Synthesis of 4-substituted- and 1,4-disubstituted-4-hydroxypyrrolidin-2- ones

Article abstract of DOI:10.1080/00397910701319023

This report describes the synthesis of 4-substituted- and 1,4-disubstituted-4-hydroxypyrrolidin-2-ones by cyclization of intermediate γ-aminoesters prepared from alkylbenzylamines, α-bromoketones, and lithio ethyl acetate. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701319023

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Synthesis of 4‐Substituted‐ and
1,4‐Disubstituted‐4‐Hydroxypyrrolidin‐2‐ones
Christopher R. Kinsinger a , Chad D. Tatko a , Christopher M. Whelan a &
Timothy J. Wilkinson a
a Department of Chemistry , Wheaton College , Wheaton, Illinois, USA
Published online: 30 Jun 2007.
To cite this article: Christopher R. Kinsinger , Chad D. Tatko , Christopher M. Whelan & Timothy J.
Wilkinson (2007) Synthesis of 4‐Substituted‐ and 1,4‐Disubstituted‐4‐Hydroxypyrrolidin‐2‐ones, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:11,
1845-1852, DOI: 10.1080/00397910701319023
To link to this article: http://dx.doi.org/10.1080/00397910701319023
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Synthetic Communicationsw, 37: 1845–1852, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701319023
Synthesis of 4-Substituted- and 1,4-
Disubstituted-4-Hydroxypyrrolidin-2-ones
Christopher R. Kinsinger, Chad D. Tatko,
Christopher M. Whelan, and Timothy J. Wilkinson
Department of Chemistry, Wheaton College, Wheaton, Illinois, USA
Abstract: This report describes the synthesis of 4-substituted- and 1,4-disubstituted-
4-hydroxypyrrolidin-2-ones by cyclization of intermediate g-aminoesters prepared
from alkylbenzylamines, a-bromoketones, and lithio ethyl acetate.
Keywords: cyclization, g-lactams, pyrrolidin-2-ones
INTRODUCTION
4-Hydroxypyrrolidin-2-ones have been prepared by the photolysis of b-
oxo-amides[1] and have been converted to pyrroles[2] by hydride reduction.
As a class, 4-hydroxypyrrolidin-2-ones have the potential to be converted to
physiologically active pyrrolidin-2-ones and g-amino butyric acids (GABA
analogues).[3] We report the synthesis of several 4-hydroxypyrrolidin-2-ones
(5) from a-bromoketones (1) and alkylbenzylamines (2) as shown Scheme 1.
RESULTS AND DISCUSSION
a-Bromoketones (1) reacted with benzylamines (2; R2 ¼ Bn or alkyl),
prepared by reductive amination, to afford aminoketones (3) following
standard procedures. The lithium enolate of EtOAc, prepared from EtOAc
and LDA, was then reacted with 3 to form aminoalcohols (4) in near quanti-
tative yields (Table 1). The aminoalcohols (4) were debenzylated with H2 (5%
Received in the USA May 4, 2006
Address correspondence to Timothy J. Wilkinson, Department of Chemistry,
Wheaton College, Wheaton, IL, 60187, USA. E-mail: timothy.j.wilkinson@wheaton.edu
1845

1846
C. R. Kinsinger et al.
Scheme 1.
Pd/C, with or without HCl) to yield intermediate primary or secondary
amines, which reacted intramolecularly to afford the 4-hydroxypyrrolidin-2-
ones (5) shown in Table 1. The hydrogenolysis rates for the first benzyl
group of 4 (R2 ¼ Bn) were faster than that of the second,[4] which was
exploited in the synthesis of N-benzyl products 5b, 5e, 5l, and 5m. Hydroge-
nolysis of the second benzyl group in 4l and 4m was too slow under these con-
ditions, resulting in 5l and 5m as the sole products. Hydrogenolysis of 4c, 4f,
4g, and 4h was done without HCl, which simplified the procedure. Interest-
ingly, hydrogenolysis of 4i showed selectivity in cleaving only the benzyl
group, resulting in 5i. Attempts to prepare 5 (R1 ¼ 4-BrPh and 4-ClPh;
R3 ¼ H) resulted in cleavage of halogen during the hydrogenolysis,
affording 5d. Attempts to prepare 5 (R1 ¼ R3 ¼ Ph) were unsuccessful
because of reduction of the N-Ph group during hydrogenolysis. All 4-hydro-
xypyrrolodin-2-ones were solids, except 1c, and were purified by recrystalli-
1
zation or flash chromatography. The H NMR spectra of these compounds
showed characteristic AB quartets for the diastereotopic protons on C-3 and
C-5. In summary, a number of 4-hydroxypyrrolidin-2-ones have been
prepared from alkylbenzylamines and a-bromoketones as shown in Scheme 1.
EXPERIMENTAL
1H NMR (300 MHz) and 13C NMR (75 MHz) were recorded on a GE-QE 300
NMR instrument. Diisopropylamine was distilled from calcium hydride. THF
was distilled from sodium and benzophenone under argon prior to use. All
hydrogenations were carried out at room temperature and atmospheric
pressure in a closed system by which hydrogen uptake was monitored.
Unless otherwise specified, all compounds were obtained commercially and
were used without further purification. Column chromatography was
˚
performed on silica gel (60 A, 32–63 mm, Sorbent Technologies). Melting
points were done on a Meltemp apparatus and are uncorrected. IR were

Table 1. Synthesis of 5-hydroxypyrrolidin-2-ones 5
Experimental Hydrogeno-
method
Cyclization
time (h)
Compound
R1
R2
R3
Yield 4 (%)
lysis time (h)
Yield 5 (%)
a
b
c
d
e
f
Me
Me
Me
Ph
Ph
Ph
Ph
Ph
Ph
Bn
Bn
Me
Bn
Bn
Me
i-Pr
H
98
—
95
93a
—
95
96
96
98
D
B
C
A
B
C
C
C
B
24
1
3
90
83
87
77
91
87
75
85
86
Bn
Me
H
1
2
0.5
3
24
0.5
6
Bn
Me
i-Pr
1
c
g
h
i
5
1.5
1
CH2CH(OMe)2
CH2CH(OMe)2
24
1.5
1
j
4-MePh
H
H
94b
98
A
A
B
B
B
4
24
4
2
3
1
1
2
79
76
85
92
85
k
l
4-MeOPh
2-Naphthyl
4-Ph-Ph
H
H
Bn
Bn
i-Pr
Bn
Bn
i-Pr
98
92
m
n
2
4-Ph-Ph
97
4
aMp 80–828C.
bMp 98–998C.
cCyclized during hydrogenolysis.

1848
C. R. Kinsinger et al.
recorded on a Perkin-Elmer Spectrum 100 FTIR. Mass spectra were recorded
on an Agilent Technologies 6890 GCMS.
a-Bromoketones 1j,[5] 1k,[6] 1l,[7] and 1m[5] were prepared following lit-
erature procedures. Compounds 2h and 2i were prepared from benzaldehyde
and aminoacetaldehyde dimethyl acetal or piperonal by reductive amination[4]
using 5% Pd/C. Compounds 3d, 3f, 3g, 3j, 3k, 3l, 3m, and 3n[8] and
compounds 3a (from chloroacetone), 3h, and 3i[9] were prepared by pro-
cedures similar to those reported in the literature. Compound 3c was
prepared by stirring 2 equivalents of dibenzylamine with chloroacetone in
acetonitrile[10] and was purified by flash chromatography. All compounds
1
gave satisfactory IR, H NMR, and 13C NMR spectra.
General Procedure for the Synthesis of 4
A solution of anhydrous EtOAc (0.933 mL) in 8.0 mL of tetrahydrofuran
(THF) was added dropwise to a stirred solution of lithium diisopropylamide
(LDA) (prepared from 1.34 mL diisopropylamine and 6.0 mL butyllithium
[1.6 M in hexanes]) in 16 mL THF) at 2788C under an argon atmosphere.
A solution 3 (8.00 mmol) in 16–20 mL of THF was added dropwise, and
the solution was stirred an additional 15 min. After reaching room tempera-
ture, the solution was quenched with 3 mL of saturated NH4Cl, washed with
brine (3 ꢀ 7 mL), and dried (Na2SO4). Rotary evaporation afforded 4. Solid
products (4d and 4j) were recrystallized from 95% EtOH. All other
products were oils and were used in the next reaction after removing
1
residual solvent (608C/0.3 Torr). Aminoalcohols (4) gave IR, H NMR, and
13C NMR spectra consistent with their structures.
General Procedure for Synthesis of 5
Method A
A solution of 4 (3.72 mmol) in 18–30 mL of absolute EtOH containing con-
centrated HCl (0.375 mL) and 5% Pd/C (0.375 g) was hydrogenated for the
times shown in Table 1 while monitoring hydrogen uptake. The mixture
was filtered and evaporated. The resulting hydrochloride was dissolved in
5 mL of water, and concentrated aqueous ammonia (0.60 mL) was added.
The solution was allowed to stand at room temperature for the time shown
in Table 1. The solid was filtered and recrystallized from 95% ethanol.
Method B
Procedure is the same as method A, but 0.190 g of 5% Pd/C was used. After
evaporation of EtOH, water (23 mL), concentrated aqueous ammonia

Synthesis of 4-Hydroxypyrrolidin-2-ones
1849
(0.60 mL), and EtOAc (50 mL) were added to the hydrochloride. After
thorough mixing, the layers were separated, and the aqueous layer was
extracted with 5 mL of EtOAc. The combined organic extracts were washed
with brine, dried (Na2SO4), and evaporated. The resulting oil was heated on
a steam bath for the time shown in Table 1. The residue was dissolved in
9 mL of MeOH, and 1.80 g of silica gel were added. Evaporation gave a
powder that was applied to a silica-gel column and eluted with EtOAc or
EtOAc/MeOH to afford the product.
Method C
Procedure is the same as method A without HCl, and 5% Pd/C (0.190 g) was
used. After evaporation of EtOH, the residue was heated on a steam bath
(except for 5f) for the time shown in Table 1; and the product was purified
by flash chromatography.
Method D
Procedure is the same as method A, but after the cyclization reaction, the
water was evaporated, and the residue was purified by flash chromatography.
Compounds 5a–n were identified by spectral methods and their charac-
teristics are summarized next.
Data
1
5a: mp 138–1398C (lit.[11] 1408C); IR: 3149, 1662; H NMR d 1.27 (s, 3H),
2.06 (d, 1H, J ¼ 16.4 Hz), 2.10 (d, 1H, J ¼ 16.4 Hz), 3.07 (d, 1H,
J ¼ 9.9 Hz), 3.13 (d, 1H, J ¼ 9.9 Hz), 4.96 (s, 1H), 7.48 (br s, 1H); 13C NMR
(DMSO-d6) d 27.0, 45.9, 55.5, 72.9, 175.4; MS m/z: 115 (Mþ). Anal. calcd.
for C5H9NO2: C, 52.16; H, 7.88; N, 12.17. Found: C, 50.76; H, 7.70; N, 11.80.
5b: mp 139–1408C (lit.[1b] 134–134.58C); IR: 3318, 1658; 1H NMR (CDCl3)
d 1.41 (s, 3H), 2.51 (d, 1H, J ¼ 17.0 Hz), 2.58 (d, 1H, J ¼ 17.0 Hz), 2.67
(s, 1H), 3.21 (d, 1H, J ¼ 10.5 Hz), 3.25 (d, 1H, J ¼ 10.5 Hz), 4.42 (d, 1H,
J ¼ 14.9 Hz), 4.52 (d, 1H, J ¼ 14.9 Hz), 7.2–7.37 (m, 5H); 13C NMR
(DMSO-d6) d 26.8, 45.1, 46.2, 60.0, 70.1, 127.1, 127.5, 128.5, 136.9,
172.4; MS m/z: 205 (Mþ). Anal. calcd. for C12H15NO2: C, 70.22; H, 7.37;
N, 6.82. Found: C, 69.26; H, 7.21; N, 6.73.
5c: oil; IR: 3329, 1659; 1H NMR (CDCl3) d 1.43 (s, 3H), 2.41(d, 1H,
J ¼ 17.0 Hz) 2.49 (d, 1H, J ¼ 17.0 Hz), 3.45 (d, 1H, J ¼ 10.4 Hz), 3.73
(d, 1H, J ¼ 10.4 Hz), 4.9 (s, 1H); 13C NMR (CDCl3) d 26.9, 29.4, 46.5,
63.3, 70.6, 173.3; MS m/z: 129 (Mþ). Anal. calcd. for C6H11NO2: C, 55.80;
H, 8.58; N, 10.84. Found: C, 49.01; H, 8.08; N, 9.55.

1850
C. R. Kinsinger et al.
1
5d: mp 196–1978C; IR: 3190, 1672; H NMR (DMSO-d6) d 2.32 (d, 1H,
J ¼ 16.3 Hz), 2.72 (d, 1H, J ¼ 16.3 Hz), 3.35 (d, 1H, J ¼ 10.3 Hz), 3.51 (d, 1H,
J ¼ 10.3 Hz), 7.2–7.5 (m, 5H), 7.74 (s, 1H); 13C NMR (DMSO-d6) d 45.5,
56.3, 76.8, 125.3, 126.8, 128.0, 145.2, 174.8; MS m/z: 177 (Mþ). Anal. calcd.
for C10H11NO2: C, 67.78; H, 6.26; N, 7.90. Found: C, 66.76; H, 6.01; N, 7.82.
5e: mp 121–1228C (lit[1b] 118–1198C); IR: 3258, 1655; 1H NMR (CDCl3) d
2.79 (d, 1H, J ¼ 17.0 Hz); 3.01 (d, 1H, J ¼ 17.0 Hz), 3.46 (s, 1H), 3.50 (d, 1H,
J ¼ 10.7 Hz), 3.58 (d, 1H, J ¼ 10.7 Hz), 4.42 (d, 1H, J ¼ 14.8 Hz), 4.55
(d, 1H, J ¼ 14.8 Hz), 7.2–7.4 (m, 10H); 13C NMR (DMSO-d6) d 45.2,
46.7, 60.9, 74.1, 125.3, 127.0, 127.1, 127.5, 128.1, 128.5, 136.9, 144.8,
171.9; MS m/z: 267 (Mþ). Anal. calcd. for C17H17NO2: C, 76.38; H, 6.41;
N, 5.24. Found: C, 75.72; H, 6.26; N, 5.29.
5f: mp 147–1488C (lit.[1a] 139–1408C); IR: 3244, 1659; 1H NMR (CDCl3) d
2.71 (d, 1H, J ¼ 17.0 Hz), 2.95 (d, 1H, J ¼ 17.0 Hz), 2.91 (s, 3H), 3.60 (d, 1H,
J ¼ 10.7 Hz), 3.74 (d, 1H, J ¼ 10.7 Hz), 3.86 (s, 1H), 7.26–7.48 (m, 5H); 13
C
NMR (DMSO-d6) d 28.9, 47.1, 63.3, 73.9, 125.3, 126.9, 128.0, 145.0, 171.5;
MS m/z: 191 (Mþ). Anal. calcd. for C11H13NO2: C, 69.09; H, 6.85; N, 7.32.
Found: C, 68.35; H, 6.73; N, 7.23.
5g: mp 124–1258C; IR: 3260, 1655; 1H NMR (CDCl3) d 1.12 (d, 3H,
J ¼ 6.8 Hz), 1.19 (d, 3H, J ¼ 6.8 Hz), 2.72 (d, 1H, J ¼ 17.0 Hz), 3.01
(d, 1H, J ¼ 17.0 Hz), 3.22 (s, 1H), 3.58 (d, 1H, J ¼ 11.2 Hz), 3.62 (d, 1H,
J ¼ 11.2 Hz), 4.46 (septet, 1 H, J ¼ 6.8 Hz), 7.24–7.51 (m, 5H); 13C NMR
(DMSO-d6) d 19.53, 19.57, 47.4, 56.1, 73.9, 125.3, 126.9, 128.0, 145.1,
170.8; MS m/z: 219 (Mþ). Anal. calcd. for C13H17NO2: C, 71.21; H, 7.81;
N, 6.39. Found: C, 70.43; H, 7.64; N, 6.40.
5h: mp 100–1018C; IR: 3249, 1660; 1H NMR (CDCl3) d 2.73 (d, 1H,
17.0 Hz), 2.90 (s, 1H), 2.99 (d, 1H, 17.0 Hz), 3.37 (s, 3H), 3.40 (s, 3H),
3.45 (dd, 1H, J ¼ 14.2 Hz, J ¼ 5.3 Hz), 3.54 (dd, 1H, J ¼ 14.2 Hz,
J ¼ 5.3 Hz), 3.72 (d, 1H, J ¼ 10.8 Hz), 3.87 (d, 1H, J ¼ 10.8 Hz), 4.51
(t, 1H, J ¼ 5.3 Hz), 7.28–7.49 (m, 5H); 13C NMR (CDCl3) d 44.3, 46.9,
54.2, 54.3 63.2, 75.3, 102.3, 125.1, 127.7, 128.60, 128.63, 143.6, 173.2; MS
no molecular ion observed. Anal. calcd. for C14H19NO4: C, 63.38; H, 7.22;
N, 5.28. Found: C, 62.79; H, 7.15; N, 5.33.
1
5i: mp 137–1388C; IR: 3326, 1658; H NMR (CDCl3) d 2.54 (s, 1H), 2.79
(d, 1H, J ¼ 17.0 Hz), 3.05 (d, 1H, J ¼ 17.0 Hz), 3.50 (d, 1H, J ¼ 10.8 Hz),
3.62 (d, 1H, J ¼ 10.8 Hz), 5.94 (s, 2H), 6.68–6.8 (m, 3H), 7.24–7.45
(m, 5H); 13C NMR (DMSO-d6) d 44.9, 46.7, 60.7, 74.1, 100.9, 108.0,
108.2, 120.9, 125.3, 127.0, 128.0, 130.6, 144.8, 146.4, 147.4, 171.8; MS no
molecular ion observed. Anal. calcd. for C18H17NO4: C, 69.44; H, 5.50; N,
4.50. Found: C, 68.48; H, 5.38; N, 4.52.

Synthesis of 4-Hydroxypyrrolidin-2-ones
1851
1
5j: mp 192–1938C; IR: 3235, 1658; H NMR (DMSO-d6) d 2.29 (d, 1H,
J ¼ 16.4 Hz), 2.28 (s, 3H), 2.68 (d, 1H, J ¼ 16.4 Hz), 3.33 (d, 1H,
J ¼ 10.2 Hz), 3.47 (d, 1H, J ¼ 10.2 Hz), 5.55 (s, 1H), 7.15 (d, 2H,
J ¼ 8.2 Hz), 7.38 (d, 2H, J ¼ 8.2 Hz), 7.72 (s, 1H); 13C NMR (DMSO-d6)
d 20.6, 46.5, 56.4, 76.7, 125.2, 128.6, 135.9, 142.3, 175.0; MS m/z: 191
(Mþ). Anal. calcd. for C11H13NO2: C, 69.09; H, 6.85; N, 7.32. Found: C,
67.97; H, 6.63; N, 7.27.
1
5k: mp 162–1638C; IR: 3195, 1679; H NMR (DMSO-d6) d 2.28 (d, 1H,
J ¼ 16.4 Hz), 2.68 (d, 1H, J ¼ 16.4 Hz), 3.33 (d, 1H, J ¼ 10.3 Hz), 3.74
(s, 3H), 5.53 (s, 1H), 6.89 (d, 2H, J ¼ 8.9 Hz), 7.41 (d, 2H, J ¼ 8.9 Hz),
7.71 (s, 1H); 13C NMR (DMSO-d6) d 46.5, 76.5, 113.4, 126.5, 137.2, 158.2,
175.0; MS m/z: 207 (Mþ). Anal. calcd. for C11H13NO3: C, 63.76; H, 6.32;
N, 6.76. Found: C, 63.01; H, 6.18; N, 6.69.
1
5l: mp 160–1618C; IR: 3240, 1647; H NMR (CDCl3) d 2.75 (s, 1H), 2.88
(d, 1H, J ¼ 17.0 Hz), 3.16 (d, 1H, 17.0 Hz), 3.57 (d, 1H, J ¼ 10.7 Hz), 3.72
(d, 1H, J ¼ 10.7 Hz), 4.54 (d, 1H, 14.8 Hz), 4.61 (d, 1H, J ¼ 14.8 Hz),
7.2–7.8 (m, 12H); 13C NMR (DMSO-d6) d 45.2, 46.6, 60.6, 74.2, 123.6,
124.1, 125.9, 126.2, 127.1, 127.4, 127.5, 127.8, 127.9, 128.5, 132.0, 132.5,
136.9, 142.2, 171.9; MS m/z: 317 (Mþ). Anal. calcd. for C21H19NO2: C,
79.47; H, 6.03; N, 4.41. Found: 78.35; H, 5.87; N, 4.45.
1
5m: mp 141–1428C; IR: 3246, 1655; H NMR (CDCl3) d 2.83 (s, 1H), 2.84
(d, 1H, J ¼ 17.0 Hz), 3.09 (d, 1H, J ¼ 17.0 Hz), 3.54 (d, 1H, J ¼ 10.8 Hz),
3.65 (d, 1H, J ¼ 10.8 Hz), 4.54 (d, 1H, J ¼ 15.9 Hz), 7.2–7.6 (m, 14H); 13
C
NMR (DMSO-d6) d 45.2, 46.8, 60.8, 74.0, 125.9, 126.4, 126.5, 126.6, 127.2,
127.4, 127.5, 128.5, 128.9, 136.9, 138.9, 139.8, 144.0, 171.9; MS m/z: 343
(Mþ). Anal. calcd. for C23H21NO2: C, 80.44; H, 6.16; N, 4.08. Found: C,
79.02; H, 5.96; N, 4.14.
5n: mp 174–1758C; IR: 3259, 1638; 1H NMR (CDCl3) d 1.14 (d, 1H,
J ¼ 6.8 Hz), 1.20 (d, J ¼ 6.8 Hz), 2.76 (d, 1H, J ¼ 17.0 Hz), 3.32 (s, 1H),
3.61 (d, 1H, J ¼ 10.8 Hz), 3.65 (d, 1H, J ¼ 10.8 Hz), 4.47 (septet, 1H,
J ¼ 6.8 Hz), 7.3–7.6 (m, 9H); 13C NMR (DMSO-d6) d 19.55, 19.58, 41.5,
47.4, 56.0, 73.9, 125.9, 126.4, 126.6, 127.4, 128.9, 138.8, 139.8, 144.3,
170.8; MS m/z: 295 (Mþ). Anal. calcd. for C19H21NO2: C, 77.26; H, 7.17;
N, 4.74. Found: C, 75.36; H, 6.86; N, 4.74.
ACKNOWLEDGMENTS
The authors thank Wheaton College for financial support and Douglass A.
Klumpp, Northern Illinois University, for mass spectral analysis.

1852
C. R. Kinsinger et al.
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