Synthesis and characterization of pentaerythritol-derived oligoglycol and their application to catalytic Wittig-type reactions

Article abstract of DOI:10.1021/jo049701v

Several pentaerythritol-derived oligoglycols 1 with free hydroxyl groups are readily prepared by a convergent approach. Quantitative ¹³C NMR proves to be an efficient tool for the characterization of oligoglycols. The corresponding telluride of oligoglycol 17 is synthesized and used as a good catalyst for Wittig-type reactions in preparing both disubstituted and trisubstituted olefins in good to high yields.

Full text of DOI:10.1021/jo049701v

SCHEME 1
Syn th esis a n d Ch a r a cter iza tion of
P en ta er yth r itol-Der ived Oligoglycol a n d
Th eir Ap p lica tion to Ca ta lytic Wittig-Typ e
Rea ction s
Kai Li, Li Ran,† Yi-Hua Yu, and Yong Tang*
State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry,
354 Fenglin Lu, Shanghai 200032, China
neutral conditions from the easily accessible diazo com-
pounds.3 Reaction conditions4 and substituents5 on phos-
phorus proved to influence the stereoselectivity. Thus the
selectivity could be improved and even be switched by
the change of these factors in certain cases.7 Despite their
wide success in numerous applications, the need for
improvement in several aspects of Wittig-type reactions
remains evident. In particular, a large amount of triph-
enylphosphine oxide is produced as a waste, resulting in
the purification problem of the desired product and
polluting environment. A catalytic process of this reac-
tion, developed first by Huang et al. using 20 mol % of
tributylarsine or 20 mol % of dibutyl telluride as the
catalyst in the presence of stoichiometric triphenyl phos-
phite,8 provided a potential way to solve this problem.
In a previous study on ylide chemistry,9 we designed
soluble poly(ethyleneglycol) (PEG)-supported telluride as
the catalyst for ylide olefination and found that the
catalytic loading could be reduced to 2 mol % (Scheme
1).10 Furthermore, an investigation of other reducing
agents shows that sodium bisulfite is better than triph-
enyl phosphite. This modification, using sodium bisulfite
instead of triphenyl phosphite, provided a very simple
procedure for the product purification. In this case,
almost pure product can be obtained just by filtering off
the inorganic salts, followed by precipitating the catalyst
in ethyl ether after the reaction is complete.
tangy@mail.sioc.ac.cn
Received February 21, 2004
Abstr a ct: Several pentaerythritol-derived oligoglycols 1
with free hydroxyl groups are readily prepared by a conver-
gent approach. Quantitative 13C NMR proves to be an
efficient tool for the characterization of oligoglycols. The
corresponding telluride of oligoglycol 17 is synthesized and
used as a good catalyst for Wittig-type reactions in preparing
both disubstituted and trisubstituted ïlefins in good to high
yields.
Wittig reaction1 and its variants have been developed
as one of the most powerful approaches in constructing
carbon-carbon double bonds due to its unambiguous
positioning and good stereoselectivity of the double bond.2
Recent developments mainly focused on the catalytic
reactions,3 the control of stereoselectivity,4,5 and new
techniques.6 The transition metal-based catalytic ap-
proach provided a new method of ylide generation under
† Current address: Chuanbei Medicinal College.
(1) Wittig, G.; Geissler, G. Liebigs Ann. Chem. 1953, 580, 44.
(2) (a) Hoffmann, R. W. Angew. Chem., Int. Ed. 2001, 40, 1411. (b)
Maryanoff, B. E.; Reitz, A. B. Chem. Rev. 1989, 89, 863. (c) Nicolaou,
K. C.; Ha¨rter, M. W.; Gunzner, J . L.; Nadin, A. Liebigs Ann./ Recl.
1997, 1283 and references therein. (d) Kolodiazhnyi, O. I. Phosphorus
Ylides: Chemistry and Application in Organic Synthesis; Wiley-VCH:
New York, 1999. (e) Forsyth, C. J .; Ahmed, F.; Cink, R. D.; Lee, C. S.
J . Am. Chem. Soc. 1998, 120, 5597. (f) Smith, A. B., III; Beauchamp,
T. J .; LaMarche, M. J .; Kaufman, M. D.; Qiu, Y.; Arimoto, H.; J ones,
D. R.; Kobayshi, K. J . Am. Chem. Soc. 2000, 122, 8654. (g) White, J .
D.; Carter, R. G.; Sundermann, K. F.; Wartmann, M. J . Am. Chem.
Soc. 2001, 123, 5407. (h) Oleg, I. K. Phosphorous Ylide; Wiley-VCH:
New York, 1998.
(3) (a) Lee, M.-Y.; Chen, Y.; Zhang, X. P. Organometallics 2003, 22,
4905. (b) Aggarwal, V. K.; Fulton, J . R.; Sheldon, C. G.; de Vicente, J .
J . Am. Chem. Soc. 2003, 125, 6034. (c) Santos, A. M.; Romao, C. C.;
Kuhn, F. E. J . Am. Chem. Soc. 2003, 125, 2414. (d) Zhang, X.; Chen,
P. Chem. Eur. J . 2003, 9, 1852. (e) Cheng, G.; Mirafzal, G. A.; Woo, L.
K. Organometallics 2003, 22, 1468. (f) Chen, Y.; Huang, L.; Ranade,
M. A.; Zhang, X. P. J . Org. Chem. 2003, 68, 3714. (g) Chen, Y.; Huang,
L.; Zhang, X. P. J . Org. Chem. 2003, 68, 5925. (h) Chen, Y.; Huang,
L.; Zhang, X. P. Org. Lett. 2003, 5, 2493. (i) Mirafzal, G. A.; Cheng,
G.; Woo, L. K. J . Am. Chem. Soc. 2002, 124, 176. (j) Lebel, H.; Paquet,
V. Org. Lett. 2002, 4, 1671. (k) Lu, X.; Fang, H.; Ni, Z. J . Organomet.
Chem. 1989, 373, 77.
(4) (a) Harcken, C.; Martin, S. F. Org. Lett. 2001, 3, 3591. (b)
Valverde, S.; Martin-Lomas, M.; Herradon, B.; Garcia-Ochoa, S.
Tetrhedron 1987, 43, 1895. (c) Mulzer, J .; Kappert, M. Angew Chem.,
Int. Ed. Engl. 1983, 22, 63. (d) Marriott, D. P.; Bantick, J . R.
Tetrahedron Lett. 1981, 22, 3657. (e) Buchacan, J . G.; Edgar, A. R.;
Power, M. J .; Theaker, P. D. Carbohydr. Res. 1974, 38, C22-24.
(5) (a) Ando, K. J . Org. Chem. 1998, 63, 8411. (b) Rubsam, F.; Evers,
A. M.; Michel, C.; Giannis, A. Tetrahedron 1997, 53, 1707. (c) Poss, M.
A.; Reid, J . A. Tetrahedron Lett. 1992, 33, 1411. (d) Xiao, X.; Prestwich,
G. D. Tetrahedron Lett. 1991, 32, 6843.
Mechanism studies show that the PEG chain promotes
the ylide formation and stabilizes the catalytic species,
suggesting that the PEG chain plays important roles in
improving the catalytic efficiency. To further investigate
the role of PEG units in more detail and to further
improve the efficiency of catalytic ylide olefination as well
as to increase the telluronium loading in the PEG
carrier,11 we designed several pentaerythritol-derived
oligoglycols 1 as a new type of carrier. In this paper, we
wish to report the synthesis and the characterization of
(7) Maryanoff, B. E.; Reitz, A. B. Chem. Rev. 1989, 89, 863.
(8) (a) Shi, L.; Wang, W.; Wang, Y.; Huang, Y.-Z. J . Org. Chem. 1989,
54, 2028. (b) Huang, Y.-Z.; Shi, L.-L.; Li, S.-W.; Wen, X.-Q. J . Chem.
Soc., Perkin Trans. 1 1989, 2397.
(9) (a) Huang, Y.-Z.; Tang, Y.; Zhou, Z.-L. Tetrahedron 1998, 53,
1668. (b) Ye, S.; Tang, Y.; Dai L.-X. J . Org. Chem. 2000, 65, 6257. (c)
Ye, S.; Tang, Y.; Dai, L.-X. J . Org. Chem. 2001, 66, 5717. (d) Ye, S.;
Huang, Z.-Z.; Xia, C.-A.; Tang, Y.; Dai, L.-X. J . Am. Chem. Soc. 2002,
124, 2432. (e) Huang, Z.-Z.; Tang, Y. J . Org. Chem. 2002, 67, 5320. (f)
Li, K.; Huang, Z.-Z.; Tang, Y. Tetrahedron Lett. 2003, 44, 4137. (g) Li,
K.; Deng, X.-M.; Tang, Y. Chem. Commun. 2003, 2704. (h) Liao, W.-
W.; Li, K.; Tang, Y. J . Am. Chem. Soc. 2003, 125, 13030.
(10) (a) Huang, Z.-Z.; Ye, S.; Xia, W.; Tang Y. Chem. Commun. 2001,
1384. (b) Huang, Z.-Z.; Ye, S.; Xia, W.; Yu, Y.-H.; Tang Y. J . Org. Chem.
2002, 67, 3096.
(11) One of the major drawbacks with PEG-telluride as the catalyst
is that the telluronium loading in PEG is low due to the unfavorable
stoichiometry between PEG and Te.
(6) Balema, V. P.; Wiench, J . W.; Pruski, M.; Pecharsky V. K. J .
Am. Chem. Soc. 2002, 124, 6244.
10.1021/jo049701v CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/05/2004
3986
J . Org. Chem. 2004, 69, 3986-3989

SCHEME 2
SCHEME 3
the oligoglycols with hydroxyl groups at the surface, as
well as their application as the catalyst carrier in
catalytic Wittig olefination.
masked sodium diglycolate or glycolate to afford com-
pound 5, which was deprotected to give the key inter-
mediate 6. It is noteworthy that the choice of the
protecting group is fundamental to the success of this
synthesis, as it must be readily removed under mild
conditions without affecting the oligoether. First, we
chose the benzyl group as the masking group but found
that it was difficult to deprotect completely by hydroge-
nation in the presence of 10% Pd/C. As the tetrahydro-
pyranyl (THP) has been proved useful in hydroxyl group
protection,14 it was selected for use in our construction
of the target molecules. Compound 6b, after being treated
with NaH, reacted with pentaerythrityl tetrabromide to
give disordered products in a variety of conditions and
no desired tetrasubstituted product was detected. Chang-
ing diglycol derivative 6b (n ) 1) into glycol derivative
6a (n ) 0), the result was still negative, presumably
because the attached long oligo(ethyleneglycol) chain
blocked the reactive site and prevented further substitu-
tion.
Syn th esis a n d Ch a r a cter iza tion of th e Oligogly-
cols. The most important requirement for the synthesis
of pentaerythritol-derived oligoglycols 1 is the efficient
formation of ether linkages. To prevent elimination
during the formation of ether under Williamson condi-
tions, we designed tribromide 4 and pentaerythritol-
derived alcohol 6 with the oligoglycol skeleton as new
monomers and chose pentaerythrityl tetrabromide as the
core for our synthesis. The initial synthetic route is
outlined in Scheme 2.
The monomer 6 was readily prepared from pentaeryth-
ritol 2 in four steps. The tribromide 3 was obtained by
treating pentaerythritol 2 with 40% HBr (aq) (1:5, v/v)
in HOAc, followed by 40% HBr (aq)/concentrated H2SO4.12
Compound 4, prepared from compound 3 by protecting
it with p-methoxybenzyl (PMB),13 reacted with THP-
Thus, when modifying the monomer 6 into 13 by
lengthening the chain of the reactive site, the etherifi-
cation reaction to form the symmetric oligoglycol worked
well (Scheme 3). Glycol was protected by THP, followed
by the reaction with pentaerythrityl tetrabromide to
afford compound 11 in 53% yield in one step just by
(12) Davis, B. G.; Khumtaveeporn, K.; Bott, R. R.; J ones, J . B.
Bioorg. Med. Chem. 1999, 7, 2308.
(13) Nakajima, N.; Hirita, K.; Abe, R.; Yonemitsu, O. Tetrahedron
Lett. 1988, 29, 4139.
(14) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis; J ohn Wiley & Sons: New York, 1999.
J . Org. Chem, Vol. 69, No. 11, 2004 3987

TABLE 1. Rea ction of Ald eh yd e w ith Br om oa ceta te
cat.
loading,
reaction
time (h)
yield
(%)
entry cat. mol %a 23
R
E/Z
1
2
3
4
5
6
7
8
9
20a
20a
20a
20a
20a
20a
20a
20a
20a
5
5
5
5
5
5
5
5
2
5
2
5
23a 4-ClC6H4
23b Ph
23c 2-ClC6H4
23d 4-CH3C6H4
23e 2-CH3OC6H4
23f furanyl
23g cinnanyl
23h n-C9H19
23a 4-ClC6H4
23a 4-ClC6H4
23a 4-ClC6H4
23a 4-ClC6H4
24
24
24
24
48
48
48
48
24
24
24
24
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
98
80
87
93
82
94
F IGURE 1. Quantitative 13C NMR of compound 15 from a
Bruker DR × 400 NMR spectrometer. The inverse gated
decoupling pulse sequence (Bruker standard pulse program:
2 gig) was used with a relaxation delay of 60 s and a pulse of
45° flip angle.
90:10 85
97:3
>99:1
>99:1
>99:1
>99:1
68
90
65
35
99
10 24a b
11 24a b
12 24bc
controlling the ratio of the reactants. Noticeably, the
material adding sequence was crucial to this reaction.
When the solution of the corresponding sodium salt of
monoalcohol 10 was added dropwise into pentaerythrityl
tertrabromide in refluxing diglyme, the desired product
11 was given in a reasonable yield. But almost nothing
was obtained when the reverse adding sequence was
employed. The Williamson etherification reaction of
compound 11 with diglycol monomasked by the 4-meth-
oxybenzyl group gave oligoether 12 in 68% yield, which
was easily deprotected by DDQ in dichloromethane in
the presence of water to produce compound 13 in 68%
yield. Reaction of alcohol 13 with pentaerythrityl tertra-
bromide in diglyme afforded oligoglycol 14 in 37% yield.
The peripheral ketal of compound 14 was easily removed
in the presence of hydrogen chloride in dioxane when
using methanol as the solvent to give the desired oli-
goglycol 15, having hydroxyl groups at the surface, in
quantitative yield (Scheme 3).
Both 14 and 15 could be purified with precise molec-
ular weight and structure. The purity and structure of
both 14 and 15 were determined by elemental analysis,
1H NMR, ESI-MS, and quantitative 13C NMR. In the ESI-
MS spectra of these two compounds, peaks corresponding
to the mass of the oligoglycol plus sodium and/or potas-
sium are observed. Quantitative 13C NMR of compound
15 showed that there are 5 tertiary carbons and 60
carbons related to -OCH2- units (Figure 1). These data
demonstrate the structure of the desired oligoglycol.
Syn th esis of th e Tellu r id e. With oligoglycol 15 at
hand, we tried to synthesize the corresponding telluride
for our study but failed. The reason is that the hydroxyl
groups of oligoglycol 15 could not be full-transformed into
the corresponding tosylates or bromides under a variety
of conditions. In all conditions, disordered compounds
were obtained and no pure product could be isolated.
Thus, we synthesized a simple telluride 19 with the oligo-
a
b
Calculated by telluride. 24a ) Bun2Te+CH2CO2But‚Br-.
c 24b ) BuTe-PEG-TeBu.
(ethyleneglycol) skeleton (Scheme 4) for our study and
tested its catalytic activity for Wittig-type olefination.
The telluronium salt 20 was easily made from THP-
masked diglycol 16 as follows: Alcohol 16 reacted with
NaH, followed by C(CH2Br)4 to afford compound 17,
which was readily transformed into corresponding bro-
mide 18 in the presence of Ph3P‚Br2.15 Bromide 18
reacted with LiTeBu, followed by the bromo compounds
to give the desired telluronium salts 20a and 20b. It was
found that salt 20a was a comparable catalyst to PEG-
telluride for the Wittig-type reaction of aldehydes with
bromoacetate.10 The results are shown in Table 1. In the
presence of NaHSO3, both aromatic aldehydes and al-
phatic aldehydes worked well when 1.25 mol % of catalyst
20a was employed. All reactions gave E-isomers with
excellent stereoselectivity and in good to high yields.16
Noticeably, compared with the known dibutyltelluronium
salt 24a , the new synthesized tellurium salt 20a was
more efficient and is comparable to the PEG-telluride
24b. Even when the loading is reduced to 2 mol %, the
isolated yield was still 90% (entries 1, 9, 10, and 11).
Although several catalytic Wittig reactions have been
developed, few involved the olefination of aldehydes with
R-bromopropionate. It was found that moderate to good
yields could be obtained when using the newly designed
20b as the catalyst for the Wittig-type reaction of
R-bromopropionate, although higher reaction tempera-
ture is necessary, compared with the corresponding
olefination of bromoacetate. For instance, the yield
decreased from 72% to 32% when p-chlorobenzylaldehyde
was used when the temperature was lowered to 80 °C.
As shown in Table 2, both aromatic and aliphatic alde-
SCHEME 4
3988 J . Org. Chem., Vol. 69, No. 11, 2004

TABLE 2. Rea ction of Ald eh yd e w ith
Oligoglycol 15. To a stirred solution of oligoglycol 14 (265
mg, 0.1 mmol) in 5 mL of methanol was added HCl (0.05 mL, 4
M in dioxane) and after 1 h, the solvent was evaporated out.
The above operation was repeated two times to give the
oligoglycol 15 in quantitative yield. No further purification was
empolyed. 1H NMR (300 MHz, CDCl3/TMS) δ 3.58 (br s); 13C
NMR (100 MHz, CDCl3/TMS) δ 45.4 (4C), 45.5 (1C), 61.3 (12C),
70.0, 70.2, 70.3 and 70.4 (28C), 71.0 (8C), 72.7 (12C); IR (net)
ν/cm- 13403, 1101; ESI-HRMS calcd for C65H132O36Na 1511.83905,
found 1511.83505.
r-br om op r op ion a te
reaction
isolated
yield (%)
entry
time (h)
25
R
E/Za
1
2
3
4
5
24
24
24
40
24
25a
25b
25c
25d
25e
4-ClC6H4
Ph
4-NO2C6H4
2-CH3OC6H4
Cy
96:4
97:3
96:4
99:1
70:30
72
69
68
67
63
Tellu r id e 19. To a stirred suspension of tellurium power (254
mg, 1.98 mmol) in 5 mL of dry THF was added dropwise 1.23
mL of butyllithium (1.6 M, 1.98 mmol) at 0 °C. After being stirred
for half an hour at room temperature, the mixture was cooled
to -78 °C and oligoglycol 18 (244 mg, 0.33 mmol) in 5 mL of
dry THF was added. The resulting mixture was stirred at this
temperature for 6 h, warmed to room temperature, and filtered.
The filtrate was concentrated. The residue (hexane/ethyl acetate,
5:1) was purified by chromatography on silica gel to afford
compound 19 as a pale yellow oil. Yield: 251 mg (68%). 1H NMR
(300 MHz, CDCl3/TMS) δ 0.91 (t, J ) 7.2 Hz, 12H), 1.39 (m,
8H), 1.72 (m, 8H), 2.63 (t, J ) 7.5 Hz, 8H), 2.77 (t, J ) 7.5 Hz,
8H), 3.45 (s, 8H), 3.57 (m, 16H), 3.75 (t, J ) 7.8 Hz, 8H); 13C
NMR (75 MHz, CDCl3/TMS) δ 1.8, 2.7, 13.3, 24.9, 34.2, 45.4,
69.5, 69.9, 70.8, 73.1; IR v/cm-1 2955, 2924, 2870, 1102. Anal.
Calcd for C37H76O8Te4: C, 38.34; H, 6.53. Found: C, 38.58; H,
6.47.
a
Determined by 1H NMR.
hydes were good substrates for this reaction. Aromatic
aldehydes gave high stereoselectivity (entries 1-4) and
poor selectivity was afforded when cyclohexylaldehyde
was used.
In conclusion, we have developed a convergent way to
prepare a symmetric oligoglycol having hydroxyl groups
at the surface, which is potentially useful as a catalyst
carrier. Quantitative 13C NMR proved to be an efficient
tool for the characterization of such compounds. The
simple oligo(ethyleneglycol)-derived telluride 19 was
synthesized and the corresponding telluronium salt 20
proved to be a good catalyst in Wittig-type reactions.
Noticeably, salt 20 can also catalyze the olefination of
aldehydes with R-bromopropionate to provide trisubsti-
tuted olefin.
Tellu r on iu m Sa lt 20a . To a stirred solution of oligoglycol
19 (251 mg, 0.22 mmol) was added tert-butyl bromoacetate (172
mg, 0.88 mmol) in 5 mL of dry THF at room temperature and
the mixture was stirred overnight. The solvent was removed to
1
give salt 20a in quantitative yield. H NMR (300 MHz, CDCl3/
TMS) δ 1.04 (t, J ) 6.9 Hz, 12H), 1.56 (m, 44H), 2.02 (m, 8H),
3.25 (m, 8H), 3.42-3.87 (m, 40H), 4.21 (m, 8H); 13C NMR (75
MHz, CDCl3/TMS) δ 13.5, 24.8, 27.2, 27.8, 27.9, 28.2, 30.8, 45.5,
66.2, 70.1, 70.6, 70.7, 83.0, 167.8. Anal. Calcd for C61H120Br4O16
Te4: C, 37.78; H, 6.19. Found: C, 37.97; H, 6.63.
-
Gen er a l P r oced u r e for th e Ca ta lytic Wittig-Typ e Rea c-
tion of Br om oa ceta te. To a Schlenk tube was added a 1 mL
of solution of telluronium salt 20a (1.25 × 10-2 M in THF) and
NaHSO3 (90 mg, 0.66 mmol). After the mixture was refluxed
for 10 min, 0.04 mL of water and 138 mg of K2CO3 (1.0 mmol),
followed by 0.5 mmol of aldehyde and 118 mg of tert-butyl
bromoacetate (0.6 mmol), were added. The resulting suspension
was refluxed for several hours. After the reaction was complete,
the mixture was filtered rapidly through a glass funnel with a
thin layer of silica gel (ethyl acetate as the elution). The filtrate
was concentrated and the residue was purified by chromatog-
raphy (hexane/ethyl acetate, 200:1) to afford the desired product.
Gen er a l P r oced u r e for th e Ca ta lytic Wittig-Typ e Rea c-
tion of r-Br om op r op ion a te. To a Schlenk tube was added a
0.5-mL solution of telluronium salt 20b (2.5 × 10-2 M in THF,
prepared from the telluride 19 and ethyl R-bromopropionate at
rt for 3 days in solvent-free condition) and THF was removed
under vacuum at room temperature. Then the ethyl R-bro-
mopropionate (136 mg, 0.75 mmol), triphenyl phosphite (105 mg,
0.5 mmol), aldehyde (0.5 mmol), potassium carbonate (104 mg,
0.75 mmol), potassium iodide (8 mg, 0.05 mmol), and 1 mL of
dried toluene were added and the resulting suspension was
refluxed. After the reaction was complete, the mixture was
filtered rapidly through a glass funnel with a thin layer of silica
gel (ethyl acetate as the elution). The filtrate was concentrated
and the residue was purified by chromatography (hexane/ethyl
acetate, 200:1) to afford the desired product.
Exp er im en ta l Section
All reactions were carried out with use of standard Schlenk
techniques under an atmosphere of dry, oxygen-free nitrogen
unless otherwise stated. Solvents were dried and purified by
standard method. Reagents were purchased from commercial
sources. Aromatic aldehydes were distilled before use. Compound
10 was prepared according to the literature.17 Chemical shifts
were given in ppm relative to internal tetramethylsilane.
Oligoglycol 14. To a suspension of potassium hydride (124
mg, 3.1 mmol) in diglyme (fresh-distilled over sodium, 10 mL)
at 0 °C in a three-neck flask, equipped with a reflux condenser
and a dropping funnel, was added dropwise a solution of
compound 13 (1.82 g, 3 mmol) in diglyme (5 mL) under argon
atmosphere. The resulting mixture was stirred at 0 °C for 1 h,
then at room temperature for a further 2 h, followed by heating
to reflux. To this refluxing suspension was added dropwise a
solution of pentaerythrityl tetrabromide (194 mg, 0.5 mmol) in
diglyme (10 mL) within 0.5 h. The resulting mixture was
refluxed for another 5 h, cooled to room temperature, and filtered
through a Celite pad. The filtrate was concentrated. The residue
was purified by Flash-chromatography to afford oligoglycol 14
(440 mg, 37%) as a colorless oil. 1H NMR (300 MHz, CDCl3/
TMS): δ 1.43-1.65 (m, 72H), 3.37-3.81 (m, 144H), 4.65 (t, J )
3.5 Hz, 12H); 13C NMR (75 MHz, CDCl3/TMS) 19.4 (12C), 25.6
(12C), 30.7 (12C), 45.7 (1C), 45.8 (4C), 61.9 (12C), 66.5 (12C),
70.2-70.9 (28C), 71.1-71.1 (20C), 98.8 (12C); IR v/cm-1 1124;
MS (ESI, m/z, rel intensity) 2537.4 ([M + K]+, 10%), 1288.7 ([M
+ 2K]2+, 75%), 872.1 ([M + 3K]3+, 90%). Anal. Calcd for
Ack n ow led gm en t. We are grateful for the financial
support from the National Natural Sciences Foundation
of China.
C
125H228O48: C, 60.09; H, 9.13. Found: C, 60.74; H, 9.47.
Su p p or tin g In for m a tion Ava ila ble: Detailed experi-
mental procedures and characterization data for all new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
(15) Schwarz, M.; Oliver. J . E.; Sonnet, P. E. J . Org. Chem. 1975,
40, 2410.
(16) For a proposed mechanism, please see the Supporting Informa-
tion.
(17) Bernady, K. F.; Floyd, M. B. J . Org. Chem. 1979, 44, 1438.
J O049701V
J . Org. Chem, Vol. 69, No. 11, 2004 3989