Selective monotetrahydropyranylation of symmetrical diols catalyzed by ion-exchange resins

Article abstract of DOI:10.1021/jo980659b

Primary and secondary symmetrical diols with 2-10 carbon atoms gave selectively monotetrahydropyranyl ethers in the reaction catalyzed by wet sulfonic acid-type ion-exchange resins in 3,4-dihydro-2H-pyran (DHP)/toluene or DHP/hexane. The yields of the monoethers were higher than 80% while those of the corresponding diethers were lower than 5%. In these reactions the rate of the formation of the diethers did not increase much even after most of the diols had been consumed. In the reaction of 1,10-decanediol in DHP/hexane, the yields of the monoether were increased by the addition of DMF or DMSO. Each diol was found to have a particular DHP/hydrocarbon ratio that gave the highest selectivity for the monoether. Generally, the larger the number of carbon atoms of the diols, the smaller the ratio of DHP in the solvents to give high selectivity for the monoether. This method of the selective etherification is quite simple and practical.

Full text of DOI:10.1021/jo980659b

J . Org. Chem. 1998, 63, 8183-8187
8183
Selective Mon otetr a h yd r op yr a n yla tion of Sym m etr ica l Diols
Ca ta lyzed by Ion -Exch a n ge Resin s
Takeshi Nishiguchi,*,† Shizuo Fujisaki,‡ Masahumi Kuroda,‡ Kohtaro Kajisaki,§ and
Masahiko Saitoh§
Faculty of Agriculture and Faculty of Education, Yamaguchi University, Yamaguchi 753, J apan, and
Faculty of Engineering, Yamaguchi University, Ube, Yamaguchi 755, J apan
Received April 9, 1998
Primary and secondary symmetrical diols with 2-10 carbon atoms gave selectively monotetrahy-
dropyranyl ethers in the reaction catalyzed by wet sulfonic acid-type ion-exchange resins in 3,4-
dihydro-2H-pyran (DHP)/toluene or DHP/hexane. The yields of the monoethers were higher than
80% while those of the corresponding diethers were lower than 5%. In these reactions the rate of
the formation of the diethers did not increase much even after most of the diols had been consumed.
In the reaction of 1,10-decanediol in DHP/hexane, the yields of the monoether were increased by
the addition of DMF or DMSO. Each diol was found to have a particular DHP/hydrocarbon ratio
that gave the highest selectivity for the monoether. Generally, the larger the number of carbon
atoms of the diols, the smaller the ratio of DHP in the solvents to give high selectivity for the
monoether. This method of the selective etherification is quite simple and practical.
In tr od u ction
it is inferred that the selective monoprotection results
from two factors: the selective adsorption of the diols on
the surface of the catalysts in preference to the corre-
sponding monoethers and the formation of the diol layers
of appropriate thickness on the surface of the catalysts.
The formation of the diol layers is attributed to the
limited solubility of the diols in the solvents. The latter
factor realizing the selectivity suggests that selective
reactions such as monoetherification of symmetrical diols
may occur, even if a solid catalyst is not adsorptive, when
the following conditions are fulfilled: (1) the solubility
in solvents increases in numerical order from the smallest
in starting materials (diols) to the largest in final
products (diethers) and (2) the dissolving power of
solvents is appropriate.
Although maximum yields of the monoethers are high,5
the selective monoetherification in DHP/hexane catalyzed
by metallic sulfates supported on silica gel has one
serious problem: the diethers form very rapidly after the
majority of the diols has been consumed. Therefore, close
attention must be paid to when to terminate the reaction.
Here, we report the selective formation of monoethers
from symmetrical diols in DHP/hydrocarbon catalyzed by
strongly acidic ion-exchange resins, in which the disad-
vantage mentioned above is greatly improved.
Methods for the selective protection of one of two
identical functional groups, which exist in symmetrical
sites in a molecule, are important in organic synthesis.
Selective monoacylation of symmetrical diols has been
well studied.1 Since the protection of hydroxyl groups
by etherificaion is quite common in organic syntheses,2
it would be valuable to develop the methods to obtain
monohydroxy ethers selectively from symmetric diols. In
some cases, the monoetherification of symmetrical diols
can be achieved by Williamson reaction,1g,3 by the use of
alumina and diazomethane,1e or via cyclic compounds.4
We have already reported the selective formation of
monotetrahydro-2H-pynanyl (THP) ethers from 1,n-diols
in 3,4-dihydro-2H-pyran (DHP)/hexane catalyzed by me-
tallic sulfates supported on silica gel.5 In that reaction,
† Faculty of Agriculture.
‡ Faculty of Engineering.
§ Faculty of Education.
(1) (a) Nishiguchi, T.; Fujisaki, S.; Ishii, Y.; Yano, Y.; Nishida, A.
1994, 59, 1191. (b) Nishiguchi, T.; Kawamine, K.; Ohstuka, T. J . Org.
Chem. 1992, 57, 312. (c) Babler, J . H.; Coghlan, M. J . Tetrahedron
Lett. 1979, 22, 1971. (d) Ogawa, H.; Chihara, T.; Taya, K. J . Am. Chem.
Soc. 1985, 107, 1365. (e) Ogawa, H.; Ichimura, Y.; Chihara, T.;
Teratani, S.; Taya, K. Bull. Chem. Soc. J pn. 1986, 59, 2481. (f) Ogawa,
H.; Chihara, T.; Teratani, S.; Taya, K. J . Chem. Soc., Chem. Commun.
1986, 1337. (g) De La Zerda, J .; Barak, G.; Sasson, Y. Tetrahedron
1989, 29, 1533. (h) Leznoff, C. C. Acc. Chem. Res. 1989, 11, 327. (i)
Otera, J .; Dan-Oh, N.; Nozaki, H. J . Chem. Soc., Chem. Commun. 1991,
1742. (j) Murahashi, S.; Oda, Y.; Naota, T. Chem. Lett. 1992, 2237. (k)
Zhu, P. C.; Lin, J .; Pittman, C. U., J r. J . Org. Chem. 1995, 60, 5729.
(l) Balley, W. F.; Zarcone, L. M. J .; Rivera, A. D. J . Org. Chem. 1994,
60, 2532. (m) Zhu, L.-M.; Tedford, M. C. Tetrahedron 1990, 46, 6587.
(n) Breton, G. W. J . Org. Chem. 1997, 62, 8952. (o) Enzyme Catalysis
in Organic Synthesis; Drauz, K., Waldmann, H., Eds.; VC H: Wein-
heim, 1995. See also: Breton, G. W. J . Org. Chem. 1997, 62, 8952.
(2) (a) Greene, T. W.; Wuts, P. G. M. Protecting Groups in Organic
Synthesis, 2nd ed.; Wiley: New York, 1991. (b) Kocienski, P. J .
Protecting Groups; Georg Theme Verlag: Stuttgart, 1994.
(3) (a) Bouzide, A.; Sauve, G. Tetrahedron Lett. 1997, 38, 5945. (b)
Bessodes, M.; Boukarim, C. Synlett 1996, 1119. (c) Kalinowski, H. O.;
Crass, G.; Seebach, D. Chem. Ber. 1981, 114, 477.
It is already known that alcohols are tetrahydropyra-
nylated by DHP in the presence of acidic ion-exchange
resins such as Amberlite IR-120,6 Amberlist H-15,7 Rellex
425,8 or Nafion-H.9 As for the selective reactions using
ion-exchange resins, the formation of monoesters from
symmetrical diols1a and dicarboxylic acids10 has been
(5) Nishiguchi, T.; Kawamine, K.; Ohstuka, T. J . Chem. Soc., Perkin
Trans 1 1992, 153.
(6) Haynes, L. J .; Plimmer, J . R. J . Chem. Soc. 1956, 4665.
(7) Bongini, A.; Cardillo, G.; Orena, M.; Sandri, S. Synthesis 1979,
618.
(8) J ohnston, R. D.; Marston, C. R.; Krieger, P. E.; Goe, G. L.
Synthesis 1988, 393.
(9) Olah, G. A.; Husain, A.; Singh, B. P. Synthesis 1983, 892.
(10) Saitoh, M.; Fujisaki, S.; Ishii, Y.; Nishiguchi, T. Tetrahedron
Lett. 1996, 37, 6733.
(4) (a) Takasu, M.; Naruse, U.; Yamamoto, H. Tetrahedron Lett.
1988, 29, 1947. (b) Takano, S.; Akiyama, M.; Sato, S.; Ogasawara, K.
Chem. Lett. 1983, 1593. (c) Barton, D. H. R.; Zhu, J . Tetrahedron 1992,
48, 8337.
10.1021/jo980659b CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/27/1998

8184 J . Org. Chem., Vol. 63, No. 23, 1998
Nishiguchi et al.
the cis-diol showed higher reactivity and lower selectivity
than the trans-diol (Table 1, entries 10 and 11). It is well-
known that axial hydroxyl groups on a cyclohexane ring
are more reactive than equatorial ones. We postulate
that this fact explains our result, since both the diol and
the monoether in cis-form seem to undergo the etherifi-
cation on the axial hydroxyl group while those in trans-
form seem to be etherified on the equatorial one.
In the reaction of 1,10-decanediol in DHP/toluene,
yields of the monoether were low. They increased by the
change of solvents from DHP/toluene to DHP/hexane and
with the addition of DMF or DMSO (0.1 mL) (Table 1,
entries 21 and 22). In the reaction of 1,12-dodecanediol,
the yields of the monoether were considerably lower than
those in the reactions of the diols with not more than 10
carbon atoms (Table 1, entry 23). When 67% of the
monoether and 8% of the diether were formed (Table 1,
entry 23), 21% of the unreacted diol was detected in the
organic layer and no other byproducts from the diol were
found.
2-Hydroxytetrahydropyran was formed in all reactions
involving DHP and wet strongly acidic ion-exchange
resins as byproducts. Under the conditions shown in
Figure 1, the molarity of the byproduct was about twice
as much as that of the diether formed while 1,6-hex-
anediol remained. The cyclic hydroxy ether was formed
when Dowex 50W was stirred in DHP/toluene or DHP/
hexane. This result shows that it was formed by the
reaction between DHP and the water in the resin.
F igu r e 1. Yields vs reaction time. 1,6-Hexanediol or 6-(tet-
rahydropyranyloxy)-1-hexanol (1 mmol) and Dowex 50W × 2
(50-100 mesh) (0.2 g) were stirred at 30 °C in DHP/toluene
(5:95, 6 mL): monoether (b) and diether (O) from the diol;
diether (0) from the monoether.
reported. In these reactions it was inferred that the
water contained in the ion-exchange resins was crucial
for the selectivity. A part of the results of the etherifi-
cation of 1,n-diols in DHP/hydrocarbon catalyzed by
Dowex 50 has been published as a preliminary report.11
This method of selective etherification is quite simple and
practical.
Resu lts a n d Discu ssion
Selective Mon oeth er ifica tion of Sym m etr ica l Di-
ols. The selective monotetrahydropyranyration in this
study was carried out by stirring a diol and an ion-
exchange resin in DHP/toluene or DHP/hexane under
observation by GLC. Most reactions were carried out at
30 °C in pursuit of good reproducibility, although they
proceeded at room temperature.
To examine the catalytic activity and the selectivity of
the various ion-exchange resins, 1,6-hexanediol and an
ion-exchange resin were stirred at 30 °C in a mixture of
DHP and toluene (59:5) (Table 2). The yields of the
monoether were higher than 90% when the yields of the
diether were 2% and 5% in the reactions catalyzed by
some sulfonic acid-type ion-exchange resins. Wet type
resins, such as Dowex 50W, Amberlite 118, and Amber-
lite 120, showed higher selectivity than resins for non-
aqueous solutions, such as Nafion NR50 and Amberlyst
15. Dowex 50W × 2 (50-100 mesh) lost 75% of its weight
by being dried over P2O5 (see Experimental Section). The
dried resin showed lower selectivity than the original
resin. The selectivity was low in the reaction catalyzed
by camphorsulfonic acid, which was carried out as a
control experiment. The carboxylic acid-type resin (Am-
berlite IRC-50) was inactive. Dowex 50W × 2 (50-100
mesh) was used in all etherifications described hereafter
because it dispersed most easily in the solutions.
Ra tion a liza tion of th e Selectivity. Figure 1 also
shows the yield of 1,6-bis(tetrahydropyranyloxy)hexane
in the reaction of 6-(tetrahydropyranyloxy)-1-hexanol
(starting material). Conditions of this reaction were the
same as those of the etherification of 1,6-hexanediol. The
yields of the diether in the reaction of monoether as
starting material were much lower than the yields of
monoether in the reaction of diol as starting material.
This outcome shows that the diol reacted much more
rapidly than the monoether to realize the selective
formation of the monoether from the diol.
Figure 1 shows an example of the dependence of the
product yields on the reaction period in the etherification
of 1,6-hexanediol (1 mmol) in DHP/toluene (5:95, 6 mL).
The yield of the diether was 3% when that of the
monoether reached 95%. The yield of the diether did not
increase rapidly even after the yield of the monoether
reached its maximum. This result shows that the reac-
tion rate of the monoether is far lower than that of the
diol and that the rate of the formation of the diether does
not increase very much even after most of the diol has
been consumed. This result differs from the result
obtained in the reactions catalyzed by silica gel-supported
sulfates, in which the monoethers reacted much more
rapidly in the absence of diols than in their presence.5
The result described above enhances the value of the
reaction catalyzed by ion-exchange resins because the
timing to terminate the successive etherification is not
so important in this reaction as in the reaction catalyzed
by the supported sulfates.
Table 1 shows that symmetrical primary and secondary
diols with 2-10 carbon atoms gave the corresponding
monotetrahydropyranyl ethers in higher yields than 85%.
Benzenedimethanols are among the diols (Table 1, en-
tries 17 and 18). In the reaction of 1,2-cyclohexanediols,
We presume that the selectivity for monoethers arises
from the following assumed factors: (1) a strongly acidic
(11) Nishiguchi, T.; Kuroda M.; Saitoh, M.; Nishida, A.; Fujisaki,
S. J . Chem. Soc., Chem. Commun. 1995, 2491.

Monotetrahydropyranylation of Symmetrical Diols
J . Org. Chem., Vol. 63, No. 23, 1998 8185
Ta ble 1. Selective Mon otetr a h yd r op yr a n yla tion of Sym m etr ica l Diol w ith DHP Ca ta lyzed by a n Ion -Exch a n ge Resin a
yield (%)b
entry
diol
DHP/%
time/min
monoether
diether
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
1,2-ethanediol
10
80
40
10
5
60
20
20
10
20
20
20
20
40
3
5
5
5
3
3
3
3
3
100
30
220
140
210
40
95
78
92
88
95
85
93
94
95
93
96
95
94
95
95
96
94
85
64
74
87
83
67
2
3
4
5
3
5
4
3
2
6
4
2
4
3
2
2
5
1,3-propanediol
1,3-propanediolc
cis-2-butene-1,4-diold
1,6-hexanediol
1,6-hexanediole
2,5-hexanediol
140
100
120
120
360
140
220
90
270
200
220
200
160
240
355
290
165
3-methyl-1,5-pentanediol
2-ethyl-2-methyl-1,3-propanediol
cis-1,2-cyclohexanediol
trans-1,2-cyclohexanediol
1,3-cyclohexanediol
1,4-cyclohexanediol
1,4-cyclohexanediol
1,8-octanediol
1,4-cyclohexanedimethanol
1,2-benzenedimethanol
1,4-benzenedimethanol
1,10-decanediolf
13
15
9
8
9
1,10-decanediole,f
1,10-decanediole,f,g
1,10-decanediole,f,h
1,12-dodecanediole,f,g
8
a
b
Diol (1.0 mmol) and Dowex 50W × 2 (50-100 mesh) (0.1 g) were heated at 30 °C in a DHP/toluene (6 mL). GLC yields obtained by
the use of internal standards (see Experimental Section). c Amount of the catalyst was 0.04 g. This diol was used instead of 1,4-butanediol
d
because in GLC analysis the retention time of 1,4-butanediol and 2-hydroxytetrahydropyrane was nearly the same. e The solvent was the
DHP/hexane mixture. f Reaction temperature was 40 °C. DMSO (0.1 mL) was added. DMF (0.1 mL) was added.
g
h
Ta ble 2. Selectivity a n d Ca ta lytic Activity of Ion -Exch a n ge Resin sa
yield of monoether (%)b
resin and acid
(1)
(2)
initial rate (×103) (M/min)
Dowe × 50W × 2 (50-100 mesh)
Dowe × 50W × 2 (50-100 mesh)c
Dowe × 50W × 2 (200-400 mesh)
Dowe × 50W × 4 (200-400 mesh)
Dowe × 50W × 8 (50-100 mesh)
Dowe × 50W × 8 (200-400 mesh)
Amberlyst 15d
91
60
79
72
92
86
6
96
65
92
82
94
92
9
0.81
0.83
1.3
1.4
0.65
1.4
1.2
Amberlyst 15 (wet)
50
57
89
86
3
71
64
91
96
7
0.96
0.72
0.46
0.39
0.43
1.2
Amberlyst × N-1010d
Amberlite IR-118 (H)
Amberlite IR-120 (plus)
Nafion NR50d
(+)-10-camphorsulfonic acide
17
23
a
b
1,6-Hexanediol (1 mmol) and a resin (0.1 g) were stirred at 30 °C in DHP/toluene (5:95, 6 mL). Yield of the monoether at 2% yield
of (1) and at 5% yield (2) of the diether. c Dried catalyst (0.02 g) was used. For nonaqueous applications. e The amount of the catalyst
d
was 0.01 mmol.
water layer is formed on the surface of the porous resins,
because the sulfonic acid-type ion-exchange resins usu-
ally contain 50-80% water;12 (2) the ratios of the diols
in the water layer are much higher than those of the
monoethers; (3) the diols react in preference to the
monoethers in the aqueous layer, which also contains
DHP; (4) the formed monoethers migrate from the
aqueous layer into the surrounding aprotic organic layer,
which does not contain catalytic proton.
When the dried catalyst described before was used, the
selectivity, the initial rate, and the maximum yield of the
monoether were low (Table 2). When increasing amounts
of water were added to the reaction system using the
dried catalyst, both the selectivity and the initial rate
rose, exhibited maximum values, and then declined
gradually (Figure 2). It was also found that the amount
of the water contained in the original purchased Dowex
50W was suitable for the high selectivity and reactivity.
These results support, at least in part, the presumed
mechanism noted above.
The resin (Dowex 50W) once used in the etherification
was recovered by filtration and used again. Although the
selectivity and the activity of the recovered catalyst were
a little lower than those of the fresh resin, they recovered
intensity by the addition of the same weight of water as
that of the resin. This result suggests that the water in
the catalyst was lost considerably during the reaction.
The relation between the amount of the catalyst and the
selectivity also supports this suggestion. In the reaction
of 1,6-hexanediol (1 mmol) in DHP/toluene (20:80, 6 mL),
the selectivity was hardly influenced by the amount of
the catalyst when the amount of resin used was in the
range of 0.02-0.4 g. When the amount of the catalyst
was smaller than in this range, the selectivity decreased,
probably because of the loss of the water in the catalyst
during the reaction. When too large an amount of the
catalyst was used, the reaction proceeded so fast that the
(12) Suppliers’ catalogs.

8186 J . Org. Chem., Vol. 63, No. 23, 1998
Nishiguchi et al.
the number of carbon atoms of a diol, the smaller the
DHP/hydrocarbon ratio to realize the highest selectivity.
However, the selectivity in this system did not depend
on the DHP/hydrocarbon ratio so greatly as that in the
reaction catalyzed by metallic sulfates supported on silica
gel.5 This dull response of the selectivity to reaction
conditions is also an advantage of this reaction system.
In the reaction of 1,6-hexanediol, the selectivity was
higher in DHP/toluene than in DHP/hexane, as described
before. However, it was higher in DHP/hexane than in
DHP/toluene in the reaction of 1,10-decanediol. More-
over, the lower the ratio of DHP in DHP/hexane, the
higher the selectivity, though when the percentage of
DHP in the solvent was 1%, the reaction rate was
extremely slow and the yield of the monoether did not
exceed 80%. These results may be explained by the
presumption that 1,10-decanediol has lower solubility in
the water layer of the catalyst and higher solubility in
the organic solvent than 1,6-hexanediol.
As shown in Table 1, the addition of DMF and DMSO
raised the selective in the reaction of 1,10-decanediol. The
increase of the selectivity may be explained by the
presumption that these strongly polar additives were
distributed mainly in the water layer of the catalyst and
that the solubility of the water layer for the diol is
enhanced more than that for the monoether. The effect
of the additives was not observed in the reaction of 1,8-
octanediol, which is more soluble in the water than
1,10-decanediol.
F igu r e 2. Yield and rate vs amount of water. 1,6-Hexanediol
(1 mmol) and dried Dowex 50W × 2 (50-100 mesh) (0.02 g)
and water were stirred at 30 °C in DHP/toluene (10:90, 6
mL): yield of the monoester at 4% yield of the diester (b) and
initial rate of the formation of the monoether (9). The yield
(O) and the rate (0) in the reaction catalyzed by the original
wet resin (0.08 g) are also shown.
When we increased the concentration of 1,6-hexanediol
from 0.1 M while keeping the other conditions the same
as those shown in Figure 1, the selectivity was indepen-
dent of the concentration of the diol up to 0.45 M. The
selectivity then decreased as the concentration increased.
The initial rate of monoether formation was constant in
the range of the concentration examined (0.1-0.6 M).
This result suggests that the concentration of the diol in
the water layer of the catalyst was almost constant even
if the amount of the diol added was varied and that the
water layer was nearly saturated with the diol. The
reason the rate of the formation of the diether began to
increase when the concentration of the diol reached 0.45
M is not clear yet.
F igu r e 3. Yield and initial rate vs solvent composition. 1,6-
Hexanediol (1 mmol) and Dowex 50W × 2 (50-100 mesh) (0.1
g) were stirred at 30 °C in DHP/toluene or DHP/hexane (6
mL): yield of the monoether at 3% yield of diether (b) and
initial rate of the formation of the monoether (O) in DHP/
toluene. The yield (9) and the rate (0) in DHP/hexane.
time to terminate the reaction was critical to achieve good
selectivity.
Figure 3 shows the relationship between the composi-
tion of solvents and the yields of the monoether at the
yield of 3% of the diether in the reaction of 1,6-hex-
anediol. In both DHP/toluene and DHP/hexane systems,
the selectivity depended on the solvent composition and
showed gentle peaks. The percentages of DHP at which
the peaks appeared were 5 and 60% in DHP/toluene and
in DHP/hexane, respectively. This result may be ex-
plained by the fact that the solvents dissolve the diol and
the monoether in the following decreasing order: DHP
> toluene > hexane. It was also found that the yields of
the monoether at the 3% yield of the diether in the
reaction of 1,6-hexanediol in DHP/toluene were higher
than those in DHP/hexane. The rates of the formation
of the monoether in the reaction in DHP/toluene and
those in DHP/hexane of the same DHP percentages were
not so different (Figure 3). The smaller the ratio of DHP
in the solvent, the lower the rate of the etherification and
consequently the larger the quantity of catalyst needed.
This is the reason the amount of catalyst noted in Table
1 is different in each reaction.
Exp er im en ta l Section
Reagents and solvents were purchased and used without
purification. GLC analyses were performed on an instrument
with an autoinjector. The column was a 30 m × 0.25 mm i.d.
fused silica capillary column coated with NB-5.
An a lytica l-Sca le Mon oeth er ifica tion of Sym m etr ica l
Diols. The etherification of 1,6-hexanediol is typical.
A
mixture of 1,6-hexanediol (0.118 g, 1 mmol), Dowex 50W × 2
(50-100 mesh) (0.1 g), 1-octadecane (GLC internal standard,
20 µL), and 5:95 (v/v) DHP/toluene (6 mL) was stirred at 30 (
1 °C. Samples of the supernatant liquid were then removed
periodically and analyzed by GLC. The retention times of the
monoether and the diether were identical to those of authentic
samples prepared by the conventional method described in the
previous paper.5 The yields of monoethers at a particular yield
of diethers were derived from plots of product yield vs time,
such as those shown in Figure 1.
P r ep a r a tive-Sca le Selective Mon oeth er ifica tion of
Sym m etr ica l Diols. The etherification of 1,6-hexanediol is
typical. 1,6-Hexanediol (0.59 g, 5.0 mmol) and Dowex 50W ×
2 (50-100 mesh) (1 g) were stirred at 30 + 1 °C in a mixture
of DHP (1.5 mL) and toluene (30 mL), and the mixture was
monitored by GLC. After 2.5 h, the catalyst was removed by
filtration and the solution was evaporated. The residue was
Each diol had the particular ratio of DHP/hydrocarbon
that gave the highest selectivity. Generally, the larger

Monotetrahydropyranylation of Symmetrical Diols
J . Org. Chem., Vol. 63, No. 23, 1998 8187
chromatographed with hexane/EtOAc (4:1) on silica gel column
to give the monoether (0.89 g, 89%) and the diether (0.03 g,
2%).
weight of the resin decreased to 26% in 1 day and 25% in 7
days. The resin dried for 7 days was used in the etherification.
Dr yin g of Ion -Exch a n ge Resin . Dowex 50W × 2 (50-
100 mesh) (1 g) was kept over P2O5 (30 g) in a desiccator. The
J O980659B