First triphenylphosphine promoted reduction of maleimides to succinimides

Article abstract of DOI:10.1055/s-2003-40523

Triphenylphosphine (TPP) in refluxing methanol effectively reduces maleimides 1a-g to the corresponding succinimides 2a-g in good yields. It was observed that some maleimides obtained from aromatic halogen compounds 1h-j were transformed into the corresponding succinamic acid methyl esters 3a-c by this reaction.

Full text of DOI:10.1055/s-2003-40523

PAPER
1549
First Triphenylphosphine Promoted Reduction of Maleimides to Succinimides
First
T
riphenylph
i
osphin
k
e
Promoted
R
a
e
duction o
s
f
Maleim
h
ides to Succinimide
P
s
al, Prasun K. Pradhan, Parasuraman Jaisankar, Venkatachalam S. Giri*
Department of Medicinal Chemistry, Indian Institute of Chemical Biology, 4 Raja S. C. Mullick Road, Kolkata-700 032, India
Fax +91(33)24735197; E-mail: vsgiri@iicb.res.in
Received 24 February 2003; revised 19 May 2003
Naan and coworkers8b have reported that triarylphos-
Abstract: Triphenylphosphine (TPP) in refluxing methanol effec-
phines react with 7,7,8,8-tetracyanoquino dimethane in
chloroform, acetonitrile, acetonitrile–benzene in the pres-
tively reduces maleimides 1a–g to the corresponding succinimides
2a–g in good yields. It was observed that some maleimides obtained
ence of water and catalytic quantities of hydrochloric acid
from aromatic halogen compounds 1h–j were transformed into the
corresponding succinamic acid methyl esters 3a–c by this reaction. to give quantitative yields of 1,4-bis(dicyanomethyl)ben-
zene and triarylphosphine oxide whereas tetracyanoethyl-
ene in acetonitrile in presence of aqueous acid gave
tetracyanoethane and the phosphine oxide. Electron defi-
cient propargyl ethers have been reported8c to undergo re-
duction to the corresponding allylic ethers by means of
triphenylphosphine–water. A plausible mechanism for
TPP–MeOH promoted reduction is given in Scheme 2.
The formation of a stable betaine from TPP and male-
imide in presence of an aprotic solvent is reported;7 but
presence of the protic solvent (MeOH) is crucial for the ti-
tle reaction. The formation of triphenylphosphine oxide at
the end of the reaction was confirmed by isolating it dur-
ing the purification of the reaction mixture by column
chromatography over silica gel. Triphenylphosphine ox-
ide obtained was confirmed by comparison with an au-
thentic specimen and its 31P NMR in CDCl3 showing a
singlet at = 46.7. This method was successfully applied
to prepare a number of N-substituted succinimides 2 in
good yields (Table 1). We have observed that this reaction
could not be generalized for , -unsaturated carbonyl
compounds other than maleimides.
Key words: triphenylphosphine, reductions, maleimides, succin-
imides, succinamic acid methyl esters
Triphenylphosphine1 (TPP) is a well-known reagent for
the deoxygenation of ozonides, peroxides, epoxides and
N-oxides. TPP also brings about reduction of azides to
amines2 and that of organosulfur compounds.3 It is com-
monly used in many organic reactions for the preparation
of alkyl chlorides, bromides, and iodides in combination
4
5
with CCl4 or CBr4 or I2 from the corresponding alcohols.
TPP has also been used to generate alkenes from vicinal
diols in the presence of iodoform and imidazole. The well-
known Mitsunobu reaction wherein an alcohol is replaced
by a nucleophile is performed with TPP and azodi-
carboxylates.6
R
N
R
N
O
O
PPh3
O
O
MeOH
1
2
Compounds 1a–j and 2a–g have been characterized from
their physical data and also compared with literature re-
ports. The maleimides 1a–j exhibit a characteristic two
proton singlet (methane protons) in the region = 6.5–6.9
Scheme 1
In the course of synthesizing an indole alkaloid intermedi-
ate, we observed that TPP in refluxing methanol reduces
the double bond of maleimides 1 to the corresponding
succinimides 2 (Scheme 1). Reduction of alkene is usual-
ly effected by catalytic hydrogenation or boranes whereas
, -unsaturated carbonyl compounds are reduced with
metal and an amine. In this case, protonation takes place
at the -carbon atom and the final product is obtained by
protonation of the -carbon atom. One example of deoxy-
genative dimerization of maleic anhydrides by triethyl
phosphite has been reported.7 Rapidly and stoichiometric
1
ppm in their H NMR spectra. Their 13C NMR spectra
show a single peak for the corresponding two carbons be-
tween = 133–135 ppm, and another peak between
=
169–172 ppm for the two carbonyl carbons of the imide.
Their IR spectra are also characterized by distinct bands
for the maleimide carbonyls in the region 1730–1700
cm–1. On the other hand, succinimides 2a–g exhibit a dis-
tinct singlet between = 2.60–2.95 ppm for the four me-
thylene protons in their 1H NMR spectra. Their 13C NMR
spectra are characterized by a two carbon signal between
= 28–30 ppm and another one for the two carbonyl car-
bons between = 170–180 ppm. The IR spectra of succin-
imides show distinct bands in the region 1710–1660 cm–1
for the imide carbonyls.
reduction
of
activated
olefins,
HR1C=CR1H
(R1 = COOMe or COPh) by some alkyl phosphines, PR2
3
(R2=ethyl, n-propyl, n-butyl), both free and initially
bound to cobalt, in anhydrous methanol through the for-
mation of an ylide, has been reported by Burnett et al.8a
An important observation in this series of reactions is the
behavior of maleimides obtained from aromatic halogen
compounds 1h–j which underwent not only the expected
reduction but also cleavage of one of the imide bonds re-
Synthesis 2003, No. 10, Print: 21 07 2003.
Art Id.1437-210X,E;2003,0,10,1549,1552,ftx,en;T01703SS.pdf.
© Georg Thieme Verlag Stuttgart · New York

1550
B. Pal et al.
PAPER
In conclusion, the described method provides a simple
route for direct conversion of maleimides into succin-
imides in reasonably good yields.
R
R
N
PPh3
N
O
O
O
O
MeOH
All melting points were determined in open capillaries on SPAC-N-
SERVICE (India) capillary melting point apparatus and are uncor-
rected. IR spectra were recorded on a JASCO-FT-IR Model 412 us-
ing samples as KBr plates. 1H NMR (300 MHz) and 13C NMR (75
MHz) spectra were recorded on a Bruker DPX 300 NMR instru-
ment using TMS as internal standard. 31P NMR (202 MHz) spectra
were recorded on a Bruker DRX 500 NMR instrument. Elemental
analyses were carried out on a PERKIN ELMER 2400 Series II
CHNS/O analyzer. Mass spectra (EI) were recorded on a JEOL-
AX-500 spectrometer.
Ph
Ph
Ph
Ph
Ph
Ph
H
1
P
P
Me
O
H
R
N
R
O
O
N
MeOH
O
O
+ Ph3P=O
Ph
Ph
Ph
P
MeO
2
Preparation of Maleimides; Typical Procedure
An amine (1.0 mmol) was added under stirring to maleic anhydride
(1.10 mmol, 0.108 g) at r.t. and the stirring continued for 1 h to com-
plete the reaction. The solid half-amide of the maleic acid was then
filtered, dried and warmed with either acetic anhydride (5 mL) in
case of aromatic amines or refluxed in a mixture of CH3OH and
conc. HCl (5 mL, 5:1) in case of aliphatic amines for about 4 h. The
reaction mixture was diluted with H2O (10 mL) and concentrated
under reduced pressure to remove excess solvent. It was then dilut-
ed with H2O (15 mL), basified with sat. NaHCO3 solution (5 mL)
and extracted with CHCl3 (3 × 15 mL). The extract was washed
with H2O (2 × 10 mL), dried (anhyd Na2SO4) and concentrated. The
residue was chromatographed over silica gel using CHCl3 to afford
the pure maleimides.
Scheme 2
Table 1 Reduction of Maleimides (1) to Succinimides (2) and Suc-
cinamic Acid Methyl Ester (3)
1
R
Product
2a
Isolated Yield (%)
a
-indolylethyl
75
71
70
55
75
55
60
65
62
66
b
c10
d
e
-phenylethyl
benzyl
2b9
2c11
2d
cyclohexyl
m-nitrophenyl
n-butyl
N-( -Indolylethyl)maleimide (1a)
Mp 116–118 °C.
IR (KBr): 3346, 3299, 1700 cm–1.
1H NMR (CDCl3): = 3.05 (dd, J = 7.3 Hz, 7.8 Hz, 2 H), 3.83 (dd,
J = 7.3 Hz, 7.8 Hz, 2 H), 6.64 (s, 2 H), 7.04 (br s, 1 H), 7.05–7.24
(m, 2 H), 7.34 (d, J = 8.0 Hz, 1 H), 7.66 (d, J = 7.6 Hz, 1 H), 7.99
(br s, NH).
13C NMR (CDCl3): = 24.8, 38.9, 111.6, 112.6, 119.2, 119.9, 122.5
(2 C), 127.8, 134.5 (2 C), 136.6, 171.3 (2 C).
2e12
2f13
2g15
3a
f
g14
h
i
phenyl
p-bromophenyl
m-bromophenyl
p-fluorophenyl
3b
j
3c
MS (EI, 70 eV): m/z (%) = 240 (M+, 100), 143 (85), 130 (100), 103
(30).
sulting in the half ester of the corresponding succinamic
Anal. Calcd for C14H12N2O2: C, 69.99; H, 5.03; N, 11.66. Found: C,
69.78; H, 5.14; N, 11.78.
acid methyl esters 3a–c (Figure 1).
Theoretical calculation of electron density by using Hyper
Chem. Prof. Version 6.0 reveals that the electron density
of the imide nitrogen of both N-phenylmaleimide (1g) and
N-(m-nitrophenyl)maleimide (1e) are nearly the same and
are slightly more comparable to the halogenated aromatic
maleimides 1h–j. At this stage it has not been possible to
ascertain the exact reason for the formation of succinamic
acid esters 3a–c resulting from cleavage of the imide
bonds in case of halogenated aromatic maleimides 1h–j.
N-( -Phenylethyl)maleimide (1b)
Mp 80–82 °C.
IR (KBr): 1717, 1441 cm–1.
1H NMR (CDCl3): = 2.89 (dd, J = 7.40, 7.8 Hz, 2 H), 3.76 (dd,
J = 7.40, 7.8 Hz, 2 H), 6.65 (s, 2 H), 7.10–7.35 (m, 5 H).
13C NMR (CDCl3): = 34.9, 39.5, 127.1, 128.9, 129.2, 133.8 (2 ×
C), 134.4 (2 × C), 138.2, 171.0 (2 × C).
MS (EI, 70 eV): m/z (%) = 201 (M+, 65), 113 (100), 104 (90), 85
(100).
Anal. Calcd for C12H11NO2: C, 71.63; H, 5.51; N, 6.96. Found: C,
71.49; H, 5.59; N, 7.06.
X
O
N-Benzylmaleimide (1c)
Mp 64–66 °C (Lit.10 69–70 °C).
HN
OMe
IR (KBr): 1701, 1404 cm–1.
O
1H NMR (CDCl3): = 4.67 (s, 2 H), 6.69 (s, 2 H), 7.20–7.42 (m, 5
H).
Figure 1 3a X = p-bromo; 3b X = m-bromo; 3c X = p-fluoro
Synthesis 2003, No. 10, 1549–1552 © Thieme Stuttgart · New York

PAPER
First Triphenylphosphine Promoted Reduction of Maleimides to Succinimides
1551
13C NMR (CDCl3): = 41.8, 128.3, 128.8, 129.1 (2 C), 133.8, 134.6
(2 C), 136.6, 170.8 (2 C).
Anal. Calcd for C10H6BrNO2: C, 47.65; H, 2.40; N, 5.56. Found: C,
47.52; H, 2.48; N, 5.64.
MS (EI, 70 eV): m/z (%) = 187 (M+, 100), 130 (40), 106 (50), 104
(60).
N-(4-Fluorophenyl)maleimide (1j)
Mp 136–138 °C.
N-Cyclohexylmaleimide (1d)
IR (KBr): 1715, 1518 cm–1.
Mp 92–94 °C.
IR (KBr): 1706, 1402 cm–1.
1H NMR (CDCl3): = 6.85 (s, 2 H), 7.11–7.24 (m, 2 H), 7.24–7.36
(m, 2 H).
1H NMR (CDCl3): = 1.10–2.20 (m, 10 H), 3.83–3.98 (m, 1 H),
6.62 (s, 2 H).
13C NMR (CDCl3): = 116.41, 116.72, 127.52, 128.26, 128.38,
134.64 (2 C), 163.85, 169.82 (2 C).
Anal. Calcd for C10H13NO2: C, 67.02; H, 7.31; N, 7.82. Found: C,
66.93; H, 7.40; N, 7.90.
MS (EI, 70 eV): m/z (%) = 191 (M+, 100), 162 (20), 135 (25), 109
(20).
Anal. Calcd for C10H6FNO2: C, 62.83; H, 3.16; N, 7.33. Found: C,
62.69; H, 3.25; N, 7.41.
N-(3-Nitrophenyl)maleimide (1e)
Mp 103–105 °C.
IR (KBr): 1723, 1583 cm–1.
1H NMR (CDCl3): = 6.94 (s, 2 H), 7.66 (t, J = 8.0 Hz, 1 H), 7.78
(br d, J = 7.3 Hz, 1 H), 8.22 (br d, J = 7.8 Hz, 1 H), 8.34 (s, 1 H).
13C NMR (CDCl3): = 121.1, 122.8, 130.4, 131.7, 132.8, 134.9 (2
C), 148.9, 169.0 (2 C).
MS (EI, 70 eV): m/z (%) = 218 (M+, 100), 172 (65), 144 (30), 116
Reduction of Maleimides to Succinimides; Typical Procedure
A solution of the maleimides (1.0 mmol) in anhyd CH3OH (5 mL)
was refluxed with TPP (1.1 mmol, 0.288 g) for about 3 h. The reac-
tion mixture was then allowed to cool, evaporated under reduced
pressure to remove CH3OH and the residue chromatographed over
silica gel. A fraction eluted by petroleum ether–CHCl3 (7:3) yielded
colorless needles, shown to be triphenylphosphine oxide by deter-
mination of mp, mixed mp, and comparison of the respective 31P
NMR, 1H NMR, IR and MS spectra with an authentic sample. 1–2%
MeOH in CHCl3 as eluent afforded the desired succinimides which
were recrystallized from CHCl3–petroleum ether (1:1). In the case
of maleimides 1h–j the corresponding succinamic acid methyl es-
ters 3a–c were obtained by chromatography of the above reaction
residue followed by recrystallization from CHCl3–petroleum ether
(1:1).
(55).
Anal. Calcd for C10H6N2O4: C, 55.05; H, 2.77; N, 12.84. Found: C,
54.97; H, 2.86; N, 12.96.
N-Butylmaleimide (1f)
Mp 83–85 °C.
IR (KBr): 1720, 1312 cm–1.
1H NMR (CDCl3): = 0.92 (t, J = 7.3 Hz, 3 H), 1.20–1.38 (m, 2 H),
1.45–1.65 (m, 2 H), 3.51 (t, J = 7.3 Hz, 2 H), 6.67 (s, 2 H).
MS (EI, 70eV): m/z (%) = 153 (M+, 15), 113 (100), 72 (25).
N-( -Indolylethyl)succinimide (2a)
Mp 156–158 °C.
IR (KBr): 3269,1694 cm–1.
1H NMR (CDCl3): = 2.60 (s, 4 H), 3.05 (dd, J = 7.5 Hz, 7.8 Hz, 2
H), 3.82 (dd, J = 7.5 Hz, 7.8 Hz, 2 H), 7.10 (dd, J = 6.9 Hz, 7.5 Hz,
1 H), 7.16 (dd, J = 6.9 Hz, 7.5 Hz, 1 H) 7.19 (br s, 1 H), 7.34 (d,
J = 7.9 Hz, 1 H), 7.66 (d, J = 7.6 Hz, 1 H), 8.05 (br s, NH).
13C NMR (CDCl3): = 23.7, 28.6 (2 C), 39.9, 111.6, 112.6, 119.0,
119.9, 122.5, 122.6, 127.9, 136.5, 177.7 (2 C).
Anal. Calcd for C8H11NO2: C, 62.73; H, 7.24; N, 9.14. Found: C,
62.61; H, 7.35; N, 9.22.
N-Phenylmaleimide (1g)
Mp 85–86 °C (Lit.14 88–89 °C).
IR (KBr): 3456, 1710, 1397 cm–1.
1H NMR (CDCl3): = 6.85 (s, 2 H), 7.32–7.40 (m, 3 H), 7.44–7.50
(m, 2 H).
MS (EI, 70 eV): m/z (%) = 242 (M+, 45), 143 (85), 130 (100).
Anal. Calcd for C14H14N2O2: C, 69.41; H, 5.82; N, 11.56. Found: C,
69.35; H, 5.86; N, 11.05.
N-(4-Bromophenyl)maleimide (1h)
Mp 108–110 °C.
N-( -Phenylethyl)succinimide (2b)
IR (KBr): 1717, 1488, 1389 cm–1.
1H NMR (CDCl3): = 6.86 (s, 2 H), 7.21–7.27 (br d, 2 H), 7.55–
7.63 (br d, 2 H).
13C NMR (CDCl3): = 122.0, 127.8 (2 C), 130.5, 132.7 (2 C), 134.7
(2 C), 169.5 (2 C).
MS (EI, 70 eV): m/z (%) = 253 (M + 2, 100), 251 (M+, 90), 197 (10),
Mp 128–130 °C (Lit.9 135 °C).
IR (KBr): 1700, 1401 cm–1.
1H NMR (CDCl3): = 2.65 (s, 4 H), 2.88 (dd, J = 7.6, 7.9 Hz, 2 H),
3.75 (dd, J = 7.9, 7.6 Hz, 2 H), 7.18–7.30 (m, 5 H).
13C NMR (CDCl3): = 28.5 (2 C), 33.9, 40.3, 127.1, 129.0 (2 C),
129.2 (2 C), 138.2, 177.4 (2 C).
MS (EI, 70 eV): m/z (%) = 203 (M+, 50), 104 (100), 91 (70).
116 (25).
Anal. Calcd for C10H6BrNO2: C, 47.65; H, 2.40; N, 5.56. Found: C,
47.53; H, 2.49; N, 5.66.
N-Benzylsuccinimide (2c)
Mp 97–99 °C (Lit.11 103–105 °C).
N-(3-Bromophenyl)maleimide (1i)
Mp 114–116 °C.
IR (KBr): 1697, 1187 cm–1.
IR (KBr): 1711, 1586, 1477 cm–1.
1H NMR (CDCl3): = 6.87 (s, 2 H), 7.30–7.38 (m, 2 H), 7.45–7.53
(m, 1 H), 7.55 (s, 1 H).
1H NMR (CDCl3): = 2.68 (s, 4 H), 4.64 (s, 2 H), 7.22–7.75 (m, 5
H).
13C NMR (CDCl3): = 28.6 (2 C), 42.8, 127.8 (2 C), 129.3 (2 C),
133.6, 136.2, 177.3 (2 C).
Synthesis 2003, No. 10, 1549–1552 © Thieme Stuttgart · New York

1552
B. Pal et al.
PAPER
MS (EI, 70 eV): m/z (%) = 189 (M+, 100), 160 (80), 132 (70), 104
(100), 91 (75).
Anal. Calcd for C11H12BrNO3: C, 46.18; H, 4.23; N, 4.90. Found: C,
46.10; H, 4.30; N, 4.98.
N-Cyclohexylsuccinimide (2d)
N-(4-Fluorophenyl)succinamic Acid Methyl Ester (3c)
Mp 128–130 °C.
Mp 130–132 °C.
IR (KBr): 1696, 1376 cm–1.
IR (KBr): 3360, 1713, 1680, 1548 cm–1.
1H NMR (CDCl3): = 1.20–2.35 (m, 10 H), 2.64 (s, 4 H), 3.45–3.99
(m, 1 H).
1H NMR (CDCl3): = 2.55–2.71 (m, 2 H), 2.71–2.81 (m, 2 H), 3.72
(s, 3 H), 6.95–7.11 (m, 2 H), 7.36–7.49 (m, 2 H).
Anal. Calcd for C10H15NO2: C, 66.27; H, 8.34; N, 7.73. Found: C,
66.15; H, 8.41; N, 7.81.
13C NMR (CDCl3): = 29.6, 32.3, 52.5, 116.3, 122.1, 131.3, 134.5,
137.3, 162.0, 170.2, 174.2.
MS (EI, 70 eV): m/z (%) = 225 (M+, 15), 223 (40), 193 (40), 164
(25), 111 (100).
N-(3-Nitrophenyl)succinimide (2e)
Mp 140–142 °C (Lit.12 129–154 °C).
Anal. Calcd for C11H12FNO3: C, 58.66; H, 5.37; N, 6.22. Found: C,
58.58; H, 5.44; N, 6.29.
IR (KBr): 1711, 1527 cm–1.
1H NMR (CDCl3): = 2.96 (s, 4 H), 7.65–7.78 (m, 2 H), 8.25–8.31
(m, 2 H).
13C NMR (CDCl3): = 28.8 (2 C), 122.1, 123.6, 130.4, 132.7,
133.3, 148.9, 175.8 (2 C).
MS (EI, 70 eV): m/z (%) = 220 (M+, 100), 90 (45).
Acknowledgment
The authors thank CSIR, New Delhi and DST, Govt. of India for the
generous grants.
N-Butylsuccinimide (2f)
Colorless oil.
References
Bp 165–167 °C/20 mm (Lit.13 137–139 °C/12 mm).
IR (Neat): 1700, 1403 cm–1.
1H NMR (CDCl3): = 0.92 (t, J = 7.3 Hz, 3 H), 1.20–1.37 (m, 2 H),
1.48–1.59 (m, 2 H), 2.69 (s, 4 H), 3.50 (t, J = 7.4 Hz, 2 H).
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C).
MS (EI, 70 eV): m/z (%) = 155 (M+, 50), 113 (60), 100 (100), 85
(95).
N-Phenylsuccinimide (2g)
Mp 152–154 °C, (Lit.15 157 °C).
IR (KBr): 3502, 1700, 1437 cm–1.
1H NMR (CDCl3): = 2.45 (s, 4 H), 7.43–7.58 (m, 3 H), 7.63–7.73
(m, 2 H).
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N-(4-bromophenyl)succinamic Acid Methyl Ester (3a)
Mp 146–148 °C.
IR (KBr): 3350, 1720, 1675, 1535 cm–1.
1H NMR (CDCl3): = 2.64–2.70 (m, 2 H), 2.70–2.79 (m, 2 H), 3.71
(s, 3 H), 7.40–7.58 (m, 4 H).
13C NMR (CDCl3): = 29.6, 32.5, 52.5, 117.2, 122.0, 131.6, 132.5,
137.0, 137.3, 170.2, 174.1.
MS (EI, 70 eV): m/z (%) = 287 (M + 2, 30), 285 (M+, 40), 254 (20),
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173 (100), 171 (100), 115 (90).
Anal. Calcd for C11H12BrNO3: C, 46.18; H, 4.23; N, 4.90. Found: C,
46.11; H, 4.30; N, 4.98.
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(15) Warren, W. H.; Briggs, R. A. Chem. Ber. 1931, 64, 29.
N-(3-Bromophenyl)succinamic Acid Methyl Ester (3b)
Mp 78–80 °C.
IR (KBr): 3363, 1721, 1697, 1591 cm–1.
1H NMR (CDCl3): = 2.62–2.69 (m, 2 H), 2.69–2.95 (m, 2 H), 3.72
(s, 3 H), 7.08–7.27 (m, 2 H), 7.38 (br d, 1 H), 7.78 (br s, 1 H).
Synthesis 2003, No. 10, 1549–1552 © Thieme Stuttgart · New York