α-Nitro Ketone As An Electrophile and Nucleophile: Synthesis of 3-Substituted 2-Nitromethylenetetrahydrothiophene and -Tetrahydrofuran As Drosophila Nicotinic Receptor Probes

Article abstract of DOI:10.1021/jo035457g

3-(6-Chloropyridin-3-yl)methyl-2-nitromethylenetetrahydrothiophene 2 and -tetrahydrofuran 3 were synthesized through novel approaches using α-nitro ketone intermediates as an electrophile and nucleophile, respectively. The 2-nitromethylenetetrahydrothioph

Full text of DOI:10.1021/jo035457g

r-Nitr o Keton e a s a n Electr op h ile a n d Nu cleop h ile: Syn th esis of
3-Su bstitu ted 2-Nitr om eth ylen etetr a h yd r oth iop h en e a n d
-tetr a h yd r ofu r a n a s Dr osoph ila Nicotin ic Recep tor P r obes
Nanjing Zhang, Motohiro Tomizawa, and J ohn E. Casida*
Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science,
Policy and Management, University of California, Berkeley, California 94720-3112
ectl@nature.berkeley.edu
Received October 3, 2003
3-(6-Chloropyridin-3-yl)methyl-2-nitromethylenetetrahydrothiophene 2 and -tetrahydrofuran 3 were
synthesized through novel approaches using R-nitro ketone intermediates as an electrophile and
nucleophile, respectively. The 2-nitromethylenetetrahydrothiophene 2 was formed exclusively as
the Z-isomer through intramolecular attack by a thiol substituent at the carbonyl group of an R-nitro
ketone, in which the R-nitro ketone served as an electrophile. In contrast, the corresponding
2-nitromethylenetetrahydrofuran 3, not accessible by the above route due to limited stability, was
prepared as a mixture of E- and Z-isomers by intramolecular attack of the R-nitro ketone enol
anion in which the deprotonated R-nitro ketone served as a nucleophile. These compounds, together
with the corresponding 2-nitromethylenepyrrolidine (1), were used to probe the Drosophila
neonicotinoid-nicotinic acetylcholine receptor interaction.
In tr od u ction
Neonicotinoids represented by imidacloprid are the
only major new class of insecticides introduced in the past
three decades. They act as selective agonists at the insect
nicotinic acetylcholine receptor (nAChR) and are there-
fore highly toxic toward important insect pests but
relatively safe to mammals.1 The nitroguanidine/nitro-
methylene moiety is an important structural requirement
of these neonicotinoid insecticides (Figure 1). Three
models (Figure 2) have been proposed to account for the
high binding affinity of neonicotinoids. The first two
models (a and b) suggest a primary role for N1 of the
neonicotinoid equating it to the pyrrolidine nitrogen of
nicotine. In addition, the pyridine nitrogen of nicotine is
superimposed on that of the neonicotinoid in model a 2
and on an oxygen of the nitro group in model b.3 The
third and most recent model (c) involves a crucial role
for the nitro group, an important contribution from the
pyridine nitrogen and a supplemental role for N1.4
F IGURE 1. Imidacloprid (a nitroguanidine) and its nitrom-
ethylene analogue.
To refine the binding model, in particular the role of
N1, we synthesized three nitromethylene analogues of
imidacloprid to further explore the structure-activity
relationships. Specifically, compounds 1-3 were prepared
with N1 replaced by CH comparing nitrogen, sulfur, and
oxygen heterocycles (Figure 3). While compound 1 was
F IGURE 2. Three proposals for neonicotinoid sites involved
in high-affinity binding.
* To whom correspondence should be addressed. Phone: 510-642-
5424. Fax: 510-642-6497.
(1) Tomizawa, M.; Casida, J . E. Annu. Rev. Entomol. 2003, 48, 339-
made by a conventional method,5 the substituted 2-ni-
tromethylenetetrahydrothiophene 2 and substituted 2-ni-
364.
(2) Tomizawa, M.; Yamamoto, I. J . Pesticide Sci. 1993, 18, 91-98.
(3) Kagabu, S.; Matsuno, H. J . Agric. Food Chem. 1997, 45, 276-
281.
(4) Tomizawa, M.; Zhang, N.; Durkin, K. A.; Olmstead, M. M.;
Casida, J . E. Biochemistry 2003, 42, 7819-7827.
(5) Maienfisch, P.; Gonda, J .; J acob, O.; Gsell, L. U.S. Patent
6,048,824, 2000.
10.1021/jo035457g CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/09/2004
876
J . Org. Chem. 2004, 69, 876-881

R-Nitro Ketone as an Electrophile and Nucleophile
SCHEME 2 a
F IGURE 3. Probes to study the neonicotinoid-nAChR inter-
action.
SCHEME 1
tromethylenetetrahydrofuran 3 were synthesized by
novel approaches using an R-nitro ketone as either an
electrophile or a nucleophile, as we report here.
a
Resu lts a n d Discu ssion
Reagents and conditions: (i) (a) dihydropyran, pyridinium
p-toluenesulfonate, CH2Cl2, rt, overnight, (b) DCC, DMAP, PhOH,
CH2Cl2, rt, overnight, overall 53%; (ii) LDA, CIMP, HMPA, THF,
-78 °C to rt, overnight, 62%; (iii) CH3NO2, KOBut, DMSO, <20
°C, overnight, 79%; (iv) 37% HCl, rt, 30 min, 86%.
Our initial synthesis focused on 2-nitromethylenetet-
rahydrothiophene 2, a 1,1-disubstituted 2-nitroethylene.
There are only two reports of 2-nitroethylenes with both
carbon and thio substituents at the 1 position (Scheme
1). One reacts the commercially available 1,1-bis(meth-
ylthio)-2-nitroethylene with an organocopper reagent in
the presence of TMSCl to introduce a carbon substituent.6
The other converts an R-nitro ketone to a thioacetal fol-
lowed by elimination of a thiol to produce the nitroeth-
ylene moiety with a sulfur substituent.7 Although these
procedures are not directly applicable to the synthesis
of compound 2, we envisioned an R-nitro ketone precursor
of the nitroethylene moiety; i.e., an intramolecular attack
of a thiol group could produce a hemimercaptal and
following elimination of water could generate the nitro-
ethylene moiety with a thio substituent at the 1-position.
The synthesis of 2 involving R-nitro ketone 7 as the
critical intermediate is shown in Scheme 2. The thiol
group of 4-mercaptobutyric acid (4), prepared from hy-
drolysis of γ-butyrothiolactone,8 was protected with a
THP group, and the acid moiety was coupled with phenol
and DCC to give phenyl ester 5 useful for further
transformation to the R-nitro ketone.9 The 6-chloropyri-
din-3-ylmethylene moiety was introduced by deprotona-
tion of 5 with LDA followed by reaction with 2-chloro-5-
iodomethylpyridine (CIMP). The resulting phenyl ester
6 was then converted to R-nitro ketone 7 in excellent yield
by its reaction with the anion generated by treatment of
nitromethane with potassium tert-butoxide.9
hydrolyzed under strong acidic conditions.10 Thus, R-nitro
ketone 7 was treated with concentrated HCl (37%, 12 M)
at room temperature, leading to an immediate dark
solution and precipitation after several minutes; the
precipitate was collected after 30 min and identified as
target compound 2 by NMR, MS, and elemental analysis.
In this one-pot synthesis, three consecutive reactions are
efficiently carried out under the strong acidic conditions,
i.e., removal of the THP group, intramolecular attack at
the carbonyl group, and elimination of water. The R-nitro
ketone acts as an electrophile and is attacked by the thiol
group. The elimination produced the desired Z-isomer
exclusively, as evidenced by the NOE effect between the
nitromethylene proton and one of the pyridinylmethylene
protons, which is in contrast to the mixture of E- and
Z-isomers obtained from the elimination of an alkylthiol
from an R-nitro thioacetal.7
With the successful synthesis of 2-nitromethylenetet-
rahydrothiophene 2, it was expected that tetrahydrofuran
analogue 3 could be synthesized analogously to build the
O1-C2 bond where O1 came from the hydroxyl group
(Scheme 3). The synthesis started from TBS-protected
4-hydroxybutyric acid (8), which was readily prepared
from the sodium salt of 4-hydroxybutyric acid with TBSCl
in DMF by a novel silyl-transfer process.11,12 Compound
8 was converted to its phenyl ester 9 with DCC, and the
6-chloropyridin-3-ylmethylene moiety was similarly in-
troduced by treatment with LDA and then CIMP to give
10. Further reaction with deprotonated nitromethane
provided the R-nitro ketone 11. Compound 11 was
subjected to the same conditions as that of 7 by mixing
with 37% HCl. However, although all starting material
The next step was to remove the THP protecting group
of R-nitro ketone 7 to provide a free thiol for intramo-
lecular attack at the carbonyl site to form a hemimer-
captal. Although the THP-protected thiol group is rela-
tively stable toward acids and usually cleaved by metal-
catalyzed procedures, the S-THP linkage can also be
(6) Terang, N.; Mehta, B. K.; Ila, H.; J unjappa, H. Tetrahedron 1998,
54, 12973-12984.
(7) Node, M.; Kawabata, T.; Fujimoto, M.; Fuji, K. Synthesis 1984,
(10) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; J ohn Wiley & Sons: New York, 1999.
(11) Renton, P.; Shen, L.; Eckert, J .; Lee, G. M.; Gala, D.; Chen, G.;
Pramanik, B.; Schumacher, D. Org. Process Res. Dev. 2002, 6, 36-41.
(12) Renton, P.; Gala, D.; Lee, G. M. Tetrahedron Lett. 2001, 42,
7141-7143.
234-236.
(8) Hanefeld, W.; Schuetz, H. J . Heterocycl. Chem. 1999, 36, 1167-
1174.
(9) Field, G. F.; Zally, W. J . Synthesis 1979, 295-296.
J . Org. Chem, Vol. 69, No. 3, 2004 877

Zhang et al.
SCHEME 3 a
and then 15 which was further transformed into the
R-nitro ketone 16 by reaction with nitromethane. Com-
pound 16 was treated with iodomethane and potassium
tert-butoxide successively to finish the cyclization in one
pot. The major product was the desired (Z)-3 with lesser
amounts of (E)-3 and a double bond shifted isomer 17.
The NOE effect was observed between the nitromethyl-
ene proton and one of the pyridinylmethylene protons for
(Z)-3 but not (E)-3.
The final one-pot cyclization includes three consecutive
reactions: methylation at the sulfur atom, generation of
the enol anion of the R-nitro ketone, and intramolecular
attack of the enol anion at C5 (Scheme 4). Selective
methylation at the methylthio group was done with 10
times excess of iodomethane using methanol as the
solvent; simply reacting the R-nitro ketone 16 with
iodomethane without solvent or using DMF as solvent
complicated the reaction with significant methylation at
the pyridine nitrogen. The addition of 18-crown-6 is
crucial for the cyclization; without it, little (E/Z)-3 was
formed.
The biological activities of the new compounds were
determined at the Drosophila nAChR with [3H]imidaclo-
prid binding assays. The nitromethylene analogue of
imidacloprid is one of the most potent agonists known
for the Drosophila nAChR, in this assay with a Ki of 0.13
nM versus 2.2 nM for imidacloprid14 (Table 1). Compound
1 has very high activity (Ki 1.2 nM) followed by the sulfur
analogue 2 (Ki 180 nM). However, (E)-3 and (Z)-3 have
significantly lower potencies than 1 and 2, and interest-
ingly, there is no big difference between their activities,
suggesting hydrolytic instability. The stability of com-
pounds (E)-3 and (Z)-3 was examined under the binding
assay conditions, revealing half-life times of 9.1 and 8.6
min, respectively, in pH 7.4 buffer. Lactone 12 was
identified as the product from hydrolysis. The hydrolysis
of 3 to 12 could go through the hemiacetal intermediate
11b possibly formed by a Michael-type addition, as shown
in Scheme 3. Thus, the measured apparent activity of 3
is probably actually that of compound 12. In addition, a
check of the stability for compound 2 under the same
condition showed no hydrolysis.
a
Reagents and conditions: (i) DCC, PhOH, DMAP, CH2Cl2, rt,
overnight, 80%; (ii) LDA, CIMP, HMPA, THF, -78 °C to rt,
overnight, 30%; (iii) CH3NO2, KOBut, DMSO, <20 °C, overnight,
44%; (iv) 37% HCl, rt, 30 min, 80% or TBAF, rt, 4 h, 98%.
was consumed, no desired product was found and instead
lactone 12 was the major product isolated by silica gel
chromatography. A rationalization for the production of
12 is that the hydroxy group released under strong acidic
conditions attacks the carbonyl group (11a ) to form a
hemiacetal (11b), which is subjected to a retro-Henry
reaction with elimination of the nitromethylene moiety
(Scheme 3), in contrast to the elimination of water in the
synthesis of tetrahydrothiophene 2. Since the TBS group
can be usually removed with TBAF,10 a reaction of 11
with TBAF will presumably give the deprotected alcohol
11a . However, upon chromatography of the reaction
mixture, the major isolated product was again 12. It
seems that R-nitro ketone 11a is unstable and once the
hydroxy group is freed, it will attack the carbonyl site
simultaneously and retro-Henry reaction gives lactone
12, no matter whether acidic or basic conditions are used.
The high binding affinities of ligands 1 and 2 suggest
that N1 is not absolutely essential for activity, but the
considerably reduced activity of 1 relative to that of the
imidacloprid nitromethylene analogue indicates that N1
distinctly enhances potency. This finding favors binding
model c (Figure 2).
Another option to form the tetrahydrofuran ring is to
build the O1-C5 bond (see Figure 3), possibly by attack
of the enol anion of the R-nitro ketone at C5 bearing a
good leaving group. Although halides and tosylates
qualify for this role, in our synthesis (Scheme 4) we intro-
duced a methylthio group at C5 to simplify the protec-
tion-deprotection process. The methylthio substituent is
usually not a leaving group, but it can be activated by
methylation since a dimethyl sulfide is a good leaving
group. The synthesis started from 4-methylsulfanylbu-
tyric acid (13), prepared from γ-butyrolactone with
sodium methylthioate.13 Similar to the previous synthe-
ses, the acid 13 was converted to the phenyl esters 14
In conclusion, we synthesized the biologically impor-
tant imidacloprid analogues 3-(6-chloropyridin-3-yl)-
methyl-2-nitromethylenetetrahydrothiophene (2) and -tet-
rahydrofuran (3) via R-nitro ketone intermediates which
served as an electrophile and nucleophile, respectively.
The 2-nitromethylenetetrahydrothiophene 2 was formed
through intramolecular attack by a thiol substituent at
the carbonyl group of the R-nitro ketone, serving as an
electrophile, providing the Z-isomer exclusively. In con-
trast, the corresponding 2-nitromethylenetetrahydrofu-
ran 3, not accessible by the aforementioned route due to
limited stability, was prepared by intramolecular attack
of the enol anion in which the deprotonated R-nitro
(13) Williams, K. A.; Doi, J . T.; Musker, W. K. J . Org. Chem. 1985,
50, 4-10.
(14) Zhang, N.; Tomizawa, M.; Casida, J . E. J . Med. Chem. 2002,
45, 2832-2840.
878 J . Org. Chem., Vol. 69, No. 3, 2004

R-Nitro Ketone as an Electrophile and Nucleophile
SCHEME 4 a
a
Reagents and conditions: (i) DCC, PhOH, DMAP, CH2Cl2, rt, overnight, 91%; (ii) LDA, CIMP, HMPA, THF, -78 °C to rt, overnight,
75%; (iii) CH3NO2, KOBut, DMSO, <20 °C, overnight, 87%; (iv) MeI, MeOH, rt, overnight; then KOBut, 18-crown-6, DMF, rt, 2h, 27% for
(Z)-3 and 21% for (E)-3.
TABLE 1. Bin d in g Affin ities of 1-3 to th e Dr osoph ila
solved in EtOAc, and filtered. The filtrate was concentrated
and subjected to silica gel column chromatography with EtOAc
and hexanes (1:6) to give 5 as an oil (2.0 g, 53%): 1H NMR δ
7.41-7.07 (m, 5H), 4.89 (dd, 1H, J ) 3.6, 6.2 Hz), 4.13-4.06
(m, 1H), 3.56-3.48 (m, 1H), 2.85-2.78 (m, 1H), 2.73-2.66 (m,
3H), 2.11-1.58 (m, 8H); 13C NMR δ 171.6, 150.7, 129.4, 125.7,
121.5, 82.3, 64.6, 33.2, 31.4, 29.6, 25.6, 25.2, 21.7. Anal. Calcd
for C15H20O3S: C, 64.26; H, 7.19. Found: C, 64.15; H, 7.20.
2-(6-Ch lor op yr id in -3-ylm eth yl)-4-(tetr a h yd r op yr a n -2-
ylsu lfa n yl)bu tyr ic Acid P h en yl Ester (6). To a stirred
solution of LDA (2.0 M, 4.5 mL, 9.0 mmol) in THF (30 mL)
was added dropwise a solution of 5 (1.68 g, 6.0 mmol) in THF
(10 mL) at -78 °C, and the mixture was stirred for 30 min at
the same temperature. CIMP (2.28 g, 9.0 mmol, prepared from
2-chloro-5-chloromethylpyridine by reaction with NaI in ace-
tone) and HMPA (1.6 mL, 9.0 mmol) were added. The mixture
was then stirred at rt overnight, and the reaction was
quenched with saturated NH4Cl solution and extracted with
EtOAc. The extract was washed with water and brine, dried,
and concentrated. Silica gel column chromatography of the
residue with CH2Cl2 and hexanes (30:1) provided 6 (pair of
diastereomers) as an oil (1.50 g, 62%): 1H NMR δ 8.31 (d, 1H,
J ) 2.5 Hz), 7.57 (dd, 1H, J ) 2.5, 8.2 Hz), 7.38-7.19 (m, 4H),
6.91 (dd, 2H, J ) 1.5, 7.7 Hz), 4.90-4.82 (m, 1H), 4.08-4.01
(m, 1H), 3.51-3.46 (m, 1H), 3.13-2.75 (m, 5H), 2.25-1.58 (m,
8H); 13C NMR δ 172.8, 150.4, 150.1, 150.0, 139.4, 133.1, 129.5,
126.3, 126.0, 124.1, 121.3, 82.5, 82.2, 64.6, 46.0, 34.4, 34.3, 32.4,
31.3, 28.0, 27.8, 25.6, 21.7. Anal. Calcd for C21H24ClNO3S: C,
62.14; H, 5.96; N, 3.45. Found: C, 62.30; H, 5.98; N, 3.30.
3-(6-Ch lor op yr id in -3-ylm eth yl)-1-n itr o-5-(tetr a h yd r o-
p yr a n -2-ylsu lfa n yl)p en ta n -2-on e (7). To a suspension of
potassium tert-butoxide (0.69 g, 6.6 mmol) in DMSO (5.0 mL)
was added nitromethane (0.36 mL, 6.6 mmol) at <20 °C. The
mixture was stirred for 1 h at the same temperature followed
by dropwise addition of a solution of 6 (0.90 g, 2.2 mmol) in
DMSO (2.0 mL). The reaction mixture was stirred overnight
and then poured into ice-water (15 mL). The solution was
acidified with concentrated HCl to pH 1 and extracted with
EtOAc. The extract was dried and concentrated. Chromatog-
raphy with EtOAc and hexanes (1:1) on silica gel column
provided 7 as an oil (0.65 g, 79%), which was a mixture of a
pair of diastereomers and their corresponding tautomers: 1H
NMR δ 8.23-8.19 (m, 1H), 7.48-7.44 (m, 1H), 7.31-7.28 (m,
1H), 6.66 and 6.64 (s, 0.18H), 5.54 (dd, 0.91H, J ) 6.2, 14.9
n ACh R
compd
no.
1b
X
Ki (nM ( SD, n ) 3)a
NH
S
O
1.2 ( 0.3
180 ( 15
24000 ( 1800
48000 ( 3700
2
(Z)-3c
(E)-3c
O
a
Ki values are calculated with the equation of Cheng and
Prusoff,15 i.e., Ki ) IC50/(1 + [L]/KD) with [L] ) 3 nM and KD
)
b
2.4 nM. For comparison, the corresponding Ki values for imida-
cloprid and its nitromethylene analogue are 2.214 and 0.13 ( 0.01
nM, respectively. The 2-nitromethylpyrrolidine analogue of 1
(synthesis not described here) has a Ki value of 600 ( 18 nM.
2-Nitromethyleneimidazolidine, an imidacloprid analogue without
the chloropyridinylmethyl moiety, has a Ki value of 110000 ( 8500
nM compared with 2-nitromethylene[1,3]thiazinane (nithiazine)
with a Ki value of 2400 ( 300 nM. c Hydrolytically unstable so
the reported activity is probably for the hydrolysis product 12.
ketone served as a nucleophile. These compounds and
the corresponding 2-nitromethylenepyrrolidine (1) estab-
lish a distinct role but not absolute necessity for N1 in
conferring high affinity at the Drosophila nAChR.
Exp er im en ta l Section
4-(Tetr a h yd r op yr a n -2-ylsu lfa n yl)bu tyr ic Acid P h en yl
Ester (5). To a solution of 4-mercaptobutyric acid (4) (2.20 g,
18.3 mmol) in CH2Cl2 (50 mL) were added dihydropyran (2.30
g, 27.4 mmol) and pyridinium p-toluenesulfonate (0.46 g, 1.8
mmol). The solution was stirred overnight at rt, after which
time the solvent and excess dihydropyran were removed. The
residue was mixed with DCC (4.20 g, 20 mmol), DMAP (0.44
g, 3.6 mmol), and PhOH (2.10 g, 22 mmol) in CH2Cl2 (40 mL).
The solution was stirred overnight at rt, concentrated, dis-
J . Org. Chem, Vol. 69, No. 3, 2004 879

Zhang et al.
Hz), 5.04 (dd, 0.91H, J ) 5.1, 14.9 Hz), 4.83-4.68 (m, 1H),
4.02-3.96 (m, 1H), 3.53-3.45 (m, 1H), 3.27-2.52 (m, 5H),
83.2, 60.4, 49.0, 34.5, 33.4, 25.9, 18.4, -5.6. Anal. Calcd for
C17H27ClN2O4Si: C, 52.77; H, 7.03; N, 7.24. Found: C, 52.39;
H, 7.14; N, 6.93.
2.22-2.03 (m, 1H), 1.97-1.58 (m, 7H). Anal. Calcd for C16H21
-
ClN2O4S: C, 51.54; H, 5.68; N, 7.51; S, 8.60. Found: C, 51.29;
H, 5.82; N, 7.36; S, 8.31.
Rea ction of 11 w ith Con cen tr a ted HCl. A solution of
11 (100 mg, 0.26 mmol) and concentrated HCl (1.0 mL) was
allowed to react at rt for 1 h, diluted with water, and extracted
with EtOAc. The extract was dried and concentrated. The
residue was subjected to chromatography on silica gel with
EtOAc and hexanes (1:2). The major product was lactone 12
(43 mg, 80%): 1H NMR δ 8.22 (d, 1H, J ) 2.6 Hz), 7.56 (dd,
1H, J ) 2.6, 8.2 Hz), 7.29 (d, 1H, J ) 8.2 Hz), 4.34-4.13 (m,
2H), 3.23-3.14 (m, 1H), 2.91-2.78 (m, 2H), 2.35-2.25 (m, 1H),
2.04-1.90 (m, 1H); 13C NMR δ 177.7, 150.2, 149.9, 139.4, 132.6,
124.3, 66.4, 40.5, 32.3, 27.8. Anal. Calcd for C10H10ClNO2: C,
56.75; H, 4.76; N, 6.62. Found: C, 56.90; H, 4.70; N, 6.47.
Rea ction of 11 w ith TBAF . Compound 11 (140 mg, 0.36
mmol) was mixed with a solution of TBAF in THF (1.0 M, 2.0
mL, 2.0 mmol) and stirred at rt for 4 h. The solution was then
diluted with water and extracted with EtOAc. The extract was
dried and concentrated. The residue was subjected to chro-
matography with EtOAc and hexanes (1:2). The major product
was lactone 12 (75 mg, 98%).
4-Meth ylsu lfa n ylbu tyr ic Acid P h en yl Ester (14). To a
stirred solution of 4-methylsulfanylbutyric acid (13) (0.91 g,
6.8 mmol, prepared by reaction of γ-butyrolactone and sodium
thiomethoxide in HMPA13), DCC (1.55 g, 7.5 mmol), and
DMAP (0.17 g, 1.4 mmol) in CH2Cl2 (14 mL) was added a
solution of PhOH (0.77 g, 8.2 mmol) in CH2Cl2 (4.0 mL). The
mixture was stirred overnight at rt, concentrated, dissolved
in EtOAc, and filtered. The filtrate was concentrated and
subjected to silica gel column chromatography with EtOAc and
hexanes (1:10) to give 14 as an oil (1.30 g, 91%): 1H NMR δ
7.42-7.08 (m, 5H), 2.72 (t, 2H, J ) 7.2 Hz), 2.63 (t, 2H, J )
7.2 Hz), 2.14 (t, 3H), 2.06 (quintet, 2H, J ) 7.2 Hz); 13C NMR
δ 171.6, 150.6, 129.3, 125.7, 121.4, 33.4, 32.9, 23.9, 15.3. Anal.
Calcd for C11H14O2S: C, 62.83; H, 6.71. Found: C, 62.96; H,
6.90.
3-(6-Ch lor op yr id in -3-yl)m et h yl-2-n it r om et h ylen et et -
r a h yd r oth iop h en e (2). Compound 7 (0.40 g, 1.1 mmol) was
mixed with concentrated HCl (6.0 mL), kept at rt for 30 min,
and then diluted with water (40 mL). The aqueous solution
was extracted with EtOAc, dried with Na2SO4, and concen-
trated. The residue was subjected to silica gel chromatography
with EtOAc and hexanes (1:1) to give 2 as a pale yellow solid
(0.25 g, 86%), which was identified as the Z-isomer by NOESY
1
experiment: mp 103-104 °C; H NMR δ 8.24 (d, 1H, J ) 2.6
Hz), 7.48 (dd, 1H, J ) 2.6, 8.2 Hz), 7.32 (d, 1H, J ) 8.2 Hz),
7.26 (d, 1H, J ) 1.0 Hz), 3.33-3.25 (m, 1H), 3.21-3.06 (m,
2H), 2.96 (dd, 1H, J ) 6.2, 13.9 Hz), 2.75 (dd, 1H, J ) 8.7,
13.9 Hz), 2.23-2.12 (m, 1H), 2.05-1.95 (m, 1H); 13C NMR δ
167.4, 150.5, 149.9, 139.2, 132.3, 128.4, 124.4, 50.1, 35.8, 33.4,
32.8; EIMS m/z 270 (17, M+). Anal. Calcd for C11H11ClN2O2S:
C, 48.80; H, 4.10; N, 10.35. Found: C, 48.93; H, 4.14; N, 10.15.
4-(ter t-Bu tyld im eth ylsila n yloxy)bu tyr ic Acid P h en yl
Ester (9). To a stirred solution of 4-(tert-butyldimethylsila-
nyloxy)butyric acid (8) (prepared from sodium 4-hydroxybu-
tyrate according to Renton’s method,11,12 5.25 g, 23.6 mmol),
DCC (5.40 g, 26.0 mmol), and DMAP (0.58 g, 4.7 mmol) in
CH2Cl2 (50 mL) was added PhOH (2.70 g, 28.4 mmol). The
mixture was stirred overnight, concentrated, dissolved in
EtOAc, and filtered. The filtrate was concentrated and sub-
jected to silica gel column chromatography with EtOAc and
hexanes (1:30) to give 9 as an oil (5.60 g, 80%): 1H NMR δ
7.42-7.08 (m, 5H), 3.74 (t, 2H, J ) 6.0 Hz), 2.67 (t, 2H, J )
7.2 Hz), 2.01-1.92 (m, 2H), 0.93 (s, 9H), 0.09 (s, 6H); 13C NMR
δ 172.1, 150.7, 129.3, 128.3, 125.6, 121.5, 61.8, 30.7, 27.8, 25.9,
18.3, -5.4. Anal. Calcd for C16H26O3Si: C, 65.26; H, 8.90.
Found: C, 65.05; H, 8.86.
4-(ter t-Bu tyld im eth ylsila n yloxy)-2-(6-ch lor op yr id in -3-
ylm eth yl)bu tyr ic Acid P h en yl Ester (10). To a stirred
solution of LDA (2.0 M, 6.0 mL, 12 mmol) in THF (50 mL)
was added dropwise a solution of 9 (2.94 g, 10 mmol) in THF
(10 mL) at -78 °C, and the mixture was stirred for 30 min at
the same temperature. CIMP (3.04 g, 12 mmol) and HMPA
(2.1 mL, 12 mmol) were added. After the mixture was stirred
at rt overnight, the reaction was quenched with saturated
NH4Cl solution and extracted with EtOAc. The extract was
washed with water and brine, dried, and concentrated. Silica
gel column chromatography of the residue with CH2Cl2 and
hexanes (1:1) provided 10 as an oil (1.2 g, 30%): 1H NMR δ
8.31 (d, 1H, J ) 2.6 Hz), 7.57 (dd, 1H, J ) 2.6, 8.2 Hz), 7.38-
7.19 (m, 4H), 6.90 (dd, 2H, J ) 1.0, 8.7 Hz), 3.82-3.73 (m,
2H), 3.16-2.92 (m, 3H), 2.14-2.03 (m, 1H), 1.91-1.80 (m, 1H),
0.91 (s, 9H), 0.07 (s, 6H); 13C NMR δ 173.1, 150.4, 150.1, 149.8,
139.3, 133.4, 129.4, 125.9, 124.0, 121.3, 60.4, 43.6, 34.8, 34.5,
25.9, 18.3, -5.4. Anal. Calcd for C22H30ClNO3Si: C, 62.91; H,
7.20; N, 3.33. Found: C, 63.13; H, 7.31; N, 3.19.
2-(6-Ch lor op yr id in -3-ylm et h yl)-4-m et h ylsu lfa n ylb u -
tyr ic Acid P h en yl Ester (15). To a stirred solution of LDA
(2.0 M, 4.8 mL, 9.6 mmol) in THF (30 mL) was added dropwise
a solution of 14 (1.0 g, 4.8 mmol) in THF (10 mL) at -78 °C,
and the mixture was stirred for 30 min at the same temper-
ature. CIMP (2.42 g, 9.6 mmol) and HMPA (1.7 g, 9.6 mmol)
were added. After the mixture was stirred at rt overnight, the
reaction was quenched with saturated NH4Cl solution and
extracted with EtOAc. The extract was washed with water and
brine, dried, and concentrated. Silica gel column chromatog-
raphy of the residue with EtOAc and hexanes (1:5) provided
15 as an oil (1.2 g, 75%): 1H NMR δ 8.32 (d, 1H, J ) 2.5 Hz),
7.58 (dd, 1H, J ) 2.5, 8.2 Hz), 7.39-7.19 (m, 4H), 6.93-6.89
(m, 2H), 3.11-3.03 (m, 2H), 2.96-2.90 (m, 1H), 2.67-2.62 (m,
2H), 2.24-2.14 (m, 1H), 2.11 (s, 3H), 1.98-1.88 (m, 1H); 13C
NMR δ 172.7, 150.3, 150.0, 139.3, 133.0, 129.4, 128.3, 126.0,
124.0, 121.2, 45.9, 34.5, 31.7, 31.2, 15.4. Anal. Calcd for C17H18
-
ClNO2S: C, 60.80; H, 5.40; N, 4.17. Found: C, 60.62; H, 5.60;
N, 4.23.
5-(ter t-Bu tyld im eth ylsila n yloxy)-3-(6-ch lor op yr id in -3-
ylm eth yl)-1-n itr op en ta n -2-on e (11). To a suspension of
potassium tert-butoxide (0.50 g, 4.8 mmol) in DMSO (4.0 mL)
was added nitromethane (0.26 mL, 4.8 mmol) at <20 °C. The
mixture was stirred for 1 h at the same temperature followed
by dropwise addition of a solution of 10 (0.68 g, 1.6 mmol) in
DMSO (2.0 mL). The reaction mixture was stirred overnight
and then poured into ice-water (10 mL). The solution was then
acidified with concentrated HCl to pH 3-4 and extracted with
EtOAc. The extract was dried and concentrated. Chromatog-
raphy with EtOAc and hexanes (1:3) on a silica gel column
provided 11 as an oil (0.28 g, 44%). NMR indicated 11 contains
∼5% of the enol form: 1H NMR δ 8.21 (d, 1H, J ) 2.6 Hz),
7.45 (dd, 1H, J ) 2.6, 8.2 Hz), 7.28 (d, 1H, J ) 8.2 Hz), 5.43
(d, 1H, J ) 14.9 Hz), 5.11 (d, 1H, J ) 14.9 Hz), 3.72-3.61 (m,
2H), 3.07-2.73 (m, 3H), 2.04-1.73 (m, 2H), 0.88 (s, 9H), 0.06
(s, 6H); 13C NMR δ 198.6, 150.1, 149.9, 139.3, 132.7, 124.3,
3-(6-Ch lor op yr id in -3-ylm eth yl)-5-m eth ylsu lfa n yl-1-n i-
tr op en ta n -2-on e (16). To a suspension of potassium tert-
butoxide (0.56 g, 5.4 mmol) in DMSO (3.0 mL) was added
nitromethane (0.29 mL, 5.4 mmol) at <20 °C. The mixture was
stirred for 1 h at the same temperature followed by dropwise
addition of a solution of 15 (0.60 g, 1.8 mmol) in DMSO (1.0
mL). The reaction mixture was stirred overnight and then
poured into ice-water (10 mL). The solution was acidified with
concentrated HCl to pH 1 and extracted with EtOAc. The
extract was dried and concentrated. Chromatography with
EtOAc and hexanes (1:1) on a silica gel column provided 16
as an oil (0.47 g, 87%). NMR indicated that 16 was a mixture
of tautomers: 1H NMR δ 11.87 (br s, 0.18H), 8.20 (d, 1H, J )
2.1 Hz), 7.45 (dd, 1H, J ) 2.1, 8.2 Hz), 7.29 (d, 1H, J ) 8.2
Hz), 6.63 (s, 0.18H), 5.50 (d, 0.82H, J ) 14.9 Hz), 5.06 (d,
0.82H, J ) 14.9 Hz), 3.02-2.43 (m, 5H), 2.21-2.05 (m, 1H),
880 J . Org. Chem., Vol. 69, No. 3, 2004

R-Nitro Ketone as an Electrophile and Nucleophile
2.04 (s, 0.5 H), 1.98 (s, 2.5 H), 1.90-1.75 (m, 1H); 13C NMR
major tautomer (16) δ 198.3, 150.3, 149.9, 139.3, 132.2, 124.4,
83.7, 50.1, 34.0, 31.7, 30.2, 15.0; minor tautomer (enol form) δ
174.1, 150.1, 149.8, 139.0, 132.4, 124.2, 116.9, 44.2, 34.6, 31.4,
30.9, 15.3. Anal. Calcd for C12H15ClN2O3S: C, 47.60; H, 4.99;
N, 9.25. Found: C, 47.54; H, 5.01; N, 9.01.
132.9, 124.6, 118.8, 72.0, 44.9, 32.9, 27.5. Anal. Calcd for
C11H11ClN2O3: C, 51.88; H, 4.35; N, 11.00. Found: C, 51.55;
H, 4.54; N, 10.57. Another isolated product (15 mg, 14%) was
2-chloro-5-(2-nitromethyl-4,5-dihydrofuran-3-ylmethyl)pyri-
dine (17): 1H NMR δ 8.25 (d, 1H, J ) 2.6 Hz), 7.54 (dd, 1H, J
) 2.6, 8.2 Hz), 7.30 (d, 1H, J ) 8.2 Hz), 5.08 (s, 2H), 4.36 (t,
2H, J ) 9.2 Hz), 3.47 (s, 2H), 2.57 (t, 2H, J ) 9.2 Hz); 13C
NMR δ 150.1, 149.5, 142.5, 138.8, 132.6, 124.4, 115.3, 70.2,
68.9, 32.8, 29.3; FAB-MS m/z 255 (100, [M + H]+). Anal. Calcd
for C11H11ClN2O3: C, 51.88; H, 4.35; N, 11.00. Found: C, 52.20;
H, 4.57; N, 10.61.
3-(6-Ch lor op yr id in -3-yl)m et h yl-2-n it r om et h ylen et et -
r a h yd r ofu r a n (3). Into a solution of 16 (0.13 g, 0.33 mmol)
in methanol (1.3 mL) was added iodomethane (0.7 g, 4.9 mmol).
The solution was kept at rt overnight, and the solvent was
then removed. The residue was dissolved in DMF (1.5 mL),
cooled to -20 °C, and then treated dropwise with a solution
of potassium tert-butoxide (0.05 g, 0.48 mmol) in DMF (1.0
mL) followed by 18-crown-6 (0.13 g, 0.49 mmol). The reaction
mixture was stirred at rt for 2 h and quenched by pouring
into a solution of 1 N HCl. The aqueous solution was extracted
with EtOAc. The extract was dried and concentrated. The
residue was purified by silica gel column chromatography with
EtOAc and hexanes (2:3 to 1:1) to give two isomers of 3 as
oils. The more polar one corresponds to the Z-isomer (30 mg,
27%) as confirmed by a NOESY experiment: 1H NMR δ 8.27
(d, 1H, J ) 2.6 Hz), 7.52 (dd, 1H, J ) 2.6, 8.2 Hz), 7.34 (d, 1H,
J ) 8.2 Hz), 6.60 (d, 1H, J ) 1.1 Hz), 4.65-4.58 (m, 1H), 4.54-
4.46 (m, 1H), 3.32-3.22 (m, 1H), 3.02 (dd, 1H, J ) 5.1, 13.9
Hz), 2.76 (dd, 1H, J ) 9.7, 13.9 Hz), 2.26-2.15 (m, 1H), 1.96-
1.84 (m, 1H); 13C NMR δ 168.8, 150.6, 149.8, 139.0, 131.8,
Hyd r olysis of 3. In the kinetic studies, the hydrolysis of 3
in 0.1 M pH 7.4 phosphate buffer (66 µM) was followed with
UV. The absorption at 306 nm was recorded, and the reaction
rate was calculated according to Kezdy-Swinbourne’s method.16
In the characterization studies, a solution of 3 (10 mg) in 0.1
M pH 7.4 phosphate buffer (5.0 mL) was stirred at rt for 2 h
and then extracted with EtOAc. The organic layer was dried
with Na2SO4 and concentrated. The residue was identified as
1
12 by H and 13C NMR.
Ack n ow led gm en t. This work was supported by
Grant No. R01 ES08424 from the National Institute of
Environmental Health Sciences (NIEHS), NIH, and its
contents are solely the responsibility of the authors and
do not necessarily represent the official views of NIEHS,
NIH.
124.5, 114.1, 74.4, 44.8, 34.6, 28.7. Anal. Calcd for C11H11
-
ClN2O3: C, 51.88; H, 4.35; N, 11.00. Found: C, 52.02; H, 4.40;
N, 10.83. Accordingly, the less polar isomer (23 mg, 21%) was
assigned as the (E)- isomer. 1H NMR δ 8.30 (d, 1H, J ) 2.5
Hz), 7.72 (dd, 1H, J ) 2.5, 8.2 Hz), 7.35 (d, 1H, J ) 8.2 Hz),
7.17 (s, 1H), 4.56-4.50 (m, 1H), 4.35-4.24 (m, 1H), 4.19-4.12
(m, 1H), 3.21-3.16 (m, 1H), 2.67-2.60 (m, 1H), 2.23-2.15 (m,
1H), 2.03-1.96 (m, 1H). 13C NMR δ 178.2, 150.4, 149.8, 139.4,
J O035457G
(15) Cheng, Y.-C.; Prusoff, W. H. Biochem. Pharmacol. 1973, 22,
3099-3108.
(16) Espenson, J . H. Chemical Kinetics and Reaction Mechanisms;
McGraw-Hill Inc.: New York, 1981.
J . Org. Chem, Vol. 69, No. 3, 2004 881