Lewis acid and hexamethyldisilazane-promoted efficient synthesis of N-alkyl- and N-arylimide derivatives

Full text of DOI:10.1021/jo962202c

2652
J . Org. Chem. 1997, 62, 2652-2654
Sch em e 1
Lew is Acid a n d
Hexa m eth yld isila za n e-P r om oted Efficien t
Syn th esis of N-Alk yl- a n d N-Ar ylim id e
Der iva tives
Paidi Yella Reddy, Satoru Kondo, Takeshi Toru,* and
Yoshio Ueno
proceeds in quantitative yield, the subsequent cyclization
results in only low yields of the desired maleimide
derivatives together with extensive byproducts due to the
incompatibility of the olefin functionality with harsh
reaction conditions.5 Similarly, in the Mitsunobu reac-
tion only a narrow range of imide derivatives can be
synthesized because alkanols are used as starting ma-
terials. Therefore, synthesis of functionalized imide
derivatives is still a challenging endeavor. We describe
herein an efficient and mild approach for the synthesis
of imide derivatives.
Taking the lead from the pioneering work of Vor-
bru¨ggen6 on hexamethyldisilazane (HMDS)-mediated
reactions as a logical extension, we envisaged that the
reaction of an anhydride with an appropriately substi-
tuted amine and subsequent in situ cyclization of the
resulting amic acid in the presence of a Lewis acid and
HMDS would give the corresponding imide derivative.7
In order to substantiate the concept, the N-benzyl-
maleamic acid generated from maleic anhydride and
benzylamine in a benzene solution was heated at reflux
with equimolar amounts of HMDS and ZnCl2 for 4 h to
afford the corresponding maleimide derivative (Scheme
1). This favorable result encouraged us to further
improve the efficiency of the reaction to get high yields
of imide derivatives in a short reaction time.
Department of Applied Chemistry, Nagoya Institute of
Technology, Gokiso, Showa-ku, Nagoya 466, J apan
Received November 25, 1996
The development of simple and general synthetic
routes for widely used organic compounds from readily
available reagents is one of the major challenges in
organic synthesis. Imide derivatives are among such
types of organic compounds with numerous applications
in biology1 and synthetic2 and polymer3 chemistry. De-
spite their wide applicability, available routes for the
synthesis of imide derivatives are limited.4 Among them,
the dehydrative condensation of an anhydride and an
amine at high temperature1a and the cyclization of the
amic acid in the presence of acidic reagents are the
typical methods of choice.4i The direct N-alkylation of
maleimide with alcohols under Mitsunobu reaction con-
ditions is an alternative method for the synthesis of imide
derivatives in reasonably good yield.4a However, each of
these routes has its own synthetic problems when applied
to a range of derivatives. For instance, synthesis of
functionalized maleimide derivatives either by the direct
condensation or through the intermediate amic acid
cyclization method gives poor yields of the desired
maleimide derivatives. Although the amic acid formation
In order to optimize the reaction conditions, we briefly
investigated the stoichiometric ratio of the reagents and
reactants. The amic acid formation was observed almost
quantitatively in 1-4 h, stirring in benzene with equi-
molar amounts of an anhydride and an amine, whereas
the molar ratios of HMDS and ZnCl2 showed a significant
influence on the reaction time and the yield of imides.
Although, theoretically, 1 molar equiv of HMDS seems
to be sufficient to complete the reaction, practically the
isolated yield of imides was higher using 1.5 molar equiv
of HMDS and 1 equiv of ZnCl2. When the reaction was
carried out with an excess amount of HMDS (>1.5 equiv)
and/or ZnCl2 (>1 equiv), the yield of the imide was
reduced drastically and formation of undesired products
was observed upon prolonged reflux. In the presence of
less than an equimolar quantity of HMDS or ZnCl2, the
reaction was not complete even after long refluxing times.
The imide formation was not observed even in a trace
amount in the absence of either ZnCl2 or HMDS.
(1) For some recent biological applications, see: (a) Da Settimo, A.;
Primofiore, G.; Da Settimo, F.; Simorini, F.; La Motta, C.; Martinelli,
A.; Boldrini, E. Eur. J . Med. Chem. 1996, 31, 49. (b) Langmuir, M. E.;
Yang, J .-R.; Moussa, A. M.; Laura, R.; Lecompte, K. A. Tetrahedron
Lett. 1995, 36, 3989. (c) Mayer, A.; Neuenhofer, S. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1044. (d) Rusiecki, V. K.; Warne, S. A. Biorg. Med.
Chem. Lett. 1993, 3, 707. (e) Wong, S. S. Chemistry of Protein
Conjugation and Cross-linking; CRC Press: Boca Raton, 1991. (f)
J anda, D. K.; Ashley, A. J .; J ones, T. M.; McLeod, D. A.; Schloeder, D.
M.; Weinhouse, M. I. J . Am. Chem. Soc. 1990, 112, 8886. (g) FitzGerald,
D.; Idziorek, T.; Batra, J . K.; Willingham, M.; Pastan, I. Bioconjugate
Chem. 1990, 1, 264. (h) Maeda, M.; Kumano, A.; Tirrell, D. A. J . Am.
Chem. Soc. 1988, 110, 7455.
(2) For recent synthetic applications, see: (a) Ohkubo, M.; Nish-
imura, T.; J ona, H.; Honma, T.; Morishima, H. Tetrahedron 1996, 52,
8099. (b) Hamper, B. C.; Dukesherer, D. R.; South, M. S. Tetrahedron
Lett. 1996, 37, 3671. (c) Yoon, U. C.; Kim, D. K.; Lee, C. W.; Choi, Y.
S.; Lee, Y.-J .; Ammon, H. L.; Mariano, P. S. J . Am. Chem. Soc. 1995,
117, 2698. (d) Kang, J .; Lee, J . W.; Kim, J . J .; Pyun, C. Tetrahedron
Lett. 1995, 36, 4265. (e) Faul, M. M.; Sullivan, K. A.; Winneroski, L.
L. Synthesis 1995, 1511. (f) Romagnoli, R.; Roos, E. C.; Hiemstra, H.;
Moolenaar, M. J .; Speckamp, W. N.; Kaptein, B.; Schoemaker, H. E.
Tetrahedron Lett. 1994, 35, 1087. (g) Arai, Y.; Matsui, M.; Fujii, A.;
Kontani, T.; Ohno, T.; Koizumi, T.; Shiro, M. J . Chem. Soc., Perkin
Trans. 1 1994, 25. (h) Baldwin, S. W.; Greenspan, P.; Alaimo, C.;
McPhail, A. T. Tetrahedron Lett. 1991, 32, 5877. (i) Miller, S. A.;
Chamberlin, A. R. J . Org. Chem. 1989, 54, 2502 and references cited
therein.
(3) For recent applications of maleimide derivatives in polymer
chemistry, see: (a) Iijima, T.; Suzuki, N.; Fukuda, W.; Tomoi, M. J .
Eur. Polym. 1995, 31, 775. (b) Amou, S.; Nishimura, S.; Takahashi,
A.; Hagiwara, T.; Hamana, H.; Narita, T. J . Polym. Sci. Tech. 1994,
51, 764. (c) Bharel, R.; Choudhary, V.; Varma, I. K. J . Appl. Polym.
Sci. 1993, 49, 31. (d) Dean, B. D. J . Appl. Polym. Sci. 1987, 33, 2259.
(4) (a) Walker, M. A. J . Org. Chem. 1995, 60, 5352; Tetrahedron
Lett. 1994, 35, 665. (b) Corrie, J . E. T. J . Chem. Soc., Perkin Trans. 1
1994, 2975. (c) Gill, G. B.; J ames, G. D.; Oates, K. V.; Pattenden, G. J .
Chem. Soc., Perkin Trans. 1 1993, 2567. (d) Braish, T. F.; Fox, D. E.
Synlett 1992, 979. (e) Dorta, R. L.; Francisco, C. G.; Suarez, E.
Tetrahedron Lett. 1991, 35, 1083. (f) Nielsen, O.; Buchardt, O. Synthesis
1991, 819. (g) Rangnekar, V. M.; Bharmaria, R. P.; Khadse, B. G. Ind.
J . Chem. 1986, 25B, 342. (h) Schwartz, A. L.; Lerner, L. M. J . Org.
Chem. 1974, 39, 21. (i) Mehta, N. B.; Phillips, A. P.; Lui, F. F.; Brooks,
R. E. J . Org. Chem. 1960, 25, 1012.
Next, cyclization of N-benzylsuccinamic acid was ex-
amined with various Lewis acids. The results are sum-
marized in Table 1. Among the Lewis acids examined,
ZnBr2 gave significantly good results in a short reaction
time. ZnCl2 and ZnI2 also gave good yields of imide, but
the reaction was found to be relatively slow with these
(5) (a) Garner, P.; Ho, W. B.; Grandhee, S. K.; Youngs, W. J .;
Kennedy, V. O. J . Org. Chem. 1991, 56, 5893. (b) Meyers, A. I.; Lefker,
B. A.; Sowin, T. J .; Westrum, L. J . J . Org. Chem. 1989, 54, 4243.
(6) Vorbru¨ggen, H. Acc. Chem. Res. 1995, 28, 509 and references
cited therein.
(7) Catalytic trimethylsilylation of organic compounds having acidic
protons such as alcohols and carboxylic acids by using HMDS and
Lewis acids is well known; see: (a) Firouzabadi, H.; Karimi, B. Synth.
Commun. 1993, 23, 1633 and references cited therein. (b) Bruynes, C.
A.; J urriens, T. K. J . Org. Chem. 1982, 47, 3966.
S0022-3263(96)02202-5 CCC: $14.00 © 1997 American Chemical Society

Notes
J . Org. Chem., Vol. 62, No. 8, 1997 2653
Ta ble 1. Cycliza tion of N-Ben zylsu ccin a m ic Acid in th e
Ta ble 2. Lew is Acid a n d HMDS-P r om oted Syn th esis of
Im id e Der iva tives fr om An h yd r id es a n d Am in esa
P r esen ce of Va r iou s Lew is Acid s
entry
Lewis acid
time (h)
yielda (%)
94
94
94
70
65
11
1
2
3
4
5
6
7
ZnCl2
ZnBr2
ZnI2
SnCl4
SnCl2
AlCl3
MgCl2
2
0.5
1.5
5
2.5
4
6
no reaction
a
Isolated yield.
Lewis acids. The yield of the imide was reduced in the
presence of strong Lewis acids such as SnCl2 and AlCl3,
whereas the imide formation was not observed even in a
trace amount with MgCl2. Among various polar and
nonpolar solvents examined, the reaction proceeded
smoothly in refluxing benzene, giving a high yield of the
imide in a short reaction time. Although the amic acid
formation in polar solvents such as THF or acetonitrile
was found to be better than in nonpolar solvents, the
subsequent cyclization step did not afford the concurrent
yields of imide derivative.
To show the generality and scope of the Lewis acid and
HMDS-promoted imide synthesis, the reaction was ex-
amined with various structurally diverse amines and
anhydrides. These results are summarized in Table 2.
In most cases, the amic acid cyclization proceeded
smoothly with 1 molar equiv of ZnBr2 and 1.5 molar equiv
of HMDS in refluxing benzene, giving good to excellent
yields of the desired succinimide, maleimide, phthal-
imide, and glutarimide derivatives. Yields of imides
derived from maleic anhydride and amines such as
allylamine and (-)-phenylglycinol were found to be better
with ZnCl2 than with ZnBr2 (Table 2, entries 7 and 9).
When chiral amines such as (-)-R-methylbenzylamine,
(-)-phenylglycinol, and (+)-phenylglycine methyl ester
were used, the corresponding imide derivatives were
isolated without racemization under the described reac-
tion conditions (Table 2, entries 8-10 and 16). Surpris-
ingly, no formation of the isoimide was observed in the
reaction of citraconic anhydride with benzylamine under
our reaction conditions (Table 2, entry 13) in contrast to
the recently reported reaction in refluxing acetic acid
with sodium acetate affording the isoimide as the major
product.8 Although the mechanistic aspect of the amic
acid cyclization cannot be defined clearly, it can be
reasonably assumed on the basis of earlier reports6 that
the Lewis acid and HMDS-promoted silylation of an
intermediate amic acid to a labile trimethylsilyl ester and
subsequent thermal deoxysilylation gives an imide. The
formation of thermodynamically stable hexamethyl-
disiloxane or trimethylsilanol9 makes this reaction fea-
sible under mild conditions.
a
Unless specified, a solution of an amine and an anhydride in
benzene was stirred at rt for 1 h and subsequently refluxed with
b
1 equiv of ZnBr2 and 1.5 equiv of HMDS. Refluxing time.
c Isolated yield. ZnCl2 was used as a Lewis acid. e Stirred for 4
d
h before reflux.
high efficiency, the procedure is expected to have broad
utility, especially in the synthesis of functionalized imide
derivatives, for future biological and chemical applica-
tions.
In summary, we have demonstrated an economical and
practical method for the synthesis of a wide range of
imide derivatives by using inexpensive and readily avail-
able reagents under mild conditions. In light of its
operational simplicity, simple purification procedure, and
Exp er im en ta l Section
Gen er a l Meth od s. (R)-(-)-phenylglycinol was prepared
according to previously reported method.10 All other reactants
and reagents were purchased from appropriate commercial
(8) Corrie, J . E. T.; Moore, H.; Wilson, G. D. J . Chem. Soc., Perkin
Trans. 1 1996, 777.
(9) (a) Grubb, W. T. J . Am. Chem. Soc. 1954, 76, 3408. (b) Sommer,
L. H.; Pietrusza, E. W.; Whitemore, F. C. J . Am. Chem. Soc. 1946, 68,
2282.
(10) McKennon, M. J .; Meyers A. I. J . Org. Chem. 1993, 58, 3568.

2654 J . Org. Chem., Vol. 62, No. 8, 1997
Notes
sources. Succinic, maleic, and phthalic anhydrides were distilled
and ZnCl2 sublimed before use. HMDS and all other amines
were distilled before use. All solvents were dried and distilled
according to standard procedures. All reactions were carried
out under an argon atmosphere. 1H NMR and 13C NMR spectra
were recorded in CDCl3 with TMS as internal standard. Melting
points were determined with a hotstage apparatus and are
uncorrected. Enantiomeric purity of chiral imides 2h , 2j, and
2p was determined by HPLC using a 0.46 × 25 cm Daicel
Chiralcel OD-H column (flow rate, 0.5 mL/min). For this
purpose, the corresponding racemic imides were prepared and
coinjected with samples. Enantiomeric purity of 2i was con-
firmed by the 1H NMR of its Mosher ester.
N-P h en ylm a leim id e (2k ): canary yellow solid; mp 89.0-
1
90.0 °C (hexane, lit.15 mp 89.0-89.8 °C); H NMR δ 7.30-7.55
(m, 5H), 6.86 (s, 2H).
N-[p-(Eth oxyca r bon yl)p h en yl]m a leim id e (2l). A solution
of maleic anhydride (100 mg, 1.02 mmol) and ethyl 4-amino-
benzoate (168 mg, 1.02 mmol) in dry benzene was stirred for 4
h at 50 °C and then refluxed for 1 h under similar reaction
conditions as described for 2a to give 2l (233 mg, 93%) as a
colorless solid: mp 114.5-115.5 °C (hexane, lit.16 mp 112.0 °C);
1H NMR δ 8.10-8.20 (m, 2H), 7.45-7.55 (m, 2H), 6.89 (s, 2H),
1.40 (t, J ) 7.1 Hz, 3H).
N-Ben zylcitr a con im id e4i (2m ): colorless oil; 1H NMR δ
7.20-7.40 (m, 5H) 6.33 (q, J ) 1.8 Hz, 1H), 4.65 (s, 2H), 2.07 (d,
J ) 1.8 Hz, 3H).
N-Ben zyld ich lor om a leim id e (2n ): colorless solid; mp 111.5
°C (hexane, lit.17 mp 111.5 °C); 1H NMR δ 7.23-7.42 (m, 5H),
4.74 (s, 2H).
Gen er a l P r oced u r e for th e Syn th esis of Im id e Der iva -
tives 2a -h a n d 2j-q. N-Ben zylsu ccin im id e (2a ). To a
stirred solution of succinic anhydride (160 mg, 1.6 mmol) in dry
benzene (12 mL) was added dropwise at rt
a solution of
benzylamine (0.174 mL, 1.6 mmol) in dry benzene (5 mL).
During the addition, an exothermic reaction occurred with
instantaneous formation of white precipitates. After the addi-
tion was complete, the resulting suspension was stirred for an
additional 1 h and then ZnBr2 (360 mg, 1.6 mmol) was added in
one portion. While the resulting reaction mixture was heated
(80 °C), a solution of HMDS (0.506 mL, 2.4 mmol) in dry benzene
(5 mL) was added slowly over a period of 30 min, and then the
mixture was refluxed for an additional 1 h. The reaction mixture
was cooled to room temperature and poured into 0.5 N HCl (30
mL). The aqueous phase was extracted with ethyl acetate (3 ×
25 mL). The combined organic extracts were washed succes-
sively with 30 mL of saturated NaHCO3 and brine and dried
over anhydrous Na2SO4. The solution was concentrated under
reduced pressure to leave the residue, which was purified by
flash chromatography (silica gel, 90:10 hexane/EtOAc) to afford
2a (276 mg, 91%) as a colorless solid: mp 102.5-103.5 °C
(hexane, lit.13 98.0-99.0 °C); 1H NMR δ 7.26-7.43 (m, 5H), 4.65
(s, 2H), 2.70 (s, 4H).
N-Ben zylp h th a lim id e (2o): colorless solid; mp 118.5-119.5
°C (hexane, lit.18 mp 117.0-118.0 °C); 1H NMR δ 7.65-7.88 (m,
4H), 7.26-7.40 (m, 5H), 4.85 (s, 2H).
(S)-(+)-N-[r-(Meth oxyca r bon yl)ben zyl]p h th a lim id e (2p ).
Under the reaction conditions as described for 2j, starting from
phthalic anhydride (200 mg, 1.35 mmol) and (S)-(+)-phenyl-
glycine methyl ester (223 mg, 1.35 mmol), 2p (374 mg, 94%) was
obtained as a colorless solid: mp 116.0-117.0 °C (90:10 hexane/
EtOAc); [R]22D + 7.2 (c 1.4, CHCl3); IR (CHCl3) 1750, 1720, 1390
1
cm-1; H NMR δ 7.89-7.82 (m, 2H), 7.76-7.69 (m, 2H), 7.59-
7.53 (m, 2H) and 7.42-7.32 (m, 3H), 6.02 (s, 1H), 3.82 (s, 3H);
13C NMR δ 168.4, 166.9, 134.3, 134.1, 131.6, 129.6, 128.4, 128.4,
128.0, 123.5, 55.7, 52.9; chiral HPLC >98% ee (tR 24.49 min,
95:5 hexane/2-propanol). Anal. Calcd for C17H13O4N: C, 69.14;
H, 4.43; N, 4.74. Found: C, 69.20; H, 4.38; N, 4.39.
N-Ben zylglu ta r im id e18 (2q): colorless oil; 1H NMR δ 7.20-
7.40 (m, 5H), 4.96 (s, 2H), 2.67 (t, J ) 6.5 Hz, 4H), 1.93 (m, 2H).
(R)-(+)-N-(1-P h en yl-2-h yd r oxyeth yl)m a leim id e (2i). To
a solution of maleic anhydride (286 mg, 2.91 mmol) in dry THF
(15 mL) was added a solution of (R)-(-)-phenylglycinol (400 mg,
2.91 mmol) in THF (4 mL). The resulting reaction mixture was
stirred for 4 h, and then hexane (10 mL) was added. Precipitated
maleamic acid was separated by decanting the solvent and
washed with dry ether. To a suspension of the amic acid in dry
benzene (25 mL) was added ZnCl2 (397 mg, 2.91 mmol), and the
mixture was heated to 80 °C. A solution of HMDS (1.1 mL, 5.25
mmol) in dry benzene (5 mL) was added in three equal portions
over 30 min. The reaction mixture was refluxed for an ad-
ditional 6 h and concentrated under reduced pressure to leave
the residual solid, which was dissolved in THF (5 mL) containing
0.1 N HCl (9:1). The solution was stirred for 15 min and
evaporated to dryness. The residue was partitioned between
EtOAc and saturated NaHCO3 solution, and the aqueous layer
was extracted with EtOAc (3 × 25 mL). The combined organic
solvents were washed with saturated brine, dried over Na2SO4,
filtered, and concentrated to give a thick liquid, which was
purified by flash chromatography (silica gel, 70:30 hexane/
EtOAc-hexane) to furnish 2i (532 mg, 84%) as a colorless
N-P h en eth ylsu ccin im id e (2b): colorless solid; mp 134.0-
1
135.0 °C (hexane, lit.12 mp 135.0 °C); H NMR δ 7.16-7.35 (m,
5H), 3.71-3.80 (m, 2H), 2.84-2.93 (m, 2H), 2.65 (s, 4H).
N-P h en ylsu ccin im id e (2c): colorless solid; mp 156.0-157.0
°C (hexane, lit.13 mp 153.0-154.0 °C); 1H NMR δ 7.22-7.55 (m,
5H), 2.90 (s, 4H).
N-Ben zylm a leim id e (2d ): colorless solid; mp 69.5-70.5 °C
(hexane, lit.4d mp 68.5-70.0 °C); 1H NMR δ 7.26-7.43 (m, 5H),
6.71 (s, 2H), 4.68 (s, 2H).
N-P h en eth ylm a leim id e (2e): colorless solid; mp 111.5-
112.5 °C (hexane, lit.4a mp 110.0-111.0 °C); 1H NMR δ 7.16-
7.35 (m, 5H), 6.65 (s, 2H), 3.71-3.82 (m, 2H), 2.85-2.96 (m, 2H).
N-Bu tylm a leim id e4i (2f): colorless oil; 1H NMR δ 6.69 (s,
2H), 3.52 (t, J ) 7.2 Hz, 2H), 1.49-1.65 (m, 2H), 1.21-1.41 (m,
2H), 0.92 (t, J ) 7.2 Hz, 3H).
N-Allylm a leim id e (2g). ZnCl2 was used as a Lewis acid:
colorless solid; mp 42.5-43.5 °C (hexane, lit.4d mp 42.0-44.0 °C);
1H NMR δ 6.72 (s, 2H), 5.80 (ddt, J ) 17.2, 10.0, 5.6 Hz, 1H),
5.12-5.24 (m, 2H), 4.13 (dt, J ) 5.6, 1.4 Hz, 2H).
(S)-(-)-N-r-Meth ylben zylm a leim id e (2h ): colorless oil;
[R]22D -89.3° (c 1.29, CHCl3, lit.14 [R]25D -69.25°, neat); 1H NMR
δ 7.20-7.40 (m, 5H), 6.63 (s, 2H), 5.36 (q, J ) 7.4 Hz, 1H), 1.83
(d, J ) 7.4 Hz, 3H); chiral HPLC >98% ee (tR 9.40 min, 95:5
hexane/2-propanol).
solid: mp 48.0-49.0 °C (80:20 hexane/EtOAc); [R]22 +47.8° (c
D
0.5, CHCl3); IR (CHCl3) 3450 (br), 1710, 1405, 1370 cm-1
;
1H
NMR δ 7.31-7.38 (m, 5H), 6.71 (s, 2H), 5.26 (dd, J ) 5.1, 9.1
Hz, 1H), 4.51 (dd, J ) 9.2, 11.6 Hz, 1H), 4.08 (dd, J ) 5.1, 11.6
Hz, 1H), 2.30 (br, 1H, OH); 13C NMR δ 171.4, 136.6, 134.1, 128.7,
128.2, 127.8, 127.7, 62.0, 57.3. Anal. Calcd for C12H11O3N: C,
66.35; H, 5.10; N, 6.44. Found: C, 65.89; H, 5.19; N, 6.16. The
(S)-(+)-N-[r-(Meth oxyca r bon yl)ben zyl]m a leim id e (2j).
A solution of maleic anhydride (200 mg, 2.04 mmol) and (S)-
(+)-phenylglycine methyl ester (0.336 mg, 2.04 mmol) in dry
benzene was stirred for 4 h at 50 °C and then refluxed for 2 h to
give 2j (450 mg, 90%) as a colorless solid: mp 88.0 °C (90:10
1
Mosher ester19 of 2i: >98% ee; H NMR δ 7.33-7.45 (m, 5H),
6.58 (s, 2H), 5.48 (dd, J ) 5.2, 10.7 Hz, 1H), 5.31 (t, J ) 10.8
Hz, 1H), 4.82 (dd, J ) 5.3, 10.8 Hz, 1H), 3.46 (m, 3H).
hexane/EtOAc; lit.5a mp 87.0-88.0 °C); [R]22 +77.2° (c 0.74,
D
CHCl3); IR (CHCl3) 1750, 1720, 1400, 1380 cm-1
;
1H NMR δ
Ack n ow led gm en t. One of us (P.Y.R.) thanks the
Ministry of Education, Science and Culture, J apan, for
a fellowship.
7.48-7.32 (m, 5H), 6.73 (s, 2 H), 5.83 (s, 1 H), 3.79 (s, 3H); 13C
NMR δ 169.3, 168.3, 134.2, 134.1, 129.4, 128.5, 128.3, 55.6, 52.9;
chiral HPLC >98% ee (tR 26.52 min, 95:5 hexane/2-propanol).
Anal. Calcd for C13H11O4N: C, 63.67; H, 4.52; N, 5.71. Found:
C, 64.00; H, 4.46; N, 5.43.
J O962202C
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