Applications of Baylis-Hillman acetates: One-pot, facile and convenient synthesis of substituted γ-lactams

Article abstract of DOI:10.1016/j.tetlet.2003.12.133

A simple, convenient and one-pot transformation of the acetates of Baylis-Hillman adducts into substituted γ-lactams, that is, (E)-5-alkyl-3-arylidenepyrrolidin-2-ones via treatment with nitroalkanes in the presence of a base, followed by reductive cyclization, using Fe/AcOH, is described.

Full text of DOI:10.1016/j.tetlet.2003.12.133

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 1621–1625
Applications of Baylis–Hillman acetates: one-pot, facile and
convenient synthesis of substituted c-lactams
Deevi Basavaiah* and Jamjanam Srivardhana Rao
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
Received 19 November 2003; revised 18 December 2003; accepted 23 December 2003
Abstract—A simple, convenient and one-pot transformation of the acetates of Baylis–Hillman adducts into substituted c-lactams,
that is, (E)-5-alkyl-3-arylidenepyrrolidin-2-ones via treatment with nitroalkanes in the presence of a base, followed by reductive
cyclization, using Fe/AcOH, is described.
ꢀ 2004 Elsevier Ltd. All rights reserved.
The Baylis–Hillman reaction has become a useful syn-
thetic reaction in organic chemistry in recent years
because it provides a simple and convenient method for
the synthesis of interesting classes of densely function-
alized molecules in operationally simple, one-pot, atom
economic procedures.1;2 The c-lactam framework occu-
pies an important place in nitrogen heterocycles because
it is present in various natural products and pharma-
ceutical agents3 and hence the development of conve-
nient methods for the synthesis of c-lactams represents
an interesting and attractive endeavor in organic syn-
thesis.3b;e;k;n;4 In continuation of our interest in the syn-
thesis of heterocyclic molecules,5 we herein report a
facile one-pot synthesis of substituted c-lactams, that is,
(E)-5-alkyl-3-arylidenepyrrolidin-2-ones using the ace-
tates of Baylis–Hillman adducts.
corresponding (E)-2-arylidene-4-nitroalkanoates6b [or
(E)-2-alkylidene-4-nitroalkanoates6h] and (E)-2-alkylid-
ene-4-nitroalkanones6g [via treatment with nitroalkanes
in the presence of K2CO3/DMF (or NaOH/THF) and
NaOH/THF, respectively], which were subsequently
converted into c-keto esters6b;h and 1,4-diketones6g
(Scheme 1).
It occurred to us that reductive cyclization of the (E)-2-
arylidene-4-nitroalkanoates, which would be obtained in
situ via treatment of acetates of Baylis–Hillman adducts
with nitroalkanes, with an appropriate reagent could
result in the one-pot formation of 5-alkyl-3-arylidene-
pyrrolidin-2-ones. Accordingly, we first selected methyl
3-acetoxy-3-phenyl-2-methylenepropanoate (2a) for
reaction with nitroethane (1a) in the presence of a base
followed by reductive cyclization. The best results were
obtained when the ester 2a (2 mmol) was treated with
nitroethane (1a) (8 mmol) in the presence of K2CO3
(8 mmol) in THF/H2O at room temperature for 12 h
followed by the treatment with Fe/AcOH (after removal
of THF and nitroethane under reduced pressure) at
reflux temperature for 2 h, providing the product (E)-5-
methyl-3-benzylidenepyrrolidin-2-one (3) in 66% iso-
lated yield after work-up and purification by column
chromatography.7 With a view to examine whether the
reaction was more facile and whether the yield of 3
would be higher using a stepwise method, we also iso-
lated the trisubstituted alkene, that is, methyl (E)-2-
benzylidene-4-nitropentanoate (3A). Thus, treatment of
the starting material 2a (2 mmol) with nitroethane
(8 mmol) in the presence of K2CO3 (8 mmol) in THF
(5 mL) and water (0.1 mL) at room temperature for 12 h
provided the desired trisubstituted alkene 3A in 80%
Acetates of the Baylis–Hillman adducts have been suc-
cessfully employed in a number of transformations
leading to the synthesis of various important and useful
molecules often involving high levels of stereoselectivi-
ties.6 Although there are a number of methods available
for the synthesis of c-lactams,4 a literature survey
revealed no report on the synthesis of 3-arylidene-c-
lactams using acetates of Baylis–Hillman adducts.
The literature also revealed that acetates of the Baylis–
Hillman adducts were conveniently transformed into the
Keywords: Baylis–Hillman chemistry; c-Lactams; Reductive cycliza-
tion; Fe/AcOH.
* Corresponding author. Tel.: +91-40-2301-0221; fax: +91-40-2301-
2460; e-mail: dbsc@uohyd.ernet.in
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.12.133

1622
D. Basavaiah, J. Srivardhana Rao / Tetrahedron Letters 45 (2004) 1621–1625
1.MeONa / MeOH
COOR'
NO2
COOR'
O
2.H+, -50 o
61-84%
C
R
R
R=alkyl
E/Z:80-85:20-15
R''
R'= Et
R''
R''=Me, Et
E/Z:80-85:20-15
Ref. 6h
R''CH2NO2
NaOH (0.45 N), THF
48-86 h
EWG=COOR'
67-85%
R''CH2NO2 / NaOH(0.6N)
, 3 h-4 d
OAc
R''CH2NO2 (2.0 equiv)
K2CO3 (3.0 equiv)
COOR'
NO2
R''
THF, 0-20 o
C
COR'
NO2
EWG
R
R
R
E
E
66-75%
DMF, rt, 1 h
EWG=COOR'
Ref. 6b
64-78%
EWG= COR'
Ref. 6g
R''
1. MeONa / MeOH
2. H+, -50 o
50-75%
1. EtOH / EtONa, 0 oC, 30 min
2. EtOH / H2SO4, 0 oC, 30 min
44-61%
C
R=alkyl
R'=Me, Et
R''=Me, Et
R=aryl
R
COOR'
O
COR'
O
R'=Me, Et
R''=Me, Et
E
R
E
R''
R''
Scheme 1. Synthesis of c-keto esters and 1,4-diketones using acetates of the Baylis–Hillman adducts.
isolated yield after the usual work-up and column
1
6.86 (olefinic proton) with a very low intensity. Sub-
sequent treatment of 3A with Fe/AcOH at 110 ꢁC for 2 h
provided the desired c-lactam 3 in 71% yield (57%
overall) (Scheme 2).
chromatography. The H NMR spectrum of the crude
product indicated the presence of ꢀ5% of the Z-isomer
as was evident from the appearance of a singlet at ca. d
O
i. x ; ii. y
NH
Ph
66%
Path A
OAc O
3
NO
2
OMe
Ph
1a
O
Path B
2a
y
x
OMe
NO
Ph
3
x = K2CO3 / THF / H2O, rt, 12 h
y = Fe / AcOH, reflux, 2 h
2
80%
71%
3A
Scheme 2. SN02 reaction of methyl 3-acetoxy-3-phenyl-2-methylenepropanoate (2a) with nitroethane (1a) followed by reductive cyclization with
Fe/AcOH.
OAc O
O
R
K2CO3 /THF / H2O
rt , 12 h
R
NO2
R'
OMe
R'
OMe
NO2
1a-b
R = methyl, ethyl
2a-i
3A-16A
R' = phenyl, 4-methylphenyl, 4-ethylphenyl,
4-chlorophenyl, 4-methoxyphenyl, 2-chlorophenyl,
naphth-1-yl, propyl, hexyl
Fe / AcOH
reflux, 2 h
O
O
R
_
O
-MeOH
49-68%
OMe
NH2
R'
OMe
..
R'
NH
R
R'
NH2
R
3-16
Scheme 3. SN02 reaction on acetates of Baylis–Hillman adducts with nitroalkanes followed by reductive cyclization with Fe/AcOH.

D. Basavaiah, J. Srivardhana Rao / Tetrahedron Letters 45 (2004) 1621–1625
1623
Since the yield was better in the case of the one-pot
01
method we selected the one-pot procedure as the method
of choice and extended this strategy to a representative
class of the acetates of Baylis–Hillman adducts to pro-
vide the desired (E)-5-alkyl-3-arylidenepyrrolidin-2-ones
4–14 in 55–68% yields (Scheme 3, Table 1). The (E)-
selectivity of these reactions was established from single
crystal X-ray data for pyrrolidinone 11 (Fig. 1).8
C6
C9
N1
C5
C8
C10
C11
C7
C1
C14
C4
C2
C3
C13
C12
When we extended this strategy to the acetates 2h,i of
Baylis–Hillman adducts derived from butyraldehyde
and heptanal, the resulting products, that is, (E)-5-
methyl-3-butylidenepyrrolidin-2-one 15 and (E)-5-
methyl-3-heptylidenepyrrolidin-2-one 16 were obtained
in 52% and 49% yields, respectively, after column purifi-
Figure 1. ORTEP diagram of compound 11.
thesis of substituted c-lactams from Baylis–Hillman
acetates.
1
cation. However, the H NMR and 13C NMR spectral
analysis of the purified products 15 and 16 indicated the
presence of ꢀ8% and ꢀ10% impurities, respectively.
Compound 15 was obtained in pure form after pre-
parative HPLC (Shim pack PREP-ODS column, meth-
anol). However, similar attempts to obtain 16 in
chemically pure form were unsuccessful. A plausible
mechanism for the one-pot transformation of the ace-
tates of Baylis–Hillman adducts into substituted c-lac-
tams is presented in Scheme 3.
Acknowledgements
We thank the CSIR (New Delhi) for funding this pro-
ject. We thank UGC (New Delhi) for recognizing our
University of Hyderabad as ‘University with potential for
excellence (UPE)’ and funding generously and also for
the Special Assistance Program in Organic Chemistry in
the School of Chemistry, University of Hyderabad.
J.S.R. thanks UGC and DST (New Delhi) for his
In conclusion, we have developed a convenient,
operationally simple, one-pot procedure for the syn-
Table 1. Synthesis of (E)-5-alkyl-3-arylidenepyrrolidin-2-onesa–f
Nitroalkane
R
Acetate
R0
Product
Yield (%)
Mp (ꢁC)
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1a
1a
Me
Me
Me
Me
Me
Me
Me
Et
2a
2b
2c
2d
2e
2f
Phenyl
3g
4
66
65
68
64
62
55
67
64
62
63
60
61
52i
49i
101–103
170–172
128–130
161–163
169–171
124–126
179–181
125–127
142–144
132–134
128–130
123–125
––
4-Methylphenyl
4-Ethylphenyl
4-Chlorophenyl
4-Methoxyphenyl
2-Chlorophenyl
Naphth-1-yl
Phenyl
5
6
7
8
9g
2g
2a
2b
2d
2f
10g
11
12
13
14
15g;h
16h
Et
Et
4-Methylphenyl
4-Chlorophenyl
2-Chlorophenyl
Naphth-1-yl
Propyl
Et
Et
2g
2h
2i
Me
Me
Hexyl
––
a All reactions were carried out on 2 mmol of the Baylis–Hillman acetate with the nitroalkane (8 mmol), in the presence of K2CO3 (8 mmol) in THF/
water at room temperature for 12 h and then the reaction mixture was treated with Fe powder (12 mmol)/AcOH (5 mL) (after removal of THF and
nitroalkane under reduced pressure) at 110 ꢁC for 2 h.
b The compounds 3–14 were obtained as solids while compounds 15 and 16 were obtained as viscous liquids. All the compounds 3–15 were char-
acterized by IR, 1H NMR (200 MHz), 13C NMR (50 MHz) spectral data and elemental analyses.
c The (E)-stereochemistry of compound 11 was established by single crystal X-ray data and the stereochemistry of the other compounds was assigned
in analogy to 11.
d Yields are of the pure products (based on acetates) after purification via silica gel column chromatography.
e In the case of molecules 6, 10, 12–14, the 1H NMR spectra of the crude products showed ꢀ5–10% of uncyclized compound as evidenced by the
singlet at ꢀd 7.81–8.30 (olefinic proton) and the singlet at ꢀd 3.85–3.92 (COOCH3) with low intensity.
f The 1H NMR spectra of the crude products did not indicate clearly the presence of any isomeric impurity [on the basis of the 1H NMR spectrum of
the crude product 3A (uncyclized product), which showed the presence of ꢀ5% (Z)-isomeric impurity; we believe that all these reactions are at least
ꢀ95% (E)-selective].
g Structures were further confirmed by mass spectral analyses.
h The 1H NMR spectra of the crude nitro compounds 15A and 16A derived from aliphatic acetates 2h and 2i indicated the presence of ꢀ11% and 13%
(Z)-isomers as evidenced by the triplet at ꢀd 6.05 (olefinic proton trans to the ester group).
i
1H NMR and 13C NMR spectral analysis of the column purified products 15 and 16 indicated the presence of ꢀ8% and ꢀ10% impurities,
respectively. However, compound 15 was obtained in pure form after preparative HPLC (Shim pack PREP-ODS column, methanol).

1624
D. Basavaiah, J. Srivardhana Rao / Tetrahedron Letters 45 (2004) 1621–1625
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7. Typical experimental procedure: (E)-5-Methyl-3-benzylid-
enepyrrolidin-2-one 3: To a stirred mixture of nitroethane
(8 mmol, 0.6 g) and K2CO3 (8 mmol, 1.104 g) in THF (5 mL)
and water (0.1 mL), was added methyl 3-acetoxy-3-phenyl-
2-methylenepropanoate (2a) (2 mmol, 0.468 g) at room
temperature. After stirring at room temperature for 12 h,
THF and nitroethane were removed under reduced
pressure. The reaction mixture was diluted with acetic acid
(5 mL) and Fe powder (12 mmol, 0.67 g) was added. The
reaction mixture was heated under reflux (at 110 ꢁC) for 2 h
and then was allowed to cool to room temperature. Acetic
acid was removed under reduced pressure and the reaction
mixture was diluted with EtOAc (10 mL), stirred for 2 min
and filtered to remove any iron impurities. The insoluble
iron residue was washed with EtOAc (10 mL). The filtrate
and washings were combined and dried over anhydrous
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D. Basavaiah, J. Srivardhana Rao / Tetrahedron Letters 45 (2004) 1621–1625
1625
Na2SO4. The solvent (EtOAc) was removed under reduced
pressure and the residue thus obtained was purified by
column chromatography (silica gel) using 70% EtOAc in
hexanes to afford (E)-5-methyl-3-benzylidenepyrrolidin-2-
one (3) as a light yellow solid in 66% yield (0.247 g). Mp:
101–103 ꢁC; IR (KBr): 3200–2800 (multiple bands), 1685,
8. Detailed X-ray crystallographic data is available from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK (for compound 11 CCDC
#217594). Crystal data for 11: empirical formula,
C14H17NO; formula weight, 215.29; crystal colour, habit:
light
yellow,
rectangular;
crystal
dimensions,
1
1647 cmꢁ1; H NMR: d 1.32 (d, 3H, J ¼ 6:0 Hz), 2.58–2.77
0.64 · 0.55 · 0.48 mm; crystal system, monoclinic; lattice
ꢀ
(m, 1H), 3.32 (ddd, 1H, J ¼ 2:6, 7.8, 17.6 Hz), 3.82–4.03 (m,
1H), 7.04 (br, 1H), 7.28–7.54 (m, 6H); 13C NMR: d 23.26,
34.95, 47.52, 128.35, 128.54, 129.41, 130.12, 131.33, 135.73,
172.05; EIMS: 187 (Mþ). Anal. Calcd for C12H13NO: C,
76.98; H, 7.00; N, 7.48. Found: C, 76.85; H, 7.03; N, 7.52.
type, primitive; lattice parameters, a ¼ 10:048ð4Þ A,
ꢀ
3
ꢀ
b ¼ 11:595ð5Þ A, c ¼ 11:158ð3Þ A; b ¼ 112:97ð3Þ; V ¼
ꢀ
1196:9ð8Þ A ; space group, P21/a (no. 14); Z ¼ 4;
Dcalcd ¼ 1:195 g/cm3; F000 ¼ 464; k(MoKa) ¼ 0.71073 A;
ꢀ
RðI P 3r1Þ ¼ 0:0660, wR2 ¼ 0:1914.