Enantiodivergent synthesis of trans-3,4-disubstituted succinimides by SmI2-mediated Reformatsky-type reaction

Article abstract of DOI:10.1016/j.tetlet.2008.04.090

An enantiodivergent strategy for the synthesis of trans-3,4-disubstituted succinimides is reported. The key step is a highly trans-stereoselective SmI₂-induced Reformatsky-type reaction of 4-substituted-O-benzoylated malimides with carbonyl compounds. Double chirality transmissions were performed with good to excellent diastereoselectivities.

Full text of DOI:10.1016/j.tetlet.2008.04.090

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 4007–4010
Enantiodivergent synthesis of trans-3,4-disubstituted
succinimides by SmI2-mediated Reformatsky-type reaction
Geng-Jie Lin, Shi-Peng Luo, Xiao Zheng, Jian-Liang Ye, Pei-Qiang Huang *
Department of Chemistry and Key Laboratory for Chemical Biology of Fujian Province, College of Chemistry and Chemical Engineering,
Xiamen University, Xiamen, Fujian 361005, PR China
Received 14 February 2008; revised 11 April 2008; accepted 15 April 2008
Available online 18 April 2008
Abstract
An enantiodivergent strategy for the synthesis of trans-3,4-disubstituted succinimides is reported. The key step is a highly trans-
stereoselective SmI2-induced Reformatsky-type reaction of 4-substituted-O-benzoylated malimides with carbonyl compounds. Double
chirality transmissions were performed with good to excellent diastereoselectivities.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Succinimides; Reformatsky-type reaction; Samarium diiodide; Chiral relay; Enantioselective synthesis
O
Since the report of Komura and co-workers in 1987 on
the isolation of andrimid as a new and highly specific anti-
biotic,1 3-substituted and 3,4-disubstituted succinimide
substructure-containing compounds are emerging as a
new class of natural products possessing important bioac-
tivities. In addition to its original isolation from the culture
broth of an intracellular symbiont of Nilaparvata lugens
(brown planthopper), in 1994, andrimid has also been iso-
lated along with moiramides A, B (2), and C from the mar-
ine bacterium Pseudomonas fluorescens.2 Andrimid3 (1) and
moiramide B (2) (Fig. 1) were found to exhibit potent in
vitro antibacterial activity against methicillin resistant
Staphylococcus aureus and a range of other antibiotic resis-
tant human pathogens.1,2 The 3,4-disubstituted succini-
mide subunit was shown to be the key structural feature
for efficient target binding.1–4 More recently, hirsutellones
A–E were isolated from the insect pathogenic fungus
Hirsutella nivea BCC 2594, which display a significant
growth inhibitory activity against Mycobacterium tubercu-
losis H37Ra;5 while haterumaimides A–Q are cytotoxic
labdane alkaloids isolated from an ascidian Lissoclinum
O
Ph
O
N H
N
H
N
H
n
O
O
O
andrimid (1) (n = 2)
moiramide B (2) (n = 1)
H
O
O
H
N
H
H
N
OH
O
H
O
O
H
H
Cl
OAc
haterumaimide A (4)
H
H
H
hirsutellone A (3)
Fig. 1. Structure of some 3,4-disubstituted succinimide subunit containing
natural products.
sp.,6 which have attracted considerable interest because
of their potential use as protein synthesis inhibitors,7 and
as antitumor drugs.8
In continuation of our efforts toward the development
of synthetic methodologies based on cheap and easily avail-
able optically active a-hydroxy acids9 and considering the
*
Corresponding author. Tel.: +86 592 2180992; fax: +86 592 2186400.
E-mail address: pqhuang@xmu.edu.cn (P.-Q. Huang).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.04.090

4008
G.-J. Lin et al. / Tetrahedron Letters 49 (2008) 4007–4010
El1
El2
El1
that compounds 8/9, and thus 6/7 are diastereomers at C-4.
The trans-stereochemistry of compounds 6 and 8 was
assigned according to the observed characteristic vicinal
coupling constants (J3,4 = 3.9–4.0 Hz).
HO
HO
O
O
O
O
O
O
N
Bn
5
N
Bn
A
N
Bn
B
After securing access to 4-benzylmalimide 6 in substan-
tial amount, we turned our attention to the key issue of the
strategy, namely the dehydroxylative enolate formation-
nucleophilic reaction with an aldehyde (A?B; D?ent-B)
(Scheme 1). Although a stepwise SmI2-induced deoxygen-
ation13 and enolate formation followed by an aldol-type
reaction can be envisioned, there exist several drawbacks
in such an approach, for example, low chemical yields,
low diastereoselectivity,14 as well as possible epimerization
or racemization of the aldol-type reaction due to the high
basicity of the enolates. To tackle these problems, SmI2-
mediated tandem deoxygenation-nucleophilic addition,
namely a Reformatsky-type reaction, was envisioned.
Several SmI2-mediated Reformatsky-type reactions15–18
have been reported; however, most of them involve a-
bromo-, a-phenylthio-, or a-pyridinylthio-substituted
ketones, imide, or carboxylic acid derivatives.15,17 The
most attractive method is the SmI2-promoted Reformat-
sky-type reaction of a-benzoyloxy lactone derivatives
developed by Enholm.16
Path A
HO
RO2C
HO
O
CO2R
El1
Path B
El1
El2
El1
HO
O
O
O
RO2C
CO2R
N
Bn
N
Bn
D
C
ent-B
Scheme 1. Enantiodivergent approach to B or ent-B based on double
chirality relay method.
substituent diversity of succinimide-type natural products,
we envisioned the development of a chirality relay-based
approach to 3,4-disubstituted succinimides by exploring
an SmI2-mediated Reformatsky-type reaction. The results
of these investigations are described herein.
As can be seen from Scheme 1, the aim of our research
was to develop an enantiodivergent and stepwise chirality
relay-based concept that differs from Seebach’s well-known
SRS (self-regeneration of stereocenters) methodology10 in
that the original chirality is also the temporary one, and
both enantiomers are accessible from the same chiron via
two variants.
To validate this concept, we first investigated the instal-
lation of the alkyl group at C-4 of malimide 5. Because
initial attempts to perform a direct alkylation3,11,12 of mal-
imide 5 yielded a mixture of two inseparable diastereomers
6/7, we explored a two-step procedure. Thus, treatment of
Thus 3-O-benzoylmalimide derivative 10 was selected as
our starting material, which was prepared from 6. Treat-
ment of a THF solution of malimide 3-O-benzoate 1020a
19
with 4.0 mol equiv of a 0.1 M THF solution of SmI2 at
ꢀ78 °C and in situ quenching of the organosamarium(III)
intermediate E with methanol gave the desired deoxygen-
ated product 3-benzylsuccinimide 11 in quantitative yield
(Scheme 3, Table 1, entry 1). The formation of 11 in high
yield implied that the reductive samariation of 10 occurred
smoothly. The optical rotation for 3-benzylsuccinimide 11
17
{½aꢁD 81.1 (c 0.95, CHCl3)} consists with those of the S-
the dianion generated from malimide
5 (LHMDS
enantiomers of its N-substituted analogs.3c,24b
2.2 equiv, ꢀ100 °C, 0.5 h) with benzaldehyde gave the
desired aldol-type products 8 and 9 as a mixture of four
diastereomers in 42% yield (69% based on the recovered
starting material) (Scheme 2). Subjection of the diastereo-
meric mixture of benzylic alcohols 8/9 to hydrogenolysis
(H2, Pd/C. EtOH, HCl, rt, 1 d) led to the deoxygenated
products 6 and 7 in 6:1 ratio with a combined yield of
96%. This result showed that the stereoselectivity of the
imide aldol-type reaction at the malimide ring (C-3/C-4)
was 6:1 in favor of trans-diastereomer 8. Similar deoxygen-
ation of the major diastereomers 8 afforded the benzylated
diastereomer 6 as the sole diastereomer. These results imply
Next, the SmI2-mediated Reformatsky-type reaction
of malimide derivative 10 with a variety of ketones or
HO
O
PhOCO
O
Ph
Ph
BzCl, Py.
CH2Cl2, 1 d
95%
O
O
N
N
Bn
Bn
10
6
Ph
O
0.1 M SmI2/THF
El
I2SmO
RL
N
(4−6 equiv.)
−78 ˚C, 3 h
Bn
E
Ph
RS
(1) LHMDS, THF, −100 °C;
H
HO
Ph
X
Ph
PhCHO, −78 °C, 0.5 h
4
HO
O
42% (SM 40% recovered);
or
C4-epimer
+
O
O
O
O
O
N
5
N
N
(2) Pd/C, H2, HCl
EtOH, r.t., 1 d
96%
Bn
Bn
Bn
O
7. (X = H)
6. (X = H)
(El = MeOH)
11
12a-12j
El =
(via 9. X = OH)
(via 8. X = OH)
RS
RL
Scheme 2. Synthesis of 1,4-dibenzylmalimide.
Scheme 3. SmI2-promoted deoxygenation-coupling reactions of 10.

G.-J. Lin et al. / Tetrahedron Letters 49 (2008) 4007–4010
4009
Table 1
After accomplishing the synthesis of trans-3,4-disubsti-
tuted succinimides of type B via route A (Scheme 1), we
next turned our attention to explore the synthesis of succin-
imides of type ent-B. To avoid the use of the more expen-
sive (R)-malic acid for establishing 4R-chirality, an
alternative route (route B, Scheme 1) was investigated.
To this end, methyl (S)-3-methylmalate 13 was prepared
according to Seebach’s method,21 and then converted suc-
cessively into the known 4-methylmalimide 1422 and benzo-
ate 15 (Scheme 4). The latter was subjected to an SmI2-
mediated Reformatsky-type reaction with a-aminoalde-
hyde 16,23 which afforded 17 as a mixture of two diastereo-
mers in 1:1.6 ratio along with 12% of the reduced product
18.24 In the light of the high level of stereochemical trans-
mission observed in the SmI2-mediated Reformatsky-type
reaction of 10 (Table 1), the two diastereomers obtained
from the reaction of 15 were assigned as diastereomeric
17, which may be used as key intermediates for the synthe-
sis of andrimid. More importantly, this result implies that
even with the small methyl group, the SmI2-mediated
Reformatsky-type reaction still provides excellent diastere-
oselectivity. Comparison of the optical rotation of succini-
SmI2-mediated Reformatsky-type reaction of malimide derivative 10 with
electrophiles
Entry
Electrophile
Producta
(yield, %)
Diastereoselectivity
d
at C-10 (%)
1
2
3
4
5
6
7
8
9
CH3OH
MeCOMe
MeCOEt
11 (100)b
12a (92)b
12b (94)b
12c (90)b
12d (82)b
12e (90)b
12f (94)b
12g (94)c
12h (90)c
12i (92)c
12j (91)c
—
Single diastereomer
1:5.2
1:2.7
n-PrCOEt
t-BuCOMe
(CH2)4CO
(CH2)5CO
n-C5H11CHO
n-C7H15CHO
i-PrCHO
Single diastereomer
Single diastereomer
Single diastereomer
1:6.5e
1:4e
10
11
a
Single diastereomer
Single diastereomer
t-BuCHOf
Isolated yield, only the trans-diastereomers were obtained.
4.0 mol equiv of SmI2.
6.0 mol equiv of SmI2.
Diastereoselectivity (at the carbinolic center) determined by 1H NMR.
Diastereoselectivity determined by HPLC.
A solution of 75% pivalaldehyde in t-BuOH was used.
b
c
d
e
f
25
aldehydes was investigated under Barbier-type condi-
tions20b and the results are summarized in Table 1. As
can be seen from the table, all the reactions gave the desired
Reformatsky-type products 12a–12j in excellent yields.
What is surprising is that not only did the reactions with
symmetric ketones give a single diastereomer in each case
(Table 1, entries 2, 6, and 7), but coupling with sterically
hindered pinacolone, i-butanal, and pivalaldehyde (Table
1, entries 5, 10, and 11) also resulted in a single diastereo-
mer in each case. The reactions with 2-butanone and n-hex-
anal also afforded good diastereoselectivities (Table 1,
entries 3 and 8).
The stereochemistry of compound 12d was determined
by single crystal X-ray crystallographic analysis,20c which
shows that the stereochemistry at the C-10 is R and the rel-
ative stereochemistry is trans-threo. The stereoselectivity of
the reaction can therefore be rationalized with the favored
transition state F (Fig. 2), which implies that carbonyl com-
pounds approach trans to the alkyl group of enolate E
(Scheme 3) and with the si-face of the approaching
carbonyl group.
mide 18 {½aꢁD +17.8 (c 1.13, CHCl3)} with that reported
23
for its antipode {½aꢁD ꢀ17.3 (c 1.10, CHCl3)}24b allowed
us to conclude that no appreciable racemization or epimer-
ization occurred in the synthetic sequence. The low diaste-
reoselectivity at C-10 might be attributed to the presence of
a chelating group in 16, and/or a mismatched situation.
In summary, by combining different chirality relay strat-
egies (alicyclic chelation control and cyclic steric control)
and a synthetic methodology (SmI2-induced Reformat-
sky-type reaction of succinimide derivatives), we have
established an enantiodivergent approach to 3,4-disubsti-
tuted succinimides. The highly diastereoselective SmI2-
induced Reformatsky-type reaction of a-benzoyloxy imides
(4-substituted-O-benzoylated malimides) will find applica-
tions in organic synthesis.
HO
HO
ref. 22
ref. 21
MeO2C
CO2Me
)-malate
HO
MeO2C
CO2Me
(S
13
BzO
BzCl, Py.
O
O
CH2Cl2, 1 d.
95%
O
O
N
PMB
N
PMB
15
RL
X2Sm
RS
X2Sm
R
R
RS
N
RL
14 (ds = 9:1, separable)
O
O
O
O
O
(d
s
= 1.6:1)
(d
O
N
s
=
ca.100:0)
OH
Bn
F (favored)
Bn
G (unfavored)
BocHN
CHO
16
+
O
O
BocHN
N
PMB
18 (12%)
0.1 M SmI2/THF
(6 equiv.), HMPA
−78 °C, 30 min.
O
O
N
threo-diastereromer
erythro-diastereromer
PMB
17 (70%)
12
Fig. 2. Proposed transition state for the SmI2-mediated Reformatsky-type
reaction of 10 with carbonyl compounds. RS = smaller alkyl groups;
Scheme 4. An access to ent-B via an alternative double chirality relay
RL = larger alkyl groups.
method.

4010
G.-J. Lin et al. / Tetrahedron Letters 49 (2008) 4007–4010
14. For aldol reaction of b-hydroxy-c-lactam dianion, see: (a) Huang,
Acknowledgments
P.-Q.; Zheng, X.; Wang, S.-L.; Ye, J.-L.; Jin, L.-R.; Chen, Z.
Tetrahedron: Asymmetry 1999, 10, 3309–3317; For aldol reaction of b-
hydroxy-c-butyrolactone dianion, see: (b) Shieh, H.-M.; Prestwich, G.
D. J. Org. Chem. 1981, 46, 4319–4321.
The authors are grateful to the NSFC (20572088), Qiu
Shi Science and Technologies Foundation, and the pro-
gram for Innovative Research Team in Science and Tech-
nology (University) in Fujian Province for financial
support. The project is partially supported by Fujian Pro-
vincial Training Foundation for ‘Bai-Qian-Wan Talents
Engineering’ and NFFTBS (No. J0630429). We thank Pro-
fessor G. M. Blackburn for valuable discussions.
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