Molecular sieves 5A as an acidic reagent: The discovery and applications

Article abstract of DOI:10.1016/j.tetlet.2010.11.113

The first use of molecular sieves (MS) 5A as an acidic reagent is described. We observed the acidic property during a dehydration reaction of 2-methyl-4-phenyl-3-butyn-2-ol. The acidity was sufficient to introduce ethoxyethyl and methoxyisopropyl protecting groups into alcohols. Additionally, the employment of MS 5A improved the synthesis of 1,2,4-orthoacetyl-α-d- glucopyranose at the intramolecular transorthoesterification step. In the other step of the synthesis, MS 4A was also applied to demonstrate that the manipulation of MS simplified the total operations.

Full text of DOI:10.1016/j.tetlet.2010.11.113

Tetrahedron Letters 52 (2011) 534–537
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Molecular sieves 5A as an acidic reagent: the discovery and applications
⇑
Noriaki Asakura , Tsukasa Hirokane, Hayato Hoshida, Hidetoshi Yamada
School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The first use of molecular sieves (MS) 5A as an acidic reagent is described. We observed the acidic prop-
erty during a dehydration reaction of 2-methyl-4-phenyl-3-butyn-2-ol. The acidity was sufficient to
introduce ethoxyethyl and methoxyisopropyl protecting groups into alcohols. Additionally, the employ-
Received 6 November 2010
Accepted 19 November 2010
Available online 25 November 2010
ment of MS 5A improved the synthesis of 1,2,4-orthoacetyl-a-D-glucopyranose at the intramolecular
transorthoesterification step. In the other step of the synthesis, MS 4A was also applied to demonstrate
that the manipulation of MS simplified the total operations.
Keywords:
Molecular sieves
Acidic reagent
Acetalic protections
Ó 2010 Elsevier Ltd. All rights reserved.
1,2,4-Orthoacetyl-a-D-glucopyranose
Intramolecular transorthoesterification
1. Introduction
2. Results and discussion
Molecular sieves (MS) 4A and 5A (both type A zeolite, Na and
Ca/Na form, respectively) are artificial zeolites, which are crystal-
line microporous aluminosilicates and possess uniformly sized
and shaped cavities. The cavities of a definite size are present in
the rigid, three-dimensional network composed of AlO4 and SiO4
tetrahedra that linked together through oxygen bridges. The shape
selectivity, that is, a salient feature of zeolites arises from the reg-
ular structure. Additionally, zeolites encompass simultaneously
both acidic and basic natures.1 Many types of zeolites that take
advantage of its acidic feature are known and adopted as heteroge-
neous catalysis for the organic syntheses.2 On the other hand, MS
4A and 5A have principally acted as water scavengers in organic
reactions as well as drying agents for organic solvents due to their
small pore sizes (0.4 nm and 0.5 nm in diameter for MS 4A and 5A,
respectively) that preclude the adsorption of the larger molecules.3
Nevertheless, a few synthetic conversions utilizing the acidic or
basic attributes of MS have recently been reported. For instance,
MS 3A (type A zeolite, K/Na form) and/or 4A have induced acety-
lation,4 deacetylation,5,6 and cyclization of epoxypolyene.7 How-
ever, to the best of our knowledge, MS 5A has not been
exploited as an alternative to the conventional acidic reagents. In
this letter, we report the discovery that MS 5A can behave as an
acidic reagent for an organic transformation along with practical
applications.
In our preliminary investigations, we realized that MS 5A func-
tioned as an acidic reagent for the dehydration of an -alkynol.
a
When we treated 2-methyl-4-phenyl-3-butyn-2-ol (1) with MS
5A in 1,2-dichloroethane (DCE), the dehydration reaction pro-
ceeded smoothly to afford enyne 2 in 92% yield (Scheme 1). In con-
trast, handling of 1 with MS 4A induced no reaction. The previously
reported transformation of 1 into 2 took place under acidic condi-
tions that employed p-toluenesulfonyl chloride as the reagent with
an excess amount of neutral alumina as
Intriguingly, Huang and Kaliaguine proposed a similar
a
dry medium.8
-alkynol,
a
2-methyl-3-butyn-2-ol, as a probe molecule to test the acid/base
properties of solid catalysts in the gas phase.9 Additionally, Sartori
et al. converted various
gate enynes or
a-alkynols into the corresponding conju-
a
,b-unsaturated ketones by treatment with acid
zeolites in liquid phase.10 These relevant information support the
idea that MS 5A obviously acted as the acidic reagent in the
reaction.
The acetalic protections of alcohol catalyzed by MS 5A proved
the acidity. Specifically, we investigated the introductions of eth-
oxyethyl (EE), tetrahydropyranyl (THP), and methoxyisopropyl
CH3
H3C CH3
OH
MS 5A (1.0 g/mmol)
DCE, reflux, 1 h
92%
2
1
1
MS 4A (1.0 g/mmol)
DCE, reflux, 1 h
⇑
Corresponding author. Tel.: +81 79 565 8342; fax: +81 79 565 9077.
No Reaction
E-mail address: hidetosh@kwansei.ac.jp (H. Yamada).
Department of Chemistry, Graduate School of Science, Osaka University, Toyo-
naka, Osaka 560-0043, Japan.
Scheme 1. Reaction of a-alkynol with MS.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.11.113

N. Asakura et al. / Tetrahedron Letters 52 (2011) 534–537
535
Table 1
MS 5A induced acetalic protections of alcohols
PG = protecting group
Entry
1
Substrate
Reagent
amount of MS 5A
Temp
rt
Time
Results
Product
(g/mmol)
0.3
(h)
7
Yield (%)
92
6
2
3
8
0.3
1
rt
5.5
14
3
no reaction
rt
36
then reflux
(S.M. recovery 63%)
4
5
10
6
0.3
0.3
rt
1
93
rt
4
24
then reflux
reflux
14.5
19
(S.M. recovery 70%)
89
6
7
1
1
8
reflux
21
19
8
9
10
6
1
1
rt
4
18
then reflux
17
(S.M. recovery 81%)
reflux
6
no reaction
10
11
8
1
1
reflux
reflux
21
6
no reaction
no reaction
10
(MIP) groups. We arranged 3, 4, and 5 as the substrates including
primary, secondary, and tertiary alcohols. Glances over Table 1
especially at the columns of substrate and results exhibit that (1)
the protection of the primary alcohol was practically possible
depending on the choice of the protecting group, (2) the yield of
the protection of the secondary one decreased although the reac-
tions revealed the acidic property of MS 5A, and (3) MS 5A could
not avail to protect the tertiary alcohol.
of the MIP-protected 11 was satisfactory (see the typical procedure
and Supplementary data). The MIP group has been recognized sen-
sitive because its introduction is seriously affected by the intensity
and volume of the acid catalyst15 and the protected compound is
unstable under acidic conditions;16–19 even the treatment with sil-
ica gel partly cleavages the protecting group.20 Therefore, the ease
of isolation, which requires only filtration and evaporation, seems
practically advantageous.
Introductions of EE and MIP groups into the primary alcohol
were practically useful (Table 1). Thus, addition of MS 5A (0.3 g/
mmol based on the amount of the substrate 3) to a solution of 3
and ethyl vinyl ether (6) in CH2Cl2 followed by stirring the mixture
at room temperature provided the corresponding EE-protected 711
in 92% yield after chromatographic isolation (entry 1).12 In con-
trast, THP protection using 0.3 g/mmol of MS 5A did not proceed
at room temperature (entry 2). Increase of the amount of MS into
1.0 g/mmol and raise of the reaction temperature induced the
THP-introduction slowly to afford 9 in 36% yield (entry 3).13 Intro-
duction of MIP group was faster than that of EE providing 11 in 1 h
using 0.3 g/mmol of MS 5A (entry 4).14 The indicated yield of 11
(93%) was the value after the filtration of the reaction mixture to
remove MS 5A followed by the concentration of the filtrate. De-
spite the omission of purification protocols such as liquid–liquid
distribution using separating funnel or chromatography, the purity
In the acetalic protections of the secondary alcohol using MS 5A,
introduction of the EE group demonstrated practical potential. Use
of 1.0 g/mmol of MS 5A and heating were necessary to get the sat-
isfactory yield of 12 (entries 5 and 6).21 None of significant produc-
tivity appeared in the installation of the THP and MIP groups
(entries 7 and 8).22,23 These results intimate that the acidic prop-
erty of MS 5A is quite weak because various protic, Lewis, and solid
acids have induced the acetalic protections in very high yield.16
MS 5A itself induced the acid-mediated reactions but not any
dissolutive substance from MS 5A into the solvent. In the basic
usage of MS 4A, Mizuno et al. reported that some dissolutive sub-
stance from the MS acted as the actual reagent of the observed sol-
volytic deacetylation.5 We investigated the similar possibility
applying the high-yield EE protection (Table 1, entry 1). A mixture
of MS 5A (1.5 g) in CH2Cl2 (15 mL) was stirred for 1 h at room tem-
perature, and then it stood for 4 h to precipitate the MS. Addition of

536
N. Asakura et al. / Tetrahedron Letters 52 (2011) 534–537
Table 2
Typical experimental methods for the MIP protection and the
synthesis of 15 are the following.
Synthesis of 15 utilizing MS 4A and 5A
OH
The MIP protection (Table 1, entry 4): 2-phenyl-1-ethanol (3)
(61.2 mg, 0.50 mmol) and 2-methoxy-1-propene (10) (145 mg,
OAc
O
OH
O
HO
AcO
AcO
HO
HO
MS 5A
MS 4A
O
2.0 mmol) was added to
a mixture of pretreated MS 5A
O
O
DCE
MeOH
reflux
Time (1)
(150 mg)12 in CH2Cl2 (5.0 mL). The mixture was stirred for 1 h at
room temperature and filtered through a cotton-CeliteÒ pad to
remove the MS. The filtrate was concentrated to give the MIP-pro-
tected compound 11 (94 mg, 93% yield). The crude product con-
tained a trace of unprotected 3. Further purification was possible
using silica-gel column chromatography (elution: n-hexane then
a 30:1 mixture of n-hexane and AcOEt) to furnish pure 11, but
the yield decreased to 80%.
O
O
OO
CH3
H3C
H3C
reflux
O
Time (2)
OEt
OEt
17
16
15
Entry
MS 4A
(g/mmol)
Time (1)
MS 5A
(g/mmol)
Time (2)
Yielda
(%)
(h)
(h)
1
2
3
4
5
6
0.2
1
1
1
1
1
0.2
1
3
1.5
1
21
1
35
58
75
9
2
0
0.5
0.5
0.5
0.5
0.5
3
3
The synthesis of 15 (Table 2, entry 3): a solution of 17 (102 mg,
0.271 mmol) in MeOH (2.7 mL) was refluxed with MS 4A
(266 mg)12 for 0.5 h. The mixture was filtered through a cotton-
CeliteÒ pad to remove MS 4A, and then, the filtrate was evaporated.
To a solution of the resulting residue was added MS 5A (798 mg),12
and the mixture was refluxed for 1 h. The mixture was filtered
through a cotton-CeliteÒ pad to remove MS 5A. The concentrated
filtrate contained mainly 15 and a small amount of more polar
compounds. Because of the significant crystallinity of 15, adsorp-
tion of the crude products onto silica gel was required before its
column chromatography. Hence, to a solution of the crude product
in CHCl3 (20 mL) was added silica gel (500 mg) and it was concen-
trated under reduced pressure. The resulting silica gel powder was
put on the top of a silica gel column (5 g of SiO2). Elution with n-
hexane/ethyl acetate (1/1) provided pure 15 (41.2 mg, 75% yield).
In conclusion, MS 5A successfully acts as an acidic reagent. MS
5A catalyzed the acetalic protections, including the introduction of
EE and MIP groups into the primary alcohol. Installation of the EE
group was potentially practical regarding the protection of the sec-
ondary alcohol. In the reactions, the acidic character is on MS 5A
itself but not any dissolutive substance from MS 5A into the sol-
3b
c
1
—
0.5
a
b
c
Isolation yield.
Using MS 4A in place of MS 5A.
Using p-TsOH (0.02 equiv) in place of MS 5A.
the resulting supernatant liquid (5 mL) to a mixture of the primary
alcohol 3 and ethyl vinyl ether (6) triggered no reaction. This result
evidently displays that none of the acidic components dissolves in
the solvent; hence, the acidity is on MS 5A.
The weak acidity of MS 5A and facility of its removal from the
reaction system simplified the synthesis of 1,2,4-orthoacetyl-a-D-
glucopyranose (15).24–26 The tricyclic compound 15 is a convenient
derivative of carbohydrate, which allows the regioselective modifi-
cation at the O-3 and O-6 of glucose. Additionally, the axial-rich
structure attracted our attention because we have been interested
in conformational restriction of sugars.27 Bochkov et al. reported
the synthesis of 15, where p-toluenesulfonic acid catalyzed the
intramolecular transorthoesterification of the 1,2-orthoester.25
However, in our hands, the known method furnished 15 in low
to moderate yield. We attributed the poor reproducibility to the
instability of 15 under acidic conditions since decomposition of
15 was observed during the reaction. Moreover, 15 dissolves read-
ily in water, therefore, extractive separation of 15 and the used
acidic reagent is not possible. For these reasons, we have examined
the employment of MS 5A for the transorthoesterification as a mild
acid. In addition, for the preparation of the precursor, that is, 1,2-
orthoester 16, we exerted MS 4A as a basic reagent to emphasize
the operational ease.6
vent. As the improvement of the synthesis of 1,2,4-orthoacetyl-
a-
D-glucopyranose (15) disclosed here, the weak acidity of MS 5A
and the ease of removal from the reaction system would simplify
many synthetic conversions.
Acknowledgments
SUNBOR foundation and KAKENHI partly supported this work.
We thank Prof. Hirokazu Tsukamoto (Tohoku University) for help-
ful discussions. We thank Ms. Yasuko Okamoto (Tokushima Bunri
University) for observation of mass spectra.
The two-step conversions involving deacetylation of 1728 and
intramolecular transorthoesterification of 16 provided the tricyclic
compound 15 (Table 2), whose respective steps were induced by
MS 4A and 5A.12 Thus, reflux of the mixture of the triacetylated
1,2-orthoester 17 and MS 4A (0.2 g/mmol) for 1 h followed by sim-
ple filtration and concentration cleanly produced triol 16. Without
purification, treatment of 16 with 0.2 g/mmol of MS 5A in DCE in-
duced slow intramolecular transorthoesterification (entry 1). Opti-
mization of the volume of MS 4A and 5A in each step improved the
yield of 15. The increased amount of MS 4A and 5A to 1.0 g/mmol
reduced the reaction time (entry 2). The use of 1.0 and 3.0 g/mmol
of MS 4A and 5A, respectively, shortened the time further and en-
hanced the yield of 15 (entry 3). The prolonged reaction time de-
creased the yield (entry 4). Surprisingly, trace amount of 15
appeared when we employed MS 4A instead of MS 5A (entry 5).
It is not clear yet that whether MS 4A worked as acidic or basic pro-
moter for the orthoesterification. The operation with p-toluenesul-
fonic acid produced complex mixtures of highly polar products
(entry 6). Compared to the usage of traditional homogeneous acid
catalysts, the MS-promoted transformations are far more conve-
nient, requiring only filtration for the work up.
Supplementary data
Supplementary data (1H NMR of 11) associated with this article
can be found, in the online version, at doi:10.1016/j.tetlet.
2010.11.113.
References and notes
1. Ono, Y.; Yashima, T. Science and Technology of Zeolite; Kodansha: Tokyo, 2000.
2. For recent examples of utilizing of zeolites as heterogeneous acid catalyst, see:
(a) Jones, C. W.; Tsuji, K.; Davis, M. E. Nature 1998, 393, 52–54; (b) Bigi, F.;
Carloni, S.; Maggi, R.; Muchetti, C.; Sartori, G. J. Org. Chem. 1997, 62, 7024–7027.
3. For a recent review, see: Sen, S. E.; Smith, S. M.; Sullivan, K. A. Tetrahedron 1999,
55, 12657–12698.
4. Adinolfi, M.; Barone, G.; Iadonisi, A.; Schiattarella, M. Tetrahedron Lett. 2003, 44,
4661–4663.
5. Mizuno, M.; Kobayashi, K.; Nakajima, H.; Koya, M.; Inazu, T. Synth. Commun.
2002, 32, 1665–1670.
6. Kartha, K. P. R.; Mukhopadhyay, B.; Field, R. A. Carbohydr. Res. 2004, 339, 729–
732.
7. Sen, S. E.; Zhang, Y.-z.; Roach, S. L. J. Org. Chem. 1996, 61, 9534–9537.
8. Pourjavadi, A.; Marandi, G. B. J. Chem. Res. (S) 2002, 552–555.

N. Asakura et al. / Tetrahedron Letters 52 (2011) 534–537
537
9. Huang, M.; Kaliaguine, S. Catal. Lett. 1993, 18, 373–389.
(m, 10H Â 1/2), 4.76 (q, J = 5.2 Hz, 1H), 4.70 (q, J = 5.2 Hz, 1H), 3.76 (sext,
J = 6.2 Hz, 1H), 3.74–3.58 (m, 3H Â 1/2), 3.52–3.43 (m, 2H Â 1/2), 2.80–2.58 (m,
4H Â 1/2), 1.92–1.68 (m, 4H Â 1/2), 1.32 (d, J = 5.2 Hz, 6H Â 1/2), 1.24–1.16 (m,
12H); 13C NMR (100 MHz in CDCl3) d 142.4 (s, 1C), 142.3 (s, 1C), 128.4 (d, 4C),
128.4 (d, 4C), 125.8 (d, 1C), 125.7 (d, 1C), 99.3 (d, 1C), 97.8 (d, 1C), 72.5 (d, 1C),
71.0 (d, 1C), 60.0 (t, 1C), 60.0 (t, 1C), 39.3 (t, 1C), 38.7 (t, 1C), 32.1 (t, 1C), 31.8 (t,
1C), 21.2 (q, 1C), 20.9 (q, 1C), 20.7 (q, 1C), 20.2 (q, 1C), 15.4 (q, 1C), 15.4 (q, 1C);
HRMS-CI+ (m/z): [M+H]+ calcd for C14H23O2 223.1698, found 223.1690.
22. The 13C and 1H NMR of 13 were identical to the literature data: Suzuki, T.;
Oriyama, T. Synthesis 2001, 555–558.
10. Sartori, G.; Pastorio, A.; Maggi, R.; Bigi, F. Tetrahedron 1996, 52, 8287–8296.
11. The 13C and 1H NMR was identical to the literature data: (13C NMR) Mohler, D.
L.; Thompson, D. W. Tetrahedron Lett. 1987, 23, 2567–2570; (1H NMR)
Freudenberger, J. H.; Matsui, Y.; Orchin, M. Chem. Lett. 1982, 11, 1811–1814.
12. MS 4A (Fluka, Molecular sieves Type 4A, powder) and 5A (SIGMA–ALDRICH,
Molecular sieves, 5A, powder, undried) were dried under reduced pressure by
heating with a heat-gun before use. For activation of the MS more than ca. 10 g
at a time, use of a microwave oven would be convenient. Caution: a single
heating period should be shorter than 1 min using a 500 W-oven and repeated
heating is normally required. MS was stirred using a spatula between every
interval of the heating. Further continuous heating melted the MS to glow and
lump.
23. Data for 3-(1-methoxy-1-methylethoxy)-1-phenylbutane (14): IR (neat) 3062,
3026, 2965, 2930, 1603, 1495, 1455, 1377, 1259, 1204, 1181, 1153, 1125, 1067,
1051, 1027, 1001, 985, 832, 744, 698 cmÀ1 1H NMR (400 MHz in CDCl3) d
;
13. The 13C and 1H NMR was identical to the literature data: Kumar, B.; Aga, M. A.;
Mukherjee, D.; Chimni, S. S.; Taneja, S. C. Tetrahedron Lett. 2009, 50, 6236–6240.
14. Data for 2-(1-methoxy-1-methylethoxy)-1-phenylethane (11): IR (neat) 3085,
3063, 3027, 2990, 2940, 2874, 2828, 1604, 1496, 1454, 1378, 1367, 1259, 1212,
7.30–7.25 (m, 2H, Ph), 7.20–7.15 (m, 3H, Ph), 3.99 (sext, J = 6.2 Hz, 1H, H-3),
3.24 (s, 3H, OCH3), 2.64 (t, J = 8.0 Hz, 2H, H-1), 1.90–1.67 (m, 2H, H-2), 1.36 (s.
3H, –OC(CH3)2O–), 1.34 (s, 3H, –OC(CH3)2O–), 1.21 (d, J = 6.2 Hz, 3H, H-4); 13C
NMR (100 MHz in CDCl3) d 142.5 (s, 1C, Ph), 128.5 (d, 2C, Ph), 128.4 (d, 2C, Ph),
125.8 (d, 1C, Ph), 100.6 (s, 1C, –OC(CH3)2O–), 66.8 (d, 1C, C-3), 49.2 (q, 1C,
OCH3), 39.9 (t, 1C, C-1), 32.0 (t, 1C, C-2), 25.5 (q, 1C, –OC(CH3)2O–), 25.5 (q, 1C,
–OC(CH3)2O–), 21.7 (q, 1C, C-4); HRMS-CI+ (m/z): [M+H]+ calcd for C14H23O2
223.1698, found 223.1702.
1183, 1150, 1078, 1058, 1046, 1030, 889, 865, 816, 749, 698 cmÀ1 1H NMR
;
(400 MHz in CDCl3) d 7.30–7.17 (m, 5H, Ph), 3.63 (t, J = 7.3 Hz, 2H, H-2), 3.06 (s,
3H, OCH3), 2.85 (t, J = 7.3 Hz, 2H, H-1), 1.32 (s, 6H, –OC(CH3)2O–); 13C NMR
(100 MHz in CDCl3) d 139.4 (s, 1C, Ph), 129.1 (d, 2C, Ph), 128.3 (d, 2C, Ph), 126.2
(d, 1C, Ph), 100.0 (s, 1C, –OC(CH3)2O–), 61.9 (t, 1C, C-2), 48.4 (q, 1C, OCH3), 36.8
(t, 1C, C-1), 24.5 (q, 2C, –OC(CH3)2O–); HRMS-CI+ (m/z): [M+H]+ calcd for
24. Bochkov, A. F.; Voznyi, Y. V.; Kalinevich, V. M.; Shashkov, A. S.; Kochetkov, N. K.
Izv. Akad. Nauk SSSR, Ser. Khim. 1975, 415–420.
C
12H19O2 195.1385, found 195.1375.
25. Bochkov, A. F.; Voznyi, Y. V.; Chernetskii, V. N.; Dashunin, V. M.; Rodionov, A. V.
Izv. Akad. Nauk SSSR, Ser. Khim. 1975, 420–423.
15. The acid catalyst (phosphorous oxychloride) was introduced by using capillary
when the reaction scale was 20 mmol: Kluge, A. F.; Untch, K. G.; Fried, J. H. J.
Am. Chem. Soc. 1972, 94, 7827–7832.
16. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 4th ed.; John
Wiley and Sons: New York, 2007.
17. Kocienski, P. J. Protecting Groups; Georg Thieme: Stuttgart, 1994.
18. Zhang, G.; Zhang, L. J. Am. Chem. Soc. 2008, 130, 12598–12599.
19. Tietze, L. F.; Fischer, R.; Lögers, M.; Beller, M. Carbohydr. Res. 1989, 194, 155–
162.
20. Matsumoto, Y.; Mita, K.; Hashimoto, K.; Iio, H.; Tokoroyama, T. Tetrahedron
1996, 52, 9387–9398.
26. Moradei, O. M.; du Mortier, C.; Cirelli, A. F. Arkivoc 2005, xii, 189–194.
27. (a) Cao, Y.; Kasai, Y.; Bando, M.; Kawagoe, M.; Yamada, H. Tetrahedron 2009, 65,
2574–2578; (b) Yamada, H.; Nagao, K.; Dokei, K.; Kasai, Y.; Michihata, N. J. Am.
Chem. Soc. 2008, 130, 7566–7567; (c) Okada, Y.; Nagata, O.; Taira, M.; Yamada,
H. Org. Lett. 2007, 9, 2755–2758; (d) Okada, Y.; Mukae, T.; Okajima, K.; Taira,
M.; Fujita, M.; Yamada, H. Org. Lett. 2007, 9, 1573–1576; (e) Yamada, H.;
Tanigakiuchi, K.; Nagao, K.; Okajima, K.; Mukae, T. Tetrahedron Lett. 2004, 45,
9207–9209; (f) Yamada, H.; Tanigakiuchi, K.; Nagao, K.; Okajima, K.; Mukae, T.
Tetrahedron Lett. 2004, 45, 5615–5618; (g) Ikeda, T.; Yamada, H. Carbohydr. Res.
2000, 329, 889–893; (h) Yamada, H.; Ikeda, T. Chem. Lett. 2000, 432–433; (i)
Yamada, H.; Nakatani, M.; Ikeda, T.; Marumoto, Y. Tetrahedron Lett. 1999, 40,
5573–5576.
21. Data for 3-(1-ethoxyethoxy)-1-phenylbutane (12): Diastereomixtures: IR (neat)
3062, 3026, 2973, 2930, 1603, 1495, 1455, 1375, 1333, 1123, 1098, 1078, 1053,
1030, 969, 925, 841, 746, 698 cmÀ1
;
1H NMR (400 MHz in CDCl3) d 7.30–7.15
28. Lemieux, R. U.; Morgan, A. R. Can. J. Chem. 1965, 43, 2199–2204.