Synthesis of novel chiral semicrown ether-like bis(oxazoline) ligands and application in enantioselective cyclopropanation of styrene

Article abstract of DOI:10.1081/SCC-200048469

A series of chiral C₂-symmetric bis(oxazoline) ligands containing semicrown ether unit were synthesized. The copper complexes prepared in situ from copper(I)-triflate, and the new chiral oxazoline ligands were assessed as chiral catalysts in th

Full text of DOI:10.1081/SCC-200048469

This article was downloaded by: [Nova Southeastern University]
On: 01 January 2015, At: 03:17
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic
Organic Chemistry
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
Synthesis of Novel Chiral
Semicrown Ether‐Like
Bis(oxazoline) Ligands and
Application in Enantioselective
Cyclopropanation of Styrene
Zhan‐Yue Wang a b , Da‐Ming Du a b & Jia‐Xi Xu b
a School of Pharmacy , Wenzhou Medical College ,
Wenzhou, Zhejiang, P.R. China
b Key Laboratory of Bioorganic Chemistry and
Molecular Engineering of Ministry of Education,
College of Chemistry and Molecular Engineering ,
Peking University , Beijing, P.R. China
Published online: 28 Jul 2007.
To cite this article: Zhan‐Yue Wang , Da‐Ming Du & Jia‐Xi Xu (2005) Synthesis
of Novel Chiral Semicrown Ether‐Like Bis(oxazoline) Ligands and Application in
Enantioselective Cyclopropanation of Styrene, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 35:2,
299-313, DOI: 10.1081/SCC-200048469
To link to this article: http://dx.doi.org/10.1081/SCC-200048469
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.

However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Synthetic Communicationsw, 35: 299–313, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048469
Synthesis of Novel Chiral Semicrown
Ether-Like Bis(oxazoline) Ligands and
Application in Enantioselective
Cyclopropanation of Styrene
Zhan-Yue Wang
School of Pharmacy, Wenzhou Medical College, Wenzhou, Zhejiang,
P.R. China and Key Laboratory of Bioorganic Chemistry and Molecular
Engineering of Ministry of Education, College of Chemistry and
Molecular Engineering, Peking University, Beijing, P.R. China
Da-Ming Du, and Jia-Xi Xu
Key Laboratory of Bioorganic Chemistry and Molecular Engineering of
Ministry of Education, College of Chemistry and Molecular Engineering,
Peking University, Beijing, P.R. China
Abstract: A series of chiral C2-symmetric bis(oxazoline) ligands containing semicrown
etherunitweresynthesized. The coppercomplexespreparedinsitufrom copper(I)-triflate,
and the new chiral oxazoline ligands were assessed as chiral catalysts in the enantioselec-
tive cyclopropanation of styrene with diazoacetates. Enantioselectivities up to 84% and up
to 65%, respectively, for trans- and cis-2-phenylcyclopropanecarboxylate were observed.
Keywords: Bis(oxazoline), synthesis, enantioselective cyclopropanation, styrene,
asymmetric catalysis
Received in the UK June 26, 2004
Address correspondence to Da-Ming Du, School of Pharmacy, Wenzhou Medical
College, Wenzhou, Zhejiang, P.R. China and Key Laboratory of Bioorganic
Chemistry and Molecular Engineering of Ministry of Education, College of
Chemistry and Molecular Engineering, Peking University, Beijing, P.R. China.
Fax: 86-10-62751708; E-mail: dudm@pku.edu.cn

300
Z.-Y. Wang, D.-M. Du, and J.-X. Xu
INTRODUCTION
Cyclopropane is found as a basic structural unit in a wide variety of synthetic
and naturally occurring compounds[1–5] A number of catalyst systems have
been developed for the asymmetric cyclopropanation of olefins.[6–10] Many
of these are based on the decomposition of diazo compounds, and the corre-
sponding reaction mechanism is believed to proceed through metal
carbenoid intermediate. These systems include copper complexes of semicor-
rin, bis(oxazoline), chiral Schiff base and bipyridine as well as rhodium
carboxamides and porphyrins, ruthenium pybox, and cobalt and ruthenium
salen complexes. In recent years, C2-symmetric bis(oxazoline) are versatile
chiral ligands, and their metal complexes have been recognized as an
effective class of chiral catalyst in a variety of transition metal catalyzed
asymmetric reactions.[11–16] Thus, the design and synthesis of new chiral
bis(oxazoline) ligands has inspired many chemists to work with great
efforts. The search for chiral ligands with broad applicability is a particularly
interesting aspect in the field of chemical research on enantioselective
reactions promoted by chiral catalysts. Continuing on our ongoing project
on the synthesis, structure and catalytic enantioselective reaction of novel
chiral bis(oxazoline) ligands,[17–23] in this article, we report the synthesis
and the primary catalytic enantioselective cyclopropanation of styrene by
copper(I) complex of a series of new bis(oxazoline) ligands 4 and 5 containing
semicrown ether unit. Crown ether has inclusion ability to a variety of ions
and neutral molecules; we expect the combination of semicrown ether and
chiral oxazoline unit in new ligands may result in unique characteristics
for catalytic reaction.
RESULTS AND DISCUSSION
Many methods have been reported for the synthesis of oxazoline
ligands.[24–27] The usual method for preparation of chiral bis(oxazoline) is
the reaction of diacid derivatives with chiral b-amino alcohols. The enantio-
merically pure b-amino alcohols are either commercially available or easily
obtained by reduction of the corresponding a-amino acids.[28–31] The diacid
1 were synthesized according to literature procedure from corresponding
dibromide and methyl salicylate.[32] The diacid 1 was refluxed with thionyl
chloride to afford the diacyl chloride. The diacyl chloride was treated
with b-amino alcohols and triethylamine to afford the corresponding chiral
intermediate dihydroxy diamides 2 and 3 in 60–97% yields. The procedure
for synthesis of bis(oxazoline) developed by Denmark et al.[33] was used to
synthesize the desired chiral bis(oxazoline) ligands 4 and 5. The dihydroxy
diamides were treated with methanesulfonyl chloride (MsCl) (2.3 eq.) and
Et3N (5 eq.) in dichloromethane to afford the corresponding bismesylates,

Synthesis of Chiral Semicrown Ether-Like Bis(oxazoline) Ligands
301
Scheme 1. Synthesis of new bis(oxazoline) 4 and 5.
which were treated with an aqueous methanolic solution of NaOH to furnish
the bis(oxazoline) 4 and 5 in good yields (53–85%) (Scheme 1). The struc-
1
tures of these new chiral bis(oxazoline) ligands were characterized by H
NMR, MS, IR, and elemental analysis or HRMS.
With the new ligands in hand, we try to evaluate the efficiency of these
bis(oxazoline) ligands in the copper (I)-catalyzed asymmetric cyclopropana-
tion of olefins. We first carried out the model reaction of styrene with ethyl
diazoacetate to give the trans- and cis-cyclopropanes 7 and 8 (Scheme 2).
The asymmetric cyclopropanation was carried out in dichloromethane in the
presence of 2% mol of copper(I) catalyst generated in situ by mixing
Cu(OTf).1/2C6H6 and the bis(oxazoline). The reaction was first performed
at room temperature by slow addition of ethyl diazoacetate to a solution of
styrene in dichloromethane containing the copper (I)-bis(oxazoline) catalyst.
1
The ratio of trans- and cis-isomers were determined by H NMR analysis,
Scheme 2. Cyclopropanation reaction of styrene with diazoacetates.

302
Z.-Y. Wang, D.-M. Du, and J.-X. Xu

Synthesis of Chiral Semicrown Ether-Like Bis(oxazoline) Ligands
303
and the enantiomeric excesses were determined by HPLC analysis using a
chiral column (Chiracel OJ). The results are summarized in Table 1.
Among the bis(oxazoline) ligands tested, 5a containing phenyl substitu-
ent on its oxazolines gave the highest enantiomeric excess for trans-7 in
45% ee and cis-8 in 43% ee (entry 5), the ligands 4b and 5b containing
benzyl group afforded comparably lower enantioselectivity (trans-7% ee
and 8% ee, respectively, entries 2 and 6). In addition, the ligands 4c and 5c
with iso-butyl substituent afford moderate enantioselectivity for cyclopropa-
nation in 32% ee and 35% ee (entries 3 and 7). It is of interest that the
phenyl substituent on the oxazoline 5a provides the best enantiomeric
excess of trans-7 and cis-8. However, in the same reaction, the introduction
of a phenyl substituent at the 4-position of the oxazoline has been previouly
reported to have a pronounced effect on enantioselectivity.[17] This phenom-
enon may be ascribed to the flexibility of 5a, resulting in little torsional
strain between the two oxazoline units in corresponding copper(I) complex.
Meanwhile, we examined the effect of temperature for cyclopropanation of
the ligands 5a and 5c as shown in Table 1. The reactions were carried out
under the same condition as above, except addition of diazoacetate for 4 hr
and the reaction was proceeding for 18 hr at 08C, the ee value of copper(I)-
catalyzed cyclopropanation rise to 68% and 56% ee, respectively (entries 9
and 10). As expected, when the steric bulkier diazoacetate ester t-butyl diazoa-
cetate was used instead of ethyl diazoacetate, the enantioselectivity was
improved. The reaction of t-butyl diazoacetate with styrene in the presence
of Cu(I)-ligand 5a catalyst gave trans-t-butyl cyclopropanecarboxylates up
to 84% ee and cis isomer in 65% ee (entry 8).
The following conclusion can also be made from the results gathered in
Table 1. (1) The diastereoselectivity of the reaction is in favor of trans-
selectivity. Preference for the trans-isomer has been previously observed
for the same reaction using alternative bis(oxazoline) ligands.[35–41] (2) The
enantioselectivity of cis-isomer is almost the same level as that of trans-
isomer. (3) The enantioselectivity was improved when temperature was
reduced with a slight lower chemical yield (entries 9 and 10 vs entries 5
and 7). (4) The enantioselectivity of 5a–d was better than 4a–d. (5) The
predominant formation of (1R, 2R)-trans-cyclopropane 7 and (1R, 2S)-cis-
cyclopropane 8 were observed irrespective of the reaction temperature
(room temperature or 08C) with S-bis(oxazoline). As expected, the preferred
absolute configurations of trans-cyclopropane 7 and cis-cyclopropane 8
were antipodal when use R-bis(oxazoline) 4a and 5a.
Although the enantioselectivity is moderate for these new ligands, one
advantage is that the moderate enantioselectivity can be obtained by using
the very cheap ligand 5a or 5c synthesized from cheap b-amino alcohol
(R-phenylglycinol or S-leucinol). In contrast, very expensive ligands
derivated from L-t-leucinol were usually used in literature.[42–44] Further-
more, we obtained moderate enantioselectivity of the cis-isomer 8 and did

304
Z.-Y. Wang, D.-M. Du, and J.-X. Xu
not need to use the bulky adamantyl substituted bis(oxazoline). There still
exists potential to optimize the enantioselectivity; the enantioselectivity of
the metal catalyzed cyclopropanation is usually higher when the steric
bulky ester is used.[45–47] It seem that the combination of semicrown ether
and chiral oxazoline unit in these new ligands may result in many coordination
sites with copper for formation of suitable chiral complexes, which may
explain the moderate enantioselectivity obtained.
In conclusion, an efficient synthetic procedure was developed for
synthesis of new chiral semicrown ether-like bis(oxazoline) ligands. Prelimi-
nary results in asymmetric cyclopropanation of styrene with ethyl diazoacetate
have been obtained. The C2-symmetric bis(oxazoline) 4 and 5 derived from
m-phenylenebis(methyleneoxy) and 2,6-pyridinediylbis(methyleneoxy) units
present different reactivities in the asymmetric copper-catalyzed cyclopropa-
nation. The highest enantioselectivity was obtained with phenyl substituted
bis(oxazoline) 5a. Although the trans-enantioselectivity is moderate, these
primary results suggest that these novel semicrown ether-like bis(oxazolines)
may have potential to become catalyst for other asymmetric reactions. The
semicrown ether-like chiral bis(oxazolines) have many coordination sites
may be suitable for chiral complexes formation with other metals such as
zinc, cobalt, and rhodium. Further studies in other asymmetric reactions are
in progress in our laboratory.
EXPERIMENTAL
Melting points were measured on an XT-4 melting point apparatus and were
1
uncorrected. H NMR and 13C NMR spectra were recorded on a Mercury
300 MHz or 200 MHz spectrometer with tetramethylsilane (TMS) serving
as internal standard. Infrared spectra were obtained on a Bruker Vector 22
spectrometer. Mass spectra were obtained on a VG-ZAB-HS mass spec-
trometer. Optical rotations were measured on a Perkin–Elmer 241 MC
spectrometer. Elemental analyses were carried out on an Elementar Vario
EL instrument. Solvents used were purified and dried by standard procedures.
2,20-[1,3-phenylenebis(methyleneoxy)]-bisbenzoic acid 1a and 2,20-[2,6-
pyridinediylbis(methyleneoxy)]-bisbenzoic acid 1b were synthesized accord-
ing to literature procedure (Elwahy and Abbas, 2000).
General Procedure A
1,3-Bis[2-[N-(2-hydroxy-(1R)-1-phenylethyl)carbamoyl]
phenoxymethyl]benzene (2a)
A solution of diacid 1a (3.0 g, 8 mmol), SOCl2 (50 mL) and 3 drops of DMF
was refluxed for 12 hr. The excess SOCl2 was removed under reduced

Synthesis of Chiral Semicrown Ether-Like Bis(oxazoline) Ligands
305
pressure, and then anhydrous benzene (20 mL) was added and the solvent was
removed again to dryness to remove the trace of SOCl2 and afford the diacyl
dichloride. The above diacyl dichloride in CH2Cl2 (150 mL) was added
dropwise to a solution of R-phenylglycinol (2.19 g, 16 mmol) and Et3N
(10 mL) in CH2Cl2 (50 mL) at 08C and stirred at room temperature for
24 hr. The reaction mixture was washed with 2 N HCl, 10% NaHCO3, and
H2O. The organic layer was dried over anhydrous Na2SO4 and concentrated
to give crude product. Purification by silica gel column chromatography
(petroleum ether-ethyl acetate-methanol 5 : 3 : 1) afforded the dihydroxy
diamide 2a as colorless solid (3.92 g, 79.5%). m.p. 78–808C. [a]D20
¼
1
þ 91.78 (c ¼ 0.38, CHCl3); H NMR (300 MHz, CDCl3): d 3.07 (2H, s,
OH), 3.54–3.68 (4H, m, CH2), 5.09 (4H, s, OCH2), 5.16–5.22 (2H, m,
CH), 6.99–7.14 (14H, m, ArH), 7.37–7.45 (5H, m, ArH), 7.60 (1H, s,
ArH), 8.14–8.17 (2H, s, ArH), 8.54 (2H, d, J ¼ 7.8 Hz, NH). 13C NMR
(CDCl3): d 55.64, 66.29, 70.84, 112.37, 121.40, 121.59, 126.49, 127.27,
128.25, 128.46, 128.65, 129.27, 132.33, 132.93, 136.15, 139.19, 156.62,
165.29. IR(KBr): n 3384, 3061, 3030, 2932, 1708,1638, 1599, 1530, 1482,
1450, 1384, 1300, 1223, 1162, 1105, 996, 755, 700 cm21. ESIMS: m/z 617
(M þ H, 48), 639 (M þ Na, 100), 360 (20), 223 (18). Anal. Calcd. for
.
C38H36N2O6 0.5H2O: C, 72.94; H, 5.91; N, 4.47. Found: C, 72.89; H, 5.64;
N, 4.35.
1,3-Bis[2-[N-((1S)-1-benzyl-2-hydroxyethyl)carbamoyl]
phenoxymethyl]benzene (2b)
Following general procedure A, from diacid 1a (2.64 g, 7 mmol), SOCl2
(45 mL), S-Phenylalanol (2.12 g, 14 mmol) and Et3N (10 mL) to give a
colorless solid 2b in 71.8% yield (3.24 g). m.p. 59–608C. [a]2D0 ¼ 263.58
1
(c ¼ 0.38, CHCl3); H NMR (200 MHz, CDCl3): d 2.72 (4H, d, J ¼ 7.2 Hz,
CH2), 3.35–3.59 (6H, m, CH2 þ OH), 4.27–4.31 (2H, m, CH), 5.11 (4H, s,
OCH2), 6.94–7.54 (20H, m, ArH), 8.12–8.18 (4H, m, ArH þ NH). 13C
NMR (CDCl3): d 36.89, 52.97, 63.40, 70.78, 112.58, 112.56, 121.61,
126.31, 127.31, 128.11, 128.31, 129.10, 132.13, 132.79, 136.39, 137.82,
156.53, 165.41. IR(KBr): n 3389, 3072, 2960, 1735, 1637, 1599, 1537,
1479, 1449, 1385, 1298, 1221, 1161, 1101, 993, 754 cm21. ESIMS: m/z
645 (M þ H, 76), 667 (M þ Na, 100), 525 (80), 374 (20). Anal. Calcd. for
.
C40H40N2O6 2H2O: C, 70.56; H, 6.51; N, 4.11. Found: C, 70.67; H, 6.39;
N, 3.91.
1,3-Bis[2-[N-(2-hydroxy-(1S)-1-isobutylethyl)carbamoyl]
phenoxymethyl]benzene (2c)
Following general procedure A, from diacid 1a (2.64 g, 7 mmol), SOCl2
(40 mL), S-leucinol (1.65 g, 14 mmol) and Et3N (10 mL) to give a colorless

306
Z.-Y. Wang, D.-M. Du, and J.-X. Xu
solid 2c in 91.6% yield (3.7 g). m.p. 60–618C. [a]2D0 ¼ 265.88 (c ¼ 0.39,
1
CHCl3); H NMR (200 MHz, CDCl3): d 0.74 (6H, d, J ¼ 6.8 Hz, CH3), 0.80
(6H, d, J ¼ 6.4 Hz, CH3), 0.95–1.28 (4H, m, CH2), 1.28–1.48 (2H, m,
CH), 3.25 (2H, s, OH), 3.37–3.66 (4H, m, CH2), 4.05–4.16 (2H, m, CH),
5.19 (4H, s, OCH2), 7.02–7.13 (4H, m, ArH), 7.40–7.62 (6H, m, ArH),
7.95 (2H, d, J ¼ 7.4 Hz, ArH), 8.18 (2H, d, J ¼ 7.8 Hz, NH). 13C NMR
(CDCl3): d 22.07, 22.92, 24.76, 40.08, 50.17, 66.18, 70.91, 112.43, 115.95,
121.58, 121.73, 128.52, 129.50, 132.32, 132.86, 136.38, 156.56, 165.80.
IR(KBr): n 3384, 3073, 2955, 2869, 1739, 1637, 1600, 1537, 1483, 1449,
1384, 1299, 1222, 1160, 1101, 754 cm21. ESIMS: m/z 577 (M þ H, 100),
599 (M þ Na, 86), 559 (15), 340 (40), 197 (70). Anal. Calcd. for
.
C34H44N2O6 0.5H2O: C, 69.71; H, 7.74; N, 4.78. Found: C, 69.58; H, 7.65;
N, 4.63.
1,3-Bis[2-[N-(2-hydroxy-(1S)-1-isopropylethyl)carbamoyl]
phenoxymethyl]benzene (2d)
Following general procedure A, from diacid 1a (2.64 g, 7 mmol), SOCl2
(40 mL), S- leucinol (1.44 g, 14 mmol) and Et3N (10 mL) to give a colorless
1
oil 2c in 97.4% yield (3.74 g). [a]2D0 ¼ 247.58 (c ¼ 0.48, CHCl3); H NMR
(200 MHz, CDCl3): d 0.67 (6H, d, J ¼ 7.0 Hz, CH3), 0.76 (6H, d,
J ¼ 6.4 Hz, CH3), 1.65–1.76 (2H, m, CH), 3.31 (2H, s, OH), 3.45–3.60
(4H, m, CH2), 3.82–3.90 (2H, m, CH), 5.20 (4H, s, OCH2), 7.01–7.14 (4H,
m, ArH), 7.41–7.49 (5H, m, ArH), 7.64 (1H, s, ArH), 8.02 (2H, d,
J ¼ 8.2 Hz, NH), 8.20 (2H, d, J ¼ 7.6 Hz, ArH). 13C NMR (CDCl3): d
18.33, 19.32, 28.95, 57.35, 64.06, 70.85, 112.30, 121.62, 121.67, 128.16,
128.73, 129.44, 132.42, 132.85, 136.28, 156.55, 166.10. IR(KBr): n 3391,
3073, 2960, 2873, 1735, 1636, 1599, 1537, 1483, 1449, 1385, 1298, 1223,
1163, 1102, 996, 755 cm21. ESIMS: m/z 549 (M þ H, 8), 571 (M þ Na,
.
100), 197 (5). Anal. Calcd. for C32H40N2O6 0.5H2O: C, 68.92; H, 7.41; N,
5.02. Found: C, 68.70; H, 7.26; N, 4.83.
2,6-Bis[2-[N-(2-hydroxy-(1R)-1-phenylethyl)carbamoyl]
phenoxymethyl]pyridine (3a)
Following general procedure A, from diacid 1b (2.28 g, 6 mmol), SOCl2
(40 mL), R-phenylglycinol (1.65 g, 12 mmol) and Et3N (8 mL) to give a
colorless solid 3a in 76.8% yield (2.85 g). m.p. 118–1198C. [a]2D0 ¼ þ81.48
1
(c ¼ 0.35, CHCl3); H NMR (200 MHz, CDCl3): d 3.41 (2H, t, J ¼ 6.0 Hz,
OH), 3.65–3.80 (4H, m, CH2), 5.21(4H, s, OCH2), 5.20–5.32 (2H, m, CH),
6.97–7.19 (14H, m, ArH), 7.27–7.44 (4H, m, ArH), 7.64 (1H, t,
J ¼ 7.8 Hz, ArH), 8.12–8.18 (2H, dd, J ¼ 1.6, 7.6 Hz, ArH), 8.60 (2H, d,
J ¼ 7.6 Hz, NH). 13C NMR (CDCl3): d 55.78, 66.25, 71.47, 112.72, 121.97,
122.27, 126.61, 127.40, 128.54, 132.39, 132.95, 138.25, 139.33, 155.31,

Synthesis of Chiral Semicrown Ether-Like Bis(oxazoline) Ligands
307
156.21, 165.42. IR(KBr): n 3381, 3287, 3059, 2921, 1737, 1636, 1599, 1529,
1489, 1439, 1384, 1287, 1244, 1163, 1060, 1026, 752, 702 cm21. ESIMS: m/z
618 (M þ H, 80), 640 (M þ Na, 100), 600 (10), 498 (15), 481 (25), 343 (25),
.
225 (10). Anal. Calcd. for C37H35N3O6 0.5H2O: C, 70.91; H, 5.79; N, 6.70.
Found: C, 71.13; H, 5.85; N, 6.48.
2,6-Bis[2-[N-((1S)-1-benzyl-2-hydroxyethyl)carbamoyl]
phenoxymethyl]pyridine (3b)
Following general procedure A, from diacid 1b (2.28 g, 6 mmol), SOCl2
(40 mL), S-phenylalaninol (1.82 g, 12 mmol) and Et3N (8 mL) to give a
colorless solid 3b in 68.2% yield (2.64 g). m.p. 173–1758C. [a]2D0 ¼ 256.78
1
(c ¼ 0.12, CHCl3); H NMR (200 MHz, CDCl3): d 2.85 (4H, d, J ¼ 7.2 Hz,
CH2), 3.34 (2H, J ¼ 6.0 Hz, OH), 3.51–3.73 (4H, m, CH2), 4.34–4.42 (2H,
m, CH), 5.28 (4H, s, OCH2), 6.96–7.29 (14H, m, ArH), 7.35–7.44 (4H, m,
ArH), 7.69 (1H, t, J ¼ 7.8 Hz, ArH), 8.13–8.18 (4H, dd, J ¼ 1.6, 7.8 Hz,
ArH þ NH). 13C NMR (CDCl3): d 37.07, 53.30, 63.93, 71.35, 112.99,
122.06, 122.34, 126.49, 128.47, 129.19, 132.27, 132.82, 137.86, 155.60,
156.00, 165.61. IR(KBr): n 3300, 3027, 2931, 2873, 1637, 1599, 1534,
1489, 1439, 1375, 1239, 1113, 1045, 1027, 752, 700 cm21. ESIMS: m/z
646(M þ H, 100), 668 (M þ Na, 95), 628 (30), 495 (46), 362 (15), 344 (12),
.
225 (5). Anal. Calcd. for C39H39N3O6 0.5H2O: C, 71.50; H, 6.16; N, 6.41.
Found: C, 71.67; H, 6.11; N, 6.24.
2,6-Bis[2-[N-(2-hydroxy-(1S)-1-isobutylethyl)carbamoyl]
phenoxymethyl]pyridine (3c)
Following general procedure A, from diacid 1b (2.28 g, 6 mmol), SOCl2
(40 mL), S-leucinol (1.41 g, 12 mmol) and Et3N (8 mL) to give a colorless
solid 3c in 87.3% yield (3.03 g). m.p. 116–1188C. [a]2D0 ¼ 262.28
1
(c ¼ 0.37, CHCl3); H NMR (200 MHz, CDCl3): d 0.80 (6H, d, J ¼ 6.4 Hz,
CH3), 0.86 (6H, d, J ¼ 6.4 Hz, CH3), 1.20–1.39 (4H, m, CH2), 1.47–1.64
(2H, m, CH), 3.45–3.76 (6H, m, OH þ CH2), 4.10–4.25 (2H, m, CH), 5.32
(4H, s, OCH2), 7.02–7.13 (4H, m, ArH), 7.38–7.49 (4H, m, ArH), 7.82
(1H, t, J ¼ 7.8 Hz, ArH), 7.96 (2H, d, J ¼ 7.8 Hz, NH), 8.12–8.17 (2H, dd,
J ¼ 1.8, 7.6Hz, ArH). 13C NMR (CDCl3): d 22.16, 23.00, 24.86, 40.27,
50.19, 65.84, 71.44, 112.83, 122.02, 122.19, 122.41, 132.25, 132.73,
138.30, 155.62, 156.00, 165.75. IR(KBr): n 3383, 3286, 3074, 2953, 2869,
1743, 1637, 1598, 1538, 1490, 1440, 1369, 1288, 1239, 1162, 1111, 1061,
750 cm21. ESIMS: m/z 578 (M þ H, 100), 600 (M þ Na, 35), 461 (30), 362
.
(12), 343(8). Anal. Calcd. for C33H43N3O6 0.5H2O: C, 67.55; H, 7.55; N,
7.16. Found: C, 67.90; H, 7.36; N, 6.85.

308
Z.-Y. Wang, D.-M. Du, and J.-X. Xu
2,6-Bis[2-[N-(2-hydroxy-(1S)-1-isopropylethyl)carbamoyl]
phenoxymethyl]pyridine (3d)
Following general procedure A, from diacid 1b (2.28 g, 6 mmol), SOCl2
(40 mL), S-leucinol (1.24 g, 12 mmol) and Et3N (8 mL) to give a colorless
solid 3d in 59.7% yield (1.97 g). m.p. 140–1428C. [a]2D0 ¼ 243.58
1
(c ¼ 0.23, CHCl3); H NMR (200 MHz, CDCl3): d 0.78 (6H, d, J ¼ 6.6 Hz,
CH3), 0.85 (6H, d, J ¼ 6.8 Hz, CH3), 1.74–1.85 (2H, m, CH), 3.52–3.70
(6H, m, OH þ CH2), 3.89–3.96 (2H, m, CH), 5.32 (4H, s, OCH2), 7.01–
7.13 (4H, m, ArH), 7.37–7.48 (4H, m, ArH), 7.80 (1H, t, J ¼ 7.8 Hz, ArH),
8.04 (2H, d, J ¼ 8.2 Hz, NH), 8.13–8.18 (2H, dd, J ¼ 1.8, 7.6 Hz, ArH).
13C NMR (CDCl3): d 18.65, 19.48, 29.04, 57.41, 63.69, 71.41, 112.69,
121.95, 122.37, 122.45, 132.32, 132.71, 138.33, 155.51, 156.03, 165.97.
IR(KBr): n 3406, 3311, 3075, 2956, 2870, 1771, 1616, 1580, 1535, 1491,
1441, 1384, 1296, 1234, 1170, 1109, 1078, 754 cm21. ESIMS: m/z 550
(M þ H, 100), 572 (M þ Na, 38), 532 (32), 447 (35), 362 (18), 343 (15),
.
225 (10). Anal. Calcd. for C31H39N3O6 0.5H2O: C, 66.65; H, 7.21; N, 7.52.
Found: C, 67.01; H, 6.86; N, 7.35.
General Procedure B
1,3-Bis[2-((4R)-4-phenyl-4,5-dihydro-1,3-oxazol-2-yl)phenoxymethyl]
benzene (4a)
To an ice-cooled solution of the dihydroxy diamide 2a (1.23 g, 2.0 mmol) and
Et3N (1.4 mL, 10 mmol) in CH2Cl2 (20 mL) was added, dropwise MsCl
(0.36 mL, 4.6 mmol). The mixture was allowed to warm to room temperature
and was stirred for 12 hr. The mixture was quenched with water and extracted
with CH2Cl2 (3 ꢀ 50 mL). The organic layer was dried over anhydrous
Na2SO4 and concentrated to dryness in vacuo to give the crude bismesylate
as a yellow oil. The crude bismesylate was dissolved in CH3OH (30 mL)
and NaOH solution (11 mL, 0.25 N), The mixture was refluxed for 3 hr. The
methanol was removed in vacuo and the residue was extracted with CH2Cl2
(2 ꢀ 30 mL). The combined organic phase was washed with 1 N HCl, 5%
NaHCO3 and H2O. The organic layer was dried over anhydrous Na2SO4
and concentrated in vacuo to give a pale yellow oil. Purification by silica
gel column chromatography (petroleum ether-ethyl acetate 1 : 1) to afford
light yellow oil 4a 0.85 g (73.3 yield). [a]2D0 ¼ þ28.58 (c ¼ 0.33, CHCl3);
1H NMR (200 MHz, CDCl3): d 4.18 (2H, t, J ¼ 8.2 Hz, CH2), 4.71 (2H, dd,
J ¼ 8.2, 9.8 Hz, CH2), 5.07 (4H, s, OCH2), 5.40 (2H, dd, J ¼ 8.2, 9.8 Hz,
CH), 6.90–7.43 (19H, m, ArH), 7.71 (1H, s, ArH), 7.85 (2H, dd, J ¼ 1.8,
7.8 Hz, ArH). 13C NMR (CDCl3): d 70.15, 70.19, 74.19, 113.40, 117.63,
120.53, 125.16, 125.87, 126.62, 127.29, 128.39, 128.50, 131.22, 132.17,

Synthesis of Chiral Semicrown Ether-Like Bis(oxazoline) Ligands
309
136.98, 142.53, 157.39, 163.54. IR(KBr): n3061, 3029, 2959, 2894, 1643,
1600, 1582, 1494, 1451, 1384, 1355, 1250, 1163, 1034, 949, 752,
699 cm21. EIMS: m/z 580 (Mþ, 28), 355 (20), 341 (15), 239 (32), 121 (40),
104 (38). HREIMS Calcd. for C38H32N2O4: 580.23621. Found: 580.23656.
1,3-Bis[2-((4S)-4-benzyl-4,5-dihydro-1,3-oxazol-2-yl)phenoxymethyl]
benzene (4b)
Following general procedure B, from dihydroxy diamide 2b (0.95 g,
1.47 mmol) to afford light yellow oil 0.723 g (76.1% yield). [a]2D0 ¼ 24.58
1
(c ¼ 0.27, CHCl3); H NMR (200 MHz, CDCl3): d 2.74 (2H, dd, J ¼ 8.8,
13.6 Hz, CH2), 3.24 (2H, dd, J ¼ 5.0, 13.6 Hz, CH2), 4.08 (2H, t,
J ¼ 8.2 Hz, CH2), 4.29 (2H, t, J ¼ 8.2 Hz, CH2), 4.55–4.67 (2H, m, CH),
5.17 (4H, s, OCH2), 6.93–7.46 (19H, m, ArH), 7.68 (1H, s, ArH), 7.77 (2H,
dd, J ¼ 1.4, 7.6 Hz, ArH). 13C NMR (CDCl3): d 41.62, 67.75, 70.36, 71.23,
74.19, 113.53, 117.85, 120.59, 124.94, 125.87, 126.24, 128.31, 128.41,
129.08, 131.13, 132.04, 137.05, 137.86, 157.25, 162.81. IR(KBr): n3062,
3027, 2922, 1647, 1601, 1581, 1495, 1453, 1384, 1356, 1256, 1164, 1030,
965, 752, 700 cm21. EIMS: m/z 608 (Mþ, 25), 517 (48), 489 (15), 355
(45), 264 (26), 213 (40), 105 (100). HREIMS Calcd. for C40H36N2O4:
608.26751. Found: 608.26829.
1,3-Bis[2-((4S)-4-isobutyl-4,5-dihydro-1,3-oxazol-2-yl)
phenoxymethyl]benzene (4c)
Following general procedure B, from dihydroxy diamide 2c (1.5 g, 2.6 mmol)
to afford a colorless oil 1.16 g (82.3% yield). [a]2D0 ¼ 276.58 (c ¼ 0.27,
1
CHCl3); H NMR (200 MHz, CDCl3): d 0.97 (12H, t, J ¼ 5.8 Hz, CH3),
1.33–1.46 (2H, m, CH), 1.68–1.89 (4H, m, CH2), 3.95 (2H, t, J ¼ 7.6 Hz,
CH2), 4.31–4.53 (4H, m, CH þ CH2), 5.20 (4H, s, OCH2), 6.97–7.03 (4H,
m, ArH), 7.33–7.53 (5H, m, ArH), 7.61 (1H, s, ArH), 7.77 (2H, dd,
J ¼ 1.8, 8.0 Hz, ArH). 13C NMR (CDCl3): d 22.70, 22.78, 25.38, 45.58,
65.20, 70.45, 72.63, 113.57, 118.28, 120.70, 124.90, 126.01, 128.48,
131.25, 131.94, 137.15, 157.31, 162.20. IR(KBr): n3045, 2956, 2867, 1651,
1637, 1579, 1498, 1443, 1385, 1356, 1256, 1166, 1057, 1029, 792,
750 cm21. EIMS: m/z 540 (Mþ, 14), 483 (10), 429 (15), 321 (60), 219 (36),
121 (37), 105 (100). HREIMS Calcd. for C34H40N2O4: 540.29881. Found:
540.29790.
1,3-Bis[2-((4S)-4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl)
phenoxymethyl]benzene (4d)
Following general procedure B, from dihydroxy diamide 2d (1.1 g, 2.0 mmol)
to afford a colorless oil 0.665 g (64.6% yield). [a]2D0 ¼ 284.58 (c ¼ 0.20,

310
Z.-Y. Wang, D.-M. Du, and J.-X. Xu
1
CHCl3); H NMR (200 MHz, CDCl3): d 0.92 (6H, d, J ¼ 6.8 Hz, CH3), 1.02
(6H, d, J ¼ 6.6 Hz, CH3), 1.81–1.91 (2H, m, CH), 4.04–4.19 (4H, m,
CH2), 4.31–4.41 (2H, m, CH), 5.19 (4H, s, OCH2), 6.97–7.03 (4H, m,
ArH), 7.33–7.51 (5H, m, ArH), 7.61 (1H, s, ArH), 7.7 (2H, dd, J ¼ 1.8,
7.8 Hz, ArH). 13C NMR (CDCl3): d 18.16, 18.87, 32.77, 69.72, 70.44,
72.79, 113.43, 118.35, 120.68, 125.16, 126.19, 128.50, 131.24, 131.92,
137.10, 157.31, 162.32. IR(KBr): n3069, 2958, 2898, 1647, 1601, 1581,
1496, 1449, 1384, 1354, 1256, 1165, 1042, 752 cm21. EIMS: m/z 512 (Mþ,
8), 469 (8), 415 (5), 321 (6), 307 (48), 105 (54). HREIMS Calcd. for
C32H36N2O4: 512.26751. Found: 512.26562.
2,6-Bis[2-((4R)-4-phenyl-4,5-dihydro-1,3-oxazol-2-yl)
phenoxymethyl]pyridine (5a)
Following general procedure B, from dihydroxy diamide 3a (1.22 g,
1.97 mmol) to afford a colorless oil 0.963 g (83.7% yield). [a]2D0 ¼ þ 43.18
1
(c ¼ 0.13, CHCl3); H NMR (200 MHz, CDCl3): d 4.30 (2H, t, J ¼ 8.2 Hz,
CH2), 4.81 (2H, dd, J ¼ 8.2, 10.0 Hz, CH2), 5.29 (4H, s, OCH2), 5.47 (2H,
dd, J ¼ 8.2, 10.0 Hz, CH), 7.01–7.09 (5H, m, ArH), 7.29–7.50 (12H, m,
ArH), 7.66 (2H, d, J ¼ 7.8 Hz, ArH), 7.90 (2H, dd, J ¼ 1.6, 7.8 Hz, ArH).
13C NMR (CDCl3): d 70.54, 70.84, 74.07, 112.97, 117.35, 120.02, 120.79,
126.86, 127.49, 128.66, 131.49, 132.55, 142.57, 156.24, 157.19, 163.29.
IR(KBr): n 3062, 3026, 2893, 1640, 1595, 1579, 1494, 1441, 1375, 1356,
1294, 1252, 1126, 1063, 1030, 952, 748, 699 cm21. EIMS: m/z 581 (Mþ,
32), 550 (8), 431 (10), 342 (44), 238 (100), 121 (73), 104 (49). HREIMS
Calcd. for C37H31N3O4: 581.23280. Found: 581.23214.
2,6-Bis[2-((4S)-4-benzyl-4,5-dihydro-1,3-oxazol-2-yl)
phenoxymethyl]pyridine (5b)
Following general procedure B, from dihydroxy diamide 3b (0.969 g,
1.5 mmol) to afford a colorless oil 0.784 g (85.7% yield). m.p. 117–118 8C.
[a]2D0 ¼ 216.48 (c ¼ 0.14, CHCl3); 1H NMR (200 MHz, CDCl3): d 2.82
(2H, dd, J ¼ 8.8, 13.8 Hz, CH2), 3.31 (2H, dd, J ¼ 5.2, 13.6 Hz, CH2), 4.14
(2H, t, J ¼ 8.0 Hz, CH2), 4.38 (2H, t, J ¼ 8.8 Hz, CH2), 4.64–4.72 (2H, m,
CH), 5.30 (4H, s, OCH2), 6.99–7.06 (5H, m, ArH), 7.20–7.46 (11H, m,
ArH), 7.58–7.84 (5H, m, ArH). 13C NMR (CDCl3): d 41.84, 68.13, 70.85,
71.24, 113.04, 117.54, 119.91, 120.80, 126.45, 128.53, 129.24, 131.41,
132.38, 137.71, 138.08, 156.43, 157.03, 162.69. IR(KBr): n 3084, 3025,
2923, 1642, 1625, 1593, 1492, 1441, 1384, 1355, 1294, 1253, 1128, 1064,
1026, 962, 798, 751, 701 cm21. EIMS: m/z 609 (Mþ, 20), 518 (100),
490 (15), 356 (56), 266 (24), 213 (33), 162 (48). Anal. Calcd. for
.
C39H35N3O4 0.5H2O: C, 75.71; H, 5.86; N, 6.79. Found: C, 75.84; H,
5.80; N, 6.56.

Synthesis of Chiral Semicrown Ether-Like Bis(oxazoline) Ligands
311
2,6-Bis[2-((4S)-4-isobutyl-4,5-dihydro-1,3-oxazol-2-yl)
phenoxymethyl]pyridine (5c)
Following general procedure B, from dihydroxy diamide 3c (0.967 g,
1.67 mmol) to afford a colorless solid 0.756 g (83.5% yield). m.p. 97–988C.
1
[a]2D0 ¼ 286.98 (c ¼ 0.236, CHCl3); H NMR (200 MHz, CDCl3): d 1.02
(12H, t, J ¼ 6.8 Hz, CH3), 1.37–1.51 (2H, m, CH), 1.71–2.00 (4H, m,
CH2), 3.97 (2H, t, J ¼ 7.0 Hz, CH2), 4.38–4.57 (4H, m, CH þ CH2), 5.30
(4H, s, OCH2), 6.98–7.06 (4H, m, ArH), 7.37–7.46 (2H, m, ArH), 7.74–
7.90 (5H, m, ArH). 13C NMR (CDCl3): d 22.57, 23.01, 25.47, 45.70, 65.48,
70.76, 72.43, 112.88, 117.68, 119.96, 120.77, 131.38, 132.25, 137.52,
156.51, 157.00, 161.85. IR(KBr): n 3073, 2950, 2868, 1635, 1595, 1580,
1495, 1446, 1384, 1368, 1292, 1256, 1167, 1063, 1028, 799, 749 cm21
.
EIMS: m/z 541 (Mþ, 18), 498 (15), 484 (34), 430 (28), 322 (100), 268
(55), 224 (65), 121 (72), 106 (53). Anal. Calcd. for C33H39N3O4: C, 73.17;
H, 7.26; N, 7.76. Found: C, 72.84; H, 7.26; N, 7.60.
2,6-Bis[2-((4S)-4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl)
phenoxymethyl]pyridine (5d)
Following general procedure B, from dihydroxy diamide 3d (1.26 g,
2.29 mmol) to afford a colorless solid 0.625 g (53% yield). m.p. 91–938C.
1
[a]2D0 ¼ 274.18 (c ¼ 0.116, CHCl3); H NMR (200 MHz, CDCl3): d 0.99
(6H, d, J ¼ 6.8 Hz, CH3), 1.09 (6H, d, J ¼ 6.8 Hz, CH3), 1.87–1.97 (2H, m,
CH), 4.07–4.25 (4H, m, CH2), 4.36–4.47 (2H, m, CH), 5.29 (4H, s,
OCH2), 6.98–7.05 (5H, m, ArH), 7.37–7.46 (2H, m, ArH), 7.71 (4H, m,
ArH). 13C NMR (CDCl3): d 18.27, 18.99, 32.83, 69.59, 70.73, 73.07,
112.84, 117.73, 120.03, 120.75, 131.37, 132.21, 137.57, 156.45, 156.97,
162.08. IR(KBr): n 3078, 2958, 2869, 1644, 1595, 1579, 1497, 1443, 1384,
1369, 1291, 1253, 1171, 1064, 748 cm21. EIMS: m/z 513 (Mþ, 25), 470
(42), 416 (13), 385 (11), 308 (100), 266 (15), 224 (33), 106 (32). HREIMS
Calcd. for C31H35N3O4: 513.26410. Found: 513.26441.
Typical Procedure
Asymmetric Cyclopropanation
A solution of the ligand (2.4 mol%) in CH2Cl2 (2 mL) was added
[Cu(OTf)(C6H6)0.5] (2 mol%). After being stirred at room temperature for
1.5 hr, styrene (8 mmol) was added, followed by dropwise addition of ethyl
diazoacetate (2 mmol) in CH2Cl2 (1 mL) solution during 4 hr. The mixture
was stirred for another 18 hr and then quenched with 10% NH4Cl (5 mL).
The mixture was extracted with ether (25 mL), and then the organic phase

312
Z.-Y. Wang, D.-M. Du, and J.-X. Xu
was separated. The organic phase was washed with water and brine, dried over
anhydrous sodium sulfate. The solvent was removed under reduced pressure,
the residue was purified by column chromatography on silica gel (petroleum
ether/ethyl acetate 15 : 1) to afford the mixture of trans- and cis-2-phenyl-
cyclopropane-1-carboxylates as colorless oil. The trans/cis ratio of this
mixture was analyzed by 1H NMR (300 MHz) in CDCl3 using TMS as
internal standard. The diastereomeric and enantiomeric excess were deter-
mined by HPLC with a chiral column (Daicel Chiralcel OJ; eluent, hexane-
isopropyl alcohol 90 : 10; flow rate, 0.5 mL/min; UV detector, 220 nm).
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of
China (Grant No. 20372001 and 20172001), Perking University and Scientific
Research Fund of Zhejiang Provincial Education Department (Grant
No. SJY03026).
REFERENCES
1. Donaldson, W. A. Tetrahedron 2001, 57, 8589–8627.
2. Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic Methods for Organic
Synthesis with Diazo Compounds; Wiley: New York, 1998.
3. Faust, R. Angew. Chem. Int. Ed. 2001, 40, 2251–2253.
4. Suckling, C. J. Angew. Chem. Int. Ed. Engl. 1988, 27, 537.
5. Ye, T.; McKervey, M. A. Chem. Rev. 1994, 94, 1091–1160.
6. Davies, H. M.L.; Antoulinakis, E. G. Organic Reactions; Overman, L. E., Ed.;
Wiley: New York, 2001; Vol. 57, pp. 1–326.
7. Doyle, M. P. Catalytic Asymmetric Synthesis; Ojima, I., Ed.; Wiley-VCH:
New York, 2000; pp. 191–228.
8. Lebel, H.; Marcoux, J.-F.; Molinaro, C.; Charette, A. B. Chem. Rev. 2003, 103,
977–1050For a recent reviews, see:.
9. Noels, A. F.; Demonceau, A. Applied Homogeneous Catalysis with Organometal-
lic Compounds; Cornils, B., Herrman, W. A., Eds.; Wiley-VCH: Weinheim, 2002;
Vol. 2, pp. 793–808.
10. Pfaltz, A. Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer: Berlin, 1999a; pp. 513–603.
11. Fache, F.; Schulz, E.; Tommasino, M. L.; Lemaire, M. Chem. Rev. 2000, 100,
2159–2231.
12. Gosh, A. K.; Mathivanan, P.; Capiello, J. Tetrahedron Asymmetry 1998, 9,
1–45For recent reviews, see:.
13. Johnson, J. S.; Evans, D. A. Acc. Chem. Res. 2000, 32, 325–335.
14. Jørgensen, K. A.; Johannsen, M.; Yao, S. L.; Audrain, H.; Thorhauge, J. Acc.
Chem. Res. 1999, 32, 605–613.
15. Pfaltz, A. J. Heterocyclic Chem. 1999b, 36, 1437–1451.
16. Pfaltz, A. Synlett 1999c, 835–842.

Synthesis of Chiral Semicrown Ether-Like Bis(oxazoline) Ligands
313
17. Du, D. M.; Wang, Z. Y.; Xu, D. C.; Hua, W. T. Synthesis 2002, 2347–2352.
18. Du, D. M.; Fu, B.; Hua, W. T. Tetrahedron 2003, 59, 1933–1938.
19. Fu, B.; Du, D. M. Chinese J. Chem. 2003, 21, 597–599.
20. Fu, B.; Du, D. M.; Wang, J. B. Tetrahedron. Asymmetry 2004a, 15, 119–126.
21. Fu, B.; Du, D. M.; Xia, Q. Synthesis 2004b, 221–226.
22. Wang, Z. Y.; Du, D. M.; Wu, D.; Hua, W. T. Synth. Commun. 2003, 33,
1275–1283.
23. Xu, D. C.; Du, D. M.; Ji, N.; Wang, Z. Y.; Hua, W. T. Synth. Commun. 2003, 33,
2563–2574.
24. Breton, P.; Andre-Barres, C.; Langlois, Y. Synth. Commun. 1992, 22, 2543.
25. Gant, T. G.; Meyers, A. I. Tetrahedron 1994, 50, 2297.
26. Jones, R. C.F.; Ward, G. J. Tetrahedron Lett. 1988, 29, 3853.
27. Reuman, M.; Meyers, A. I. Tetrahedron 1985, 41, 837.
28. Giannis, A.; Sandhoff, K. Angew. Chem. Int. Ed. Engl. 1989, 28, 218.
29. Mckennon, M. J.; Meyers, A. I.; Drauz, K.; Schwarm, M. J. Org. Chem. 1993, 58,
3568.
30. Seki, H.; Koga, K.; Matsuo, H.; Ohki, S.; Matsuo, I. I.; Yamada, S. Chem. Pharm.
Bull. 1965, 13, 995.
31. Stanfield, C. F.; Parker, J. E.; Kanellis, P. J. Org. Chem. 1981, 46, 4799.
32. Elwahy, A. H.M.; Abbas, A. A. Tetrahedron 2000, 56, 885–895.
33. Denmark, S. E.; Nakajima, N.; Nicaise, O. J. C.; Faucher, A. M.; Edwards, J. P.
J. Org. Chem. 1995, 60, 4884.
34. Aratani, T.; Nakanisi, Y.; Nozaki, H. Tetrahedron 1970, 26, 1675.
35. Chelucci, G.; Sanna, M. G.; Gladiali, S. Tetrahedron 2000, 56, 2889–2893.
36. France, M. B.; Milojevich, A. K.; Stitt, T. A.; Kim, A. J. Tetrahedron Lett. 2003,
44, 9287–9290.
37. Ito, K.; Katsuki, T. Tetrahedron Lett. 1993, 34, 2661.
38. Iwasa, S.; Tsushima, S.; Nishiyama, K.; Tsuchiya, Y.; Takezawa, F.;
Nishiyama, H. Tetrahedron Asymmetry 2003, 14, 855–865.
39. Lyle, M. P.A.; Wilson, P. D. Org. Lett. 2004, 6, 855–857See for examples:.
40. Nishiyama, H.; Itoh, Y.; Matsumoto, H.; Park, S.-B.; Itoh, K. J. Am. Chem. Soc.
1994, 116, 2223–2224.
¨
41. Schinnerl, M.; Bohm, C.; Seitz, M.; Reiser, O. Tetrahedron: Asymmetry 2003, 14,
765–771.
42. Bedekar, A. V.; Andersson, P. G. Terahedron Lett. 1996, 37, 4073.
43. Bedekar, A. V.; Koroleva, E. B.; Andersson, P. G. J. Org. Chem. 1997, 62, 2518.
44. Evans, D. A.; Wocrpel, K. A.; Hinman, M. M. J. Am. Chem. Soc. 1991, 113, 726.
45. Alexander, K.; Cook, S.; Gibsona, C. L. Tetrahedron Lett. 2000, 41, 7135.
46. Boulch, R.; Scheurer, A.; Mosset, P.; Saalfrank, R. W. Tetrahedron Lett. 2000, 41,
1023.
47. Uchida, T.; Irie, R.; Katsuki, T. Tetrahedron 2000, 56, 3501.