A convenient synthesis and cytotoxic evaluation of β-aryl-α- methylidene-γ-lactones and β-aryl-α-methylidene-γ-lactams

Article abstract of DOI:10.1039/b9nj00740g

3-Aryl-2-diethoxyphosphoryl-4-nitrohexanoates 8, obtained by Michael addition of ethyl diethoxyphosphorylacetate 6 to 1-aryl-2-nitro-1-butenes 7, were utilized as convenient common intermediates in the synthesis of β-aryl-γ-ethyl-α-methylidene-γ-lactones 17 and β-aryl-γ-ethyl-α-methylidene-γ-lactams 21. Transformation of the nitro functionality in 8 into a hydroxyl or amino group and cyclization yielded lactones 16 or lactams 19, which were used in Horner-Wadsworth-Emmons olefination of formaldehyde to give target compounds in good yields. Cytotoxicity of these compounds was evaluated in vitro against mouse leukemia cell line L-1210 and two human leukemia cell lines, HL-60 and NALM-6. Two of the obtained compounds 17b,c with 4-bromophenyl and 4-methylphenyl substituents in the β position proved to be very potent against all three cell lines with IC₅₀ values lower than 6 μM. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b9nj00740g

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PAPER
www.rsc.org/njc | New Journal of Chemistry
A convenient synthesis and cytotoxic evaluation of
b-aryl-a-methylidene-c-lactones and b-aryl-a-methylidene-c-lactams
a
a
b
b
´
˙
Anna Albrecht, Łukasz Albrecht, Marek Rozalski, Urszula Krajewska,
Anna Janecka,c Kazimierz Studzianc and Tomasz Janecki*a
Received (in Montpellier, France) 8th December 2009, Accepted 15th January 2010
First published as an Advance Article on the web 24th February 2010
DOI: 10.1039/b9nj00740g
3-Aryl-2-diethoxyphosphoryl-4-nitrohexanoates 8, obtained by Michael addition of ethyl
diethoxyphosphorylacetate 6 to 1-aryl-2-nitro-1-butenes 7, were utilized as convenient common
intermediates in the synthesis of b-aryl-g-ethyl-a-methylidene-g-lactones 17 and
b-aryl-g-ethyl-a-methylidene-g-lactams 21. Transformation of the nitro functionality in 8 into a
hydroxyl or amino group and cyclization yielded lactones 16 or lactams 19, which were used in
Horner–Wadsworth–Emmons olefination of formaldehyde to give target compounds in good
yields. Cytotoxicity of these compounds was evaluated in vitro against mouse leukemia cell line
L-1210 and two human leukemia cell lines, HL-60 and NALM-6. Two of the obtained
compounds 17b,c with 4-bromophenyl and 4-methylphenyl substituents in the b position proved
to be very potent against all three cell lines with IC50 values lower than 6 mM.
using thus formed lactones or lactams give access to the target
Introduction
compounds 1 or 2. Phosphorylnitroalkanoates 5 have so far
been synthesized by Michael addition of nitroalkanes 4 to
2-diethoxyphosphorylacrylates 3 in the presence of base
(Scheme 1). However, the scope of these reactions is limited
to diethoxyphosphorylacrylate 3 (R2 = H) as Michael acceptor13
or to nitromethane (R3 = H) or nitroethane (R3 = Me) as
Michael donors.15
Sesquiterpene lactones are a large and diverse group of natural
products which are the active components of many medicinal
plants mainly from the Asteraceae family.1,2 Their phytotoxic,
antimicrobial, antifungal, cardiovascular, anti-inflammatory
and in particular anticancer activity make them an extremely
interesting group of potentially useful drugs with many
possible applications, e.g. in both cancer chemotherapy and
chemoprevention.3 Bioactivity, molecular mechanism of
action as well as structure–activity relationship (SAR) of these
compounds have been intensively studied.3–6 Numerous
investigations confirmed that the presence of a-methylidene-
g-lactone moiety 1 (Fig. 1) in the sesquiterpene lactone
structure is the most important parameter for their activity.
It is now generally accepted that the covalent binding of this
moiety, via Michael-type addition, to free mercapto groups in
proteins or free intracellular glutathione leads to reduction of
enzyme activity or causes the disruption of glutathione
metabolism and the vitally important intracellular cell redox
balance.3 a-Methylidene-g-lactams 2 (Fig. 1) are less prevalent
in nature and their activity is much less recognized. However,
moderate cytotoxic activity of these compounds was reported.7–9
Not surprisingly, many strategies for the synthesis of
a-methylidene-g-lactones and lactams with diverse substitution
patterns have been developed.1,10–12 One of them uses
In this paper we report that the Michael addition of ethyl
diethoxyphosphorylacetate 6 to 1-aryl-2-nitro-1-butenes 7
gives access to, so far unknown, 3-aryl-2-diethoxyphosphoryl-
4-nitrohexanoates 8. These compounds were next transformed
into b-aryl-g-ethyl-a-methylidene-g-lactones 17 and b-aryl-g-
ethyl-a-methylidene-g-lactams 21, employing
a Horner–
Wadsworth–Emmons olefination pathway. Target compounds
were next tested for their cytotoxic activity against mouse
leukemia cell line L-1210 and two human leukemia cell lines,
HL-60 and NALM-6.
Results and discussion
Starting (E)-1-aryl-2-nitro-1-butenes 7a–d were prepared by
nitroaldol condensation of nitropropane with selected aromatic
aldehydes applying a modified literature procedure.16 Additions
of diethoxyphosphorylacetate 6 to nitrobutenes 7a–d were
performed in THF using sodium hydride as a base and were
completed after 24 h. Crude products were purified by column
2-diethoxyphosphoryl-4-nitroalkanoates
5
as convenient
common intermediates.9,13,14 Transformation of the nitro
functionality into a hydroxyl or amino group, cyclization
and Horner–Wadsworth–Emmons olefination of formaldehyde
a
´
´
Institute of Organic Chemistry, Technical University of Łodz,
˙
´
´
Zeromskiego 116, 90-924 Łodz, Poland. E-mail: tjanecki@p.lodz.pl
b Department of Pharmaceutical Biochemistry, Medical University of
´
´
´
´,
Łodz Muszynskiego 1, 90-151 Łodz Poland
´,
c
´
Department of Biomolecular Chemistry, Medical University of Łodz
´,
´
Mazowiecka 6/8, 92-215 Łodz Poland
´,
Fig. 1 General structures of a-methylidene-g-lactones and -g-lactams.
ꢀc
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Fig. 2 Newman projections for syn- and anti-14a–d.
Scheme 1 Methods for the synthesis of 2-diethoxyphosphoryl-4-
nitroalkanoates 5.
assign the relative stereochemistry at the C-2 and C-3 stereogenic
3
chromatography. Pure ethyl 3-aryl-2-diethoxyphosphoryl-4-
nitrohexanoates 8a–d were obtained in good yields as mixtures
of four diastereomers (Scheme 2, Table 1). Their ratios were
determined from the signals integration in 31P NMR spectra. For
8c only three signals were visible in 31P NMR spectra, probably
because of the overlap of the signals of two diastereomers. Due to
the complex diastereomeric mixtures of the adducts 8 their full
characterization by 13C NMR was not possible.
centers. Diagnostic were large coupling constants JH2H3 in
1H NMR spectra of both diastereomers (7.9–8.4 Hz for major
and 9.9–10.4 Hz for minor diastereomer) which clearly proves
an antiperiplanar arrangement of H-2 and H-3.18 Furthermore,
in 13C NMR spectra of major diastereomers signals of the carbonyl
carbon atoms appeared as doublets with large phosphorus–
carbon coupling constants (3JPCQO = 16.1–16.4 Hz) and
signals of the aromatic carbon atoms in the ipso position were
singlets (3JPCipso = 0 Hz). These values clearly indicate an
antiperiplanar arrangement of the carbonyl and phosphoryl
groups as well as a gauche arrangement of the aromatic
substituent and phosphoryl group (Fig. 2).19 Therefore the
syn configuration was assigned to major diastereomers of
14a–d. Corresponding coupling constants for minor diastereomers
Obtained nitrohexanoates 8a–d were next tested in the Nef
reaction. In this regard, our initial reactions were performed in
classic conditions (MeONa/MeOH, r.t. then H2SO4/MeOH,
À60 1C), which worked well in our laboratory for 3-unsubstituted
analogues.13 However, in these conditions rather complex
1
mixtures of products were formed. H and 31P NMR analysis
3
3
of the reaction mixtures revealed that ethyl diethoxyphosphoryl-
acetate 6 and nitropropane 11, along with the starting material,
were among the products. Formation of these compounds can
be rationalized assuming that in strongly basic conditions
retro-Michael reaction takes place instead of the Nef reaction
(Scheme 3). Evidently, the presence of an aromatic substituent
in position 3 facilitates the retro-Michael reaction due to the
conjugation of the newly formed double bond with this
substituent.
were JPCQO = 0 Hz and JPCipso = 16.4–16.7 Hz which
proves an antiperiplanar relationship of phosphoryl and aryl
groups and a gauche relationship of carbonyl and phosphoryl
groups. Consequently, the anti configuration was assigned to
minor diastereomers of 14a–d.
Oxohexanoates 14a–d were next subjected to chemoselective
reduction of the carbonyl group using potassium borohydride
in methanol. Short reaction time (B50 min) appeared to be
crucial for the efficiency of the reductions. Initially formed
4-hydroxyalkanoates 15 lactonized spontaneously providing
a-diethoxyphosphoryl-g-lactones 16a–c in good yields
(Scheme 4). Only reduction of 14d was not chemoselective
and gave a complex mixture of compounds which were
difficult to identify. Interestingly, lactones 16a–c were formed
as a mixtures of only two, out of four possible diastereomers in
the ratio given in Table 2. Attempts to separate these mixtures
failed.
Pleasingly, careful analysis of 1H, 13C and 31P NMR spectra
of lactones 16a–c allowed us to assign the (r-3, t-4, c-5)
configuration for all major diastereomers and the (r-3, t-4, t-5)
configuration for all minor diastereomers. The observed values
of coupling constant 3JPCipso = 0 Hz (Table 3) clearly proved
the trans arrangement of the phosphoryl and aryl groups in
both major and minor diastereomers. On the other hand,
lower values of the chemical shifts observed for H-5 protons
in major diastereomers in comparison with the same protons
in minor diastereomers (e.g. for 16a corresponding values
were 4.35 ppm and 4.88 ppm, respectively) indicated a trans
relationship of ethyl and aryl groups in the former due to the
shielding effect exerted by the benzene ring on the cis-oriented
proton H-5. Also, coupling constants 3JPC5 and JH3H4 were in
agreement with this assignment. Dihedral angles estimated
from these coupling constants, using the Karplus equation,18,19
had values given in parentheses in Table 3 and were in good
agreement with the dihedral angles taken from the corresponding
Cochranes orbit size molecular models of (r-3,t-4,c-5)-16a–c
In view of the above, we decided to perform the Nef reaction
under much milder, ozonolytic conditions.17 Passing ozone
through the solution of nitroalkanoates 8a–d in the presence of
Triton B at À78 1C and standard work up of the reaction
mixture gave crude ethyl 3-aryl-2-diethoxyphosphoryl-4-
oxohexanoates 14a–d which were purified by column
chromatography. Pure hexanoates 14 were obtained in good
yields as mixtures of two diastereomers (Scheme 2, Table 1).
Efforts undertaken to separate these diastereomers by column
chromatography were unsuccessful.
Careful analysis of 1H, 13C and 31P NMR spectra confirmed
the structure of all obtained products 14a–d and allowed us to
Scheme 2 Reagents and conditions: (i) NaH/THF; (ii) Triton Bs/O3,
EtOH/Me2S, À78 1C to r.t.
ꢀc
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Table 1 Synthesis of ethyl 3-aryl-2-diethoxyphosphoryl-4-nitrohexanoates 8a–d and ethyl 3-aryl-2-diethoxyphosphoryl-4-oxohexanoates 14a–d
8
14
Yield [%]a
Diastereomeric ratiob
Yield [%]a
Diastereomeric ratiob
Ar
a
b
c
C6H5-
89
80
70
75
3 : 33 : 21 : 43
45 : 21 : 34
8 : 35 : 22 : 35
6 : 19 : 26 : 39
66
65
53
53
65 : 35
65 : 35
60 : 40
60 : 40
4-Br-C6H4-
4-CH3-C6H4-
4-NO2-C6H4-
d
a
b
Yield of isolated, pure product based on 6 or 8 respectively. Taken from 31P NMR spectra of the crude products.
Scheme 3 Reagents and conditions: (i) MeONa/MeOH.
Finally, olefination of the formaldehyde using phosphoryl-
ated lactones 16a–c as the Horner–Wadsworth–Emmons
reagents in the presence of potassium tert-butoxide gave, after
standard work-up and purification by column chromatography,
pure a-methylidene-g-lactones 17a–c in good yields. These
compounds were formed as mixtures of two diastereoisomers
in the same ratio as starting lactones 16a–c (Scheme 4,
Table 2). Their structure was confirmed by the analysis of
1H and 13C NMR spectra. For example, values of the chemical
shifts of H-4 and H-5 protons were always smaller for the
protons of the major diastereomers (dH-4 = 3.74–3.79 ppm,
dH-5 = 4.30–4.35 ppm) in comparison with the corresponding
protons of the minor diastereomers (dH-4 = 4.10–4.32 ppm,
dH-5 = 4.60–4.63 ppm). This observation can be rationalized
by the shielding effect of the phenyl ring or ethyl group exerted
on the protons which are cis-orientated to one of these groups
and proves that major diastereomers have the trans configuration.
Furthermore it confirms the correctness of the configurational
assignments made for lactones 16.
Scheme 4 Reagents and conditions: (i) KBH4/MeOH then HCl/H2O;
(ii) t-BuOK/Et2O then (CH2O)n/Et2O.
and (r-3,t-4,t-5)-16a–c, in which the diethoxyphosphoryl and
aryl groups were assumed to occupy pseudo-equatorial
positions. Based on these results it can be assumed that
reduction followed by lactonization proceeds with epimerization
at the C-3 carbon atom giving lactones 16 with a more stable
trans arrangement of the phosphoryl and aryl groups.
Next we turned our attention to the application of nitro-
hexanoates 8a–d in the synthesis of b-aryl-g-ethyl-a-methyl-
idene-g-lactams 21. Chemoselective reduction of the nitro
Table 2 Synthesis of a-diethoxyphosphoryl-g-lactones 16a–c and a-methylidene-g-lactones 17a–c
16
17
Yield [%]a
Diastereomeric ratiob
Yield [%]a
trans : cisc
Ar
a
b
c
C6H5-
4-Br-C6H4-
4-CH3-C6H4-
60
59
80
70 : 30
70 : 30
60 : 40
68
69
71
70 : 30
70 : 30
60 : 40
a
b
c
1
Yield of isolated, pure product based on 14 or 16 respectively. Taken from 31P NMR spectra of the crude products. Taken from H NMR
spectra of the crude products.
ꢀc
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Table 3 Selected chemical shifts and coupling constants for (r-3,t-4,c-5)-16a–c and (r-3,t-4,t-5)-16a–ca
d (1H) H-5 [ppm]
3JPCipso/Hz
3JPC5/Hz
3JH3H4/Hz
(r-3,t-4,c-5)-16a
(r-3,t-4,t-5)-16a
(r-3,t-4,c-5)-16b
(r-3,t-4,t-5)-16b
(r-3,t-4,c-5)-16c
(r-3,t-4,t-5)-16c
4.35
4.88
4.20
4.83
4.51
4.85
0 (110–1201)
13.3 (150–1601)
10.4 (150–1601)
0
0
0
0
0
3.2 (130–401)
12.9
3.5
13.1
3.3
2.6 (120–1301)
10.5
2.7
10.4
2.6
a
1
Taken from the H and 13C NMR spectra of the mixtures of diastereomers.
group by sodium borohydride in the presence of NiCl2Á6H2O20–22
yielded 4-aminohexanoates 18a–c which lactamized
spontaneously to a-diethoxyphosphoryl-g-lactams 19a–c
(Scheme 5, Table 4). Disappointingly the reduction of 8d
was not chemoselective and proceeded with partial reduction
of the aromatic nitro group. Our efforts to improve chemo-
selectivity of this reaction or separate the desired product were
unsuccessful. Lactams 19a–c were formed as mixtures of two,
out of four possible stereoisomers. Spectroscopic studies
confirmed their structure, but did not allow us to assign
unequivocally the relative configuration at C-2, C-3 and C-4
stereogenic centers. However, keeping in mind the facile
epimerization of lactones 16 and taking into account the
strongly basic conditions of the reduction, it can be assumed
that similar epimerization of lactams 19 at the C-3 carbon
atom gives rise to two thermodynamically more stable
diastereomers with trans configuration at C-3 and C-4 carbon
atoms but opposite configuration at C-4 and C-5 carbon atoms.
When lactams 19a–c were used in the Horner–
Wadsworth–Emmons olefination of formaldehyde applying
conditions tested for lactones 16, along with the desired
a-methylidene-g-lactams 22, their N-hydroxymethyl derivatives
were also formed in substantial amounts. To overcome this
problem the Boc protecting group was introduced onto the
amide nitrogen atom by treatment of lactams 19a–c with
Boc2O in the presence of a catalytic amount of DMAP.
Obtained N-Boc lactams 20a–c were purified by column
chromatography and used in the olefination of formaldehyde.
We were pleased to observe that the reactions proceeded
effectively yielding, after purification by column chromato-
graphy, N-Boc-a-methylidene-g-lactams 21a–c in good yields
(Scheme 5, Table 4). Furthermore, analysis of the H and 13C
NMR spectra revealed that chemical shifts of H-4 and H-5
carbon atoms in major diastereomers have smaller values than
chemical shifts of the same protons in minor diastereomers. On
this basis, using the same rationale as for lactones 17a–c, we
assigned the trans configuration to all major diastereomers and
the cis configuration to all minor diastereomers of lactams 21.
Deprotection of a-methylidene-g-lactams 21 can be easily
achieved using a standard procedure. This was demonstrated
by treatment of lactam 21b with 33% TFA in CH2Cl2 at room
temperature. Standard work-up and purification by column
chromatography provided pure a-methylidene-g-lactam 22b in
68% yield.
1
Due to the anticipated biological activity, lactones 17a–c as
well as lactam 22b were tested in vitro against mouse leukemia
cell line L-1210 and two human leukemia cell lines, HL-60 and
NALM-6. Cytotoxic activity of these compounds is expressed
as the concentration (mM) required to inhibit tumor cells
proliferation by 50% after 48 h exposure of the cells to a
tested compound (IC50 values). Carboplatin was used as a
reference compound.23 Obtained results are shown in Table 5.
All tested compounds exhibited a consistent cytotoxic
activity with IC50 values ranging from 0.60 to 81.2 mM.
Furthermore, we were pleased to observe that the IC50 values
of 4-bromophenyl and 4-methylphenyl substituted lactones
17b,c were in all tests smaller than 5.6 mM and therefore these
compounds can be considered as highly potent according to
Kupchan’s classification (IC50 r 15 mM).24 It is also
noteworthy that introduction of the unsubstituted phenyl
group in the b-position (lactone 17a) diminishes the activity
significantly against all three cell lines. Lactam 22b displayed
Scheme 5 Reagents and conditions: (i) NiCl2Á6H2O/MeOH then NaBH4/MeOH; (ii) Boc2O, DMAP/CH2Cl2; (iii) t-BuOK/THF then
(CH2O)n/THF; (iv) CF3CO2H/CH2Cl2.
ꢀc
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Table 4 Synthesis of a-diethoxyphosphoryl-g-lactams 19a–c, N-Boc-a-diethoxyphosphoryl-g-lactams 20a–c and N-Boc-a-methylidene-g-lactams
21a–c
19
20
21
Yield [%]a
Diastereomeric ratiob
Yield [%]a
Diastereomeric ratiob
Yield [%]a
trans : cisc
Ar
a
b
c
C6H5-
4-Br-C6H4-
4-CH3-C6H4-
92
79
85
55 : 45
60 : 40
60 : 40
69
72
82
55 : 45
60 : 40
60 : 40
59
52
80
55 : 45
60 : 40
60 : 40
a
b
c
Yield of isolated, pure product based on 8, 19 or 20 respectively. Taken from 31P NMR spectra of the crude products. Taken from 1H NMR
spectra of the crude products.
Table 5 Cytotoxic activity of compounds 17a–c, 22b and 23
Cytotoxicity IC50/mMa
spectra were recorded using broad-band proton decoupling.
J values are given in Hz. 1-aryl-2-nitro-1-butenes 7a–d were
prepared according to a modified literature procedure.16
L-1210
HL-60
NALM-6
Compound
General procedure for the preparation of ethyl 3-aryl-2-
diethoxyphosphoryl-4-nitrohexanoates 8a–d
17a
17b
35.0 Æ 2.8
1.60 Æ 0.21
0.85 Æ 0.06
43.0 Æ 1.9
56.05 Æ 3.53
1.16 Æ 0.02
5.5 Æ 0.5
59.99 Æ 4.05
0.60 Æ 0.03
5.6 Æ 0.3
17c
22b
To a slurry of sodium hydride (0.45 g, 18.7 mmol) in THF
(40 mL) at room temperature a solution of ethyl diethoxy-
phosphorylacetate (6) (4.0 g, 17.8 mmol) in THF (5 mL) was
added dropwise. The resulting solution was stirred for 30 min
at room temperature and then cooled to À5 1C. A solution of
the corresponding 1-aryl-2-nitro-1-butene 7 (35.6 mmol) in
THF (15 mL) was next added dropwise. The reaction mixture
was allowed to warm to room temperature, stirred for an
additional 24 h at that temperature and quenched with
saturated ammonium chloride solution (50 mL). THF was
removed under reduced pressure and the residue extracted
with CH2Cl2 (3 Â 30 mL). Combined organic layers were dried
over MgSO4, filtered and the solvents were removed in vacuo.
Crude product was purified by column chromatography
(eluent: chloroform–acetone 95 : 5).
65.8 Æ 2.2
515.7 Æ 47.6
2.9 Æ 0.1
81.2 Æ 2.5
439.2 Æ 40.8
0.7 Æ 0.3
23b
Carboplatin
9.7 Æ 1.2
a
IC50, 50% inhibitory concentration represents the mean from dose
b
response curves of at least three experiments. Data taken from ref. 9.
moderate cytotoxicity, confirming previous reports that the
cytotoxicities of a-methylidene-g-lactones are generally much
higher than the cytotoxicities of a-methylidene-g-lactams.8
However, the cytotoxicity of lactam 22b was significantly
higher than the reported cytotoxicity9 of its g-methyl analogue
b-(4-bromophenyl)-g-methyl-a-methylidene-g-lactone 23
(Table 5). Evidently, a very small structural change such as
the presence of an ethyl instead of a methyl substituent in the
g position increases the cytotoxicity several times.
Ethyl 2-(diethoxyphosphoryl)-4-nitro-3-phenylhexanoate (8a).
(89%) yellow oil (Found: C, 53.6; H, 6.8. C18H28NO7P
requires C, 53.9; H, 7.0%); nmax(film)/cmÀ1 1724, 1552,
1386, 1368, 1256, 1164 and 1020; dH(250 MHz; CDCl3; Me4Si)
0.84–1.14 (6 H, m, CH3CH2, CH3CH2O), 1.26–1.40 (8 H, m,
(CH3CH2O)2P(O), CH2), 1.60–1.99 (2 H, m, CH2), 3.43–3.56
(1 H, m, CHP), 3.71–3.90 (4 H, m, CH3CH2O, CH, CHP),
3.96–4.38 (4 H, m, (CH3CH2O)2P(O)), 4.69–4.77 (1 H, m,
CHN), 5.11–5.28 (1 H, m, CHN), 7.07–7.17 (2 H, m, Ph) and
7.24–7.31 (3 H, m, Ph); dP(101 MHz; CDCl3; H3PO4) 19.7
(3%), 19.9 (33%), 20.3 (21%) and 20.93 (43%).
Conclusions
We have developed an efficient and straightforward route to
b-aryl-g-ethyl-a-methylidene-g-lactones 17 and b-aryl-g-ethyl-
a-methylidene-g-lactams 21 via 3-aryl-2-diethoxyphosphoryl-
4-nitrohexanoates
8 as the key intermediates. Relative
configurations of the intermediates and all target compounds
were unequivocally assigned using spectroscopic techniques.
Furthermore, all target compounds were evaluated for their
cytotoxic activity towards mouse leukemia cell line L-1210 and
two human leukemia cell lines, HL-60 and NALM-6, and two
of the prepared lactones 17b,c exhibited remarkable cytotoxicity
against all three cell lines.
Ethyl
3-(4-bromophenyl)-2-(diethoxyphosphoryl)-4-nitro-
hexanoate (8b). (80%) yellow oil (Found: C, 45.3; H, 6.0.
C18H27BrNO7P requires C, 45.0; H, 5.6%); nmax(film)/cmÀ1
1724, 1548, 1392, 1288, 1248, 1156 and 1024; dH(250 MHz;
CDCl3; Me4Si) 0.83–1.11 (6 H, m, CH3CH2, CH3CH2O),
1.29–1.44 (8 H, m, (CH3CH2O)2P(O), CH2), 1.58–1.97
(2 H, m, CH2), 3.36–3.49 (1 H, m, CHP), 3.58–4.37 (8 H, m,
(CH3CH2O)2P(O), CH3CH2O, CH, CHP), 4.68–4.87 (1 H, m,
CHN), 5.10–5.28 (1 H, m, CHN), 7.00–7.20 (2 H, m, 2 Â CH-Ar)
and 7.37–7.47 (2 H, m, 2 Â CH-Ar); dP(101 MHz; CDCl3;
H3PO4) 19.3 (45%), 19.9 (21%) and 20.4 (34%).
Experimental results
General information
Organic solvents and reagents were purified by the appropriate
standard procedures. Column chromatography was performed
on Flukas silica gel 60 (230–400 mesh). IR spectra were
recorded on
a Specord M
80 spectrometer. 1H NMR
(250 MHz), 13C NMR (62.9 MHz) and 31P NMR (101 MHz)
spectra were recorded on a Bruker DPX-250 spectrometer with
TMS as an internal standard for 1H NMR and 13C NMR, and
85% H3PO4 as an external standard for 31P NMR. 31P NMR
Ethyl 2-(diethoxyphosphoryl)-4-nitro-3-p-tolylhexanoate (8c).
(70%) yellow oil (Found: C, 54.9; H, 7.0. C19H30NO7P requires
C, 54.9; H, 7.3%); nmax(film)/cmÀ1 1732, 1552, 1392, 1368, 1252,
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1160 and 1028; dH(250 MHz; CDCl3; Me4Si) 0.84–1.16 (6 H, m,
CH3CH2, CH3CH2O), 1.26–1.41 (8 H, m, (CH3CH2O)2P(O),
CH2), 1.60–1.83 (2 H, m, CH2), 2.28 (3 H, s, CH3), 2.29 (3 H, s,
CH3), 2.32 (3 H, s, CH3), 2.34 (3 H, s, CH3), 3.41–3.54 (1 H, m,
CHP), 3.75–4.07 (3 H, m, CH3CH2O, CH), 4.15–4.30 (4 H, m,
(CH3CH2O)2P(O)), 4.67–4.77 (1 H, m, CHN), 5.09–5.27
(1 H, m, CHN) and 6.95–7.21 (4 H, m, 4 Â CH-Ar);
dP(101 MHz; CDCl3; H3PO4) 20.1 (8%), 20.3 (35%), 20.7
(22%) and 21.4 (35%).
35%), 128.7 (2 Â C-Ar, 65%), 128.8 (2 Â C-Ar, 35%), 129.4
(2 Â C-Ar, 65%), 134.9 (C-Ar, 65%), 135.5 (d, J 16.2, C-Ar,
35%), 167.2 (d, J 5.0, C-1, 35%), 168.8 (d, J 4.7, C-1, 65%),
207.5 (C-4, 35%) and 208.7 (d,
J 16.4, C-4, 65%);
dP(101 MHz; CDCl3; H3PO4) 21.3 (65%) and 21.5 (35%).
Ethyl 3-(4-bromophenyl)-2-(diethoxyphosphoryl)-4-oxohexanoate
(14b). (65%) yellow oil (Found: C, 48.3; H, 6.0. C18H26BrO6P
requires C, 48.1; H, 5.8%); nmax(film)/cmÀ1 1714, 1589, 1392,
1368, 1245, 1155 and 1009; dH(250 MHz; CDCl3; Me4Si)
0.90–1.41 (12 H, m, P(O)(OCH2CH3)2, CH3, OCH2CH3, 65%
+ 35%), 2.33–2.39 (2 H, m, CH2, 65% + 35%), 3.64–4.26
(9 H, m, H-2, (CH3CH2O)2P(O), CH2, OCH2CH3, 65% + 35%),
4.41 (1 H, dd, J 10.2 and 11.9, H-3, 35%), 4.51 (1 H, dd, J 8.2 and
11.8, H-3, 65%), 7.14–7.20 (2 H, m, 2 Â CH-Ar, 65% + 35%)
and 7.40–7.48 (2 H, m, 2 Â CH-Ar, 65% + 35%); dC(62.9 MHz;
CDCl3; Me4Si) 7.3 (CH2CH3, 35%), 7.6 (CH2CH3, 65%), 13.6
(C(O)OCH2CH3, 35%), 13.8 (C(O)OCH2CH3, 65%), 15.8 (d,
J 5.9, CH3CH2OP(O), 65%), 15.9 (d, J 5.9, CH3CH2OP(O),
65%), 16.0 (d, J 5.7, CH3CH2OP(O), 35%), 16.1 (d, J 5.3,
CH3CH2OP(O), 35%), 34.3 (CH2CH3, 65%), 35.3 (CH2CH3,
35%), 48.1 (d, J 126.8, C-2, 35%), 48.3 (d, J 131.7, C-2, 65%),
55.0 (d, J 2.3, C-3, 35%), 55.8 (d, J 2.2, C-3, 65%), 61.1
(C(O)OCH2CH3, 35%), 61.5 (C(O)OCH2CH3, 65%), 62.2
(d, J 6.7, CH3CH2OP(O), 65%), 62.4 (d, J 6.8, CH3CH2OP(O),
65%), 62.7 (d, J 6.6, CH3CH2OP(O), 35%), 62.9 (d, J 6.6,
CH3CH2OP(O), 35%), 121.9 (C-Ar, 35%), 122.0 (C-Ar, 65%),
130.2 (2 Â C-Ar, 35%), 130.9 (2 Â C-Ar, 65%), 131.7 (2 Â C-Ar,
35%), 131.8 (2 Â C-Ar, 65%), 133.8 (C-Ar, 35%), 134.5 (d, J 16.3,
C-Ar, 65%), 166.8 (d, J 5.2, C-1, 35%), 168.3 (d, J 4.8, C-1, 65%),
207.9 (C-4, 35%) and 208.0 (d, J 16.1, C-4, 65%); dP(101 MHz;
CDCl3; H3PO4) 21.2 (65%), 21.4 (35%).
Ethyl 2-(diethoxyphosphoryl)-4-nitro-3-(4-nitrophenyl)hexanoate
(8d). (75%) yellow oil (Found: C, 48.2; H, 6.4. C18H27N2O9P
requires C, 48.4; H, 6.1%); nmax(film)/cmÀ1 1720, 1548, 1368,
1252, 1172 and 1024; dH(250 MHz; CDCl3; Me4Si) 0.88–1.42
(12 H, m, CH3CH2, CH3CH2O, (CH3CH2O)2P(O), CH2),
1.54–1.84 (2 H, m, CH2), 3.36–4.38 (8 H, m, (CH3CH2O)2P(O),
CH3CH2O, CH, CHP), 4.77–5.01 (1 H, m, CHN), 7.31–7.55 (2 H,
m, 2 Â CH-Ar) and 8.12–8.20 (2 H, m, 2 Â CH-Ar); dP(101 MHz;
CDCl3; H3PO4) 19.0 (39%), 19.1 (6%), 19.6 (19%) and
20.0 (26%).
General procedure for the preparation of ethyl 3-aryl-2-
diethoxyphosphoryl-4-oxohexanoates 14a–d
A solution of the corresponding ethyl 3-aryl-2-diethoxy-
phosphoryl-4-nitrohexanoate 8 (2.15 mmol) and Triton B
(40% solution in methanol, 1.02 mL, 2.24 mmol) in anhydrous
ethanol (10 mL) was cooled to À78 1C and treated with a
stream of ozone until the reaction mixture turned light blue
(about 30 min). Dimethyl sulfide (0.58 mL, 7.90 mmol) was
then added and the mixture was allowed to warm to room
temperature. The reaction mixture was stirred for an additional
20 h at that temperature and then evaporated to dryness under
reduced pressure. The residue was acidified with 3 M HCl and
extracted with chloroform (3 Â 15 mL). Combined organic
layers were dried over MgSO4, filtered and the solvents were
removed in vacuo. Crude product was purified by column
chromatography (eluent: ethyl acetate–hexane 6 : 4).
Ethyl 2-(diethoxyphosphoryl)-4-oxo-3-(p-tolyl)hexanoate (14c).
(53%) yellow oil (Found: C, 59.0; H, 7.3. C19H29O6P requires
C, 59.4; H, 7.6%); nmax(film)/cmÀ1 1733, 1548, 1391, 1368,
1250, 1154 and 1016; dH(250 MHz; CDCl3; Me4Si) 0.88–1.40
(12 H, m, (CH3CH2O)2P(O), CH3, OCH2CH3, 60% + 40%),
2.28 (3 H, s, CH3, 40%, 2.32 (3 H, s, CH3, 60%), 2.37 (2 H, q,
CH2, J 7.3, 60% + 40%), 3.59–4.26 (9 H, m, H-2,
(CH3CH2O)2P(O), CH2, OCH2CH3, 60% + 40%), 4.40
(1 H, dd, J 10.3 and 11.8, H-3, 40%), 4.51 (1 H, dd, J 8.4
and 11.8, H-3, 60%) and 7.06–7.20 (4 H, m, 4 Â CH-Ar,
60% + 40%); dC(62.9 MHz; CDCl3; Me4Si) 7.6 (CH2CH3,
40%), 7.8 (CH2CH3, 60%), 13.7 (C(O)OCH2CH3, 40%), 14.0
(C(O)OCH2CH3, 60%), 15.9 (d, J 6.0, CH3CH2OP(O), 60%),
16.0 (d, J 6.1, CH3CH2OP(O), 60%), 16.2 (d, J 5.9,
(CH3CH2O)2P(O), 40%), 16.3 (d, J 5.8, CH3CH2OP(O),
40%), 21.0 (CH3, 60% + 40%), 34.2 (CH2CH3, 60%), 35.2
(CH2CH3, 40%), 48.3 (d, J 126.5, C-2, 40%), 48.6 (d, J 131.5,
C-2, 60%), 55.5 (d, J 2.8, C-3, 40%), 56.3 (C-3, 60%), 61.1
(C(O)OCH2CH3, 40%), 61.6 (C(O)OCH2CH3, 60%), 62.2
(d, J 7.5, CH3CH2OP(O), 60%), 62.3 (d, J 7.4, CH3CH2OP(O),
60%), 62.7 (d, J 6.5, CH3CH2OP(O), 40%), 63.0 (d, J 6.4,
CH3CH2OP(O), 40%), 128.6 (2 Â C-Ar, 40%), 129.2 (2 Â C-Ar,
60%), 129.4 (2 Â C-Ar, 40%), 129.5 (2 Â C-Ar, 60%), 131.8
(C-Ar, 40%), 132.5 (d, J 16.3,C-Ar, 60%), 137.6 (C-Ar, 40%),
137.7 (C-Ar, 60%), 167.3 (d, J 5.1, C-1, 40%), 168.9 (d, J 5.0,
Ethyl 2-(diethoxyphosphoryl)-4-oxo-3-phenylhexanoate (14a).
(66%) yellow oil (Found: C, 58.7; H, 7.4. C18H27O6P requires
C, 58.4; H, 7.35%); nmax(film)/cmÀ1 1717, 1640, 1551, 1392,
1368, 1248, 1154 and 1016; dH(250 MHz; CDCl3; Me4Si)
0.88–1.41 (12 H, m, (CH3CH2O)2P(O), CH3, OCH2CH3,
65% + 35%), 2.34–2.61 (2 H, m, CH2, 65% + 35%),
3.55–4.22 (9 H, m, H-2, (CH3CH2O)2P(O) CH2, OCH2CH3,
65% + 35%), 4.45 (1 H, dd, J 10.4 and 11.8, H-3, 35%), 4.56
(1 H, dd, J 8.4 and 11.7, H-3, 65%) and 7.23–7.34 (5 H, m,
5 Â CH-Ar, 65% + 35%); dC(62.9 MHz; CDCl3; Me4Si) 7.5
(CH2CH3, 35%), 7.8 (CH2CH3, 65%), 13.6 (C(O)OCH2CH3,
35%), 14.0 (C(O)OCH2CH3, 65%), 15.9 (d, J 6.1, CH3CH2O-
P(O), 65%), 16.0 (d, J 6.2, CH3CH2OP(O), 65%), 16.2 (d, J
5.8, CH3CH2OP(O), 35%), 16.3 (d, J 5.6, CH3CH2OP(O),
35%), 34.3 (CH2CH3, 65%), 35.3 (CH2CH3, 35%), 48.2 (d, J
126.8, C-2, 35%), 48.6 (d, J 131.6, C-2, 65%), 55.8 (d, J 1.9,
C-3, 35%), 56.7 (C-3, 65%), 61.1 (C(O)OCH2CH3, 35%), 61.6
(C(O)OCH2CH3, 65%), 62.2 (d, J 6.7, CH3CH2OP(O), 65%),
62.4 (d, J 7.0, CH3CH2OP(O), 65%), 62.8 (d, J 6.5,
CH3CH2OP(O), 35%), 63.0 (d, J 6.3, CH3CH2OP(O), 35%),
127.8 (CH-Ar, 35%), 127.9 (CH-Ar, 65%), 128.7 (2 Â C-Ar,
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C-1, 60%), 207.6 (C-4, 40%) and 208.8 (d, J 16.2, C-4, 60%);
dP(101 MHz; CDCl3; H3PO4) 21.4 (60%) and 21.7 (40%).
9.7 (CH3CH2, 70% + 30%), 16.0 (d, J 5.9, (CH3CH2O)2P(O),
30% + 70%), 16.1 (d, J 6.5, (CH3CH2O)2P(O), 70% + 30%),
27.1 (CH3CH2, 70%
+ 30%), 47.3 (C-4, 70%), 50.1
Ethyl 2-(diethoxyphosphoryl)-3-(4-nitrophenyl)-4-oxohexanoate
(14d). (53%) colourless oil (Found: C, 52.4; H, 6.2. C18H26NO8P
requires C, 52.1; H, 6.3%); nmax(film)/cmÀ1 1712, 1636, 1551,
1392, 1364, 1248, 1154 and 1024; dH(250 MHz; CDCl3; Me4Si)
0.91–1.42 (12 H, m, (CH3CH2O)2P(O), CH3, OCH2CH3, 60%
+ 40%), 2.32–2.53 (2 H, m, CH2, 60% + 40%), 3.73–4.28
(9 H, m, H-2, (CH3CH2O)2P(O), CH2, OCH2CH3, 60% + 40%),
4.58 (1 H, dd, J 9.9 and 11.7, H-3, 40%), 4.67 (1 H, dd, J 7.9
and 11.8, H-3, 60%), 7.47–7.52 (2 H, m, 2 Â CH-Ar, 60% + 40%)
and 8.14–8.22 (2 H, m, 2 Â CH-Ar, 60% + 40%); dC(62.9 MHz;
CDCl3; Me4Si) 7.7 (CH2CH3, 40%), 7.9 (CH2CH3, 60%),
14.1 (C(O)OCH2CH3, 40%), 14.3 (C(O)OCH2CH3, 60%),
16.3 (d, J 7.7, CH3CH2OP(O), 60%), 16.3 (d, J 5.1,
CH3CH2OP(O), 60%), 16.5 (d, J 6.0, CH3CH2OP(O), 40%),
16.5 (d, J 5.6, CH3CH2OP(O), 40%), 35.3 (CH2CH3, 60%),
36.3 (CH2CH3, 40%), 48.6 (d, J 127.0, C-2, 40%), 48.8
(d, J 127.6, C-2, 60%), 55.7 (d, J 2.4, C-3, 40%), 56.6
(C-3, 60%), 61.8 (C(O)OCH2CH3, 40%), 62.2 (C(O)OCH2CH3,
60%), 62.8 (d, J 6.7, CH3CH2OP(O), 60%), 63.1 (d, J 7.1,
CH3CH2OP(O), 60%), 63.4 (d, J 6.5, CH3CH2OP(O), 40%),
63.5 (d, J 6.8, CH3CH2OP(O), 40%), 123.6 (2 Â CH-Ar,
40%), 124.1 (2 Â CH-Ar, 60%), 129.9 (2 Â C-Ar, 40%),
130.6 (2 Â C-Ar, 60%), 142.7 (C-Ar, 60 + 40%), 146.8 (C-Ar,
40%), 147.9 (d, J 5.4, C-Ar, 60%), 167.1 (d, J 5.5, C-1, 40%),
168.6 (d, J 3.9, C-1, 60%), 207.7 (C-4, 40%), and 207.9
(d, J 7.1, C-4, 60%); dP(101 MHz; CDCl3; H3PO4) 20.3
(60%) and 20.5 (40%).
(d, J 130.8, C-3, 70%), 51.4 (d, J 143.9, C-3, 30%), 53.3
(C-4, 30%), 63.8 (d, J 6.4, (CH3CH2O)2P(O), 70% + 30%),
64.9 (d, J 6.5, (CH3CH2O)2P(O), 70% + 30%), 83.7 (d, J 3.2,
C-5, 30%), 87.7 (d, J 13.3, C-5, 70%), 125.3 (C-Ar, 70%),
125.7 (C-Ar, 30%), 128.7 (2 Â C-Ar, 70% + 30%), 130.1
(2 Â C-Ar, 70%), 131.3 (2 Â C-Ar, 30%), 141.9 (C-Ar, 30%),
142.6 (C-Ar, 70%), 170.4 (d, J 6.5, C-2, 70%) and 172.9
(d, J 4.4, C-2, 30%); dP(101 MHz; CDCl3; H3PO4) 19.8
(30%) and 20.2 (70%).
4-(4-Bromophenyl)-3-diethoxyphosphoryl-5-ethyldihydrofuran-
2(3H)-one (16b). (59%) colourless oil (Found: C, 47.1; H, 5.2.
C16H22BrO5P requires C, 47.4; H, 5.5%); nmax(film)/cmÀ1 1770,
1508, 1168 and 1024; dH(250 MHz; CDCl3; Me4Si) 0.97 (3 H, t,
J 7.1, CH3CH2, 30%), 0.98 (3 H, t, J 7.4, CH3CH2, 70%), 1.15
(3 H, t, J 7.1, CH3CH2OP(O), 70%), 1.26 (3 H, t, J 7.1,
CH3CH2OP(O), 70%), 1.36 (3 H, t, J 6.5, CH3CH2OP, 30%),
1.41 (3 H, t, J 7.1, CH3CH2OP, 30%), 1.75 (2 H, q, J 7.4,
CH3CH2, 70%), 1.76 (2 H, q, J 7.1, CH3CH2, 30%), 3.20
(1 H, dd, J 2.7 and 24.7, CHP, 30%), 3.25 (1 H, dd, J 10.5 and
23.7, CHP, 70%), 3.43–3.70 (1 H, m, CHAr, 70% + 30%),
3.94–4.09 (4 H, m, (CH3CH2O)2P(O), 70% + 30%), 4.20 (1 H,
dt, J 7.1 and 9.1, OCH, 70%), 4.83 (1 H, ddd, J 5.3, 6.1 and
11.6, OCH, 30%), 7.13–7.17 (2 H, m, 2 Â CH-Ar, 70% + 30%)
and 7.47–7.52 (2 H, m, 2 Â CH-Ar, 70% + 30%); dC(62.9 MHz;
CDCl3; Me4Si) 9.8 (CH3CH2, 70% + 30%), 16.1 (d, J 5.8,
(CH3CH2O)2P(O), 30% + 70%), 16.3 (d, J 6.4, CH3CH2OP,
70% + 30%), 25.0 (CH3CH2, 70% + 30%), 41.0 (C-4, 70%),
49.9 (d, J 98.4, C-3, 70%), 50.4 (d, J 144.8, C-3, 30%), 56.6
(C-4, 30%), 62.6 (d, J 6.3, (CH3CH2O)2P(O), 70% + 30%),
63.8 (d, J 6.5, (CH3CH2O)2P(O), 70% + 30%), 83.6 (d, J 3.5,
C-5, 30%), 87.5 (d, J 12.9, C-5, 70%), 129.3 (2 Â C-Ar, 30%),
129.7 (2 Â C-Ar, 70%), 131.1 (C-Ar, 70% + 30%), 132.2
(2 Â C-Ar, 30%), 134.7 (2 x C-Ar, 70%), 140.8 (C-Ar, 70%),
141.4 (C-Ar, 30%), 172.3 (d, J 6.5, C-2, 70%) and 173.0
(d, J 4.4, C-2, 30%); dP(101 MHz; CDCl3; H3PO4) 19.1
(30%) and 19.6 (70%).
General procedure for the preparation of 4-aryl-3-diethoxy-
phosphoryl-5-ethyldihydrofuran-2(3H)-ones 16a–c
To a stirred solution of the corresponding ethyl 3-aryl-2-
diethoxyphosphoryl-4-oxohexanoate 14 (5 mmol) in methanol
(20 mL) potassium borohydride (405 mg, 7.5 mmol) was
added in portions at 0 1C. Stirring was continued for 45 min
(for compounds 14c,d) or 55 min (for compound 14a) and the
reaction mixture was acidified to pH 1.5 with concentrated
HCl. Next water (15 mL) was added and methanol was
evaporated under reduced pressure. The residue was extracted
with chloroform (4 Â 20 mL). The combined organic layers
were dried over MgSO4 and the solvent was evaporated under
reduced pressure to afford a crude product which was purified
by column chromatography (eluent: CHCl3).
3-Diethoxyphosphoryl-5-ethyl-4-(4-methylphenyl)dihydrofuran-
2(3H)-one (16c). (80%) colourless oil (Found: C, 59.8; H, 7.0.
C17H25O5P requires C, 60.0; H, 7.4%); nmax(film)/cmÀ1 1772,
1388, 1256 and 1028; dH(250 MHz; CDCl3; Me4Si) 0.86–1.20
(3 H, m, CH3CH2, 60% + 40%), 1.25–1.46 (6 H, m, (CH3CH2O)2-
P(O), 60% + 40%), 1.70–1.81 (2 H, m, CH3CH2, 60% + 40%),
2.32 (3 H, s, CH3, 40%), 2.33 (3 H, s, CH3, 60%), 3.23 (1 H, dd,
J 2.6 and 24.7, CHP, 40%), 3.29 (1 H, dd, J 10.4 and 23.6, CHP,
60%), 3.39–3.62 (1 H, m, CHAr, 60% + 40%), 3.94–4.09 (4 H,
m, (CH3CH2O)2P(O), 60% + 40%), 4.51 (ddd, 1 H, J 8.5, 8.5
and 11.8, OCH, 40%), 4.85 (1 H, ddd, J 5.3, 6.2 and 11.4, OCH,
60%), 6.98–7.02 (2 H, m, 2 x CH-Ar, 60% + 40%) and
7.12–7.15 (2 H, m, 2 Â CH-Ar, 60% + 40%); dC(62.9 MHz;
CDCl3; Me4Si) 9.9 (CH3CH2, 60%), 10.6 (CH3CH2, 40%),
16.0 (d, J 6.1, CH3CH2OP(O), 60% + 40%), 16.2 (d, J 6.2,
CH3CH2OP(O), 60% + 40%), 21.0 (CH3, 60% + 40%),
3-Diethoxyphosphoryl-5-ethyl-4-phenyldihydrofuran-2(3H)-one
(16a). (60%) colourless oil (Found: C, 58.7; H, 7.5. C16H23O5P
requires C, 58.9; H, 7.1%); nmax(film)/cmÀ1 1772, 1508, 1164
and 1028; dH(250 MHz; CDCl3; Me4Si) 0.85–1.11 (3 H, m,
CH3CH2, 70% + 30%), 1.23–1.44 (6 H, m, (CH3CH2O)2P(O),
70% + 30%), 1.65–1.80 (2 H, m, CH3CH2, 70% + 30%),
3.27 (1 H, dd, J 2.6 and 24.6, CHP, 30%), 3.32 (1 H, dd, J 10.4
and 23.6, CHP, 70%), 3.53–3.69 (1 H, m, CHAr, 70% +
30%), 3.92–4.24 (4 H, m, (CH3CH2O)2P(O), 70% + 30%),
4.35 (1 H, ddd, J 6.1, 8.5 and 12.3, OCH, 70%), 4.88 (1 H,
ddd, J 5.3, 9.4 and 11.7, OCH, 30%) and 7.01–7.34 (5 H, m,
5 Â CH-Ar, 70% + 30%); dC(62.9 MHz; CDCl3; Me4Si)
26.9 (CH3CH2, 60%
+ 40%), 34.1 (C-4, 60%), 48.0
(d, J 137.2, C-3, 40%), 48.2 (d, J 147.8, C-3, 60%), 56.3
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(C-4, 40%), 62.2 (d, J 7.1, CH3CH2OP(O), 40%), 62.5 (d, J 6.7,
CH3CH2OP(O), 60%), 63.0 (d, J 7.3, CH3CH2OP(O), 40%),
63.5 (d, J 6.2, CH3CH2OP(O), 60%), 83.7 (d, J 3.3, C-5, 40%),
87.8 (d, J 13.1, C-5, 60%), 126.2 (2 Â CH-Ar, 60%), 127.4
(2 Â CH-Ar, 40%), 128.6 (CH-Ar, 60%), 128.9 (CH-Ar, 40%),
129.2 (2 Â CH-Ar, 40%), 129.6 (2 Â CH-Ar, 60%), 135.6 (C-Ar,
40%), 137.6 (C-Ar, 60%), 168.8 (d, J 4.5, C-2, 40%) and 170.7
(d, J 6.4, C-2, 60%); dP(101 MHz; CDCl3; H3PO4) 19.6 (40%)
and 20.0 (60%).
(2 H, m, CH3CH2), 4.32 (1 H, ddd, J 7.8, 2.5 and 2.5, H-4),
4.61 (1 H, ddd, J 4.2, 7.8, and 9.7, H-5), 5.59 (1 H, d, J 2.5,
H2CC), 6.45 (1 H, d, J 2.5, H2CC), 7.03 (2 H, d, J 8.3, 2 Â CH-Ar)
and 7.16 (2 H, d, J 8.5, 2 Â CH-Ar); dC(62.9 MHz; CDCl3;
Me4Si) 10.3 (CH3CH2), 25.8 (CH3CH2), 48.8 (C-4), 82.8 (C-5),
121.7 (C-Ar), 124.5 (CH2C), 130.7 (2 Â CH-Ar), 131.9 (2 x CH-Ar),
136.7 (C-Ar), 138.8 (CH2C) and 170.0 (C-2).
5-Ethyl-3-methylidene-4-p-tolyldihydrofuran-2(3H)-one
(17c). (71%) yellow oil (Found: C, 77.5; H, 7.9. C14H16O2
requires C, 77.7; H, 7.5%); nmax(film)/cmÀ1 1772, 1256 and
1132; dH(250 MHz; CDCl3; Me4Si) 0.89 (3 H, t, J 7.2,
CH3CH2, 40%), 1.01 (3 H, t, J 7.3, CH3CH2, 60%),
1.07–1.43 (2 H, m, CH3CH2, 40%), 1.69–1.86 (2 H, m,
CH3CH2, 60%), 2.34 (3 H, s, CH3, 40%), 2.35 (3 H, s, CH3,
60%), 3.74 (1 H, ddd, J 7.6, 3.0 and 3.0, H-4, 60%), 4.21
(1 H, ddd, J 7.5, 2.5 and 2.5, H-4, 40%), 4.31 (ddd, 1 H, J 4.7
and 7.6, J 12.2, H-5, 60%), 4.60 (ddd, 1 H, J 4.2, 7.5 and 9.3,
H-5, 40%), 5.37 (1 H, d, J 3.0, H2CC, 60%), 5.59 (1 H, d,
J 2.5, H2CC, 40%), 6.33 (1 H, d, J 3.0, H2CC, 60%), 6.42
(1 H, d, J 2.5, H2CC, 40%) and 7.01–7.19 (4 H, m, 2 Â CH-Ar,
60% + 40%); dC(62.9 MHz; CDCl3; Me4Si) 9.6 (CH3CH2,
60%), 10.2 (CH3CH2, 40%), 21.0 (CH3, 60% i 40%), 25.7
(CH3CH2, 40%), 27.6 (CH3CH2, 60%), 49.0 (C-4, 40%), 51.7
(C-4, 60%), 83.3 (C-5, 40%), 86.7 (C-5, 60%), 123.9 (CH2C,
40%), 123.3 (CH2C, 60%), 128.1 (2 Â CH-Ar, 60%), 128.9
(2 Â CH-Ar, 40%), 129.3 (2 Â CH-Ar, 60%), 129.7 (2 Â CH-Ar,
40%), 134.5 (C-Ar, 40%), 136.1 (C-Ar, 60%), 137.3 (C-Ar,
40%), 137.5 (C-Ar, 60%), 139.2 (CH2C, 40%), 140.6 (CH2C,
60%) and 169.8 (C-2, 60% + 40%).
General procedure for the preparation of 4-aryl-5-ethyl-3-methyl-
idenedihydrofuran-2(3H)-ones 17a–c
To a stirred solution of a corresponding 4-aryl-3-diethoxy-
phosphoryl-5-ethyldihydrofuran-2(3H)-one 16 (1 mmol) in
diethyl ether (5 mL) potassium tert-butoxide (134 mg, 1.2
mmol) was added and the resulting mixture was stirred at
room temperature for 30 min. Then paraformaldehyde
(150 mg, 5 mmol) was added in one portion. After 1 h the
reaction mixture was quenched with brine (5 mL) and the
water layer was extracted with diethyl ether (4 Â 10 mL).
The combined organic layers were dried over MgSO4 and
evaporated. The crude product was purified by column
chromatography (eluent: CHCl3).
5-Ethyl-3-methylidene-4-phenyldihydrofuran-2(3H)-one (17a).
(68%) colourless oil (Found: C, 77.5; H, 6.9. C13H14O2
requires C, 77.2; H, 7.0%); nmax(film)/cmÀ1 1768, 1276 and
1128; dH(250 MHz; CDCl3; Me4Si) 0.89 (3 H, t, J 7.3,
CH3CH2, 30%), 1.02 (3 H, t, J 7.4, CH3CH2, 70%),
1.13–1.30 (2 H, m, CH3CH2, 30%), 1.69–1.86 (2 H, m,
CH3CH2, 70%), 3.79 (1 H, ddd, J 7.4, 3.0 and 3.0, H-4,
70%), 4.10 (ddd, 1 H, J 7.2, 2.5, and 2.5, H-4, 30%), 4.35
(1 H, ddd, J 4.9, 7.4 and 12.2, H-5, 70%), 4.63 (1 H, ddd, J 4.2,
7.2 and 9.6, H-5, 30%), 5.39 (1 H, d, J 3.0, H2CC, 70%), 5.61
(1 H, d, J 2.5, H2CC, 30%), 6.35 (1 H, d, J 3.0, H2CC, 70%),
6.45 (1 H, d, J 2.5, H2CC, 30%) and 7.13–7.41 (5 H, m,
5 Â CH Ar, 70% + 30%); dC(62.9 MHz; CDCl3; Me4Si) 9.6
(CH3CH2, 70%), 10.3 (CH3CH2, 30%), 25.8 (CH3CH2, 30%),
27.6 (CH3CH2, 70%), 49.2 (C-4, 30%), 51.6 (C-4, 70%), 83.0
(C-5, 30%), 86.8 (C-5, 70%), 123.9 (CH2C, 30%), 124.0
(CH2C, 70%), 128.2 (2 Â CH-Ar, 70%), 129.0 (2 Â CH-Ar,
30%), 129.2 (2 Â CH-Ar, 70%), 129.8 (2 Â CH-Ar, 30%),
135.4 (CH-Ar, 30%), 136.7 (CH-Ar, 70%), 137.9 (C-Ar,
30%), 138.2 (C-Ar, 70%), 139.0 (CH2C, 30%), 140.6
(CH2C, 70%) and 170.0 (C-2, 70% + 30%).
General procedure for the preparation of 4-aryl-3-
(diethoxyphosphoryl)-5-ethylpyrrolidin-2-ones 19a–c
To a stirred solution of ethyl 3-aryl-2-diethoxyphosphoryl-4-
nitrohexanoate 8 (4 mmol) in MeOH (40 mL) NiCl2Á6H2O
(1.90 g, 8 mmol) was added at room temperature. After
stirring for 10 min, NaBH4 (1.52 g, 40 mmol) was added in
small portions. The resulting mixture was stirred for 1 h at
room temperature and filtered through a pad of Celites. The
solid material was thoroughly washed with MeOH. Methanol
was removed under reduced pressure and the residue dissolved
in CHCl3 (30 mL) and washed with NaHCO3 (15 mL). The
aqueous layer was extracted with CHCl3 (2 Â 15 mL) and the
combined organic layers dried over MgSO4. Evaporation of
the solvent under reduced pressure afforded a crude product
which was purified by column chromatography (eluent:
CHCl3–MeOH 97 : 3).
4-(4-Bromophenyl)-5-ethyl-3-methylidenedihydrofuran-2(3H)-
one (17b). (69%) colourless oil (Found: C, 56.0; H, 5.0.
C13H13BrO2 requires C, 55.5; H, 4.7%); nmax(film)/cmÀ1
1768, 1276 and 1128; trans-17b: dH(250 MHz; CDCl3; Me4Si)
1.03 (3 H, t, J 7.4, CH3CH2), 1.73–1.84 (2 H, m, CH3CH2),
3.77 (1 H, ddd, J 6.3, 3.0 and 3.0, H-4), 4.30 (1 H, ddd, J 5.2,
6.3 and 12.2, H-5), 5.39 (1 H, d, J 3.0, H2CC), 6.37 (1 H, d, J
3.0, H2CC), 7.10 (2 H, d, J 8.4, 2 Â CH-Ar) and 7.52 (2 H, d, J
8.5, 2 Â CH-Ar); dC(62.9 MHz; CDCl3; Me4Si) 9.5 (CH3CH2),
27.7 (CH3CH2), 51.5 (C-4), 86.3 (C-5), 121.8 (C-Ar), 123.8
(CH2C), 130.0 (2 Â CH-Ar), 132.3 (2 Â CH-Ar), 138.3 (C-Ar),
140.1 (CH2C) and 169.3 (C-2). cis-17b: dH(250 MHz;
CDCl3; Me4Si) 0.91 (3 H, t, J 7.3, CH3CH2), 1.07–1.29
3-(Diethoxyphosphoryl)-5-ethyl-4-phenylpyrrolidin-2-one
(19a). (92%) yellow oil (Found: C, 59.4; H, 7.4. C16H24NO4P
requires C, 59.1; H, 7.4%); nmax(film)/cmÀ1 1704, 1544, 1456,
1384, 1248, 1164 and 1032; dH(250 MHz; CDCl3; Me4Si) 0.80
(3 H, t, J 7.5, CH3CH2, 55%), 0.91 (3 H, t, J 7.5, CH3CH2,
45%), 1.04–1.35 (8 H, m, (CH3CH2O)2P(O), 55% + 45%,
CH3CH2, 45%), 1.55–1.85 (2 H, m, CH3CH2, 55%), 3.08
(1 H, dd, J 8.1 and 23.1, PCH, 45%), 3.12 (1 H, dd, J 1.1
and 22.2, PCH, 55%), 3.39–3.56 (1 H, m, CHAr, 55% + 45%),
3.91–4.26 (5 H, m, (CH3CH2O)2P(O), 55% + 45% CHN,
55% + 45%), 6.20 (1 H, s, NH, 55%), 6.41 (1 H, s, NH, 45%)
ꢀc
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View Article Online
and 7.18–7.34 (5 H, m, 5 Â CH-Ar, 55% + 45%); dC(62.9
MHz; CDCl3; Me4Si) 9.4 (CH3CH2, 45%), 9.9 (CH3CH2,
55%), 15.1 (d, J 6.9, (CH3CH2O)2P(O), 55%), 15.3 (d, J 6.3,
(CH3CH2O)2P(O), 45%), 24.0 (CH3CH2, 55%), 27.4
(CH3CH2, 45%), 45.3 (C-4, 55%), 47.7 (C-4, 45%), 47.8
(d, J 137.4, C-3, 55%), 48.6 (d, J 145.9, C-3, 45%), 58.2
(d, J 3.8, C-5, 55%), 61.1 (d, J 6.9, CH3CH2OP(O), 45%), 61.3
(d, J 6.9, CH3CH2OP(O), 55%), 62.2 (d, J 6.3, CH3CH2OP(O),
45%), 63.2 (d, J 6.3, CH3CH2OP(O), 55%), 62.4 (d, J 8.8, C-5,
45%), 126.3 (CH-Ar, 45%), 126.4 (CH-Ar, 55%), 126.6
(2 Â CH-Ar, 45%), 127.2 (2 Â CH-Ar, 55%), 127.5
(2 Â CH-Ar, 55%), 127.8 (2 Â CH-Ar, 45%), 138.4
(d, J 10.7, C-Ar, 55%), 140.9 (C-Ar, 45%), 170.5 (C-2, 45%)
and 171.5 (C-2, 55%); dP(101 MHz; CDCl3; H3PO4) 22.7
(55%) and 23.0 (45%).
(CH3CH2O)2P(O), 60%), 16.3 (d, J 6.1, (CH3CH2O)2P(O),
40%), 20.9 (CH3, 60% + 40%), 24.9 (CH3CH2, 60%), 28.4
(CH3CH2, 40%), 45.8 (C-4, 60%), 48.2 (d, J 2.5, C-4, 40%),
49.0 (d, J 136.7, C-3, 60%), 49.6 (d, J 145.3, C-3, 40%), 59.3
(d, J 2.1, C-5, 60%), 62.0 (d, J 6.3, CH3CH2OP(O), 40%), 62.2
(d, J 6.7, CH3CH2OP(O), 60%), 63.0 (d, J 6.5, CH3CH2OP(O),
40%), 63.2 (d, J 6.7, CH3CH2OP(O), 60%), 63.4 (d, J 9.4, C-5,
40%), 127.4 (2 Â CH-Ar, 40%), 128.0 (2 Â CH-Ar, 60%),
129.4 (2 Â CH-Ar, 60%), 129.4 (2 Â CH-Ar, 40%), 136.3
(C-Ar, 60%), 136.4 (C-Ar, 40%), 136.9 (d, J 6.7, C-Ar, 60%),
138.9 (d, J 4.4, C-Ar, 40%), 171.5 (C-2, 40%) and 172.5
(C-2, 60%); dP(101 MHz; CDCl3; H3PO4) 23.1 (60%) and
23.4 (40%).
General procedure for the preparation of tert-butyl 4-aryl-3-
(diethoxyphosphoryl)-5-ethyl-2-oxopyrrolidine-1-carboxylates
20a–c
4-(Bromophenyl)-3-(diethoxyphosphoryl)-5-ethylpyrrolidin-
2-one (19b). (79%) yellow oil (Found: C, 47.9; H, 6.0.
C16H23BrNO4P requires C, 47.5; H, 5.7%); nmax(film)/cmÀ1
1708, 1548, 1492, 1456, 1388, 1248, 1164 and 1056; dH(250
MHz; CDCl3; Me4Si) 0.80 (3 H, t, J 7.1, CH3CH2, 40%), 0.92
To a stirred solution of a corresponding 4-aryl-3-(diethoxy-
phosphoryl)-5-ethylpyrrolidin-2-one 19 (3 mmol) in CH2Cl2
(15 mL) Boc2O (785 mg, 3.6 mmol) and DMAP (92 mg,
0.75 mmol) were added. The resulting mixture was left at
room temperature for 3 h and then washed with 3% aqueous
solution of KHSO4 (10 mL), water (10 mL) and dried over
MgSO4. Evaporation of the solvent under reduced pressure
afforded a crude product which was purified by column
chromatography (eluent: CHCl3–acetone 95 : 5).
(3 H, t,
J 7.2, CH3CH2, 60%), 1.05–1.39 (8 H, m,
(CH3CH2O)2P(O), 60% + 40%, CH3CH2, 40%), 1.61–1.72
(2 H, m, CH3CH2, 60%), 3.08 (1 H, dd, J 7.8 and 23.5, PCH,
40%), 3.12 (1 H, dd, J 3.2 and 22.9, PCH, 60%), 3.39–3.56
(1 H, m, CHAr, 60% + 40%), 3.92–4.25 (5 H, m,
(CH3CH2O)2P(O), 60% + 40% CHN, 60% + 40%), 6.35
(1 H, s, NH, 60%), 6.59 (1 H, s, NH, 40%) and 7.17–7.48 (4 H, m,
4 Â CH-Ar, 60% + 40%); dC(62.9 MHz; CDCl3; Me4Si) 10.3
(CH3CH2, 40%), 10.7 (CH3CH2, 60%), 15.9 (d, J 7.1,
CH3CH2OP(O), 40%), 16.0 (d, J 6.4, CH3CH2OP(O), 60%),
16.1 (d, J 7.8, CH3CH2OP(O), 60%), 16.2 (d, J 5.6,
CH3CH2OP(O), 40%), 24.9 (CH3CH2, 60%), 28.3 (CH3CH2,
40%), 46.1 (C-4, 60%), 48.1 (C-4, 40%), 48.7 (d, J 137.7, C-3,
60%), 49.6 (d, J 145.9, C-3, 40%), 59.3 (d, J 4.1, C-5, 60%),
61.9 (d, J 6.9, CH3CH2OP(O), 40%), 62.2 (d, J 6.9,
CH3CH2OP(O), 60%), 62.9 (d, J 6.3, CH3CH2OP(O), 40%),
63.1 (d, J 6.3, CH3CH2OP(O), 60%), 63.4 (d, J 9.4, C-5, 40%),
120.9 (C-Ar, 40%), 127.1 (C-Ar, 60%), 127.2 (2 Â CH-Ar,
40%), 127.5 (2 0Â CH-Ar, 40%), 128.0 (2 Â CH-Ar, 60%),
128.3 (2 Â CH-Ar, 60%), 139.3 (C-Ar, 60%), 141.8 (C-Ar,
40%), 171.6 (C-2, 40%) and 172.6 (d, J 3.1, C-2, 60%);
dP(101 MHz; CDCl3; H3PO4) 23.1 (60%) and 23.3 (40%).
tert-Butyl 3-(diethoxyphosphoryl)-5-ethyl-4-phenyl-2-oxopyrro-
lidine-1-carboxylate (20a). (69%) yellow oil (Found: C, 59.6; H,
7.9. C21H32NO6P requires C, 59.3; H, 7.6%); nmax(film)/cmÀ1
1764, 1724, 1364, 1300, 1252, 1164 and 1012; dH(250 MHz;
CDCl3; Me4Si) 0.52 (3 H, t, J 7.5, CH3CH2, 45%), 0.94 (3 H, t,
J 7.1, CH3CH2, 55%), 1.24–1.35 (8 H, m, (CH3CH2O)2P(O),
55% + 45%, CH3CH2, 45%), 1.53 (9 H, s, (CH3)3C, 45%), 1.54
(9 H, s, (CH3)3C, 55%), 1.77–2.03 (2 H, m, CH3CH2, 55%), 3.15
(1 H, dd, J 5.4 and 26.0, PCH, 45%), 3.53 (1 H, dd, J 11.6 and
22.3, PCH, 55%), 3.75–3.94 (1 H, m, CHAr, 55% + 45%),
3.97–4.31 (4 H, m, (CH3CH2O)2P(O), 55% + 45%) and
7.21–7.38 (5 H, m, 5 Â CH-Ar, 55% + 45%); dC(62.9 MHz;
CDCl3; Me4Si) 9.0 (CH3CH2, 45%), 10.2 (CH3CH2, 55%), 15.6
(d, J 6.5, (CH3CH2O)2P(O), 45%), 16.1 (d, J 6.5, (CH3CH2O)2-
P(O), 55%), 23.8 (CH3CH2, 55%), 26.5 (CH3CH2, 45%), 27.8
((CH3)3C, 55% + 45%), 42.2 (C-4, 45%), 43.2 (d, J 2.2, C-4,
55%), 45.7 (d, J 149.7, C-3, 55%), 51.1 (d, J 140.1, C-3, 45%),
61.8 (d, J 11.7, C-5, 45%), 61.9 (d, J 6.9, CH3CH2OP(O), 55%),
62.3 (d, J 6.7, (CH3CH2O)2P(O), 45%), 63.4 (d, J 6.2,
3-(Diethoxyphosphoryl)-5-ethyl-4-(4-methylphenyl)pyrrolidin-
2-one (19c). (85%) yellow oil (Found: C, 60.4; H, 7.5.
C17H26NO4P requires C, 60.2; H, 7.7%); nmax(film)/cmÀ1
1704, 1520, 1440, 1372, 1336, 1312, 1256, 1184, 1160, 1052
and 1016; dH(250 MHz; CDCl3; Me4Si) 0.79 (3 H, t, J 7.4,
CH3CH2, 60%), 0.91 (3 H, t, J 7.4, CH3CH2, 40%), 1.03–1.35
(8 H, m, (CH3CH2O)2P(O), 60% + 40%, CH3CH2, 40%),
1.54–1.71 (2 H, m, CH3CH2, 60%), 2.33 (3 H, s, CH3, 60%),
2.34 (3 H, s, CH3, 40%), 3.06 (1 H, dd, J 5.8 and 23.3, PCH,
40%), 3.08 (1 H, dd, J 3.5 and 23.1, PCH, 60%), 3.71–3.91
(1 H, m, CHAr, 60% + 40%), 3.96–4.25 (5 H, m, (CH3CH2O)2-
P(O), 60% + 40% CHN, 60% + 40%), 6.07 (1 H, s, NH,
60%), 6.29 (1 H, s, NH, 40%) and 7.08–7.15 (4 H, m, 4 Â
CH3CH2OP(O), 55%), 66.0 (d,
J 5.2, C-5, 55%), 83.1
((CH3)3C, 55%), 83.2 ((CH3)3C, 45%), 126.6 (CH-Ar, 45%),
127.4 (2 Â CH-Ar, 45%), 128.2 (2 Â CH-Ar, 55%), 128.3 (2 Â
CH-Ar, 55% + 45%), 129.0 (CH-Ar, 55%), 135.8 (C-Ar, 45%),
143.5 (d, J 7.7, C-Ar, 55%), 149.5 (NC(O), 45% + 55%), 168.1
(C-2, 55%) and 169.6 (C-2, 45%); dP(101 MHz; CDCl3; H3PO4)
21.2 (45%) and 21.9 (55%).
tert-Butyl 4-(bromophenyl)-3-(diethoxyphosphoryl)-5-ethyl-
2-oxopyrrolidine-1-carboxylate (20b). (72%) yellow oil (Found:
C, 50.3; H, 5.9. C21H31BrNO6P requires C, 50.0; H, 6.2%);
CH-Ar, 60%
+ 40%); dC(62.9 MHz; CDCl3; Me4Si)
10.3 (CH3CH2, 40%), 10.8 (CH3CH2, 60%), 16.0 (d, J 6.4,
n
max(film)/cmÀ1 1784, 1724, 1368, 1300, 1256, 1156 and 1028;
ꢀc
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758 | New J. Chem., 2010, 34, 750–761

View Article Online
General procedure for the preparation of tert-butyl 3-aryl-2-ethyl-
dH(250 MHz; CDCl3; Me4Si) 0.54 (3 H, t, J 7.6, CH3CH2,
40%), 0.96 (3 H, t, J 7.6, CH3CH2, 60%), 1.23–1.46 (8 H, m,
(CH3CH2O)2P(O), 60% + 40%, CH3CH2, 40%), 1.55 (9 H, s,
(CH3)3C, 40%), 1.55 (9 H, s, (CH3)3C, 60%), 1.91–2.01 (2 H, m,
CH3CH2, 60%), 3.18 (1 H, dd, J 4.9 and 26.0, PCH, 40%), 3.56
(1 H, dd, J 11.7 and 22.4, PCH, 60%), 3.72–3.91 (1 H, m,
CHAr, 60% + 40%), 4.08–4.31 (4 H, m, (CH3CH2O)2P(O),
60% + 40%) and 7.10–7.51 (4 H, m, 4 Â CH-Ar, 60% +
40%); dC(62.9 MHz; CDCl3; Me4Si) 9.0 (CH3CH2, 40%), 10.3
(CH3CH2, 60%), 15.7 (d, J 6.6, CH3CH2OP(O), 40%), 16.1
(d, J 6.8, CH3CH2OP(O), 40%), 16.2 (d, J 6.4, (CH3CH2O)2P(O),
60%), 23.8 (CH3CH2, 60%), 26.6 (CH3CH2, 40%), 27.9
((CH3)3C, 60% + 40%), 42.2 (d, J 1.8, C-4, 40%), 43.3
(J 2.7, C-4, 60%), 45.8 (d, J 149.4, C-3, 60%), 51.2 (d, J
140.2, C-3, 40%), 61.8 (d, J 11.6, C-5, 40%), 62.0 (d, J 6.7,
CH3CH2OP(O), 60%), 62.3 (d, J 6.9, CH3CH2OP(O), 40%),
63.5 (d, J 6.4, CH3CH2OP(O), 60%), 63.6 (d, J 6.6, CH3CH2O-
P(O), 40%), 66.1 (d, J 5.0, C-5, 60%), 83.2 ((CH3)3C, 60%),
83.3 ((CH3)3C, 40%), 126.6 (2 Â CH-Ar, 60%), 127.3 (C-Ar,
40%), 127.4 (C-Ar, 40%), 128.3 (2 Â CH-Ar, 40%), 128.3
(2 Â CH-Ar, 60%), 129.1 (2 Â CH-Ar, 40%), 135.9 (d, J 2.0,
C-Ar, 40%), 143.6 (d, J 7.5, C-Ar, 60%), 149.5 (NC(O),
60% + 40%), 168.0 (d, J 2.9, C-2, 40%) and 168.2 (d, J 1.2,
C-2, 60%);. dP(101 MHz; CDCl3; H3PO4) 21.2 (60%) and
21.9 (40%).
4-methylidene-5-oxopyrrolidine-1-carboxylates 21a–c
To a stirred solution of a corresponding tert-butyl 4-aryl-3-
(diethoxyphosphoryl)-5-ethyl-2-oxopyrrolidine-1-carboxylate
20 (1 mmol) in THF (5 mL) potassium tert-butoxide (269 mg,
2.4 mmol) was added and the resulting mixture was stirred at
room temperature for 30 min. Then paraformaldehyde
(150 mg, 5 mmol) was added in one portion. After 1 h the
reaction mixture was quenched with brine (15 mL), THF was
removed under reduced pressure and the water layer was
extracted with CH2Cl2 (2 Â 15 mL). The combined organic
layers were dried over MgSO4 and evaporated. The crude
product was purified by column chromatography (eluent:
CHCl3–acetone 98 : 2).
tert-Butyl 2-ethyl-3-phenyl-4-methylidene-5-oxopyrrolidine-
1-carboxylate (21a). (59%) pale-yellow oil (Found: C, 71.3; H,
7.9. C18H23NO3 requires C, 71.7; H, 7.7%); nmax(film)/cmÀ1
1782, 1736, 1296 and 1146; dH(250 MHz; CDCl3; Me4Si) 0.48
(3 H, t, J 7.5, CH3CH2, 45%), 0.98 (3 H, t, J 7.5, CH3CH2, 55%),
1.36–1.43 (2 H, m, CH3CH2, 45%), 1.57 (9 H, s, (CH3)3C,
55%), 1.59 (9 H, s, (CH3)3C, 45%), 1.82–1.90 (2 H, m,
CH3CH2, 55%), 3.73–3.75 (1 H, m, CHAr, 55%), 4.02 (1 H,
dt, J 2.7 and 8.2, CHN, 55%), 4.28–4.32 (2 H, m, CHN, CHAr,
45%), 5.43 (1 H, d, J 2.2, CH2C, 45%), 5.48 (1 H, d, J 2.6,
CH2C, 55%), 6.37 (1 H, d, J 2.2, CH2C, 45%), 6.42 (1 H, d,
J 2.6, CH2C, 55%) and 7.31–7.45 (5 H, m, 5 Â CH-Ar, 55% +
45%); dC(62.9 MHz; CDCl3; Me4Si) 5.5 (CH3CH2, 55%), 9.7
(CH3CH2, 45%), 22.4 (CH3CH2, 55%), 22.6 (CH3CH2, 45%),
27.9 ((CH3)3C, 45%), 28.0 ((CH3)3C, 55%), 47.9 (C-3, 55%),
61.2 (C-4, 55%), 64.5 (C-3, 45%), 68.7 (C-4, 45%), 82.6
((CH3)3C, 55%), 83.2 ((CH3)3C, 45%), 120.9 (CH2C, 55%),
122.7 (CH2C, 45%), 128.0 (2 Â CH-Ar, 55%), 128.4 (2 Â CH-Ar,
45%), 128.6 (2 Â CH-Ar, 55%), 129.0 (2 Â CH-Ar, 45%), 129.2
(CH-Ar, 55%), 129.9 (CH-Ar, 45%), 130.4 (C-Ar, 55%), 130.8
(C-Ar, 45%), 132.3 (CH2C, 55%), 135.6 (CH2C, 45%), 149.6
(NC(O), 45%), 153.5 (NC(O), 55%), 169.8 (C-5, 45%) and
170.4 (C-5, 55%).
tert-Butyl 3-(diethoxyphosphoryl)-5-ethyl-4-(4-methylphenyl)-
2-oxopyrrolidine-1-carboxylate (20c). (82%) yellow oil (Found:
C, 59.9; H, 7.4. C22H34NO6P requires C, 60.1; H, 7.8%);
n
max(film)/cmÀ1 1784, 1724, 1368, 1300, 1256, 1160 and 1024;
dH(250 MHz; CDCl3; Me4Si) 0.53 (3 H, t, J 7.6, CH3CH2,
30%), 0.95 (3 H, t, J 7.6, CH3CH2, 70%), 1.27 (3 H, t, J 7.0,
CH3CH2OP(O), 70% + 30%), 1.31 (3 H, t, J 7.0, CH3CH2O-
P(O), 70% + 30%), 1.32–1.42(2 H, m, CH3CH2, 30%), 1.53
(9 H, s, (CH3)3C, 30%), 1.53 (9 H, s, (CH3)3C, 70%), 1.71–1.94
(2 H, m, CH3CH2, 70%), 2.32 (3 H, s, CH3, 30%), 2.34 (3 H, s,
CH3, 70%), 2.98 (1 H, dd, J 4.2 and 26.1, PCH, 30%), 3.50
(1 H, dd, J 5.7 and 22.4, PCH, 70%), 3.75–4.07 (1 H, m, CHAr,
70% + 30%), 4.19–4.29 (4 H, m, (CH3CH2O)2P(O), 70% +
30%) and 7.05–7.16 (4 H, m, 4 Â CH-Ar, 70% + 30%);
dC(62.9 MHz; CDCl3; Me4Si) 8.9 (CH3CH2, 30%), 10.0
(CH3CH2, 70%), 15.5 (d, J 6.5, CH3CH2OP(O), 70%), 15.9
(d, J 6.9, CH3CH2OP(O), 30%), 16.0 (d, J 6.3, CH3CH2OP(O),
70%), 16.1 (d, J 6.6, CH3CH2OP(O), 30%), 20.7 (CH3, 70%),
20.7 (CH3, 30%), 23.5 (CH3CH2, 70%), 26.4 (CH3CH2, 30%),
27.6 ((CH3)3C, 70%), 27.7 ((CH3)3C, 30%), 41.7 (C-4, 30%),
42.7 (C-4, 70%), 45.7 (d, J 149.1, C-3, 70%), 51.1 (d, J 140.0,
C-3, 30%), 61.6 (d, J 13.0, C-5, 30%), 61.8 (d, J 7.2, CH3CH2O-
P(O), 70%), 62.2 (d, J 6.8, CH3CH2OP(O), 30%), 63.1 (d, J 6.4,
CH3CH2OP(O), 70%), 63.4 (d, J 6.4, CH3CH2OP(O), 30%),
66.18 (d, J 4.8, C-5, 70%), 82.8 ((CH3)3C, 70%), 83.1 ((CH3)3C,
30%), 126.4 (2 Â CH-Ar, 30%), 127.9 (2 Â CH-Ar, 70%), 128.7
(2 Â CH-Ar, 70%), 129.5 (2 Â CH-Ar, 30%), 132.6 (C-Ar,
70%), 136.8 (C-Ar, 30%), 136.9 (C-Ar, 30%), 140.5 (d, J 7.5,
C-Ar, 70%), 149.3 (NC(O), 70%), 149.4 (NC(O), 70%), 168.0
(C-2, 30%) and 168.1 (C-2, 70%); dP(101 MHz; CDCl3; H3PO4)
21.6 (30%) and 22.3 (70%).
tert-Butyl 3-(4-bromophenyl)-2-ethyl-4-methylidene-5-oxo-
pyrrolidine-1-carboxylate (21b). (52%) pale-yellow oil (Found:
C, 57.0; H, 6.1. C18H22BrNO3 requires C, 56.8; H, 5.8%);
n
max(film)/cmÀ1 1780, 1736, 1296 and 1152; dH(250 MHz;
CDCl3; Me4Si) 0.55 (3 H, t, J 7.2, CH3CH2, 40%), 0.98
(3 H, t, J 7.5, CH3CH2, 60%), 1.18–1.28 (2 H, m, CH3CH2,
40%), 1.54 (9 H, s, (CH3)3C, 40%), 1.60 (9 H, s, (CH3)3C,
60%), 1.83–1.99 (2 H, m, CH3CH2, 60%), 3.74 (1 H, dt, J 2.4
and 6.7, CHAr, 60%), 4.03 (1 H, dt, J 2.8 and 8.4, CHN,
60%), 4.24–4.34 (2 H, m, CHN, CHAr, 40%), 5.44 (1 H, d, J
2.0, CH2C, 60%), 5.48 (1 H, d, J 2.6, CH2C, 40%), 6.37 (1 H,
d, J 2.0, CH2C, 60%), 6.42 (1 H, d, J 2.6, CH2C, 40%) and
7.29–7.51 (4 H, m, 4 Â CH-Ar, 60% + 40%); dC(62.9 MHz;
CDCl3; Me4Si) 5.3 (CH3CH2, 60%), 8.68 (CH3CH2, 40%),
22.4 (CH3CH2, 60%), 27.2 (CH3CH2, 40%), 27.7 ((CH3)3C,
60%), 27.8 ((CH3)3C, 40%), 46.3 (C-3, 60%), 61.6 (C-4, 60%),
64.4 (C-3, 40%), 68.2 (C-4, 40%), 82.9 ((CH3)3C, 40%), 83.0
((CH3)3C, 60%), 120.7 (CH2C, 40%), 122.5 (CH2C, 60%),
126.8 (C-Ar, 60%), 126.9 (C-Ar, 40%), 128.3 (2 Â CH-Ar,
60%), 128.4 (2 Â CH-Ar, 40%), 128.7 (2 Â CH-Ar, 40%),
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128.8 (2 Â CH-Ar, 60%), 130.2 (C-Ar, 60%), 130.7 (C-Ar,
40%), 142.7 (CH2C, 60%), 142.9 (CH2C, 40%), 149.2 (NC(O),
60%), 150.1 (NC(O), 40%), 160.5 (C-5, 40%) and 169.6
(C-5, 60%).
128.2 (2 Â CH-Ar, 60%), 128.3 (2 Â CH-Ar, 40%), 128.6
(C-Ar, 60%), 128.7 (C-Ar, 40%), 128.9 (2 Â CH-Ar, 60%),
132.0 (C-Ar, 60%), 133.1 (C-Ar, 40%), 141.5 (CH2C, 40%),
144.7 (CH2C, 60%), 169.9 (C-2, 40%) and 170.3 (C-2, 60%).
Cells and cytotoxicity assays
tert-Butyl 2-ethyl-4-methylidene-3-(4-methylphenyl)-5-oxo-
pyrrolidine-1-carboxylate (21c). (80%) pale-yellow oil (Found:
C, 72.5; H, 8.2. C19H25NO3 requires C, 72.4; H, 8.0%);
Mouse leukemia L-1210 cells were cultured in RPMI 1640
medium (Sigma, St. Louis, MO) supplemented with 10%
foetal calf serum (Gibco, Berlin, Germany), gentamycin
(50 mg mLÀ1) and 0.02 M HEPES buffer (Gibco). Cytostatic
effects were assayed by measuring inhibitory effects on L-1210
cell proliferation. In this assay, cells were seeded in 2 mL
aliquots onto a 24-well plate (NUNC, Denmark) at a
concentration of 1.5 Â 103 cells mLÀ1. After 24 h drug solution
was added and incubation was carried out for an additional 48 h.
The cell number relative to control was determined by a
tetrazolium dye method.25
n
max(film)/cmÀ1 1780, 1716, 1368, 1300 and 1156; dH(250 MHz;
CDCl3; Me4Si) 0.49 (3 H, t, J 7.4, CH3CH2, 30%), 0.99 (3 H, t,
J 7.5, CH3CH2, 70%), 1.22–1.42 (2 H, m, CH3CH2, 30%),
1.56 (9 H, s, (CH3)3C, 70% + 30%), 1.86–1.95 (2 H, m,
CH3CH2, 70%), 2.34 (3 H, s, CH3, 70%), 2.36 (3 H, s, CH3,
30%), 3.70–3.71 (1 H, m, CHAr, 70%), 4.01 (1 H, dt, J 2.8 and
8.4, CHN, 70%), 4.25–4.28 (2 H, m, CHN, CHAr, 30%), 5.43
(1 H, d, J 2.0, CH2C, 70%), 5.46 (1 H, d, J 2.5, CH2C, 30%),
6.38 (1 H, d, J 2.0, CH2C, 70%), 6.40 (1 H, d, J 2.5, CH2C,
30%) and 7.05–7.19 (4 H, m, 4 Â CH-Ar, 70% + 30%);
dC(62.9 MHz; CDCl3; Me4Si) 5.3 (CH3CH2, 30%), 10.1
(CH3CH2, 70%), 20.9 (CH3, 70%), 21.2 (CH3, 30%), 22.6
(CH3CH2, 30%), 25.2 (CH3CH2, 70%), 27.8 ((CH3)3C, 70%),
27.9 ((CH3)3C, 30%), 47.4 (C-3, 70%), 60.9 (C-4, 70%), 61.6
(C-3, 30%), 68.6 (C-4, 30%), 82.7 ((CH3)3C, 70%), 82.9
((CH3)3C, 30%), 120.6 (CH2C, 70%), 126.8 (C-Ar, 70%),
127.0 (C-Ar, 30%), 127.9 (CH2C, 30%), 128.3 (2 Â CH-Ar,
30%), 129.2 (2 Â CH-Ar, 70%), 129.3 (2 Â CH-Ar, 70%),
128.6 (2 Â CH-Ar, 30%), 132.4 (C-Ar, 70%), 137.2 (C-Ar,
30%), 140.7 (CH2C, 30%), 142.0 (CH2C, 70%), 149.3 (NC(O),
30%), 150.3 (NC(O), 70%), 166.3 (C-5, 70%) and 169.8
(C-5, 30%).
Human leukemia promyelocytic HL-60 and lymphoblastic
NALM-6 cell lines were used. Leukemia cells were cultured in
RPMI 1640 medium supplemented with 10% heat-inactivated
foetal bovine serum (Invitrogen, Paisley, UK) and antibiotics
(100 mg mLÀ1 streptomycin and 100 U/mL penicillin). Cells
were grown at 37 1C in a humidified atmosphere of 5% CO2 in
air. Cytotoxic activity was determined by the MTT [3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, Sigma,
St. Louis, USA] assay.26 Exponentially growing leukemia cells
were seeded at 8 Â 103/well on a 96-well plate (Nunc, Roskilde,
Denmark). Stock solutions of the analyzed compounds were
freshly prepared in DMSO and diluted with complete culture
medium to obtain the concentration range from 10À7 to 10À3
M. Cells were exposed to the test compounds for 46 h, then
MTT reagent was added and incubation was continued for 2 h.
After incubation, MTT–formazan crystals were dissolved in
20% SDS and 50% DMF at pH 4.7 and absorbance was read
at 562 and 630 nm on an ELISA-plate reader (ELX 800,
Bio-Tek, USA). As a control, cultured cells were grown in the
absence of drugs. The values of IC50 (the concentration of the
tested compound required to reduce the cells survival fraction
to 50% of the control) were calculated from concentration-
response curves and used as a measure of cellular sensitivity
to a given treatment. Data points represent means of at least 6
repeats Æ SD.
Preparation of 4-(4-bromophenyl)-5-ethyl-3-
methylidenepyrrolidin-2-one (22b)
To a solution of tert-butyl 3-(4-bromophenyl)-2-ethyl-4-
methylidene-5-oxopyrrolidine-1-carboxylate (21b) (1 mmol)
in CH2Cl2 (10 mL) trifluoroacetic acid (5 mL) was added.
The reaction mixture was left at room temperature for 1 h. The
solvent was evaporated and the residue was dissolved in
CH2Cl2 (15 mL) and washed with NaHCO3 (15 mL), water
(15 mL) and dried over MgSO4. Evaporation of the solvent
under reduced pressure afforded a crude product which was
purified by column chromatography (eluent: CHCl3–acetone
95 : 5) to afford pure 4-(4-bromophenyl)-5-ethyl-3-methylide-
nepyrrolidin-2-one (22b) (68%) as a pale-yellow oil (Found: C,
55.5; H, 5.3. C13H14BrNO requires C, 55.7; H, 5.0%);
Acknowledgements
n
max(film)/cmÀ1 1688, 1656, 1360, 1312 and 1264; dH(250 MHz;
Financial support from the Ministry of Education and Science
(Project No. 3 T09A 075 28) and in part from the Medical
CDCl3; Me4Si) 0.80 (3 H, t, J 7.3, CH3CH2, 40%), 0.96 (3 H, t,
J 7.4, CH3CH2, major), 1.17–1.34 (2 H, m, CH3CH2, 40%),
1.58–1.75 (2 H, m, CH3CH2, 60%), 3.56–3.68 (1 H, m, CH,
60% + 40%), 4.34 (1 H, dt, J 2.8 and 7.9, CHAr, 60%),
4.53–4.58 (1 H, m, CHAr, 40%), 5.12 (1 H, d, J 2.4, CH2C,
60%), 5.31 (1 H, d, J 2.5, CH2C, 40%), 6.10 (1 H, d, J 2.4,
CH2C, 60%), 6.21 (1 H, d, J 2.5, CH2C, 40%), 7.08–7.48
(4 H, m, 4 Â CH-Ar, 60% + 40%), 7.81 (1 H, bs, NH, 60%)
and 7.92 (1 H, bs, NH, 40%); dC(62.9 MHz; CDCl3; Me4Si)
7.8 (CH3CH2, 40%), 10.0 (CH3CH2, 60%), 28.7 (CH3CH2,
60%), 29.7 (CH3CH2, 40%), 51.7 (C-4, 60%), 53.4
(C-4, 40%), 62.2 (C-5, 60%), 62.3 (C-5, 40%), 117.0
(CH2C, 40%), 118.4 (CH2C, 60%), 127.2 (2 Â CH-Ar, 40%),
University of Łodz´ (503-30-15-2 to M. R.) is gratefully
´
acknowledged.
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New J. Chem., 2010, 34, 750–761 | 761