δC [(CD3)2SO] 68.60,
70.91, 77.24, 100.64, 116.56, 116.79, 123.40, 123.73, 123.80,
124.02, 126.79, 127.04, 130.43, 130.51, 150.97, 151.52.
(system A); [α]2D0 ϩ15.7 (c 1.5, ethanol). The H and 13C NMR
1
spectra [(CD3)2SO] were identical with those indicated above
for the racemic material.
(b) Water (1.0 cm3), sodium hydrogen carbonate (0.10 g, 1.2
mmol) and sodium metaperiodate (0.853 g, 4.0 mmol) were
added to a stirred solution of 1,2:5,6-di-O-(xanthen-9-ylidene)-
-mannitol 19a (0.538 g, 1.00 mmol) in THF (10 cm3) at room
temperature. After 4 h, the products were concentrated under
reduced pressure. The residue was dissolved in dichloromethane
(30 cm3) and the solution was washed with saturated aq.
sodium hydrogen carbonate (2 × 30 cm3). The combined aq.
layers were back-extracted with dichloromethane (2 × 20 cm3).
The combined organic layers were dried (MgSO4) and then
added dropwise over a period of 15 min to a stirred solution of
sodium borohydride (0.227 g, 6.0 mmol) in absolute ethanol
(10 cm3) at room temperature. After a further period of 1 h,
acetone (5 cm3) was added and 10 min later the products were
concentrated to dryness under reduced pressure. The residue
was dissolved in dichloromethane (20 cm3) and the solution was
washed with saturated aq. sodium hydrogen carbonate (3 × 20
cm3)Thecombinedaq. layerswereback-extractedwithdichloro-
methane (2 × 20 cm3). The combined organic layers were dried
(MgSO4), and evaporated under reduced pressure to give a
colourless residue, which was crystallized from ethyl acetate–
petroleum spirit to give the title compound 20a (0.508 g, 94%) as
a colourless solid. This material was identical in all respects
with that described under heading (a) above.
1,2:5,6-Bis-O-(2,7-dimethylxanthen-9-ylidene)-D-mannitol 19b
A solution of -mannitol 18 (0.364 g, 2.0 mmol) in dry pyridine
(5 cm3) was evaporated under reduced pressure. The residue was
re-evaporated with dry pyridine (5 cm3) and was then sus-
pended in dry pyridine (10 cm3). 9,9-Dichloro-2,7-dimethyl-
xanthene 14b (see above under preparation of 9,9-dimethoxy-
2,7-dimethylxanthene 15b; 1.34 g, ca. 4.8 mmol) was added to
the cooled (ice–water-bath), stirred solution. After 10 min, the
reactants were allowed to warm to room temperature with con-
tinued stirring. After a further period of 2 h, methanol (1 cm3)
was added and the products were concentrated under reduced
pressure. The residue was partitioned between dichloromethane
(50 cm3) and saturated aq. sodium hydrogen carbonate (50
cm3). The dried (MgSO4) organic layer was evaporated under
reduced pressure. The residue was purified by short column
chromatography on silica gel; the appropriate fractions, which
were eluted with dichloromethane–methanol (99 : 1 v/v), were
combined, and evaporated under reduced pressure to give the
(S)-(؉)-1,2-O-(2,7-Dimethylxanthen-9-ylidene)glycerol 20b
Water (1.5 cm3), sodium hydrogen carbonate (0.05 g, 0.6 mmol)
and sodium metaperiodate (0.236 g, 1.1 mmol) were added
to a stirred solution of 1,2:5,6-bis-O-(2,7-dimethylxanthen-9-
ylidene)--mannitol 19b (0.330 g, 0.55 mmol) in THF (5 cm3) at
room temperature. After 3 h, the products were concentrated
under reduced pressure and the residue was partitioned
between dichloromethane (15 cm3) and saturated aq. sodium
hydrogen carbonate (15 cm3). The aqueous layer was separated
and back-extracted with dichloromethane (2 × 5 cm3). The
combined organic layers were dried (MgSO4) and added drop-
wise over a period of 30 min to a suspension of sodium boro-
hydride (0.083 g, 2.2 mmol) in ethanol (5 cm3). After 30 min,
acetone (1 cm3) was added. After a further period of 10 min, the
products were evaporated under reduced pressure. The residue
was partitioned between dichloromethane (15 cm3) and satur-
ated aq. sodium hydrogen carbonate (15 cm3). The layers were
separated and the aqueous layer was back-extracted with
dichloromethane (2 × 5 cm3). The combined organic layers
were dried (MgSO4), and concentrated under reduced pressure.
The residue was fractionated by short-column chromatography
title compound 19b as a colourless froth (0.97 g, 81%) (Found:
12
Mϩ, 594.2231.
C
1H3416O8 requires M, 594.2254), Rf 0.59
36
(system A); δH (CDCl3) 2.00 (6 H, s), 2.37 (6 H, s), 3.93 (2 H, d,
J 7.7), 4.19 (2 H, t, J 7.8), 4.40 (2 H, m), 4.72 (2 H, m), 5.36
(2 H, d, J 7.7), 7.15 (6 H, m), 7.26 (2 H, m), 7.47 (4 H, d, J 6.9);
δC (CDCl3) 20.00, 20.44, 68.16, 70.61, 76.93, 100.51, 115.80,
116.07, 122.52, 123.21, 126.43, 130.57, 130.64, 132.13, 148.66,
149.13.
(S)-(؉)-1,2-O-(Xanthen-9-ylidene)glycerol 20a
(a) Lead() acetate (9.05 g, 20.4 mmol) was added in one
1812
J. Chem. Soc., Perkin Trans. 1, 2001, 1807–1815