Facile synthesis of (Z)- and (E)-3-allylidene-β-lactams via thermal β-elimination of trans-3-allyl-3-sulfinyl-β-lactams

Article abstract of DOI:10.1016/j.tetlet.2010.01.085

A competent synthetic route for the synthesis of novel (Z)- and (E)-3-allylidene-β-lactams is described. The strategy involves oxidation of trans-3-allyl-3-phenylthio-β-lactams 1 using sodium metaperiodate (NaIO₄) to diastereomeric trans-3-allyl-3-phenylsulfinyl-β-lactams 2 and 3, which further undergo thermal β-elimination in refluxing carbon tetrachloride to furnish (Z)- and (E)-3-allylidene-β-lactams 5 and 6 in good to excellent yields. The molecular structure of 3b has been established with the help of single crystal X-ray analysis.

Full text of DOI:10.1016/j.tetlet.2010.01.085

Tetrahedron Letters 51 (2010) 1719–1722
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Tetrahedron Letters
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Facile synthesis of (Z)- and (E)-3-allylidene-b-lactams via thermal
b-elimination of trans-3-allyl-3-sulfinyl-b-lactams
*
Shamsher S. Bari , Renu Arora, Aman Bhalla, Paloth Venugopalan
Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A competent synthetic route for the synthesis of novel (Z)- and (E)-3-allylidene-b-lactams is described.
The strategy involves oxidation of trans-3-allyl-3-phenylthio-b-lactams 1 using sodium metaperiodate
(NaIO4) to diastereomeric trans-3-allyl-3-phenylsulfinyl-b-lactams 2 and 3, which further undergo ther-
mal b-elimination in refluxing carbon tetrachloride to furnish (Z)- and (E)-3-allylidene-b-lactams 5 and 6
in good to excellent yields. The molecular structure of 3b has been established with the help of single
crystal X-ray analysis.
Received 3 December 2009
Revised 20 January 2010
Accepted 25 January 2010
Available online 1 February 2010
Keywords:
b-Lactam
Ó 2010 Elsevier Ltd. All rights reserved.
trans-3-Allyl-3-phenylsulfinyl-b-lactams
3-Allylidene-b-lactams
b-Elimination
Thermolysis
b-Lactams have attracted continued interest not only for their
diverse and powerful antibiotic activity1 but also for their utility
as versatile synthetic intermediates.2 The need for potent and
effective b-lactam antibiotics as well as effective b-lactamase
inhibitors has motivated chemists world over to design new b-lac-
tams.3 In addition, the relevance of b-lactams in many other signif-
icant non-antibiotic uses, such as cholesterol acyl transferase
inhibitors, thrombin inhibitors, human cytomegalovirus protease
inhibitors, matrix-metallo protease inhibitors, human leukocyte
elastase, cysteine protease, apoptosis inductors, gene activators,
and b-turn nucleator continues to expand at a surprising rate.4
the synthesis of 3-allylidene-b-lactams from 3-allyl-3-sulfinyl-b-
lactams.
Several synthetic methods have been listed in the literature for
the synthesis of a
-alkylidene-b-lactams.5,6 Mahajan and co-work-
ers have reported the diastereoselective synthesis of trans-3-ally-
lidene-b-lactams and their further elaboration to Diels–Alder
adducts on reaction with variety of dienophiles.20 Keeping in view
that sulfoxide can undergo a facile b-elimination leading to the
introduction of unsaturation in the target molecule,21 we envis-
aged the synthesis of 3-allylidene-b-lactams via thermal b-elimi-
nation of trans-3-allyl-3-sulfinyl-b-lactams, prepared by the
oxidation of trans-3-allyl-3-phenylthio-b-lactams using sodium
metaperiodate.
a-Alkylidene-b-lactams are well-acknowledged structural ele-
ments of ene-type b-lactamase inhibitors such as asparenomycins,
Ro 15-1903, 6-[(Z)-methoxymethylidene]penicillanic acid, and
6-(20-pyridyl)methylene penem sulfone.5 Moreover, 6-alkylidene-
penicillianate sulfoxides and sulfones have been shown to possess
antitumor properties.6 Recently, 4-alkylidene-b-lactams have been
reported to exhibit activity against human leukocyte elastase, gel-
Starting substrates, trans-3-allyl-3-phenylthio-b-lactams 1(a–d)
were prepared through Lewis acid-promoted C-3 allylation of 3a-
chloro-3-phenylthio-b-lactams with allyltrimethylsilane according
to our earlier reported synthetic route.11 The trans-3-allyl-3-phenyl-
thio-b-lactams 1(a–d) were submitted to the oxidation using
sodium metaperiodate to provide trans-3-allyl-3-phenylsulfinyl-b-
lactams 2(a–d) and 3(a–d) in good to excellent yields (Scheme 1,
Table 1, entries 1–4). Initial studies were carried out by the treat-
ment of 1a with 2 equiv of NaIO4 in MeOH–H2O (10:1) at room tem-
perature. The progress of the reaction was monitored by thin-layer
chromatography (TLC). The reaction resulted in the formation of a
mixture of two diastereomeric 3-phenylsulfinyl-b-lactams 2a and
3a as the major products in 1:1 ratio, as was evident from 1H NMR
spectroscopy, along with 3-phenylsulfonyl-b-lactam 4a as a minor
one (Scheme 1, Table 1, entry 1).22 The sulfinyl- (2a, 3a) and sulfo-
nyl-b-lactams, (4a) with different Rf values were separable through
atinase MMP-2, and MMP-9.7 Besides this,
are valuable synthetic intermediates for -keto-b-lactams, spiro-b-
lactams, bicyclic-b-lactams,8 and b-amino alcohols and acids.9
a-alkylidene-b-lactams
a
Recognition of the importance of a-alkylidene-b-lactams and in
persistence to our earlier studies4,10–19 intended toward the syn-
thesis of novel thio/seleno-b-lactams and their functionalization,
renewed efforts have been made in the present work to achieve
* Corresponding author. Tel.: +91 172 253 4405x41435; fax: +91 172 2545074.
E-mail address: ssbari@pu.ac.in (S.S. Bari).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.01.085

1720
S. S. Bari et al. / Tetrahedron Letters 51 (2010) 1719–1722
O
S
Ph
H
H
H
H
1
1
1
1
PhS
R
R
R
R
S
S
.
.
Ph
Ph
NaIO4
+
+
O
O
O
MeOH : H2O
(10 : 1)
N
N
N
N
R2
R2
R2
R2
O
O
O
O
2(a-d)
3(a-d)
1(a-d)
4(a-d)
Scheme 1. Synthesis of trans-3-allyl-3-phenylsulfinyl-b-lactams 2(a–d) and 3(a–d).
Table 1
Synthesis of trans-3-allyl-3-phenylsulfinyl-b-lactams 2(a–d) and 3(a–d)
Entry
Substrate 1
R1
R2
Products of typea (% yield)
2
3
4
1
2
3
4
1a
1b
1c
1d
Ph
4-MeOC6H4
4-MeOC6H4
4-MeC6H4
Ph
2a (36)
2b (30)
2c (28)
2d (32)
3a (46)
3bb (41)
3c (37)
3d (40)
4a (9)
4-MeOC6H4
4-ClC6H4
Ph
4b (12)
4c (14)
4d (7)
a
Isolated yields after purification by column chromatography.
The structure of this molecule was also established from single crystal X-ray data (Fig. 1).
b
column chromatography on silica gel eluting with EtOAc/hexane
(7:93) and were identified as trans-3-allyl-3-phenylsulfinyl-b-lac-
tam 2a (Rf = 0.53), trans-3-allyl-3-phenylsulfinyl-b-lactam 3a (Rf =
0.43), and trans-3-allyl-3-phenylsulfonyl-b-lactam 4a (Rf = 0.66),
respectively.22 The reaction was found to be general with other sub-
strates 1(b–d) (Scheme 1) and the results are summarized in Table 1
(entries 2–4). Although in the present reaction the diastereoselectiv-
ity was not improved using different temperature conditions, the
good yields of the two diastereomeric 3-phenylsulfinyl-b-lactams
2 and 3 were attained.
The structures of these b-lactams 2–4(a–d) were established by
spectroscopic studies such as FT-IR, 1H NMR, 13C NMR, mass spec-
trometry, and elemental (CHN) analyses.22 The stereochemistry of
the major trans-3-allyl-3-phenylsulfinyl-b-lactam 3 was confirmed
through single crystal X-ray structure analysis of 3b23 (Fig. 1). The
stereochemistry of the other isomer, that is, trans-3-allyl-3-phen-
ylsulfinyl-b-lactam 2 was tentatively assigned in relation to the
stereochemistry of 3b.
as CHCl3, CCl4, and toluene (Scheme 2). Initially, 2a underwent fac-
ile thermolysis giving isomeric 3-allylidene-b-lactams 5a and 6a in
1:1 ratio, as was evident from 1H NMR spectroscopy (Table 2, entry
1).25 These two dienes were separated by column chromatography
on silica gel eluting with EtOAc/hexane (7:93) and were identified
as (Z)-3-allylidene-b-lactam 5a (Rf = 0.60) and (E)-3-allylidene-b-
lactam 6a (Rf = 0.57), respectively, on the basis of spectroscopic
studies. This reaction was also performed successfully with other
substrates 2(b–d) and goes to nearly 80% completion without
any further rearrangement of the diene products (Scheme 2, Table
2, entries 2–4). It was observed that CCl4 is the best solvent for this
reaction as compared to CHCl3 and toluene which produce unde-
sired rearranged products from diene.
The structures of 3-allylidene-b-lactams 5–6(a–d) were con-
firmed by spectroscopic means such as UV–vis, FT-IR, 1H NMR,
13C NMR, 13C NMR (DEPT–135), and elemental (CHN) analyses.
The stereochemistry (Z)- and (E)- of 3-allylidene-b-lactams was
established on the basis of chemical shift of olefin multiplet for
The trans-3-allyl-3-phenylsulfinyl-b-lactams 2(a–d) were fur-
ther subjected to thermolysis reaction using different solvents such
c c-proton
-proton and doublet for b-proton in 1H NMR (Fig. 2). The
resonated downfield at d 7.10 ppm for the Z-isomer (5) due to
deshielding anisotropic effect of b-lactam carbonyl. The doublet
for b-proton of this isomer was observed at d 5.88 (J = 10.5 Hz)
ppm. Whereas, in E-isomer (6), the multiplet for
c-proton reso-
nated upfield at d 5.95 ppm and the doublet for b-proton appeared
downfield at d 6.52 (J = 10.5 Hz) ppm due to deshielding effect of
b-lactam carbonyl. Additionally, the disappearance of doublet for
methylene protons of allyl moiety of 2(a–d) provides evidence
indicating the formation of (Z)- and (E)-3-allylidene-b-lactams.
Further, the mass spectra (EI-MS) of 3a and 4a show peaks at
Ph
H
H
H
1
R
1
R
1
R
S
.
.
+
O
CCl4
N
N
N
O
R2
R2
R2
O
O
5(a-d)
Z-Isomer
6(a-d)
E-Isomer
2(a-d)
Scheme 2. Synthesis of (Z)- and (E)-3-allylidene-b-lactams 5(a–d) and 6(a–d) via
thermolysis of trans-3-allyl-3-phenylsulfinyl-b-lactams 2(a–d).
Figure 1. ORTEP diagram of trans-3-allyl-3-sulfinyl-b-lactam 3b.24

S. S. Bari et al. / Tetrahedron Letters 51 (2010) 1719–1722
1721
Table 2
Synthesis of (Z)- and (E)-3-allylidene-b-lactams 5 and 6 via thermolysis of trans-3-allyl-3-phenylsulfinyl-b-lactams 2
Entry
2
R1
R2
Time (h)
Products of typea (% yield)
5 (Z-isomer) 6 (E-isomer)
Unreacted 2
(% yield)
1
2
3
4
2a
2b
2c
2d
Ph
4-MeOC6H4
4-MeOC6H4
4-MeC6H4
Ph
24
45
40
12
5a (30)
5b (29)
5c (27)
5d (31)
6a (32)
6b (34)
6c (36)
6d (37)
2a (12)
2b (14)
2c (18)
2d (15)
4-MeOC6H4
4-ClC6H4
Ph
a
Isolated yields after purification by column chromatography.
Table 3
H
H
(δ 5.88)
Synthesis of (Z)- and (E)-3-allylidene-b-lactams 5 and 6 via thermolysis of trans-3-
allyl-3-phenylsulfinyl-b-lactams 3
H
N
H
N
γ
(δ 5.95)
1
1
R
R
β
(δ 6.52)
β
γ
(δ 7.10)
α
α
Entry
3
R1 R2
Time (h)
Products of
Unreacted 3
(% yield)
H
typea (% yield)
H
O
R2
R2
O
5
6
[(Z)-Isomer]
[(E)-Isomer]
6
5
(Z-isomer) (E-isomer)
1
2
3a Ph 4-MeOC6H4 90
3d Ph Ph 90
5a (14)
5d (10)
6a (40)
6d (36)
3a (30)
3d (35)
Figure 2. (Z)- and (E)-3-allylidene-b-lactams 5 and 6.
a
Isolated yields after purification by column chromatography.
Acknowledgments
H
H
H
1
R
1
R
1
R
S
Ph
We gratefully acknowledge the financial support for this work
from University Grants Commission (UGC), New Delhi, India and
Department of Science and Technology (DST), New Delhi, Govern-
ment of India, Project No. SR/FTP/CS-135/2006 dated 13-03-2007.
+
O
CCl4
N
N
N
O
R2
R2
R2
O
O
5(a-d)
Z-Isomer
6(a-d)
E-Isomer
3(a,d)
References and notes
Scheme 3. Synthesis of (Z)- and (E)-3-allylidene-b-lactams 5(a–d) and 6(a–d) via
thermolysis of trans-3-allyl-3-phenylsulfinyl-b-lactams 3(a,d).
1. For reviews on b-lactam antibiotics: (a) Morin, R. B.; Gorman, M. Chemistry and
Biology of b-lactam antibiotics; Academic: New York, 1982; (b) Durckheimer,
W.; Blumbatch, J.; Lattrell, R.; Scheunemann, K. H. Angew. Chem., Int. Ed. Engl.
1985, 24, 180–202; (c) Chu, D. T. W.; Plattner, J. J.; Katz, L. J. Med. Chem. 1996,
39, 3853–3874; (d) Singh, G. S. Mini-Rev. Med. Chem. 2004, 4, 69–92; (e) Singh,
G. S. Mini-Rev. Med. Chem. 2004, 4, 93–109.
2. (a) Ojima, I. Acc. Chem. Res. 1995, 28, 383–389; (b) Banik, B. K.; Manhas, M. S.;
Bose, A. K. J. Org. Chem. 1994, 59, 4714–4716; (c) Alcaide, B.; Almendros, P.
Synlett 2002, 381–383; (d) Palomo, C.; Aizpurua, J. M.; Ganboa, I.; Oiarbide, M.
Synlett 2001, 1813–1826; (e) Alcaide, B.; Almendros, P. Chem. Soc. Rev. 2001, 30,
226–240; (f) Palomo, C.; Aizpurua, J. M.; Ganboa, I.; Oiarbide, M. Amino Acids
1999, 16, 321–343; (g) Manhas, M. S.; Wagle, D. R.; Chiang, J.; Bose, A. K.
Heterocycles 1998, 27, 1755–1758; (h) Deshmukh, A. R. A. S.; Bhawal, B. M.;
Krishanaswamy, D.; Govande, V. V.; Shinkre, B. A.; Jayanthi, A. Curr. Med. Chem.
2004, 11, 1889–1920; (i) Alcaide, B.; Almendros, P. Curr. Med. Chem. 2004, 11,
1921–1949.
3. Buyank, J. Curr. Med. Chem. 2004, 11, 1951–1964.
4. Bhalla, A.; Venugopalan, P.; Bari, S. S. Eur. J. Org. Chem. 2006, 4943–4950. and
references therein.
5. (a) Fujiwara, S. –i.; Shimizu, Y.; Imahori, Y.; Toyofuku, M.; Shin-ike, T.; Kambe,
N. Tetrahedron Lett. 2009, 50, 3628–3630; (b) Chen, Y. L.; Chang, Ch. –W.;
Hedgerg, K. Tetrahedron Lett. 1986, 27, 3449–3452.
6. Veinberg, G.; Shestakova, I.; Vorona, M.; Kanepe, I.; Lukevics, E. Bioorg. Med.
Chem. Lett. 2004, 14, 147–150.
7. Cainelli, G.; Galletti, P.; Garbisa, S.; Giacomini, D.; Sartor, L.; Quintavalla, A.
Bioorg. Med. Chem. 2003, 11, 5391–5399.
8. (a) Tufariello, J. J.; Pinto, D. J. P.; Milowsky, A. S.; Reinhardt, D. V. Tetrahedron
Lett. 1987, 28, 5481–5484; (b) Lo, Y. S.; Sheehan, J. C. J. Am. Chem. Soc. 1972, 94,
8253; (c) Chiba, K.; Mori, M.; Ban, Y. Tetrahedron 1985, 41, 387–392; (d)
Anklam, S.; Liebscher, J. Tetrahedron 1998, 54, 6369–6384.
9. Liang, Y.; Raju, R.; Le, T.; Taylor, C. D.; Howell, A. R. Tetrahedron Lett. 2009, 50,
1020–1022. and references therein.
10. Madan, S.; Arora, R.; Venugopalan, P.; Bari, S. S. Tetrahedron Lett. 2000, 41,
5577–5581.
11. Bari, S. S.; Venugopalan, P.; Arora, R. Tetrahedron Lett. 2003, 44, 895–897.
12. Bari, S. S.; Venugopalan, P.; Arora, R.; Modi, G.; Madan, S. Heterocycles 2006, 68,
749–762.
13. Bhalla, A.; Madan, S.; Venugopalan, P.; Bari, S. S. Tetrahedron 2006, 62, 5054–
5063.
14. Bhalla, A.; Venugopalan, P.; Bari, S. S. Tetrahedron 2006, 62, 8291–8302.
15. Bhalla, A.; Rathee, S.; Madan, S.; Venugopalan, P.; Bari, S. S. Tetrahedron Lett.
2006, 47, 5255–5259.
m/z 291 (78, [(E)-3-allylidene-b-lactam 6a]+) and 291 (13, [(E)-3-
allylidene-b-lactam 6a]+) indicate the thermolysis affording more
stable (E)-3-allylidene-b-lactam.
Next, we examined the behavior of trans-3-allyl-3-phenylsulfi-
nyl-b-lactams 3(a,d) under the similar reaction conditions (Scheme
3, Table 3, entries 1–2). This reaction proceeds more slowly, leaving
the unreacted substrate (3) even after prolonged refluxing. Surpris-
ingly, thermolysis of 3(a,d) strongly favors the formation of (E)-iso-
mer of 3-allylidene-b-lactams 6(a,d) over (Z)-isomer 5(a,d).
This can be rationalized on the basis of the formation of benze-
nesulfenic (PhSOH) acid in the reaction which highlights the prox-
imity of sulfoxide oxygen to the two b-hydrogens of allyl group of 2
and 3 determining the reactivity toward thermal b-elimination.
The ORTEP diagram of 3b shows the minimum steric repulsion be-
tween the S@O, allyl group at C-3, and phenyl group at C-4 and
hence explains the greater stability with respect to 2. However,
in 2 the S@O group is much closer to the b-hydrogens of allyl
group, facilitating thermolysis rapidly. Moreover, thermolysis fa-
vors the formation of (E)-isomer 6(a,d) over (Z)-isomer 5(a,d)
which may be due to the higher stability of (E)-isomer because
of less steric interference and this could be attributed to the elec-
tronic repulsion of the carbonyl group and the terminal ethylene
in the case of (Z)-isomer. Thermolysis of trans-3-allyl-3-phenylsul-
fonyl-b-lactam 4a did not furnish any diene product under similar
reaction conditions.
In conclusion, a facile route to novel (Z)- and (E)-3-allylidene-
b-lactams has been explored and developed via thermal b-elimina-
tion of trans-3-allyl-3-phenylsulfinyl-b-lactams. Further elabora-
tion of these novel 3-allylidene-b-lactams to Diels–Alder adducts
using variety of dienophiles is underway in our laboratory.

1722
S. S. Bari et al. / Tetrahedron Letters 51 (2010) 1719–1722
16. Bhalla, A.; Sharma, S.; Bhasin, K. K.; Bari, S. S. Synth. Commun. 2007, 37, 783–
793.
17. Bhalla, A.; Venugopalan, P.; Bhasin, K. K.; Bari, S. S. Tetrahedron 2007, 63, 3195–
3204.
18. Bhalla, A.; Nagpal, Y.; Kumar, R.; Mehta, S. K.; Bhasin, K. K.; Bari, S. S. J.
Organomet. Chem. 2009, 694, 179–189.
19. Bari, S. S.; Reshma, R.; Bhalla, A.; Hundal, G. Tetrahedron 2009, 65, 10060–
10068.
(75 MHz, CDCl3) d 35.4 (–CH2–), 55.1 (OCH3), 61.9 (C-4), 80.1 (C-3), 115.2–
155.3 (C@C, ArC), 161.1 (C@O); EI-MS m/z (R.I.%, [assignment]+): 433 (44, [M]+),
291 (13, [(E)-3-allylidene-b-lactam 6a]+), 211 (100, [C6H5CH@NC6H4(OCH3)]+),
149 (65, [O@C@NC6H4(OCH3)]+); Anal. Calcd for C25H23NO4S: C, 69.26; H, 5.35;
N, 3.23. Found: C, 69.22; H, 5.31; N, 3.20.
23. Crystal data for 3b: Monoclinic; P21/n; a = 11.9440(10) Å, b = 11.4770(10) Å,
c = 17.757(2) Å;
Calcd = 1.279 mg/m3;
R1 = 0.0570, wR2 = 0.1355 for 2184 observed reflections [I > 2
R1 = 0.0900, wR2 = 0.1554 for all 3226 reflections; GOF = 1.011.
a
= 90°, b = 107.25°,
(Mo K
= 0.171 mmꢁ1; full matrix least-square on F2;
(I)] and
c q
= 90 °C; V = 2324.7(4) Å3; Z = 4;
l
a
20. Sharma, A. K.; Mahajan, M. P.; Mazumdar, S. N. J. Org. Chem. 1996, 61, 5506–5509.
21. Trost, B. M.; Salzmann, T. N. J. Am. Chem. Soc. 1973, 95, 6840–6842.
22. General procedure for the synthesis of 2–4: A solution of 1 (1.0 mmol) in MeOH
(10 mL) and THF (1 mL) was stirred with NaIO4 (2.7 mmol) and dissolved in
H2O (1 mL) at room temperature. The progress of the reaction was checked by
TLC, which showed the appearance of three new spots, all of them having Rf
lower than the substrate 1. The solvent was evaporated under reduced
pressure and the reaction mixture was extracted with dichloromethane
(5 ꢀ 20 mL), washed with H2O (10 mL) and brine (10 mL), dried over Na2SO4,
and then filtered. The solvent was evaporated under reduced pressure to give
the crude products. b-Lactams 2–4(a–d) were purified by column
chromatography on silica gel eluting with EtOAc/hexane (7:93). trans-1-(40-
Methoxyphenyl)-3-allyl-3-phenylsulfinyl-4-phenylazetidin-2-one (2a): Yield 36%,
Rf (7:93, EtOAc/hexane): 0.53; FT-IR (CHCl3) cmꢁ1: 1753 (C@O), 1638 (C@C);
1H NMR (300 MHz, CDCl3) d 2.19–2.26 (–CH2–, m, 1H), 2.81–2.89 (–CH2–, m,
1H), 3.63 (OCH3, s, 3H), 5.10–5.24 (H2C@, m, 2H), 5.16 (C4–H, s, 1H), 5.66–
5.67(@CH–, m, 1H), 6.63–7.55 (ArH, m, 14H); 13C NMR (75 MHz, CDCl3) d 28.1
(–CH2–), 55.3 (OCH3), 61.7 (C-4), 78.6 (C-3), 114.5–156.7 (C@C, ArC), 160.4
(C@O); Anal. Calcd for C25H23NO3S: C, 71.91; H, 5.55; N, 3.35. Found: C, 71.80;
H, 5.46; N, 3.28. trans-1-(40-methoxyphenyl)-3-allyl-3-phenylsulfinyl-4-
phenylazetidin-2-one (3a). Yield 46%, Rf (7:93, EtOAc/hexane): 0.43; mp: 161–
162 °C; FT-IR (CHCl3) cmꢁ1: 1748 (C@O), 1640 (C@C); 1H NMR (300 MHz,
CDCl3) d 2.22–2.30 (–CH2–, m, 1H), 2.59–2.66 (–CH2–, m, 1H), 3.73 (OCH3, s,
3H), 5.20 (C4–H, s, 1H), 5.25–5.28 (H2C@, m, 2H), 5.75–5.78 (@CH–, m, 1H),
6.76–7.56 (ArH, m, 14H); 13C NMR (75 MHz, CDCl3) d 33.7 (–CH2–), 55.4
(OCH3), 62.3 (C-4), 80.4 (C-3), 114.2–156.4 (C@C, ArC), 160.7 (C@O); EI-MS m/z
(R.I.%, [assignment]+): 417 (03, [M]+), 291 (78, [(E)-3-allylidene-b-lactam 6a]+),
211 (51, [C6H5CH@NC6H4(OCH3)]+), 149 (100, [O@C@NC6H4(OCH3)]+); Anal.
Calcd for C25H23NO3S: C, 71.91; H, 5.55; N, 3.35. Found: C, 71.85; H, 5.48; N,
3.29. trans-1-(40-Methoxyphenyl)-3-allyl-3-phenylsulfonyl-4-phenylazetidin-2-
one (4a). Yield 9%, Rf (7:93, EtOAc/hexane): 0.66; FT-IR (CHCl3) cmꢁ1: 1760
(C@O), 1639 (C@C); 1H NMR (300 MHz, CDCl3) d 2.52–2.60 (–CH2–, m, 1H),
2.66–2.73 (–CH2–, m, 1H), 3.60 (OCH3, s, 3H), 5.08 (C4–H, s, 1H), 5.14–5.23
(H2C@, m, 2H), 5.72–5.75 (@CH–, m, 1H), 6.59–7.64 (ArH, m, 14H); 13C NMR
r
Crystallographic data (excluding structure factors) for the structure 3b in
this Letter have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication number CCDC 642730. Copies of the data
can be obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: (internet) +44 1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk].
24. Sheldrick, G. M. SHELX-97: Program for the Solution and Refinement of Crystal
Structures, University of Göttingen, Göttingen, Germany.
25. General procedure for the synthesis of 3-allylidene-b-lactams 5, 6: A solution of 2
or 3 (1.0 mmol) in CCl4 (10 mL) was refluxed and the progress of the reaction
was monitored by TLC. The TLC profile of the reaction mixture showed the
appearance of two new spots, having Rf higher than the substrate 2 or 3.
Refluxing was continued until no change in TLC profile was observed. The
solvent was evaporated under reduced pressure to give the crude products. 3-
Allylidene-b-lactams 5, 6(a–d) were purified by column chromatography on
silica gel eluting with EtOAc/hexane (7:93). (Z)-1-(40-Methoxyphenyl)-3-
allylidene-4-phenylazetidin-2-one (5a): Yield 30%, Rf (7:93, EtOAc/hexane):
0.60; FT-IR (CHCl3) cmꢁ1: 1746 (C@O), 1695, 1649 (C@C); 1H NMR (300 MHz,
CDCl3) d 3.66 (OCH3, s, 3H), 5.20 (C4–H, s, 1H), 5.23–5.30 (H2C@, m, 2H), 5.88
(–CH@C–, d, 1H, J = 10.5), 6.66–7.29 (ArH and H2C@CH–, m, 10H); 13C NMR
(75 MHz, CDCl3) (DEPT–135)
d 55.1 [+, (OCH3)], 62.6 [+, (C-4)], 122.4
[ꢁ, (H2C@)], 114.4–156.1 (C@C, ArC), 159.6 (C@O); Anal. Calcd for
C19H17NO2: C, 78.32; H, 5.88; N, 4.80. Found: C, 78.24; H, 5.81; N, 4.73.
(E)-1-(40-Methoxyphenyl)-3-allylidene-4-phenylazetidin-2-one (6a): Yield 32%, Rf
(7:93, EtOAc/hexane): 0.57; UV–vis (THF) kmax (e) nm: 312 (14357); FT-IR
(CHCl3) cmꢁ1: 1736 (C@O), 1686, 1609 (C@C); 1H NMR (300 MHz, CDCl3) d 3.64
(OCH3, s, 3H), 5.21 (H2C@, d, 1H, J = 10.2), 5.32 (C4–H, s, 1H), 5.34 (H2C@, d, 1H,
J = 10.2), 5.95–6.07 (H2C@CH–, m, 1H), 6.52 (–CH@C–, d, 1H, J = 11.7), 6.62–
7.37 (ArH, m, 9H); 13C NMR (75 MHz, CDCl3) (DEPT–135) d 55.1 [+, (OCH3)],
63.1 [+, (C-4)], 124.5 [ꢁ, (H2C@)], 114.4–156.1 (C@C, ArC), 160.2 (C@O); Anal.
Calcd for C19H17NO2: C, 78.32; H, 5.88; N, 4.80. Found: C, 78.27; H, 5.83; N,
4.77.