Lewis acid catalyzed highly stereoselective domino-ring-opening cyclization of activated aziridines with enolates: Synthesis of functionalized chiral γ-lactams

Article abstract of DOI:10.1021/jo101004x

Figure presented. A highly enantio- and diastereoselective Lewis acid catalyzed S_N2-type ring opening followed by cyclization of aziridines with active methylene carbon nucleophiles to functionalized chiral γ-lactams in a domino fashion has been developed. γ-Lactams have been desulfonated and decarboxylated, providing pyrrolidone-3-carboxylate and N-tosylpyrrolidinone derivatives, respectively, in good yields.

Full text of DOI:10.1021/jo101004x

pubs.acs.org/joc
Lewis Acid Catalyzed Highly Stereoselective Domino-Ring-Opening
Cyclization of Activated Aziridines with Enolates: Synthesis
of Functionalized Chiral γ-Lactams
Manas K. Ghorai* and Deo Prakash Tiwari
Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
mkghorai@iitk.ac.in
Received May 21, 2010
A highly enantio- and diastereoselective Lewis acid catalyzed SN2-type ring opening followed by
cyclization of aziridines with active methylene carbon nucleophiles to functionalized chiral γ-lactams in
a domino fashion has been developed. γ-Lactams have been desulfonated and decarboxylated,
providing pyrrolidone-3-carboxylate and N-tosylpyrrolidinone derivatives, respectively, in good yields.
Introduction
γ-Lactams are one of the most important and widespread
subunits prevalent in many natural products1 (Figure 1) and
serve as pharmacophores in several biologically active com-
pounds.2 Synthetic utility3 as well as interesting biological
activities4 of γ-lactam ring structures have led researchers
to develop interesting routes toward their synthesis. Those
FIGURE 1. Some γ-lactam-containing natural products.
strategies include mostly intramolecular cyclization of γ-amino
esters,5 ring expansion,6 palladium-catalyzed cyclization re-
actions,7 cycloaddition,8 radical cyclization,9 and cascade
or multicomponent reactions,10 etc. In recent years, attrac-
tive routes for the stereoselective synthesis of γ-lactams have
been reported.11,12 There are a few reports for the synthesis
(1) (a) Aoki, S.; Tsukude, T.; Miyazaki, Y.; Takao, K.; Tadano, K.
Heterocycles 2006, 69, 49. (b) Cappi, M. W.; Chen, W. -P.; Flood, R. W.;
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J. Org. Chem. 2007, 2365. (c) Chouhan, G.; Alper, H. Org. Lett. 2008, 10,
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Int. Ed. 2006, 45, 5863. (b) Ishibashi, H.; Haruki, S.; Uchiyama, M.; Tamura,
O.; Matsuo, J. Tetrahedron Lett. 2006, 47, 6263.
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DOI: 10.1021/jo101004x
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Published on Web 08/13/2010
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Ghorai and Tiwari
JOCArticle
of γ-lactams from aziridines via ring opening followed by
cyclization with enolates.13,14 Although several reports are
known for the opening of aziridines15 with heteroatom and
carbon nucleophiles,16 enantioselective ring opening of aziri-
dines with enolates is still limited.17 Recently, we have reported
Lewis acid (LA) mediated SN2-type ring opening of enantiopure
2-aryl-N-tosylaziridines and azetidines by a number of nucleo-
philes to provide nonracemic products.18 In continuation of
our research activities in this area for designing enantioselective
ring-opening reactions of chiral aziridines and azetidines toward
enantiopure targets, we have developed a simple strategy for the
synthesis of chiral functionalized γ-lactams via Lewis acid
catalyzed SN2-type ring opening of enantiopure N-sulfonylazi-
ridines by enolates generated from active methylene compounds
followed by intramolecular cyclization in a domino fashion. We
report herein our results in detail.
SCHEME 1. Lewis Acid Catalyzed Domino-Ring-Opening
Cyclization of 2-Phenyl-N-tosylaziridine
TABLE 1. Optimization Study for Ring-Opening Cyclization of
2-Phenyl-N-tosylaziridine with Enolate
entry
conditions
time
7.0 h
11.0 h
6.5 h
7.0 h
11.0 h
6.0 h
30 min
30 min
<20 min
yieldd (%) ere,f (%)
1a t-BuOK, Ti(O-i-Pr)4, 0 °C to rt
2a t-BuOK, Zn(OTf)2, 0 °C to rt
3a t-BuOK, Cu(OTf)2, 0 °C to rt
4a NaH, Ti(O-i-Pr)4, 0 °C to rt
5a NaH, Zn(OTf)2, 0 °C to rt
6a NaH, Cu(OTf)2, 0 °C to rt
7b NaH, Cu(OTf)2, rt to 60 °C
73
68
68
76
79
93
93
93
84
99:1
>99:1
>99:1
99:1
>99:1
>99:1
>99:1
>99:1
>99:1
Results and Discussion
8c
9c
NaH, Cu(OTf)2, rt to 60 °C
NaH, Sc(OTf)3, rt to 60 °C
Our study began with the reaction of (R)-2-phenyl-N-
tosylaziridine 1a with enolate generated from diethyl mal-
onate (2a0, 5.0 equiv) by the treatment of t-BuOK (5.0 equiv)
in the presence of Cu(OTf)219a (1.0 equiv) in THF at 0 °C-rt
a5.0 equiv of 2a0, 5.0 equiv of base, and 1.0 equiv of LA were used. b3.0
equiv of base, 3.0 equiv of 2a0, and 1.0 equiv of LA were used. cCatalytic
amount of LA (20 mol %) was used. dYields of isolated products. eee was
determined using a Chiralpak AD-H column, hexane-2-propanol
90:10, flow rate 1.0 mL min-1 fProduct was obtained as a single
.
diastereomer after column chromatographic purification in all cases.
(13) For synthesis of γ-lactam from enantiopure N,O-ditosylates of
amino acids via intermediacy of aziridine, see: (a) Tseng, C. C.; Terashima,
S.; Yamada, S. Chem. Pharm. Bull. 1977, 25, 29. (b) Tseng, C. C.; Terashima,
S.; Yamada, S. Chem. Pharm. Bull. 1977, 25, 166. (c) An inseparable mixture
of diastereomers was obtained in the above cases.
SCHEME 2. Lewis Acid Catalyzed Domino-Ring-Opening
Cyclization of N-Sulfonylaziridines
(14) For racemic synthesis of γ-lactam from aziridine, see: (a) Stamm, H.
J. Prakt. Chem. 1999, 341, 319 and references cited therein. (b) Stamm, H.;
Fiihrling, G. Tetrahedron Lett. 1970, 22, 1937. (c) Gailius, V.; Stamm, H.
Arch. Pharm. (Weinheim) 1988, 321, 337. (d) Stamm, V. H.; Budny, J. Chem.
Ztg. 1979, 103, 156. (e) Stamm, H.; Schneider, L. Chem. Ber. 1975, 108, 500.
(f) Stamm, H. Arch. Pharm. (Weinheim) 1966, 299, 965. (g) Stamm, H. Chem.
Ber. 1966, 99, 2556. For synthesis of ring-fused γ-lactam, see: (h) Smith,
P. W.; Whittington, A. R.; Cobley, K. N.; Jaxa-Chamiec, A.; Finch, H.
J. Chem. Soc., Perkin Trans. 1 2001, 21. (h) Page, M. F. Z.; Jalisatgi, S. S.;
Maderna, A.; Hawthorne, M. F. Synthesis 2008, 555.
(15) (a) Nielsen, L. P. C.; Jacobsen, E. N. In Aziridines and Epoxides in
Organic Synthesis; Yudin, A. K., Ed.; Wiley-VCH: Weinheim, 2006; Chapter
7, p 229. For some recent reviews on aziridines, see: (b) Hu, X. E. Tetra-
hedron 2004, 60, 2701 and references cited therein. (c) Watson, I. D. G.; Yu,
L.; Yudin, A. K. Acc. Chem. Res. 2006, 39, 194. (d) Sweeney, J. B. Chem. Soc.
Rev. 2002, 31, 247. (e) Singh, G. S.; D’hooghe, M.; De Kimpe, N. Chem. Rev.
2007, 107, 2080. For some recent examples of aziridine ring opening, see:
for 6.5 h to afford γ-lactam 3a in 68% yield (Scheme 1) with
excellent stereoselectivity (er >99:1 and dr >99:1). To improve
the yield and reduce the time, the reaction was performed under
a variety of conditions (Table 1). Other Lewis acids, e.g., Ti(O-
i-Pr)4,19b Zn(OTf)2,19c and Sc(OTf)3, were studied, and in the
case of Ti(O-i-Pr)4 a reduced er was observed (entry 1).
ꢀ
(f) Forbeck, E. M.; Evans, C. D.; Gilleran, J. A.; Li, P.; Joullie, M. M. J. Am.
Chem. Soc. 2007, 129, 14463. (g) Ochoa-Teran, A.; Concellon, J. M.; Rivero,
ꢀ
ꢀ
ꢀ
ꢀ
I. A. ARKIVOC 2009, ii, 288. (h) Concellon, J. M.; Bernad, P. L.; Suarez,
J. R. J. Org. Chem. 2005, 70, 9411. (i) Couty, F.; Evano, G.; Prim, D.
Tetrahedron Lett. 2005, 46, 2253.
With a view to optimizing the reaction conditions further,
we utilized the common base NaH for this purpose20 with
different LAs (Table 1, entry 4-9). Combination of NaH
along with Cu(OTf)2 provided the best result (yield 93%,
er >99:1, and dr >99:1) in a comparable reaction time (entry
6). To our delight, the reaction time was drastically reduced
to 0.5 h when the reaction was performed at 60 °C (entry 7).
We further observed that an even lower amount of enolate
(3.0 equiv of NaH and 3.0 equiv of diethyl malonate) and a
catalytic amount of Cu(OTf)2 (20 mol %) were sufficient for
completion of the reaction (entry 8). When the amount of
enolate or the LA was reduced further, the reaction was
found to be incomplete after being continued for 2 h. It is
worth noting that the reaction was completed within 20 min,
and 3a was obtained with same stereoselectivity as observed
previously (er >99:1, dr >99:1) with relatively lower yield
(16) (a) Enders, D.; Janeck, C. F.; Raabe, G. Eur. J. Org. Chem. 2000,
3337. (b) Blyumin, E. V.; Gallon, H. J.; Yudin, A. K. Org. Lett. 2007, 9, 4677.
(c) Minakata, S.; Murakami, Y.; Satake, M.; Hidaka, I.; Okada, Y.;
Komatsu, M. Org. Biomol. Chem. 2009, 7, 641. (e) Ding, C. H.; Dai, L. X.;
Hou, X. L. Tetrahedron 2005, 61, 9586. (f) D’hooghe, M.; Van Nieuwenhove,
A.; Van Brabandt, W.; Rottiers, M.; De Kimpe, N. Tetrahedron 2008, 64,
1064.
(17) (a) Vicario, J. L.; Badıa, D.; Carrillo, L. J. Org. Chem. 2001, 66, 5801.
(b) Moss, T. A.; Fenwick, D. R.; Dixon, D. J. J. Am. Chem. Soc. 2008, 130,
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10076. (c) Paixao, M. W.; Nielsen, M.; Jacobsen, C. B.; Jørgensen, K. A. Org.
Biomol. Chem. 2008, 6, 3467.
(18) (a) Ghorai, M. K.; Das, K.; Kumar, A.; Ghosh, K. Tetrahedron Lett.
2005, 46, 4103. (b) Ghorai, M. K.; Das, K.; Kumar, A.; Das, A. Tetrahedron
Lett. 2006, 47, 5393. (c) Ghorai, M. K.; Ghosh, K.; Das, K. Tetrahedron Lett.
2006, 47, 5399. (d) Ghorai, M. K.; Ghosh, K. Tetrahedron Lett. 2007, 48,
3191. (e) Ghorai, M. K.; Das, K.; Kumar, A. Tetrahedron Lett. 2007, 48,
4373. (f) Ghorai, M. K.; Das, K.; Shukla, D. J. Org. Chem. 2007, 72, 5859.
(g) Ghorai, M. K.; Kumar, A.; Das, K. Org. Lett. 2007, 9, 5441. (h) Ghorai,
M. K.; Das, K.; Kumar, A. Tetrahedron Lett. 2009, 50, 1105. (i) Ghorai,
M. K.; Shukla, D.; Das, K. J. Org. Chem. 2009, 74, 7013. (j) Ghorai, M. K.;
Kumar, A.; Tiwari, D. P. J. Org. Chem. 2010, 75, 137.
(19) (a) Ma, S.; Han, X.; Krishnan, S.; Virgil, S. C.; Stoltz, B. M. Angew.
Chem., Int. Ed. 2009, 48, 8037. (b) Ghosh, A. K.; Onishi, M. J. Am. Chem.
Soc. 1996, 118, 2527. (c) Shao, H.; Wang, Z.; Lacroix, E.; Wu, S.-H.;
Jennings, H. J.; Zou, W. J. Am. Chem. Soc. 2002, 124, 2130.
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Compernolle, F. Tetrahedron Lett. 2000, 41, 2223.
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TABLE 2. Lewis Acid Catalyzed Domino-Ring-Opening Cyclization of Monosubstituted Aziridines
aAll reactions were performed with 3.0 equiv of nucleophile, 3.0 equiv of NaH, and 20 mol % of Cu(OTf)2. bProduct was obtained as a single
c
diastereomer in all cases. Yields of isolated products after column chromatographic purification. dDetermined by chiral HPLC analysis (see the
Supporting Information). eProduct was obtained as a mixture of keto and enol forms. fUncyclized product 5 was also obtained. ger of the product could
not be determined. hInseparable mixture of diastereomers (dr 4:1) was obtained, and the reaction was completed in 2 h. iWhen Sc(OTf)3 was used as the
LA, the reaction was completed in 30 min and higher dr (>5:1) was observed with relatively lower yield (56%).
(84%) using Sc(OTf)3 (20 mol %) as the LA (entry 9,
Table 1).
To generalize this strategy, a number of monosubstituted
aziridines were studied (Scheme 2), and the results are shown
in Table 2. (R)-1a produced the corresponding γ-lactam in
excellent yield and stereoselectivity upon reaction with di-
ethyl malonate (2a0) or ethyl acetoacetate (2b0) (entries 1 and
2, Table 2).
Substrate (R)-1b having an easily removable protecting
group (p-nitrobenzenesulfonyl) on nitrogen produced the
corresponding γ-lactam (3b) in moderate yield and excellent
er (entry 3, Table 2) along with 5 when 2a0 was used as the
enolate source. Probably because of of the higher electron-
attracting capacity of the nosyl group, lone pair/charge on
nitrogen is less available for further cyclization and led to the
The reaction of 1a proceeds in the absence of a LA but it
takes longer time (3.5 h) for completion as compared to
20-30 min using a LA at 60 °C. Without LA, the γ-lactam
3a was obtained in lower yield (79%) along with some un-
characterized compound (probably other regioisomer), but
the stereoselectivity of the crystallized product 3a remained
the same (dr >99:1, er 99:1) as obtained under LA condi-
tions. Furthermore, the reaction without LA was comple-
ted in 24 h when performed at room temperature, whereas it
took 6 h for completion using Cu(OTf)2 as the LA (entry 6,
Table 1).
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SCHEME 3. Lewis Acid Catalyzed Ring-Opening Cyclization
of 2-Phenyl-N-nosylaziridine
SCHEME 5. Lewis Acid Catalyzed Domino-Ring-Opening
Cyclization of Vinylaziridine
To extend the scope of our methodology, a variety of
disubstituted aziridines (S,S)-1f-i18j were studied (Scheme 4)
and converted into the corresponding γ-lactams (3f-i and
4e) with excellent stereoselectivity (Table 3).
SCHEME 4. Lewis Acid Catalyzed Domino-Ring-Opening
Cyclization of N-Tosyl-2,3-disubstituted Aziridines
It is noteworthy that aziridine (S, S)-1h under the same
reaction condition afforded the corresponding γ-lactam 3h
along with 6 obtained from the attack of the enolate on
vinylic carbon21 (Scheme 5) when 2a0 was used as the enolate
source.
Interestingly, when 2b0 was used as the enolate source, the
corresponding γ-lactams were obtained as mixture of keto
and enol tautomers with keto form being produced predo-
minantly in all the cases (entries 2, 4, 7, and 8, Table 2, and
entry 5, Table 3).
After successful demonstration of the ring-opening cycliz-
ation of trans-2,3-disubstituted aziridines with active methy-
lene carbon nucleophiles (Scheme 4, Table 3), we next stud-
ied the reaction of enantiomerically pure cis-2,3-disubstitut-
ed aziridine (1j).22 When 1j was reacted with the Na enolate
formation of 5 (Scheme 3). However, when 2b0 was used as
the enolate source, 4b was formed in good yield (entry 4,
Table 2) along with some uncharacterized compound.
Excellent results were obtained with aziridines bearing a
4-tert-butylphenyl sulfonyl group on nitrogen (1c,d) (entry
5-8, Table 2). Interestingly, the alkylaziridine (S)-1e pro-
duced the corresponding γ-lactam 3e (entry 9, Table 2) in
high yield as an inseparable diastereomeric mixture (4:1).
TABLE 3. Lewis Acid Catalyzed Domino-Ring-Opening Cyclization of trans-N-Tosyl-2,3-disubstituted Aziridines
aAll reactions were performed with 3.0 equiv of nucleophile, 3.0 equiv of NaH, and 20 mol % of Cu(OTf)2. bYields of isolated products after column
chromatographic purification. cProduct was obtained as a single diastereomer after column chromatography in all the cases. ddr could not be determined
(see the Experimental Section). eWhen Sc(OTf)3 was used as the LA, reaction completed in 6 h with relatively lower yield (57%). fProduct was obtained as
mixture of keto and enol forms.
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SCHEME 6. Lewis Acid Catalyzed Domino-Ring-Opening
Cyclization of cis-N-Tosyl-2,3-disubstituted Aziridine
that plays a vital role in the ring-opening process and over-
comes the steric effect. The CN bond becomes more polar-
ized in the presence of a LA as the partial þve charge at the
benzylic position could be stabilized by the Ph group and the
nucleophilic opening takes place at this position selectively.
Finally, cyclization takes place with the β-ester group to
produce the corresponding trans-product (3 and 4) as a single
diastereomer (Scheme 7).
However, in the case of 2-alkyl-N-tosylaziridine, both the
steric and electronic effects govern the reactivity and thus the
ring-opening process. With bulkier alkyl substituents at the 2-
position of the aziridine ring, nucleophilic attack takes place at
the less substituted position preferably. For example, opening
of 2-isopropyl-N-tosylaziridine 1e with enolate from diethyl
malonate 2a0 followed by possible cyclization with any one of
the two ester groups led to the formation of the product 3e
as a mixture of diastereomers (entry 9, Table 2).23
For wider applicability of the developed methodology,
the γ-lactams were desulfonated to the corresponding free
γ-lactam derivatives. As representative examples, N-tosylpyr-
rolidinone-3-carboxylate 3a was detosylated using sodium
naphthalide,24 and N-nosylpyrrolidinone-3-carboxylate 3b
was denosylated using K2CO3/PhSH17b to produce the γ-lac-
tam 7 in free form (Scheme 8).
of diethyl malonate (2a0) under our reaction conditions, the
corresponding γ-lactam 3j was obtained in excellent yield
and diastereoselectivity (dr >99:1) (Scheme 6), although the
reaction took a longer time (24 h) for completion.
On the basis of the NOE experiments (see the Supporting
Information), the relative stereochemistry as well as the ab-
solute configuration of 3j could be ascertained (Figure 2),
and the NOE was observed between protons Ha-Hortho
,
Ha-Hc, and Hc-Hortho
.
Furthermore, as a representative example, 3a was decar-
boxylated to the corresponding γ-lactam 8 in good yield
following a literature report25 (Scheme 9).
FIGURE 2. NOE experiment for determination of stereochemistry.
1
All of the new compounds were characterized by IR, H
SCHEME 9. Decarboxylation of γ-Lactam
NMR, 13C NMR, and HRMS data, and the structure of 4a
was confirmed by X-ray crystallographic analysis where 4a
was found to exist in enol form with intramolecular hydro-
gen bonding (see the Supporting Information).
Based on the experimental facts, we do believe that the ring
opening of chiral aziridines 1 with enolates proceed via an
SN2-type pathway (Scheme 7). First, the LA is coordinated to
aziridine 1 generating a highly reactive species A. Alterna-
tively, A might bind to the enolate to generate another reactive
species B. Next the SN2-type ring opening by enolate takes
place either from A or B to generate C, which finally undergoes
lactamization to produce the corresponding γ-lactams (3 and 4).
The observed regio- and stereoselectivity for the ring-
opening cyclization of 2-phenyl-N-tosylaziridines can be ex-
plained by considering the electronic effect of the Ph group
Conclusion
In conclusion, we have developed a simple strategy for the
synthesis of highly functionalized chiral γ-lactams via LA-
catalyzed SN2-type ring opening of aziridines with enolates
followed by intramolecular cyclization. This method allows
the use of a wide range of aziridines and active methylene
carbon nucleophiles to construct a variety of γ-lactams in
excellent yield and enantioselectivity. These γ-lactams can be
SCHEME 7. Proposed Mechanism of the Reaction
SCHEME 8. Desulfonation of γ-Lactams
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Ghorai and Tiwari
JOCArticle
desulfonated and decarboxylated to provide the correspond-
ing free pyrrolidinone-3-carboxylate and N-tosylpyrrolidi-
none derivatives, respectively.
and enol forms) δ 19.2, 21.9, 29.8, 30.5, 38.3, 39.0, 51.8, 54.2,
63.6, 103.4, 126.9, 127.0, 127.6, 127.9, 128.1, 128.3, 128.7, 129.2,
129.9, 130.0, 134.7, 135.2, 139.2, 142.9, 145.3, 145.8, 167.8,
171.5, 171.8, 199.9; HRMS (ESI) for C19H19NO4S (M þ H)þ
found 358.1114, calcd 358.1113; er >99:1. The enantiomeric
ratio was determined by chiral HPLC analysis (Chiralpak AD-
H column), hexane-2-propanol 90:10, flow rate =1.0 mL/min;
Experimental Section
General Experimental Procedure for the Synthesis of Chiral
γ-Lactam. To a suspension of sodium hydride (3.0 equiv) in
THF (2.0 mL) was added diethyl malonate/ethyl acetoacetate
(3.0 equiv) at room temperature under nitrogen atmosphere.
Subsequently, solutions of N-sulfonylaziridine (100 mg, 1.0
equiv) and Cu(OTf)2 (20 mol %) in THF were added to the
reaction mixture. The reaction mixture was then stirred at 60 °C
for the appropriate time. After complete consumption of start-
ing compound (monitored by TLC), the reaction was quenched
by addition of saturated aqueous NH4Cl (1.0 mL) solution. The
organic phase was separated, and the aqueous phase was
extracted with ethyl acetate (3 ꢀ 1.0 mL). The combined extracts
were washed with brine and dried over anhydrous sodium
sulfate. After removal of the solvent under reduced pressure,
the crude reaction mixture was purified by flash column chro-
matography on silica gel (230-400 mesh) using ethyl acetate in
petroleum ether as the eluent to give the pure γ-lactam.
t
R (1) = 35.95 min (minor), tR (2) = 74.38 min (major).
(3R,4S)-Ethyl 1-(4-Nitrophenylsulfonyl)-2-oxo-4-phenylpyr-
rolidine-3-carboxylate (3b). The general method described above
was followed when (R)-1b (100 mg, 0.329 mmol) was reacted
with enolate from diethyl malonate [diethyl malonate (0.15 mL,
0.99 mmol), NaH (40 mg, 0.99 mmol)] in the presence of
20 mol % of Cu(OTf)2 (23.8 mg, 0.066 mmol) at 60 °C for
15 min to afford 3b (66.5 mg, 0.159 mmol) as a white solid in
48% yield along with 5 (78 mg, 0.168 mmol) as a colorless thick
liquid in 51% yield. Data for 3b: mp 129-131 °C; Rf 0.37 (20%
ethyl acetate in petroleum ether); [R]25D = -9.2 (c 0.13, CHCl3);
IR νmax (KBr, cm-1) 2942, 1746, 1723, 1369, 1214, 1172, 1119,
1
1090, 1020, 948, 840, 817, 752, 659, 579, 544; H NMR (500
MHz, CDCl3) δ 1.15 (t, J = 7.2 Hz, 3H), 3.59 (d, J = 9.8 Hz,
1H), 3.79 (dd, J = 10.0, 8.6 Hz, 1H), 3.93 (q, J = 8.6 Hz, 1H),
4.04-4.17 (m, 2H), 4.32 (dd, J = 10.0, 8.3 Hz, 1H), 7.10-7.31
(m, 5H), 8.20 (d, J = 8.6 Hz, 2H), 8.34 (d, J = 8.6 Hz, 2H); 13C
NMR (125 MHz, CDCl3) δ 14.1, 41.3, 51.9, 56.3, 62.6, 124.5,
126.9, 128.4, 129.4, 129.9, 137.4, 142.9, 151.2, 166.8, 167.8;
HRMS (ESI) for C19H18N2O7S (M - H)þ found 417.0758,
calcd 417.0757. The enantiomeric ratio of 3b was determined
from the denosylated compound 7 (Scheme 8).
Procedure for Denosylation of Compound 3b. Compound 3b
(31 mg, 0.074 mmol) dissolved in CH3CN (1.0 mL) was added to
the suspension of K2CO3 (40.9 mg, 0.296 mmol, 4.0 equiv) in
CH3CN (1.9 mL), and PhSH (23.0 μL, 0.222 mmol, 3.0 equiv)
was added at room temperature under nitrogen atmosphere.
Next, DMSO (0.1 mL) was added to the reaction mixture, and
stirring was continued at room temperature for 2 h. After
complete consumption of the starting compound, the reaction
was quenched with water. The organic and aqueous layers were
separated, and the aqueous layer was extracted with ethyl
acetate (3 ꢀ 2.0 mL). The combined extracts were dried on
anhydrous sodium sulfate and evaporated to dryness. After
column chromatographic purification on silica gel (230-400
mesh) using 40% ethyl acetate in petroleum ether as the eluent,
pyrrolidinone-3-carboxylate 7 was obtained as white solid. The
corresponding racemic product 7 was obtained by detosylation
of the racemic 3a following the reaction conditions shown in
Scheme 8. The enantiomeric ratio (er >99:1) was determined by
chiral HPLC analysis (Chiralpak AD-H column), hexane-2-
propanol 90:10, flow rate =1.0 mL/min; tR (1) = 19.48 min
(minor), tR (2) = 24.48 min (major).
Data for (S)-diethyl 2-(2-(4-nitrophenylsulfonamido)-1-
phenylethyl) malonate (5): Rf 0.23 (20% ethyl acetate in petro-
leum ether); IR νmax (neat, cm-1) 3360, 2923, 1733, 1597, 1533,
1456, 1403, 1265, 1166, 1093, 1023, 745, 704, 614, 535, 464; 1H
NMR (400 MHz, CDCl3) δ 0.89 (t, J = 7.2 Hz, 3H), 1.22 (t, J =
7.2 Hz, 3H), 3.23-3.28 (m, 1H), 3.41-3.46 (m, 1H), 3.62 (d, J =
10.0 Hz, 1H), 3.82-3.86 (m, 2H), 4.14-4.20 (m, 2H), 4.53 (m,
1H), 6.99-7.23 (m, 5H), 7.86 (d, J = 8.6 Hz, 2H), 8.23 (d, J =
8.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 13.6, 14.0, 44.9,
46.5, 55.2, 61.6, 62.1, 124.3, 128.0, 128.2, 129.0, 129.9, 137.5,
147.2, 150.0, 167.2, 168.1; HRMS (ESI) for C21H24N2O8S (M þ
H)þ found 465.1333, calcd 465.1332.
(3S,4S)-3-Acetyl-1-(4-nitrophenylsulfonyl)-4-phenylpyrrolidine-
2-one (4b). The general method described above was followed
when (R)-1b (100 mg, 0.329 mmol) was reacted with enolate from
ethyl acetoacetate [ethyl acetoacetate (0.13 mL, 0.99 mmol), NaH
(40 mg, 0.99 mmol)] in the presence of 20 mol % of Cu(OTf)2
(23.8 mg, 0.066 mmol) at 60 °C for 1.5 h to afford 4b (81.5 mg,
(3R,4S)-Ethyl 2-Oxo-4-phenyl-1-tosylpyrrolidine-3-carboxy-
late (3a).13b. The general method described above was followed
when (R)-1a (100 mg, 0.366 mmol) was reacted with enolate
from diethyl malonate [diethyl malonate (0.17 mL, 1.098 mmol),
NaH (44 mg, 1.098 mmol)] in the presence of Cu(OTf)2 (26 mg,
0.07 mmol) at 60 °C for 30 min to afford 3a (133 mg, 0.34 mmol)
as a white solid in 93% yield: mp 108-110 °C; Rf 0.38 (20% ethyl
acetate in petroleum ether); [R]25D = þ34.5 (c 0.20, CHCl3); IR
ν
max (KBr, cm-1) 2919, 1755, 1730, 1352, 1167, 1138, 758, 697,
673, 582, 545; 1H NMR (500 MHz, CDCl3) δ 1.15 (t, J = 7.2 Hz,
3H), 2.40 (s, 3H), 3.54 (d, J = 9.9 Hz, 1H), 3.72 (dd, J = 9.8, 9.1
Hz, 1H), 3.91 (q, J = 8.6 Hz, 1H), 4.05-4.14 (m, 2H), 4.29 (dd,
J = 9.6, 8.3 Hz, 1H), 7.10 (d, J = 6.5 Hz, 2H), 7.23-7.30 (m,
5H), 7.87 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ
14.1, 21.8, 41.1, 51.7, 56.5, 62.3, 126.9, 128.1, 128.3, 129.3, 129.9,
134.7, 137.9, 145.8, 167.1, 167.5; HRMS (ESI) for C20H21NO5S
(M þ H)þ found 388.1218, calcd 388.1219; er >99:1. The
enantiomeric ratio was determined by chiral HPLC analysis
(Chiralpak AD-H column), hexane-2-propanol 90:10, flow
rate =1.0 mL/min; tR (1) = 29.74 min (minor), tR (2) = 54.15
min (major).
(3S,4S)-3-Acetyl-4-phenyl-1-tosylpyrrolidin-2-one (4a). The
general method described above was followed when (R)-1a
(100 mg, 0.366 mmol) was reacted with enolate from ethyl
acetoacetate [ethyl acetoacetate (0.14 mL, 1.098 mmol), NaH
(44 mg, 1.098 mmol)] in the presence of 20 mol % of Cu(OTf)2
(26 mg, 0.073 mmol) at 60 °C for 8 h to afford 4a (132 mg, 0.369
mmol) as a white crystalline solid in >99% yield: mp 154-156
°C; Rf 0.37 (20% ethyl acetate in petroleum ether); [R]25
=
D
þ21.9 (c 0.16, CHCl3); IR νmax (KBr, cm-1) 3032, 2923, 1752,
1715, 1342, 1167, 1129, 1089, 978, 814, 757, 698, 671, 579, 547;
1H NMR (400 MHz, CDCl3) δ 2.26 (s, 3H), 2.40 (s, 3H), 3.67 (d,
J = 9.0 Hz, 1H), 3.75 (dd, J = 9.8, 7.6 Hz, 1H), 3.95-4.02 (m,
1H), 4.22 (dd, J = 9.8, 8.6 Hz, 1H), 7.05-7.31 (m, 7H), 7.85 (d,
J = 8.1 Hz, 2H); 13C NMR (125 MHz, CDCl3) (mixture of keto
(21) Fujii, N.; Nakai, K.; Tamamura, H.; Otaka, A.; Mimura, N.; Miwa,
Y.; Taga, T.; Yamamoto, Y.; Ibuka, T. J. Chem. Soc., Perkin Trans. 1 1995,
1359.
(22) Righi, P.; Scardovi, N.; Marotta, E.; ten Holte, P.; Zwanenburg, B.
Org. Lett. 2002, 4, 497.
(23) For the mechanism of ring-opening cyclization of alkylaziridine, see
the Supporting Information.
(24) Closson, W. D.; Wriede, P.; Bank, S. J. Am. Chem. Soc. 1966, 88,
1581.
(25) Okino, T.; Hoashi, Y.; Furukawa, T.; Xu, X.; Takemoto, Y. J. Am.
Chem. Soc. 2005, 127, 119.
6178 J. Org. Chem. Vol. 75, No. 18, 2010

Ghorai and Tiwari
JOCArticle
0.209 mmol) as a white solid in 64% yield: mp 146-149 °C; Rf
0.36 (20% ethyl acetate in petroleum ether); [R]25D = þ41.4 (c
0.21, CHCl3); IR νmax (KBr, cm-1) 3449, 2925, 2855, 1749, 1714,
1532, 1356, 1310, 1267, 1212, 1162, 1131, 1086, 964, 854, 759,
737, 699, 628, 566, 527, 460; 1H NMR (400 MHz, CDCl3) δ 2.33
(s, 3H), 3.77-3.80 (m, 1H), 3.87 (dd, J = 10.0, 7.8 Hz, 1H),
4.07-4.11 (m, 1H), 4.22-4.36 (m, 1H), 7.10-7.32 (m, 5H), 8.25
(d, J = 9.0 Hz, 2H), 8.41 (dd, J = 8.8, 7.1 Hz, 2H); 13C NMR
(100 MHz, CDCl3) (mixture of keto and enol forms) δ 19.1, 30.4,
38.5, 38.9, 51.9, 54.2, 63.1, 102.8, 124.3, 124.4, 126.8, 126.9,
127.5, 127.7, 128.1, 129.3, 129.5, 129.7, 138.5, 142.4, 142.9,
143.7, 150.6, 150.61, 168.0, 170.7, 172.9, 199.3; HRMS (ESI)
for C18H16N2O6S (M þ H)þ found 389.0839, calcd 389.0807.
The er of the compound 4b could not be determined due to it is
insolubility in the available HPLC condition.
(Chiralpak AD-H column), hexane-2-propanol 90:10, flow
rate =1.0 mL/min; tR (1) = 19.18 min (minor), tR (2) = 59.17
min (major).
(3R,4R)-3-Acetyl-1-(4-tert-butylphenylsulfonyl)-4-phenylpyr-
rolidin-2-one (4d). The general method described above was
followed when (S)-1d (100 mg, 0.317 mmol) was reacted with
enolate from ethyl acetoacetate [ethyl acetoacetate (0.12 mL,
0.95 mmol), NaH (38.0 mg, 0.95 mmol)] in the presence of 20
mol % of Cu(OTf)2 (23.0 mg, 0.063 mmol) at 60 °C for 9 h to af-
ford 4d (117.0 mg, 0.293 mmol) in 92% yield; er >99:1. The
enantiomeric ratio was determined by chiral HPLC analysis
(Chiralpak AD-H column), hexane-2-propanol 90:10, flow rate
1.0 mL/min; tR (1) = 19.57 min (major), tR (2) = 56.39 min
(minor).
(S)-Ethyl 5-Isopropyl-2-oxo-1-tosylpyrrolidine-3-carboxylate
(3e).13a. The general method described above was followed when
(S)-1e (100 mg, 0.418 mmol) was reacted with enolate from
diethyl malonate [diethyl malonate (0.19 mL, 1.25 mmol), NaH
(50.0 mg, 1.25 mmol)] in the presence of 20 mol % of Cu(OTf)2
(30.0 mg, 0.084 mmol) at 60 °C for 2 h to afford 3e (108.0 mg,
0.306 mmol) as a colorless thick liquid as an inseparable
diastereomeric mixture (4:1) in 73% yield: Rf 0.37 (20% ethyl
acetate in petroleum ether); IR νmax (neat, cm-1) 2964, 1729,
1596, 1393, 1169, 1138, 1089, 815, 665, 559; 1H NMR (500 MHz,
CDCl3) δ 0.69 (d, J = 6.9 Hz, 3H), 1.22 (t, J = 7.2 Hz, 3H),
2.08-2.13 (m, 1H), 2.42 (s, 3H), 2.46-2.55 (m, 2H), 3.47 (dd,
J = 11.0, 9.3 Hz, 1H), 4.15 (q, J = 7.2 Hz, 2H), 4.38-4.41 (m,
1H), 7.31(d, J = 8.3 Hz, 2H), 7.93 (d, J = 8.3 Hz, 2H); 13C
NMR (125 MHz, CDCl3) δ 14.1, 15.1, 19.0, 21.8, 22.8, 31.2,
49.2, 62.2, 63.3, 128.6, 129.6, 135.3, 145.3, 168.2, 169.0; HRMS
(ESI) for C17H23NO5S (M þ H)þ found 354.1371, calcd
354.1375.
(3R, 4S)-Ethyl 1-(4-tert-Butylphenylsulfonyl)-2-oxo-4-phenyl-
pyrrolidine-3-carboxylate (3c). The general method described
above was followed when (R)-1c (100 mg, 0.317 mmol) was
reacted with enolate from diethyl malonate [diethyl malonate
(0.14 mL, 0.95 mmol), NaH (38 mg, 0.95 mmol)] in the presence
of 20 mol % of Cu(OTf)2 (23.0 mg, 0.063 mmol) at 60 °C for 1 h
to afford 3c (125 mg, 0.291 mmol) as a white solid in 92% yield:
mp 129-131 °C; Rf 0.36 (20% ethyl acetate in petroleum ether);
[R]25 = þ26.4 (c 0.42, CHCl3); IR νmax (KBr, cm-1) 2965,
D
2925, 1753, 1726, 1461, 1366, 1337, 1278, 1203, 1177, 1126, 1086,
1016, 841, 763, 704, 629, 581, 548; 1H NMR (400 MHz, CDCl3)
δ 1.14 (t, J = 7.2 Hz, 3H), 1.29 (s, 9H), 3.56 (d, J = 10.0 Hz, 1H),
3.73 (dd, J = 9.5, 9.3, 1H), 3.92 (q, J = 8.5 Hz, 1H), 4.02-4.17
(m, 2H), 4.30 (dd, J = 9.9, 8.1 Hz, 1H), 7.10-7.29 (m, 5H),
7.48-7.51 (m, 2H), 7.89-7.92 (m, 2H); 13C NMR (100 MHz,
CDCl3) δ 14.0, 31.0, 35.3, 41.0, 51.6, 56.4, 62.2, 126.3, 126.8,
128.0, 129.2, 134.5, 137.8, 150.2, 158.4, 167.0, 167.3; HRMS
(ESI) for C23H27NO5S (M þ H)þ found 430.1684, calcd
430.1688; er >99:1. The enantiomeric ratio was determined
by chiral HPLC analysis (Chiralpak AD-H column), hexane-2-
propanol 90:10, flow rate = 1.0 mL/min; tR (1) = 20.18 min
(minor), tR (2) = 28.97 min (major).
(3S,4R,5S)-Ethyl 5-Ethyl-2-oxo-4-phenyl-1-tosylpyrrolidine-
3-carboxylate (3f). The general method described above was
followed when (S,S)-1f (100 mg, 0.33 mmol) was reacted with
enolate from diethyl malonate [diethyl malonate (0.15 mL, 0.99
mmol), NaH (40.0 mg, 0.99 mmol)] in the presence of 20 mol %
of Cu(OTf)2 (23.8 mg, 0.066 mmol) at 60 °C for 12 h to afford 3f
(126 mg, 0.30 mmol) as a colorless thick liquid in 92% yield: Rf
0.42 (20% ethyl acetate in petroleum ether); [R]25D = -31.8 (c
0.38, CHCl3); IR νmax (neat, cm-1) 2978, 2934, 1748, 1729, 1362,
(3S,4R)-Ethyl 1-(4-tert-Butylphenylsulfonyl)-2-oxo-4-phenyl-
pyrrolidine-3-carboxylate (3d). The general method described
above was followed when (S)-1d (100 mg, 0.317 mmol) was
reacted with enolate from diethyl malonate [diethyl malonate
(0.14 mL, 0.95 mmol), NaH (38 mg, 0.95 mmol)] in the presence
of 20 mol % of Cu(OTf)2 (23.0 mg, 0.063 mmol) at 60 °C for 1 h
to afford 3d (128 mg, 0.298 mmol) in 94% yield: [R]25D = -24.8
(c 0.32, CHCl3); er >99:1. The enantiomeric ratio was deter-
mined by chiral HPLC analysis (Chiralpak AD-H column),
hexane-2-propanol 90:10, flow rate =1.0 mL/min; tR (1) =
18.78 min (major), tR (2) = 29.09 min (minor).
(3S,4S)-3-Acetyl-1-(4-tert-butylphenylsulfonyl)-4-phenylpyr-
rolidin-2-one (4c). The general method described above was
followed when (R)-1c (100 mg, 0.317 mmol) was reacted with
enolate from ethyl acetoacetate [ethyl acetoacetate (0.12 mL,
0.95 mmol), NaH (38.0 mg, 0.95 mmol)] in the presence of 20
mol % of Cu(OTf)2 (23.0 mg, 0.063 mmol) at 60 °C for 9 h to
afford 4c (116 mg, 0.290 mmol) as a white solid in 91% yield: mp
149-152 °C; Rf 0.37 (20% ethyl acetate in petroleum ether);
[R]25D = -2.3 (c 0.33, CHCl3); IR νmax (KBr, cm-1) 3443, 2966,
1737, 1712, 1594, 1402, 1364, 1210, 1179, 1127, 1086, 958, 837,
766, 703, 627, 585, 551; 1H NMR (400 MHz, CDCl3) δ 1.33 (s,
9H), 2.29 (s, 3H) 3.72 (d, J = 8.6 Hz, 1H), 3.79 (t, J = 8.9 Hz,
1H), 3.99-4.04 (m, 1H), 4.15-4.28 (m, 1H), 7.06-7.10 (m, 2H),
7.22-7.26 (m, 3H), 7.51-7.55 (m, 2H), 7.92 (d, J = 8.3 Hz, 2H);
13C NMR (100 MHz, CDCl3) (mixture of keto and enol forms) δ
19.1, 30.4, 31.0, 35.3, 35.4, 38.2, 38.8, 51.6, 54.0, 63.5, 103.4, 126.2,
126.3, 126.9, 127.0, 127.7, 127.8, 128.0, 129.0, 129.1, 134.5, 135.0,
139.1, 142.8, 158.0, 167.7, 171.4, 171.6, 199.9; HRMS (ESI) for
C22H25NO4S (M þ H)þ found 400.1581, calcd 400.1583; er >99:1.
The enantiomeric ratio was determined by chiral HPLC analysis
1
1172, 1059, 815, 702, 670, 542, 503, 466; H NMR (500 MHz,
CDCl3) δ 0.46 (t, J = 7.6 Hz, 3H), 1.12 (t, J = 7.2 Hz, 3H),
1.39-1.44 (m, 1H), 1.60-1.66 (m, 1H), 2.38 (s, 3H), 3.97 (d, J =
13.4 Hz, 1H), 4.06 (q, J = 7.0 Hz, 2H), 4.18 (dd J = 13.4, 7.9 Hz,
1H), 4.60-4.64 (m, 1H), 7.13 (d, J = 7.6 Hz, 2H), 7.22 -7.31 (m,
5H), 7.91 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ
14.0, 23.8, 29.7, 46.4, 51.6, 62.1, 63.2, 127.4, 127.9, 128.5, 129.0,
129.6, 134.4, 135.3, 145.4, 167.3, 168.0; HRMS (ESI) for
C22H25NO5S (M þ H)þ found 416.1531, calcd 416.1532.
(3S,4R,5S)-Ethyl
2-Oxo-4-phenyl-5-propyl-1-tosylpyrroli-
dine-3-carboxylate (3g). The general method described above
was followed when (S,S)-1g (100 mg, 0.317 mmol) was reacted
with enolate from diethyl malonate [diethyl malonate (0.14 mL,
0.95 mmol), NaH (38.0 mg, 0.95 mmol)] in the presence of 20
mol % of Cu(OTf)2 (23.0 mg, 0.063 mmol) at 60 °C for 26 h to
afford 3g (85.0 mg, 0.198 mmol) as a white solid in 62% yield: Rf
0.41 (20% ethyl acetate in petroleum ether); [R]25D = -25.0 (c
0.40, CHCl3); IR νmax (KBr, cm-1) 2962, 2874, 1748, 1730, 1597,
1454, 1362, 1171, 1120, 1087, 1030, 814, 763,702, 665, 584, 556;
1H NMR (500 MHz, CDCl3) δ 0.62 (t, J = 7.3 Hz, 3H),
0.69-0.75 (m, 1H), 0.99-1.06 (m, 1H), 1.18 (t, J = 7.1 Hz,
3H), 1.37-1.44 (m, 1H), 1.51-1.56 (m, 1H), 2.44 (s, 3H), 4.02 (d,
J = 13.3 Hz, 1H), 4.12 (q, J = 7.4 Hz, 2H), 4.22 (dd, J = 13.3,
7.8 Hz, 1H), 4.66-4.70 (m, 1H), 7.18 (d, J = 7.4 Hz, 2H),
7.28-7.37 (m, 5H), 7.96 (d, J = 8.3 Hz, 2H); 13C NMR (100
MHz, CDCl3) δ 13.9, 14.0, 18.4, 21.7, 33.1, 46.6, 51.6, 62.1, 62.2,
127.5, 127.9, 128.5, 129.0, 129.6, 134.4, 135.4, 145.4, 167.2,
J. Org. Chem. Vol. 75, No. 18, 2010 6179

Ghorai and Tiwari
JOCArticle
168.0; HRMS (ESI) for C23H27NO5S (M þ H)þ found 430.1685,
NMR (400 MHz, CDCl3) δ 0.53 (t, J = 7.4 Hz, 3H), 1.48-1.54
(m, 1H), 1.63-1.71 (m, 1H), 2.33 (s, 3H), 2.43 (s, 3H), 4.13 (d,
J = 12.9 Hz, 1H), 4.20 (dd, J = 12.6, 8.0 Hz, 1H), 4.58-4.63 (m,
1H), 7.11 (d, J = 7.1 Hz, 2H), 7.26-7.34 (m, 5H), 7.93 (d, J =
8.6 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 9.6, 21.7, 24.2, 30.8,
44.1, 57.6, 62.9, 127.0, 127.8, 128.4, 128.9, 129.6, 134.8, 135.3,
145.4, 168.4, 200.3; HRMS (ESI) for C21H23NO4S (M þ H)þ
found 386.1428, calcd 386.1426.
calcd 430.1688.
(3S,4R,5S)-Ethyl 2-Oxo-4-phenyl-1-tosyl-5-vinylpyrrolidine-
3-carboxylate (3h). The general method described above was
followed when (S,S)-1h (100 mg, 0.334 mmol) was reacted with
enolate from diethyl malonate [diethyl malonate (0.15 mL, 1.00
mmol), NaH (40.0 mg, 1.00 mmol)] in the presence of 20 mol %
of Cu(OTf)2 (24.1 mg, 0.067 mmol) at 60 °C for 8.5 h to afford 3h
(80 mg, 0.193 mmol) as a colorless thick liquid in 58% yield
along with 6 (38 mg, 0.083 mmol) as a colorless thick liquid in
25% yield. Data for 3h: Rf 0.43 (20% ethyl acetate in petroleum
(3S,4R,5S)-Ethyl-5-((tert-butyldimethylsilyloxy)methyl)-2-oxo-
4-phenyl-1-tosylpyrrolidine-3-carboxylate (3j). The general met-
hod described above was followed when (S,S)-1j (100 mg, 0.239
mmol) was reacted with enolate from diethyl malonate [diethyl
malonate (0.11 mL, 0.718 mmol), NaH (29.0 mg, 0.718 mmol)]
in the presence of 20 mol % of Cu(OTf)2 (17.0 mg, 0.048 mmol)
at 60 °C for 24 h to afford 3i (100.0 mg, 0.188 mmol) as a white
solid in 79% yield: mp 75-78 °C; Rf 0.33 (10% ethyl acetate in
petroleum ether); [R]25D = -36.6 (c 0.80, CHCl3); IR νmax (KBr,
cm-1) 2962, 2928, 1757, 1598, 1471, 1358, 1282, 1260, 1172,
1142, 1121, 1087, 1034, 976, 948, 833, 814, 775, 761, 670, 655,
663, 573, 543, 518; 1H NMR (400 MHz, CDCl3) δ 0.80 (s, 6H),
1.15 (t, J = 7.3 Hz, 3H), 2.38 (s, 3H), 3.45 (d, J = 6.4 Hz, 1H),
3.82 (d, J = 10.3 Hz, 1H), 3.93-4.01 (m, 2H), 4.07-4.15 (m,
3H), 6.92-6.94 (m, 2H), 7.16-7.18 (m, 3H), 7.24 (d, J = 8.0 Hz,
2H), 7.85 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ
-5.5, 0.9, 13.9, 18.2, 21.7, 25.8, 42.2, 56.3, 62.2, 62.6, 67.1, 126.9,
127.7, 128.4, 129.2, 129.6, 135.2, 141.1, 145.4, 167.1, 168.4;
HRMS (ESI) for C27H37NO6SSi (M þ H)þ found 532.2186,
calcd 532.2189.
Procedure for the Synthesis of (3R,4S)-Ethyl 2-Oxo-4-phenyl-
pyrrolidine-3-carboxylate (7)24,26. Na (30 mg, 1.29 mmol) in dry
THF (1.0 mL) was treated with naphthalene (207 mg, 1.61
mmol) in dry THF (1.0 mL) and stirred at room temperature
for 2 h. Compound 3a (100 mg, 0.258 mmol), dissolved in dry
THF (1.0 mL), was treated with the above-mentioned solution
of sodium naphthalide at -78 °C, and the reaction mixture was
stirred at this temperature for 1 h. After completion of the
reaction (monitored by TLC), the reaction was quenched with
an aqueous saturated solution of NH4Cl. The organic layer was
separated. The aqueous layer was extracted with ethyl acetate
(3 ꢀ 2.0 mL), the combined organic layer was dried over anhy-
drous Na2SO4, and the solvent was removed under reduced
pressure. After column chromatographic purification on silica
gel (230-400 mesh) using ethyl acetate in petroleum ether as the
eluent, pyrrolidinone 3-carboxylate 7 (40.5 mg, 0.174 mmol) was
obtained as a white solid in 67% yield: mp 53-55 °C; Rf 0.32
(40% ethyl acetate in petroleum ether); [R]25D = þ45.3 (c 0.29,
CHCl3); IR νmax (KBr, cm-1) 3253, 2982, 2926, 1708, 1492,
1451, 1371, 1335, 1263, 1172, 1049, 1028, 760, 701, 549; 1H
NMR (400 MHz, CDCl3) δ 1.28 (t, J = 7.1 Hz, 3H), 3.44 (dd,
J = 9.3, 8.6, 1H), 3.56 (d, J = 9.5 Hz, 1H), 3.82 (dd, J = 9.5, 8.6,
1H), 4.11 (q, J = 8.6 Hz, 1H), 4.21-4.29 (m, 2H), 6.6 (brs, 1H)
7.25-7.37 (m, 5H); 13C NMR (100 MHz, CDCl3) δ 14.1, 44.3,
47.6, 55.2, 61.8, 126.9, 127.6, 128.9, 139.8, 169.2, 172.7; HRMS
(ESI) for C13H15NO3 (M þ H)þ found 234.1132, calcd 234.1130;
er >99:1. The enantiomeric ratio was determined by chiral
HPLC analysis (Chiralcel OD-H column), hexane-2-propanol
97:3, flow rate =1.0 mL/min; tR = 15.89 min.
ether); [R]25 = -9.37 (c 0.21, CHCl3); IR νmax (neat, cm-1
)
D
2924, 2853, 1750, 1730, 1597, 1455, 1369, 1310, 1172, 1115, 1089,
1020, 815, 702, 667, 573; 1H NMR (500 MHz, CDCl3) δ 1.26 (t,
J = 7.2 Hz, 3H), 2.39 (s, 3H), 3.59 (d, J = 12.4 Hz, 1H), 3.77-
3.81 (m, 1H), 4.17-4.25 (m, 2H), 4.95-4.99 (m, 2H), 5.11-5.16
(m, 1H), 5.46 (d, J = 8.2 Hz, 1H), 6.92 (d, J = 7.3 Hz, 2H),
7.15-7.29 (m, 5H), 7.56 (d, J = 8.6 Hz, 2H); 13C NMR (125
MHz, CDCl3) δ 14.2, 21.8, 46.5, 52.8, 62.2, 64.7, 119.8, 127.3,
128.6, 128.8, 128.9, 129.3, 132.8, 134.9, 135.3, 145.4, 167.0,
167.8; HRMS (ESI) for C22H23NO5S, (M þ H)þ found
414.1374, calcd 414.1375. Dr of the compound 3h could not be
determined as it was found to contain some impurity (or
diastereomer) which could not be separated after column chro-
matographic purification (see 1H NMR spectrum in Supporting
Information).
Data for (S,E)-diethyl 2-(4-(4-methylphenylsulfonamido)-4-
phenylbut-2-enyl)malonate (6): Rf 0.29 (20% ethyl acetate in
petroleum ether); [R]25D = -14.2 (c 0.12, CHCl3); IR νmax (neat,
cm-1) 3282, 2923, 1732, 1598, 1330, 1159, 1093, 1020, 814, 700,
669, 562; 1H NMR (400 MHz, CDCl3) δ 1.15 (t, J = 7.1 Hz, 6H),
2.33 (s, 3H), 2.44 (dd, J = 7.3, 6.6 Hz, 2H), 3.19 (t, J = 7.5 Hz,
1H), 4.02-4.11 (m, 4H), 4.67 (d, J = 6.8 Hz, 1H), 4.80 (dd, J =
6.6, 6.1 Hz, 1H), 5.38-5.51 (m, 2H), 6.99-7.17 (m, 7H), 7.54 (d,
J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 14.1, 21.6, 31.3,
51.5, 59.4, 61.6, 127.0, 127.3, 127.9, 128.7, 128.7, 129.5, 132.3,
137.7, 139.7, 143.4, 168.8; HRMS (ESI) for C24H29NO6S (M þ
Na)þ found 482.1613, calcd 482.1613.
(3S,4R,5S)-Ethyl 5Allyl-2-oxo-4-phenyl-1-tosylpyrrolidine-3-
carboxylate (3i). The general method described above was
followed when (S,S)-1i (100 mg, 0.319 mmol) was reacted with
enolate from diethyl malonate [diethyl malonate (0.15 mL, 0.957
mmol), NaH (38.0 mg, 0.957 mmol)] in the presence of 20 mol %
of Cu(OTf)2 (23.0 mg, 0.064 mmol) at 60 °C for 24 h to afford 3i
(99.0 mg, 0.232 mmol) as a colorless thick liquid in 73% yield: Rf
0.46 (20% ethyl acetate in petroleum ether); [R]25D = -11.1 (c
0.18, CHCl3); IR νmax (neat, cm-1) 2924, 1748, 1730, 1597, 1365,
1172, 1121, 1089, 1019, 702, 663, 555, 542; 1H NMR (400 MHz,
CDCl3) δ 1.14 (t, J = 7.2 Hz, 3H), 2.04-2.10 (m, 1H), 2.38 (s,
3H), 2.41-2.49 (m, 1H), 4.03 (d, J = 13.4 Hz, 1H), 4.09 (q, J =
7.1 Hz, 2H), 4.21 (dd, J = 13.4, 8.0 Hz, 1H), 4.60 (d, J = 17.1
Hz, 1H), 4.73-4.77 (m, 1H), 4.82 (d, J = 10.3 Hz, 1H),
5.15-5.25 (m, 1H), 7.11 (d, J = 7.3 Hz, 2H), 7.22-7.31 (m,
5H), 7.93 (d, J = 8.3 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ
13.9, 21.7, 34.7, 46.3, 51.7, 61.7, 62.1, 120.1, 127.6, 127.9, 128.6,
128.9, 129.2, 129.6, 131.5, 134.4, 145.4, 167.3, 168.0; HRMS
(ESI) for C23H25NO5S (M þ H)þ found 428.1535, calcd
428.1532.
Procedure for the Synthesis of (S)-4-Phenyl-1-tosylpyrrolidin-
2-one (8)25,27. Compound 3a (100 mg, 0.258 mmol) dissolved in
EtOH (1.0 mL) was treated with 1.0 N NaOH (0.40 mL), and the
reaction was stirred for 48 h at room temperature. The reaction
mixture was concentrated under reduced pressure, acidified with
(3S,4R,5S)-3-Acetyl-5-ethyl-4-phenyl-1-tosylpyrrolidin-2-one
(4e). The general method described above was followed when
(S,S)-1f (100 mg, 0.33 mmol) was reacted with enolate from
ethyl acetoacetate [ethyl acetoacetate (0.13 mL, 0.99 mmol),
NaH (40.0 mg, 0.99 mmol)] in the presence of 20 mol % of
Cu(OTf)2 (23.8 mg, 0.066 mmol) at 60 °C for 24 h to afford 4e
(80 mg, 0.207 mmol) as a white solid in 63% yield: mp 135-
(26) The enantiomer of compound 7 is known; see: Wang, J.; Li, W.; Liu,
Y.; Chu, Y.; Lin, L.; Liu, X.; Feng, X. Org. Lett. 2010, 12, 1280.
(27) For racemic compound 8, see: Andreeva, O. A.; Zobacheva, M. M.
Sint., Str. Khim. Prevrashch. Org. Soedin. Azota: Nitrosoedin., Aminov
Aminokislot 1991, 3.
137 °C; Rf 0.39 (20% ethyl acetate in petroleum ether); [R]25
=
D
þ22.0 (c 0.15, CHCl3); IR νmax (KBr, cm-1) 2926, 1733, 1713,
1596, 1362, 1340, 1178, 1156, 1088, 1059, 957, 814, 664, 559; 1H
6180 J. Org. Chem. Vol. 75, No. 18, 2010

Ghorai and Tiwari
JOCArticle
5% HCl, and extracted with ethyl acetate (3 ꢀ 2.0 mL), the
organic layer was dried over anhydrous Na2SO4, and solvent
was removed under reduced pressure. The crude product was
refluxed in toluene (1.0 mL) for 8 h. Solvent was removed under
reduced pressure, and after column chromatographic purifica-
tion on silica gel (230-400 mesh) using ethyl acetate in petro-
leum ether as the eluent, pyrrolidinone 8 (41 mg, 0.13 mmol) was
obtained as a white solid in 50% yield (over two steps): mp
110-112 °C; Rf 0.42 (20% ethyl acetate in petroleum ether);
(125 MHz, CDCl3) δ 21.7, 37.1, 39.5, 53.6, 126.5, 127.6, 128.1,
129.0, 129.7, 135.0, 139.8, 145.3, 172.1; HRMS (ESI) for
C17H17NO3S (M þ H)þ found 316.1008, calcd 316.1007; er
>99:1. The enantiomeric ratio was determined by chiral HPLC
analysis (Chiralcell OD-H column), hexane-2-propanol 90:10,
flow rate =1.0 mL/min; tR = 20.36 min.
Acknowledgment. M.K.G. is grateful to DST, India, for
financial support. D.P.T. thanks UGC India for a research
fellowship.
[R]25 = þ4.88 (c 0.20, CHCl3); IR νmax (KBr, cm-1) 2922,
D
1739, 1336, 1163, 1132, 1087, 959, 819,764, 741, 702, 666, 613,
563, 543; 1H NMR (400 MHz, CDCl3) δ 2.46 (s, 3H), 2.62 (dd,
J = 17.3, 9.3 Hz, 1H), 2.85 (dd, J = 17.5, 8.4 Hz, 1H), 3.56-3.65
(m, 1H), 3.79 (dd, J = 9.9, 7.9 Hz, 1H), 4.33 (dd, J = 10.0, 7.8
Hz, 1H), 7.09-7.36 (m, 7H), 7.94 (d, J = 8.1 Hz, 2H); 13C NMR
Supporting Information Available: X-ray crystallographic
data of 4a, copies of 1H and 13C spectra for all compounds, and
HPLC chromatograms for er determination. This material is
available free of charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 18, 2010 6181