Silylation of γ-nitro ketones as a convenient approach to the synthesis of 2-[N,N-bis(silyloxy)amino]-2,3-dihydrofurans and conjugated enoximes

Article abstract of DOI:10.1023/A:1023958806825

Silylation of γ-nitro ketones of the general formula R ¹COCH(R²)CH(R³)CH(R⁴)NO₂ proceeded stereoselectively to give 2-[N,N-bis(trimethylsilyloxy)amino]-2,3- dihydrofurans, conjugated enoximes, silylation products of the carbonyl group or both functional groups, or N,N-bis(trimethylsilyloxy)enamine depending on the nature and positions of the substituents in the carbon skeleton. Dihydrofuran derivatives are formed for R¹ = Ar or cyclo-C ₃H₅. Enoximes are generated as the silylation products of the starting ketones with enhanced β-proton mobility (R³ = CO₂Me or 4-NO₂C₆H₄). The presence of an alkyl group at the carbonyl function (R¹ = Alk) is favorable for the formation of enoximes. Finally, the introduction of a substituent at the α position with respect to the nitro group (R⁴ = Me, CO₂Me, or Ph) leads to the formation of silyl enolates. Under the action of NH₄F in MeOH, dihydrofurans can be transformed into substituted furans in moderate yields.

Full text of DOI:10.1023/A:1023958806825

Russian Chemical Bulletin, International Edition, Vol. 52, No. 3, pp. 647—658, March, 2003
647
Silylation of γꢀnitro ketones as a convenient approach to the synthesis
of 2ꢀ[N,Nꢀbis(silyloxy)amino]ꢀ2,3ꢀdihydrofurans and conjugated enoximes*1,*2
ꢀ
ꢀ
K. P. Birin, A. A. Tishkov, S. L. Ioffe, Yu. A. Strelenko, and V. A. Tartakovsky
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: iof@cacr.ioc.ac.ru
Silylation of γꢀnitro ketones of the general formula R1COCH(R2)CH(R3)CH(R4)NO2
proceeded stereoselectively to give 2ꢀ[N,Nꢀbis(trimethylsilyloxy)amino]ꢀ2,3ꢀdihydrofurans,
conjugated enoximes, silylation products of the carbonyl group or both functional groups, or
N,Nꢀbis(trimethylsilyloxy)enamine depending on the nature and positions of the substituents
in the carbon skeleton. Dihydrofuran derivatives are formed for R1 = Ar or cycloꢀC3H5.
Enoximes are generated as the silylation products of the starting ketones with enhanced βꢀproton
mobility (R3 = CO2Me or 4ꢀNO2C6H4). The presence of an alkyl group at the carbonyl
function (R1 = Alk) is favorable for the formation of enoximes. Finally, the introduction of a
substituent at the α position with respect to the nitro group (R4 = Me, CO2Me, or Ph) leads to
the formation of silyl enolates. Under the action of NH4F in MeOH, dihydrofurans can be
transformed into substituted furans in moderate yields.
Key words: aliphatic nitro compounds, silylation, dihydrofurans, enoximes, furans.
Silylation of aliphatic nitro compounds (ANC) is an
Me3SiBr—Et3N system was generally used as the silylating
reagent.*
original and versatile process, which substantially extends
the possibilities for the preparative use of these reactive
nitrogenꢀcontaining substrates.2 This process involves
various reactions, which generally proceed with high
chemoselectivity to give diverse functionalized comꢀ
pounds. The formation of a particular product upon
silylation of ANC depends on the nature of substituents in
the carbon skeleton of the starting nitro compounds, acidꢀ
base properties of silylating reagents, and reaction condiꢀ
tions.
Earlier, with a number of examples, we have demonꢀ
strated that silylation of γꢀnitro ketones 1 (ANC containꢀ
ing the carbonyl group) can afford different products, viz.,
2ꢀ[N,Nꢀbis(silyloxy)amino]ꢀ2,3ꢀdihydrofurans,1 conjuꢀ
gated enoximes,3,4 N,Nꢀbis(silyloxy)enamines (BSENA),5
and some other derivatives6 (Scheme 1). However, it is
difficult to predict the pathway of the process in each
particular case. Consequently, additional information on
the influence of various factors on this process is required.
The aim of the present study was to systematically
examine silylation of γꢀnitro ketones 1 of the general forꢀ
mula R1COCH(R2)CH(R3)CH(R4)NO2 (1a—r) (R1,
R2, R3, and R4 are listed in Table 1). Particular attention
was given to a search for the reaction conditions favorꢀ
able for the generation of 2ꢀ[N,Nꢀbis(silyloxy)amino]ꢀ
2,3ꢀdihydrofurans and conjugated enoximes. The
Results and Discussion
Based on the earlier data1,3—6 on the silylation of a
number of γꢀnitro ketones 1, a rather justified model of
this complicated process can be proposed (see Scheme 1).
The first step of the process involves competitive silylation
of nitro ketone 1 at the carbonyl group or the nitro fragꢀ
ment giving rise to silyl enolate 2 or silyl nitronate 3,
respectively (steps (1) and (2)). Silyl enolate 2 can unꢀ
dergo further silylation to form nitronate 4.**
If the carbonyl group is retained in the first step of
silylation of γꢀnitro ketones 1, the resulting silyl nitronate
3 can undergo a series of interesting transformations inꢀ
volving this group.***
* Below, the choice of the silylating reagent will be substantiated
in more detail.
** In some cases,6 nitronate 4 can be transformed into
BSENA 5´.
*** In the present study, we chose the silylating reagent in an
attempt to retain the carbonyl group in the first step of the
process. It is known that Me3SiCl exhibits a rather weak reactivꢀ
ity and does not silylate the carbonyl group in some nitro keꢀ
tones,6 whereas Me3SiOTf is a very strong silylating reagent and
can silylate the carbonyl group in the presence of the nitro
fragment.6 We believed that Me3SiBr, which is intermediate in
its reactivity between the aboveꢀmentioned compounds, was the
reagent of choice for our purposes.
*1 Dedicated to Academician I. P. Beletskaya on the occasion of
her anniversary.
*2 For a preliminary communication, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 620—631, March, 2003.
1066ꢀ5285/03/5203ꢀ647 $25.00 © 2003 Plenum Publishing Corporation

648
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Birin et al.
Scheme 1
i. Me3SiY, Et3N (Y = Br or OTf); ii. aqueous treatment; iii. NH4F, MeOH; iv. retroꢀ[4+2].
Thus the reaction of nitronate 3 with a silylating reꢀ
agent can produce one of two cations (A or B), which
exist in equilibrium with nitronate 3.* The immonium
cation A can exist in equilibrium with its cyclic isomer C,
both these tautomers being able to undergo deprotonation
under the action of bases to produce BSENA 5 or
dihydrofuran 6, respectively.
Cation B also occurs in equilibrium with the cyclic
immonium cation D and deprotonation of this pair of
tautomers should lead to silyl nitronate 4 or cyclic enamꢀ
ine E, respectively. It is known3 that the latter can unꢀ
dergo [4+2]ꢀcyclofragmentation to form conjugated
silylated enoxime 9.
In addition, BSENA 5 can eliminate trimethylsilanol
either spontaneously or under the action of a base to give
silylated enoxime 7.*
Therefore, silylation of γꢀnitro ketones 1a—r can afꢀ
ford directly silyl enolates 2, silyl nitronates 3 or 4,
enoximes 7 or 9, or dihydrofurans 6. The composition of
the resulting mixture depends on the ratio between the
rates of the reactions (1)—(6) and (or) thermodynamic
parameters of the complex equilibrium between cations
A—D and nitronate 3.
Since it is difficult to determine a priori the overall
effect of different factors on the rates of the reacꢀ
* Earlier, it has been demonstrated4,8 that the introduction of
electronꢀwithdrawing substituents at the γ position with respect
to the nitro group of BSENA substantially facilitates eliminaꢀ
tion of trimethylsilanol giving rise to the corresponding silylated
conjugated enoximes, which are close analogs of 8.
* The oxonium cations B are generated as intermediates in many
reactions of the carbonyl group with neutral nucleophiles,7
whereas the carboimmonium cations of the type A are involved
in intramolecular alkylation.2

Silylation of γꢀnitro ketones
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
649
Table 1. Silylation of γꢀnitro ketones 1 a
АНС
R1
R2
R3
R4
τ/dayb
Product
Yield (%)
Variation of the substituent at the δꢀcarbon atom with respect to the nitro group
1a
1b
1c
Ph
H
H
H
H
H
H
H
H
4ꢀMeOC6H4
4ꢀMeOC6H4
4ꢀMeOC6H4
4ꢀMeOC6H4
4ꢀMeOC6H4
4ꢀMeOC6H4
4ꢀMeOC6H4
Ph
H
H
H
H
H
H
H
H
7
7
7
7
7
3
7
3
6a
6b
6c
6d, 4d
6e
9f
89
92
96
23, 60
85
40
4ꢀMeC6H4
4ꢀMeOC6H4
4ꢀNO2C6H4
cycloꢀC3H5
cycloꢀC6H11
Bui
1dc,d
1e
1f
1g
1h
9f
9h
66
53
Me
Variation of the substituent at the γꢀcarbon atom with respect to the nitro group
1i
1j
Ph
Me
Ph
Ac
Ph
Ph
H
H
14
8
6i
6j
51
78
Variation of the substituent at the βꢀcarbon atom with respect to the nitro group
1k
1l
1m
1n
1o
Ph
Ph
Ph
Ph
Ph
H
H
H
H
H
Me
Ph
4ꢀClC6H4
4ꢀNO2C6H4
COOMe
H
H
H
H
H
7
7
6
14
1
6k
6l
6m
6n, 7n
7o
94
88
86
72, 20
86
Variation of the substituent at the αꢀcarbon atom with respect to the nitro group
1pe,f
1q
1rc
Ph
Ph
Ph
H
H
H
Ph
Ph
Ph
Me
Ph
CO2Me
7
7
7
13p, 2p
2q
4r, 3r
64, 33
51
23, 63
a Silylation was carried out at –30 °C.
b The reaction time is given for silylation with a Me3SiBr (2.5 equiv.)—Et3N (3 equiv.) mixture, unless the reagent
is otherwise specified.
c The products were isolated without aqueous workup.
d Aqueous workup of the reaction mixture afforded a mixture of 6d (23%) and 2d (54%).
e Data on silylation with a Me3SiOTf (3.5 equiv.)—Et3N (4 equiv.) mixture.
f An increase in the time of silylation did not lead to a change in the 2p : 13p ratio.
tions (1)—(6) and stabilities of cations A—D, we studied
the influence of the substituents R1—R4 at all atoms of
the carbon skeleton on the direction of
silylation of γꢀnitro ketones 1.
The principal data on the silylation
of nitro ketones 1a—r are presented in
Table 1. In most cases, the compositions
of the reaction mixtures were determined
after their aqueous workup, which made
it possible to separate the resulting triꢀ
ucts was determined primarily by the nature of the subꢀ
stituents R1 and R4.
The general conclusion is as follows. Silylation of comꢀ
pounds with the substituent R1 involved in the conjuꢀ
gation with the carbonyl group produces the correꢀ
sponding dihydrofuran 6 (i.e., the process follows the
3 → A → C → 6 pathway), whereas compounds with alkyl
substituents R1 give rise to enoximes 9 regardless of the
steric parameters of the substituent (i.e., the process folꢀ
lows the 3 → B → D → E → 9 pathway). At the same time,
it can be suggested that the formation of cations D and, as
a consequence, of enoximes 9 is favored by an increase in
the electrophilicity of the carbonyl group due to localizaꢀ
tion of the positive charge on its carbon atom, whereas
dihydrofurans 6 are formed on condition that the cationic
center in the intermediate B is sufficiently stabilized. Howꢀ
ever, the results of our study did not provide a more
detailed explanation of high chemoselectivity of these two
processes.
ethylammonium salt and to remove an
excess of the silylating reagent. Derivatives of types 2, 5,
6, 7, and 9 were resistant to aqueous workup. In contrast,
aqueous workup of nitronates 3 and 4 recovered the startꢀ
ing nitro ketones 1 and silyl enolates 2, respectively. Treatꢀ
ment of the reaction mixtures with methanol in the presꢀ
ence of fluoride anions resulted in complete desilylation
of enoximes 7 and 9 (see Scheme 1).*
As can be seen from Table 1, most of the silylation
reactions of ketones 1a—r generally proceeded with high
chemoselectivity and the character of the reaction prodꢀ
Apparently, silylation of ketone 1d afforded silyl
nitronate 4d as the main product (2d after aqueous workup)
due to the fact that the keto fragment in this ANC is
highly prone to silylation (pKa(PhCOMe) = 18.4, whereas
pKa(4ꢀNO2C6H4COMe) = 16.7 9).
* Desilylation of dihydrofurans 6 will be considered in detail
below.

650
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Birin et al.
Scheme 2
ever, this seems to be unlikely, because authentic nitroꢀ
nates of type 3 or 11 were described as individual comꢀ
pounds and these compounds were not transformed into
each other under ordinary conditions.1,3,6
The introduction of the phenyl substituent at the
γꢀcarbon atom (with respect to the nitro group) of nitro
ketone 1 (R2 = Ph) did not change the direction of the
reaction and the corresponding dihydrofuran 6i was genꢀ
erated from nitro ketone 1i. In contrast, the introduction
of the acetyl group into ketone 1h (R2 = Ac) resulted in
the formation of dihydrofuran 6j rather than of the exꢀ
pected enoxime 9j. Presumably, the scheme of formation
of dihydrofuran 6j differs from that of other dihydroꢀ
furans 6 (Scheme 3).
Apparently, the dicarbonyl fragment in nitro ketone 1j
is silylated more rapidly than the nitro fragment
(pKa(MeNO2) = 10.6, pKa(Ac2CH2) = 9 10). As a conseꢀ
quence, cation A´ in which the carbonyl group is conjuꢀ
gated with the electronꢀdonating π system can be a preꢀ
cursor of dihydrofuran 6j. Such a conjugation causes an
increase in the nucleophilicity of the oxygen atom of the
carbonyl group and is favorable for the formation of
cation C´.
The electronic and steric properties of the substituent
R3 at the βꢀcarbon atom exert a strong effect on the selecꢀ
tivity of silylation of γꢀnitro ketones. The introduction of
the methyl or aryl group at the β position of nitro ketone 1
ensures the formation of dihydrofurans 6 (see Table 1).
Apparently, this is associated with deceleration of
βꢀdeprotonation of the carboimmonium ion A (see
Scheme 1, step (4)) due to steric hindrance for the apꢀ
proach of a base to the βꢀproton. An increase in the rate of
βꢀdeprotonation of cations A due to an increase in the
ability of the βꢀsubstituent (R3) to stabilize the negative
charge leads to an increase in the proportion of enoximes
i. Me3SiY, Et3N (Y = Br or OTf).
Cations D could be derived from silyl nitronates 3 not
only by the pathway presented in Scheme 1 but also acꢀ
cording to a mechanism involving intermediate cyclic
nitronates 11 (Scheme 2), which are generated either diꢀ
rectly from 3 (through a transition state F) or through the
bipolar ion 3´ produced upon reversible 1,6ꢀO,Oꢀmigraꢀ
tion of the Me3Si group. The possibility of the transforꢀ
mation 11 → D → E → 9 was confirmed by independent
experiments.3 This pathway of generation of cations D
should involve an equilibrium between 3 and 11. Howꢀ
Scheme 3
i. Me3SiBr, Et3N.

Silylation of γꢀnitro ketones
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
651
Scheme 4
i. Me3SiOTf, Et3N.
7 among the silylation products of compounds 1 in the
series 1m < 1n < 1o (see Table 1).
probable that the presence of an electronꢀwithdrawing
substituent leads to acceleration of silylation of the nitro
group in 1r to give nitronate 3r followed by its slow
silylation at the carbonyl group. The formation of cation
A from 3r is prevented by both a decrease in the nucleoꢀ
philicity of the oxygen atom of the nitronate group under
the influence of the adjacent electronꢀwithdrawing subꢀ
stituent R4 (kinetic factor) and destabilization of the catꢀ
ionic center by the same substituent R4 (thermodynamic
factor).
The introduction of the substituents R4 at the αꢀcarꢀ
bon atom (with respect to the nitro group) sharply changed
the silylation pathway of nitro ketones 1. In this case,
dihydrofurans 6 were not formed. Silylation of ketone 1p
with the Me3SiBr—Et3N system afforded unidentified
products. The use of a stronger silylating agent, viz.,
Me3SiOTf—Et3N, made it possible to obtain a mixture of
silyl enolate 2p and BSENA 13p after aqueous workup
(Scheme 4).
Proof of the structures
A twofold increase in the time of exposure did not lead
to a change in the 2p : 13p ratio, i.e., silyl enolate 2p was
not transformed into BSENA 13p under the reaction conꢀ
ditions. Presumably, this is associated with the fact that
γꢀsilyl oxo nitronate 3p rather than silyl enolate 2p was the
precursor of N,Nꢀbis(silyloxy)enamine 13p, the transforꢀ
mation of compound 3p into BSENA 13p being preceded
by its transformation into BSENA 12p. Silylation of the
nitro group is very sensitive to the steric demands of the
adjacent substituents, which is presumably responsible for
the observed selectivity of the process.
Apparently, steric hindrances cause termination of
silylation of ketone 1q in the step of formation of silyl
enolate 2q.*
Evidently, silylation of compound 1r containing an
electronꢀwithdrawing substituent at the α position with
respect to the nitro group (R4 = CO2Me) proceeded difꢀ
ferently and gave a mixture of nitronate 3r and its silylation
product at the carbonyl group (4r) in a molar ratio of
approximately 1 : 3 (see Scheme 4; the reaction mixture
was analyzed without its aqueous workup). It is highly
of silylation products of γꢀnitro ketones 1a—r
To summarize, silylation of nitro ketones 1a—r afꢀ
forded dihydrofurans 6a—n, conjugated enoximes 7n,o
and 9f,h, and BSENA 13p as the main synthetically valuꢀ
able products.
N,NꢀBis(silyloxy)aminodihydrofurans 6 contain the
illꢀstudied structural fragment, viz., the N,Nꢀbis(silylꢀ
oxy)amino group, bound to the sp3ꢀhybridized carꢀ
bon atom.*
Dihydrofurans 6 are thermally labile oils, which reꢀ
main intact upon aqueous workup but do not withstand
chromatographic purification.** Hence, their structures
were confirmed only by heteronuclear NMR spectroscopy
and chemical transformations (see below). The presence
of all structural fragments in products 6 was supported by
the data from 1H and 13C NMR spectroscopy. The
N,Nꢀbis(silyloxy)amino group was additionally identified
* Compounds containing this fragment have been described only
in two recent studies.1,11
** Due to the difficulties associated with the purification of
dihydrofurans 6, the reaction mixtures obtained by silylation
were kept over a long period of time (7 days) to achieve comꢀ
plete conversions of the starting nitro ketones 1. According to
the 1H NMR spectroscopic data, the purities of dihydrofurans 6
were no less than 90%.
* Taking into account that the treatment of the reaction mixꢀ
ture, which was obtained after silylation of compound 1q, with
methanolꢀd4 did not afford deuterated silyl enolate 2q (1H and
13C NMR spectroscopic data), the possibility of the formation
of silyl nitronate 4q in this process can be rejected.

652
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Birin et al.
Scheme 5
i. NH4F, MeOH; ii. Bu4NF, CH2Cl2.
based on the 15N and 29Si NMR spectroscopic data (for
example, δ(15N) is –145.0 and δ(29Si) are 24.5 and 26.9
for product 6l; for comparison, δ(15N) is –143.8 and
δ(29Si) is 23.4 for CH2=C(Me)N(OSiMe3)2 12). Based on
The structures of BSENA 13p, silyl nitronate 3r, and
1
silyl enolates 2d, 2p, and 2q were confirmed by H, 13C,
29Si, and 14N NMR spectroscopy. The structure of silyl
enolate 2d was additionally confirmed by the introducꢀ
tion of the deuterium label at the γꢀC atom (with reꢀ
spect to the nitro group) upon desilylation of 2d in a
CD3OD—CD3COOD medium.
3
the JH,H values and NOE data, the trans configuration
was assigned to the substituents at the C(2) and C(3)
carbon atoms of the stereoisomers of dihydrofurans 6 obꢀ
tained.
Desilylation
The presence of two signals for the OSiMe3 groups of
the N,Nꢀbis(silyloxy)amino fragment in the 1H, 13C, and
29Si NMR spectra of derivatives 6 is attributed to the
hindered inversion of the nitrogen atom in these prodꢀ
ucts. It should be noted that we failed to find evidence of
coalescence or exchange broadening of these signals in
the temperature range up to 60 °C. Consequently, the
inversion barrier in dihydrofurans 6 should be no lower
than 80 kJ mol–1 (barrier was determined according to a
procedure described earlier13). This is much higher than
the inversion barrier of the nitrogen atom estimated reꢀ
cently for BSENA,14 but it is consistent with the inversion
barriers of the nitrogen atom in bisꢀalkoxyamines15 and
Nꢀalkoxyꢀ or Nꢀsilyloxyisoxazolidines.16
The structures of silyl derivatives of enoximes 7 and 9
were confirmed by spectroscopic characteristics (NMR)
and desilylation giving rise to the corresponding oximes 8
and 10, which have been characterized not only by specꢀ
troscopic methods but also by the satisfactory results of
elemental analysis. The configurations of the oximino
groups and the C=C double bonds in the resulting
enoximes were determined based on the rules reported in
our earlier studies (see, for example, Ref. 4).
of N,Nꢀbis(silyloxy)aminodihydrofurans 6
Earlier,2,11,17 we have demonstrated that BSENA conꢀ
taining the bis(silyloxy)amino fragment were readily transꢀ
formed into unstable conjugated nitrosoalkenes under the
conditions of nucleophilic catalysis. Hence, N,Nꢀbis(silylꢀ
oxy)aminodihydrofurans 6 would be expected to be synꢀ
thetic equivalents of 2ꢀnitrosodihydrofurans 14.
However, treatment of derivatives 6 with methanol in
the presence of NH4F afforded furans 15 in moderate
yields, whereas the reaction of dihydrofuran 6b with Bu4NF
in CH2Cl2 gave Zꢀenenitrile 17b (Scheme 5, Table 2).*
The structures of substituted furans 15 and enenitrile
17b were confirmed by NMR spectroscopy and elemental
analysis. These data for known furans 15 are in good agreeꢀ
ment with those published in the literature.** The strucꢀ
ture and configuration of enenitrile 17b were additionally
confirmed by comparing its physicochemical characterisꢀ
tics and properties with the published data** for analoꢀ
gous derivatives. For instance, when exposed to sunlight,
* Unfortunately, we failed to extend the transformation 6 → 17
to other dihydrofurans 6.
** See the Experimental section.

Silylation of γꢀnitro ketones
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
653
Table 2. Desilylation of N,Nꢀbis(silyloxy)aminodihydrofurans 6
Scheme 6
Dihydroꢀ Reꢀ
Conditions
Product
Yield
furan
agent*
(%)
T/°C
τ/h
6a
6b
6b
6c
6e
6j
6l
6m
6n
NH4F
NH4F
Bu4NF
NH4F
NH4F
NH4F
NH4F
NH4F
NH4F
0
0
25
0
0
0
0
0
0
48
0.5
24
2
168
1.5
0.5
24
15a
15b
17b
15c
15e
15j
15m
15n
15o
35
51
38
22
48
38
85
61
40
1
* 20 mol.% with respect to dihydrofuran 6 in an excess of MeOH
or in CH2Cl2.
enenitrile Zꢀ17b underwent the rearrangement into the
E isomer typical of this class of substituted alkenes.18
The assumed mechanism of desilylation of dihydroꢀ
furans 6 is presented in Scheme 5.
Apparently, nitrosodihydrofuran 14 is initially generꢀ
ated. The next step involves elimination of the nitreneꢀ
like H—O—N species, which can occur both by ionic and
synchronous pathways involving both the dimer and
monomer of nitrosodihydrofuran 14. Subsequently, the
H—O—N → H—N=O rearrangement and(or) dimerizaꢀ
tion of nitrene into hyponitrous acid HO—N=N—OH
take place in methanol due to solvation. In contrast, the
reaction in aprotic dichloromethane led to the insertion
of nitrene into the C—H bond of furan 15b that formed
(as was exemplified by 15b) to give the corresponding
2ꢀhydroxyaminofuran 16b, which was transformed into
enenitrile 17b.*
i. Bu4NF, CH2Cl2, refluxing.
Scheme 7
It could be assumed that oximes 18 are direct precurꢀ
sors of 2ꢀhydroxyaminofurans 16 (Scheme 6). However,
analogous authentic oxime 18a did not undergo such
an isomerization even under more drastic conditions
than those used for desilylation of dihydrofurans 6 (see
Scheme 6).
* * *
To summarize, the present as well as earlier3,4,6 studꢀ
ies provided evidence that readily accessible γꢀnitro keꢀ
tones 1a—o can be considered as convenient precursors
of substituted furans 15 and conjugated enoximes 10
(Scheme 7).
It should be noted that aryl γꢀnitroalkyl ketones
1a—c,e,j,m—o serve as convenient sources of diꢀ and
trisubstituted furans 16, whereas alkyl γꢀnitroalkyl keꢀ
tones 1f—h give enoximes 10 upon an analogous silylaꢀ
tion—desilylation procedure. It remains unclear whether
aliphatic nitro compounds of types 1n and 1o can be
successfully used in the synthesis of other type of conjuꢀ
gated enoximes, viz., of products 8. However, one would
expect that this problem will be solved by changing the
nature of the silylating agent and directing the silylation
along the 1 → 2 → 4 pathway and further to functionalized
BSENA 5´ followed by 1,6ꢀN,Cꢀelimination of Me3SiOH
analogously to a procedure described earlier.6
In our opinion, the chemistry of dihydrofurans 6 conꢀ
taining the N,Nꢀbis(silyloxy)amino fragment holds addiꢀ
tional promise. It should be noted that these compounds
have been subjected only to such transformations in which
* According to the published data,19 2ꢀhydroxyaminofurans genꢀ
erated by reduction of 2ꢀnitrofurans can undergo fragmentation
to give conjugated enenitriles, which is indirect evidence in faꢀ
vor of Scheme 5.

654
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Birin et al.
2.07 (m, 1 H, CHMe2); 2.22 (m, 2 H, CH2Pri); 2.83 (m, 2 H,
CH2CO); 3.78 (s, 3 H, OMe); 3.97 (m, 1 H, CH—Ar); 4.55 (dd,
1 H, CH2NO2, 3J = 7.2 Hz, 3J = 12.2 Hz); 4.66 (dd, 1 H,
the proton and N(OSiMe3)2 group were eliminated with a
loss of two asymmetric centers. In the future, we plan to
investigate other aspects of the chemistry of dihydroꢀ
furans 6.
3
3
CH2NO2, J = 7.2 Hz, 3J = 12.2 Hz); 6.84 (d, 2 H, CHAr, J =
8.5 Hz); 7.13 (d, 2 H, CHAr, 3J = 8.5 Hz).
3ꢀMethylꢀ4ꢀnitroꢀ1ꢀphenylbutanꢀ1ꢀone (1k). Reaction conꢀ
ditions: 0.25 h at 0 °C. The yield was 1.53 g (85%). Colorless oil,
b.p. 98—108 °C (0.1 Torr). Found (%): C, 63.61; H, 6.18;
N, 6.49. C11H13NO3. Calculated (%): C, 63.76; H, 6.32; N, 6.76.
1H NMR (CDCl3), δ: 1.14 (d, 3 H, Me, 3J = 5.9 Hz); 2.90—3.22
(m, 3 H, CH2CO and CH—Me); 4.52 (dd, 1 H, CH2NO2, 3J =
6.6 Hz, 3J = 11.8 Hz); 4.52 (dd, 1 H, CH2NO2, 3J = 5.9 Hz, 3J =
11.8 Hz); 7.46 (m, 2 H, CHPh); 7.57 (m, 1 H, CHPh); 7.94 (m,
2 H, CHPh).
Experimental
The NMR spectra were recorded on a Bruker AMꢀ300 inꢀ
strument in CDCl3. The chemical shifts were measured relative
to the residual signal of the solvent (1H and 13C), Me4Si as the
internal standard (29Si), and MeNO2 as the external standard
(14N and 15N). The 29Si and 15N signals were observed using the
INEPT technique.
The IR spectra were measured on a Bruker Vektor 22 instruꢀ
ment in KBr pellets. The mass spectra were obtained on a
Finnigan MAT Incos 50 instrument (EI, 70 eV).
All experiments were carried out under dry argon. The solꢀ
vents were purified according to standard procedures.
The starting ANC were synthesized according to known proꢀ
cedures: 1a;20 1b,e,h,l,o;21 1c;22 1i;23 1j;24 1m;25 1n;26 1p;27
and 1q.28
Methyl 2ꢀnitroꢀ5ꢀoxoꢀ3,5ꢀdiphenylpentanoate (1r). Triethylꢀ
amine (2.1 mL, 15 mmol) and NO2CH2CO2Me (1.79 g,
15 mmol) were added to a stirred solution of chalcone (2.08 g,
10 mmol) in CH2Cl2 (40 mL) at 0 °C. The reaction mixture was
stirred at 20 °C for 48 h and then a solution of NaHSO4•H2O
(2.07 g, 15 mmol) in H2O (20 mL) was added. The aqueous
layer was separated and extracted with CH2Cl2 (4×20 mL). The
combined organic phases were washed with H2O (2×20 mL) and
a saturated NaCl solution (10 mL), dried with Na2SO4, and
concentrated in vacuo. After recrystallization of the residue from
MeOH, compound 1r was obtained in a yield of 1.31 g (40%) as
white crystals, m.p. 114—116 °C (MeOH). Found (%): C, 65.90;
H, 5.07; N, 4.39. C18H17NO5. Calculated (%): C, 66.05; H, 5.23;
Synthesis of aliphatic nitro compounds 1d, 1f, 1g, and
1k (general procedure). 1,8ꢀDiazabicyclo[5.4.0]undecꢀ7ꢀene
(DBU) (1.5 mL, 10 mmol) was added to a stirred solution of
α,βꢀunsaturated ketone R1C(O)C(R2)=CHR3 (8.7 mmol) in
CH2Cl2 (34 mL) and MeNO2 (7 mL) at 0 °C. The reaction
mixture was stirred under specified conditions (see below) and
then a solution of NaHSO4•H2O (1.93 g, 14 mmol) in H2O
(50 mL) was added. The aqueous layer was separated and exꢀ
tracted with CH2Cl2 (3×10 mL). The combined organic extracts
were washed with H2O (2×20 mL) and a saturated NaCl soluꢀ
tion (10 mL), dried with Na2SO4, and concentrated in vacuo.
The residue was recrystallized from MeOH (for 1d and 1g),
distilled in vacuo (for 1k), or purified by column chromatoꢀ
graphy on silica gel (for 1f).
3ꢀ(4ꢀMethoxyphenyl)ꢀ4ꢀnitroꢀ1ꢀ(4ꢀnitrophenyl)butanꢀ1ꢀone
(1d). Reaction conditions: 1 h at 0 °C. The yield was 1.53 g
(51%). Yellow crystals, m.p. 106—107 °C (MeOH). Found (%):
C, 59.00; H, 4.49; N, 7.89. C17H16N2O6. Calculated (%):
C, 59.30; H, 4.68; N, 8.14. 1H NMR (CDCl3), δ: 3.48 (m, 2 H,
CH2CO); 3.78 (s, 3 H, OMe); 4.17 (m, 1 H, CH—Ar); 4.66 (dd,
1 H, CH2NO2, 3J = 7.2 Hz, 3J = 12.2 Hz); 4.78 (dd, 1 H,
1
3
N, 4.28. H NMR (CDCl3), δ: 3.48 (dd, 1 H, CH2CO, J =
4.4 Hz, 3J = 17.7 Hz); 3.60 (s, 3 H, OMe); 3.69 (dd, 1 H,
3
3
CH2CO, J = 8.8 Hz, J = 17.7 Hz); 4.45 (m, 1 H, CH—Ph);
5.51 (d, 1 H, CHNO2, 3J = 8.1 Hz); 7.25 (m, 5 H, CHPh); 7.41
(m, 2 H, CHPh); 7.53 (m, 1 H, CHPh); 7.86 (m, 2 H, CHPh).
Silylation of aliphatic nitro compounds
1 with a
Me3SiBr—Et3N mixture (general procedure). Bromotrimethylꢀ
silane (0.4 mL, 3.0 mmol) was added to a stirred solution of
ANC 1 (1 mmol) in CH2Cl2 (3 mL) and Et3N (0.5 mL,
3.5 mmol) at –40 °C for 2 min. The reaction mixture was kept at
–30 °C over a period of time given in Table 1, diluted with light
petroleum (10 mL), and poured into a mixture of H2O (10 mL)
and light petroleum (5 mL). The organic layer was separated,
washed with a solution of NaHSO4•H2O (70 mg, 0.5 mmol) in
H2O (10 mL), H2O (2×10 mL) and a saturated NaCl solution
(10 mL), dried with Na2SO4, and concentrated in vacuo. The
product was analyzed by NMR spectroscopy using a quantitaꢀ
CH2NO2, 3J = 7.2 Hz, 3J = 12.2 Hz); 6.86 (d, 2 H, CHAr
,
3
3J = 8.5 Hz); 7.18 (d, 2 H, CHAr, J = 8.5 Hz); 8.05 (d, 2 H,
CHAr, 3J = 8.5 Hz); 8.30 (d, 2 H, CHAr, 3J = 8.5 Hz).
tive standard (ClCH2CH2Cl, δ = 3.73).
H
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ3ꢀ(4ꢀmethoxyphenyl)ꢀ
5ꢀphenylꢀ2,3ꢀdihydrofuran (6a), colorless thick oil. 1H NMR
(CDCl3), δ: 0.17 and 0.18 (both s, 9 H both, 2 SiMe3); 3.76 (s,
1ꢀCyclohexylꢀ3ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀnitrobutanꢀ1ꢀone (1f).
Reaction conditions: 2.5 h at 20 °C. The yield was 1.01 g
(38%). Colorless oil. Found (%): C, 66.81; H, 7.40; N, 4.69.
3
3
3 H, OMe); 4.69 (dd, 1 H, CHAr, J = 4.0 Hz, J = 3.4 Hz);
C
17H23NO4. Calculated (%): C, 66.86; H, 7.59; N, 4.59.
5.00 (d, 1 H, CH—N, 3J = 4.0 Hz); 5.54 (d, 1 H, CH=C,
3
1H NMR (CDCl3), δ: 1.12—1.35 (m, 4 H, 2 CH2); 1.58—1.84
(m, 6 H, 3 CH2); 2.26 (m, 1 H, CHCO); 2.87 (m, 2 H, CH2CO);
3.78 (s, 3 H, OMe); 3.96 (m, 1 H, CH—Ar); 4.56 (dd, 1 H,
CH2NO2, 3J = 7.4 Hz, 3J = 12.5 Hz); 4.66 (dd, 1 H, CH2NO2,
3J = 3.4 Hz); 6.83 (d, 2 H, CHAr, J = 8.7 Hz); 7.23 (d, 2 H,
3
CHAr, J = 8.7 Hz); 7.28—7.38 (m, 3 H, CHPh); 7.64 (d, 2 H,
CHAr, 3J = 7.4 Hz). 13C NMR (CDCl3), δ: 0.3 and 0.5 (2 SiMe3);
48.1 (CHAr); 100.2 (CH=C); 107.3 (CH—N); 114.0, 125.3,
128.3, 128.5, 129.0 (CHPh and CHAr); 130.4, 135.5 and 158.5
(2 CAr and CPh); 155.1 (C=CH). 29Si NMR (CDCl3), δ: 24.42
and 26.03 (2 SiMe3).
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ3ꢀ(4ꢀmethoxyphenyl)ꢀ
5ꢀ(4ꢀtolyl)ꢀ2,3ꢀdihydrofuran (6b), colorless viscous oil. 1H NMR
(CDCl3), δ: 0.17 and 0.18 (both s, 9 H each, 2 SiMe3); 2.34 (s,
3 H, Me); 3.75 (s, 3 H, OMe); 4.67 (dd, 1 H, CHAr, 3J = 4.0 Hz,
3
3
3J = 7.4 Hz, J = 12.5 Hz); 6.84 (d, 2 H, CHAr, J = 8.8 Hz);
7.12 (d, 2 H, CHAr, 3J = 8.8 Hz).
2ꢀ(4ꢀMethoxyphenyl)ꢀ6ꢀmethylꢀ1ꢀnitroheptanꢀ4ꢀone (1g).
Reaction conditions: 1.5 h at 0 °C. The yield was 1.58 g (65%).
White crystals, m.p. 50—51 °C (MeOH). Found (%): C, 64.43;
H, 7.51; N, 5.00. C15H21NO4. Calculated (%): C, 64.50; H, 7.58;
N, 5.01. 1H NMR (CDCl3), δ: 0.84 (d, 6 H, 2 Me, 3J = 6.6 Hz);

Silylation of γꢀnitro ketones
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
655
3J = 3.4 Hz); 4.99 (d, 1 H, CH—N, 3J = 4.0 Hz); 5.47 (d, 1 H,
CH=C, 3J = 3.4 Hz); 6.82 (d, 2 H, CHAr, 3J = 8.7 Hz); 7.15 (d,
2 H, CHAr, 3J = 8.1 Hz); 7.22 (d, 2 H, CHAr, 3J = 8.7 Hz); 7.53
(d, 2 H, CHAr, 3J = 8.1 Hz). 13C NMR (CDCl3), δ: 0.4 and 0.5
(2 SiMe3); 21.4 (Me); 48.1 (CHAr); 55.3 (OMe); 99.3 (CH=C);
107.3 (CH—N); 114.0, 125.3, 128.9, and 129.0 (all CHAr); 127.7,
135.7, 138.4, and 158.5 (all CAr); 155.3 (C=CH). 29Si NMR
(CDCl3), δ: 24.31 and 25.89 (2 SiMe3).
(OMe); 113.4 and 129.6 (2 CHAr); 121.3 (CH2); 125.5 and 159.6
(2 CAr); 142.2 (C=CH2); 155.4 (CH=N). 29Si NMR (CDCl3),
δ: 26.28 (SiMe3).
2ꢀPhenylpropenal Oꢀtrimethylsilyloxime (9h), thick yellowꢀ
ish oil. 1H NMR (CDCl3), δ: 0.21 (s, 9 H, SiMe3); 5.53 (s, 1 H,
CH2); 5.65 (s, 1 H, CH2); 7.33 (m, 3 H, CHPh); 7.46 (m, 2 H,
CHPh); 8.09 (s, 1 H, CH=N). 13C NMR (CDCl3), δ: –0.8
(SiMe3); 122.3 (CH2); 127.8, 128.2, and 128.0 (all CHPh); 137.4
(CPh); 142.8 (C=CH2); 154.9 (CH=N). 29Si NMR (CDCl3), δ:
26.29 (SiMe3).
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ3,5ꢀbis(4ꢀmethoxyꢀ
phenyl)ꢀ2,3ꢀdihydrofuran (6c), colorless thick oil. 1H NMR
(CDCl3), δ: 0.17 and 0.18 (both s, 9 H each, 2 SiMe3); 3.79
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ3,4,5ꢀtriphenylꢀ2,3ꢀ
3
1
(s, 3 H) and 3.84 (s, 9 H) (2 OMe); 4.65 (dd, 1 H, CHAr, J =
dihydrofuran (6i), colorless oil. H NMR (CDCl3), δ: 0.10 and
3
3
3
3.8 Hz, J = 2.9 Hz); 4.96 (d, 1 H, CH—N, J = 3.8 Hz); 5.39
(d, 1 H, CH=C, 3J = 2.8 Hz); 6.69 (d, 2 H, CHAr, 3J = 8.5 Hz);
0.14 (both s, 9 H each, 2 SiMe3); 4.91 (d, 1 H, CH—Ar, J =
3
3.3 Hz); 4.94 (d, 1 H, CH—N, J = 3.3 Hz); 7.00—7.47 (m,
3
3
6.83 (d, 2 H, CHAr, J = 8.5 Hz); 7.23 (d, 2 H, CHAr, J =
8.5 Hz); 7.57 (d, 2 H, CHAr, 3J = 8.5 Hz). 13C NMR (CDCl3),
δ: 0.3 and 0.4 (2 SiMe3); 48.1 (CHAr); 55.2 (2 OMe); 98.1
(CH=C); 107.2 (CH—N); 113.7, 113.8, 126.6, and 128.9
(all CHAr); 123.1, 135.7, 158.4, and 159.8 (all CAr); 154.9
(C=CH). 29Si NMR (CDCl3), δ: 24.26 and 25.86 (2 SiMe3).
13 H, CHPh); 7.75 (m, 2 H, CHPh). 13C NMR (CDCl3), δ: –2.8
and –2.7 (2 SiMe3); 50.8 (CH—Ph); 102.0 (CH—N); 111.9
(C=CO); 123.4, 123.7, 124.7, 125.0, 125.2, 125.4, 125.6, 125.8,
and 126.6 (all CHPh); 130.2, 131.4, and 139.1 (all CPh); 146.9
(C=CO). 29Si NMR (CDCl3), δ: 24.64 and 25.97 (2 SiMe3).
4ꢀAcetylꢀ2ꢀ[N,Nꢀbis(trimethylsilyloxy)amino]ꢀ5ꢀmethylꢀ3ꢀ
phenylꢀ2,3ꢀdihydrofuran (6j), thick colorless oil. 1H NMR
(CDCl3), δ: 0.17 and 0.22 (both s, 9 H each, 2 SiMe3); 1.92 (d,
A
mixture of 2ꢀ[N,Nꢀbis(trimethylsilyloxy)amino]ꢀ3ꢀ
(4ꢀmethoxyphenyl)ꢀ5ꢀ(4ꢀnitrophenyl)ꢀ2,3ꢀdihydrofuran (6d) and
[3ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀnitroꢀ1ꢀ(4ꢀnitrophenyl)ꢀbutꢀ1ꢀenylꢀ
oxy]trimethylsilane (2d), viscous yellowish oil.
4
3 H, MeC=C, J = 1.5 Hz); 2.39 (s, 3 H, MeC=O); 4.73 (br.s,
3
1 H, CH—Ar); 4.84 (d, 1 H, CH—N, J = 3.7 Hz); 7.15—7.39
1
Compound 6d. H NMR (C6D6), δ: 0.21 and 0.25 (both s,
(m, 5 H, CHPh). 13C NMR (CDCl3), δ: 0.3 and 0.4 (2 SiMe3);
14.9 (MeC=C); 29.8 (MeC=O); 48.9 (CH—Ph); 96.3 (C=CO);
107.0 (CH—N); 127.3, 127.8, and 129.0 (all CHPh); 142.3 (CPh);
167.5 (C=CO); 195.2 (C=O). 29Si NMR (CDCl3), δ: 25.56 and
26.51 (2 SiMe3).
9 H each, 2 SiMe3); 3.42 (s, 3 H, OMe); 5.07 (dd, 1 H, CHAr
,
3
3
3J = 3.7 Hz, J = 3.0 Hz); 5.29 (d, 1 H, CH—N, J = 3.7 Hz);
3
3
5.53 (d, 1 H, CH=C, J = 3.0 Hz); 6.85 (d, 2 H, CHAr, J =
3
8.6 Hz); 7.27 (d, 2 H, CHAr, J = 8.6 Hz); 7.47 (d, 2 H, CHAr,
3J = 8.9 Hz); 7.93 (d, 2 H, CHAr, 3J = 8.9 Hz). 13C NMR
(C6D6), δ: 0.3 and 0.6 (2 SiMe3); 48.6 (CHAr); 54.9 (OMe);
105.7 (CH=C); 107.7 (CH—N); 114.5, 123.9, 125.9, and 129.4
(all CHAr); 135.1, 136.9, 147.7, and 159.3 (all CAr); 153.5
(C=CH). 29Si NMR (C6D6), δ: 23.62 and 25.19 (2 SiMe3).
Compound 2d. H NMR (C6D6), δ: 0.09 (s, 9 H, SiMe3);
3.40 (s, 3 H, OMe); 4.29 (m, 2 H, CH2NO2); 4.70 (m, 1 H,
CH—Ar); 5.31 (d, 1 H, CH=C, 3J = 9.2 Hz); 6.79 (d, 2 H,
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ3ꢀmethylꢀ5ꢀphenylꢀ
2,3ꢀdihydrofuran (6k), thick colorless oil. 1H NMR (CDCl3), δ:
0.17 and 0.23 (both s, 9 H each, 2 SiMe3); 1.20 (d, 3 H, Me, 3J =
3
7.2 Hz); 3.39 (m, 1 H, CH—Me); 4.76 (d, 1 H, CH—N, J =
4.6 Hz); 5.37 (d, 1 H, CH=C, 3J = 2.6 Hz); 7.20—7.37 (m, 3 H,
CHPh); 7.55 (d, 2 H, CHPh, 3J = 7.9 Hz). 13C NMR (CDCl3), δ:
0.4 and 0.5 (2 SiMe3); 20.4 (Me); 38.9 (CH—Me); 102.2
(CH=C); 107.5 (CH—N); 125.1, 128.2, and 128.3 (all CHPh);
130.5 (CPh); 153.6 (C=CH). 29Si NMR (CDCl3), δ: 24.53 and
25.78 (2 SiMe3).
1
3
3
CHAr, J = 8.6 Hz); 7.07 (d, 2 H, CHAr, J = 8.6 Hz); 7.20 (d,
3
3
2 H, CHAr, J = 8.9 Hz); 7.88 (d, 2 H, CHAr, J = 8.9 Hz).
13C NMR (C6D6), δ: 0.6 (SiMe3); 41.1 (CH—Ar); 54.9 (OMe);
80.1 (CH2NO2); 112.6 (OC=CH); 114.8, 123.7, 126.7, and 128.8
(all CHAr); 131.3, 144.5, 147.9 and 159.6 (CAr); 150.4 (OC=CH).
29Si NMR (C6D6), δ: 22.09 (SiMe3). 14N NMR (C6D6), δ: –9.3
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ3,5ꢀdiphenylꢀ2,3ꢀdiꢀ
1
hydrofuran (6l), thick colorless oil. H NMR (CDCl3), δ: 0.17
and 0.19 (both s, 9 H each, 2 SiMe3); 4.75 (dd, 1 H, CH—Ph,
3
3
3J = 3.8 Hz, J = 3.0 Hz); 5.05 (d, 1 H, CH—N, J = 3.8 Hz);
5.58 (d, 1 H, CH=C, 3J = 3.0 Hz); 7.18—7.39 (m, 8 H, CHPh);
7.65—7.68 (m, 2 H, CHPh). 13C NMR (CDCl3), δ: 0.2 and 0.3
(2 SiMe3); 48.6 (CH—Ph); 99.8 (CH=C); 106.9 (CH—N);
125.1, 126.6, 127.9, 128.2, and 128.4 (all CHPh); 130.2 and
143.3 (2 CPh); 155.1 (C=CH). 29Si NMR (CDCl3), δ: 24.54 and
26.19 (2 SiMe3). 15N NMR (CDCl3), δ: –145.0 (d, N(OSiMe3)2,
2J = 9.7 Hz).
(NO2, ∆ν ≈ 1100 Hz).
1/2
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ5ꢀcyclopropylꢀ3ꢀ
(4ꢀmethoxyphenyl)ꢀ2,3ꢀdihydrofuran (6e), viscous colorless oil.
1H NMR (C6D6), δ: 0.19 and 0.31 (both s, 9 H each, 2 SiMe3);
0.50—0.58 (m, 2 H, CH2); 0.75—0.82 (m, 2 H, CH2); 1.40 (m,
1 H, CH); 3.32 (s, 3 H, OMe); 4.70 (d, 1 H, CH—N, 3J =
2.9 Hz); 4.75 (dd, 1 H, CH—Ar, 3J = 3.7 Hz, 3J = 2.9 Hz); 5.12
(d, 1 H, CH=C, 3J = 3.7 Hz); 6.79 (d, 2 H, CHAr, 3J = 8.8 Hz);
2ꢀ[N,NꢀBis(trimethylsilyloxy)amino]ꢀ3ꢀ(4ꢀchlorophenyl)ꢀ5ꢀ
phenylꢀ2,3ꢀdihydrofuran (6m), thick colorless oil. 1H NMR
(CDCl3), δ: 0.21 and 0.22 (both s, 9 H each, 2 SiMe3); 4.81 (dd,
1 H, CH—Ar, 3J = 4.0 Hz, 3J = 3.4 Hz); 5.04 (d, 1 H, CH—N,
3
7.28 (d, 2 H, CHAr, J = 8.8 Hz). 13C NMR (C6D6), δ: 0.5 and
0.6 (2 SiMe3); 5.8 (CH2); 6.2 (CH2); 9.2 (CH); 48.7 (CH—Ar);
54.8 (OMe); 98.0 (CH=C); 108.2 (CH—N); 114.3 and 129.3
(2 CHAr); 136.7 and 159.0 (2 CAr); 159.4 (C=CH). 29Si NMR
(C6D6), δ: 23.01 and 24.43 (2 SiMe3).
3
3J = 4.0 Hz); 5.56 (d, 1 H, CH=C, J = 3.4 Hz); 7.29 (m, 3 H,
3
CHPh); 7.34 (d, 2 H, CHAr, J = 7.4 Hz); 7.38 (d, 2 H, CHAr
,
2ꢀ(4ꢀMethoxyphenyl)propenal Oꢀtrimethylsilyloxime (9f),
3J = 7.4 Hz); 7.68 (d, 2 H, CHPh 3J = 8.0 Hz). 13C NMR
,
1
thick yellowish oil. H NMR (CDCl3), δ: 0.23 (s, 9 H, SiMe3);
(CDCl3), δ: 0.3 and 0.4 (2 SiMe3); 48.1 (CH—Ar); 99.3
(CH=C); 106.9 (CH—N); 125.3, 128.3, 128.4, 128.5, and 129.5
(all CHPh and all CHAr); 130.1 and 142.1 (CAr and CPh); 155.6
(C=CH). 29Si NMR (CDCl3), δ: 24.71 and 26.42 (2 SiMe3).
3.83 (s, 3 H, OMe); 5.46 (s, 1 H, CH2); 5.61 (s, 1 H, CH2); 6.89
3
3
(d, 2 H, CHAr, J = 8.1 Hz); 7.44 (d, 2 H, CHAr, J = 8.1 Hz);
8.09 (s, 1 H, CH=N). 13C NMR (CDCl3), δ: 0.6 (SiMe3); 55.4

656
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Birin et al.
A
mixture of 2ꢀ[N,Nꢀbis(trimethylsilyloxy)amino]ꢀ3ꢀ
mixture was poured into a mixture of H2O (10 mL) and light
petroleum (5 mL). The organic layer was separated, washed
with a solution of NaHSO4•H2O (70 mg, 0.5 mmol) in H2O
(10 mL), H2O (2×10 mL) and a saturated NaCl solution (10 mL),
dried with Na2SO4, and concentrated in vacuo. The yield and
purity of the product were determined from the 1H NMR specꢀ
(4ꢀnitrophenyl)ꢀ5ꢀphenylꢀ2,3ꢀdihydrofuryan (6n) and 2ꢀ(4ꢀnitroꢀ
phenyl)ꢀ4ꢀoxoꢀ4ꢀphenylbutꢀ2ꢀenal Oꢀtrimethylsilyloxime (7n),
viscous yellow oil.
1
Compound 6n. H NMR (CDCl3), δ: 0.16 and 0.18 (both s,
3
3
9 H each, 2 SiMe3); 4.96 (dd, 1 H, CH—Ar, J = 3.9 Hz, J =
3.3 Hz); 5.00 (d, 1 H, CH—N, 3J = 3.9 Hz); 5.55 (d, 1 H,
CH=C, 3J = 3.3 Hz); 7.30—7.42 (m, 3 H, CHPh); 7.51 (d, 2 H,
trum using a quantitative standard (ClCH2CH2Cl, δ 3.73).
H
A 2 : 1 mixture of compounds 13p and 2p (450 mg) was obtained
3
CHAr, J = 8.5 Hz); 7.60—7.68 (m, 2 H, CHPh); 8.17 (d, 2 H,
as a colorless thick oil.
CHAr, 3J = 8.5 Hz). 13C NMR (CDCl3), δ: 0.2 and 0.4 (2 SiMe3);
48.4 (CH—Ar); 98.4 (CH=C); 106.4 (CH—N); 123.8, 125.4,
128.5, 128.6, and 129.0 (all CHPh and CHAr); 130.3, 146.9, and
151.3 (all CAr and CPh); 156.4 (C=CH). 29Si NMR (CDCl3), δ:
25.17 and 27.00 (2 SiMe3).
Compound 13p. 1H NMR (CDCl3), δ: 0.20 and 0.26 (both s,
9 H each, 2 SiMe3); 4.87 (s, 1 H, CH2); 5.13 (d, 1 H, CH—Ph,
3
3J = 9.7 Hz); 5.39 (s, 1 H, CH2); 5.54 (d, 1 H, CH=C, J =
9.7 Hz); 7.19—7.62 (m, 10 H, CHPh). 13C NMR (CDCl3), δ:
0.2 and 0.8 (2 SiMe3); 42.8 (CH—Ph); 102.7 (CH2); 107.2
(CH=CO); 125.9, 126.0, 127.7, 127.9, 128.0, and 128.3 (all
CHPh); 139.4 and 144.1 (2 CPh); 148.9 (CH=CO); 162.2
(CH2=CN). 29Si NMR (CDCl3), δ: 19.98 and 24.02 (2 SiMe3).
1
Compound 7n. H NMR (CDCl3), δ: 7.15 (s, 1 H, CH=C);
7.56—7.68 (m, 3 H, CHPh); 7.98 (d, 2 H, CHAr, J = 8.5 Hz);
3
8.10 (m, 2 H, CHPh); 8.26 (d, 2 H, CHAr, 3J = 8.5 Hz); 9.01 (s,
1 H, CH=N). 13C NMR (CDCl3), δ: 0.1 (SiMe3); 123.1, 128.3,
128.6, 128.8, and 129.0 (all CHAr and CHPh); 130.2 (CH=C);
137.9, 144.8, and 148.0 (all CAr and CPh); 146.2 (CH=C);
152.4 (CH=N); 190.1 (C=O). 29Si NMR (CDCl3), δ: 28.55
(SiMe3).
1
Compound 2p. H NMR (CDCl3), δ: 0.21 (s, 9 H, SiMe3);
1.69 (d, 3 H, Me, 3J = 6.6 Hz); 4.57 (m, 1 H, CH—Ph);
3
4.90 (m, 1 H, CHNO2); 5.37 (d, 1 H, CH=C, J = 9.0 Hz);
7.19—7.62 (m, 10 H, CHPh). 13C NMR (CDCl3), δ: 0.7 (SiMe3);
17.3 (Me); 47.0 (CH—Ph); 88.4 (CHNO2); 113.3 (CH=CO);
126.2, 127.3, 127.7, 128.1, 128.4, and 128.8 (all CHPh); 138.5
and 139.9 (2 CPh); 152.8 (CH=CO). 29Si NMR (CDCl3), δ:
20.79 (SiMe3).
Methyl 4ꢀoxoꢀ4ꢀphenylꢀ2ꢀ(trimethylsilyloxyiminomethyl)ꢀ
butꢀ2ꢀenoate (7o), viscous yellow oil. Zꢀantiꢀ7o : Eꢀantiꢀ7o = 1 : 1.
Zꢀantiꢀ7o. 1H NMR (CDCl3), δ: 0.20 (s, 9 H, SiMe3); 3.80
(s, 3 H, OMe); 7.16 (s, 1 H, CH=C); 7.40 (m, 3 H, CHPh); 7.88
(m, 2 H, CHPh); 7.99 (s, 1 H, CH=N). Irradiation of the CH=C
signal at δ7.16 led to an increase in the intensity of the CH=N
signals at δ 7.99. 13C NMR (CDCl3), δ: –1.0 (SiMe3); 52.5
(OMe); 127.5 (CH=C); 128.4, 128.7, and 133.5 (all CHPh);
135.6 and 141.0 (CH=C and CPh); 151.3 (CH=N); 165.2
(COOMe); 192.6 (COPh). 29Si NMR (CDCl3), δ: 28.33 (SiMe3).
Silylation of aliphatic nitro compounds 1d and 1r without
aqueous workup of the reaction mixture (general procedure).
Bromotrimethylsilane (0.4 mL, 3.0 mmol) was added to a soluꢀ
tion of ANC 1 (1 mmol) in CH2Cl2 (3 mL) and Et3N (0.5 mL,
3.5 mmol) at –40 °C for 2 min. The reaction mixture was kept at
–30 °C for one week, diluted with anhydrous toluene (15 mL),
and filtered under argon. The filtrate was concentrated in vacuo.
The resulting product was analyzed by NMR spectroscopy using
15N NMR (CDCl3), δ: 16.1 (d, CH=N, J = 2.5 Hz).
2
Eꢀantiꢀ7o. 1H NMR (CDCl3), δ: –0.09 (s, 9 H, SiMe3);
3.80 (s, 3 H, OMe); 7.40 (m, 3 H, CH=C + CHPh); 7.52 (m,
1 H, CHPh); 7.88 (m, 2 H, CHPh); 8.19 (s, 1 H, CH=N).
13C NMR (CDCl3), δ: –1.3 (SiMe3); 52.2 (OMe); 128.6, 128.7,
and 133.6 (all CHPh); 131.1 and 136.6 (CH=C and CPh); 136.8
(CH=C); 147.6 (CH=N); 166.1 (COOMe); 188.4 (COPh).
29Si NMR (CDCl3), δ: 29.64 (SiMe3). 15N NMR (CDCl3), δ:
a quantitative standard (ClCH2CH2Cl, δ 3.73).
H
A
mixture of 2ꢀ[N,Nꢀbis(trimethylsilyloxy)amino]ꢀ3ꢀ
(4ꢀmethoxyphenyl)ꢀ5ꢀ(4ꢀnitrophenyl)ꢀ2,3ꢀdihydrofuran (6d) and
trimethylsilyl 2ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀ(4ꢀnitrophenyl)ꢀ4ꢀtriꢀ
methylsilyloxybutꢀ3ꢀeneꢀ1ꢀaciꢀnitronate (4d), viscous yellowish
oil, 6d : 4d = 1 : 2.6.
1
Compound 4d. H NMR (CDCl3), δ: 0.26 and 0.41 (both s,
2
9.1 (d, CH=N, J = 3.0 Hz).
9 H each, 2 SiMe3); 3.77 (s, 3 H, OMe); 5.18 (dd, 1 H, CH—Ar,
3
3
Trimethyl(4ꢀnitroꢀ1,3,4ꢀtriphenylbutꢀ1ꢀenyloxy)silane (2q),
white crystals, m.p. 103—105 °C (C5H14). Found (%): C, 76.32;
H, 5.38; N, 4.24. C22H19NO3. Calculated (%): C, 76.50; H, 5.54;
N, 4.06. 1H NMR (CDCl3), δ: 0.05 (s, 9 H, SiMe3); 4.93—5.06
(m, 2 H, 2 CH—Ph); 5.76 (m, 1 H, CH=C); 7.13—7.47 (m,
13 H, CHPh); 7.65 (m, 2 H, CHPh). 13C NMR (CDCl3), δ: 0.9
(SiMe3); 46.3 (CH—Ph); 96.9 (CH=C); 107.7 (CH—NO2);
126.4, 127.5, 128.0, 128.1, 128.3, 128.6, 128.7, 129.0, and 129.9
(all CHPh); 133.5, 138.8, and 140.4 (all CPh); 152.2 (C=CH).
29Si NMR (CDCl3), δ: 20.48 (SiMe3). 14N NMR (CDCl3), δ:
3J = 7.7 Hz, J = 9.6 Hz); 5.65 (d, 1 H, CH=C, J = 9.6 Hz);
3
3
6.45 (d, 1 H, CH=N, J = 7.7 Hz); 6.92 (d, 2 H, CHAr, J =
3
8.7 Hz); 7.18 (d, 2 H, CHAr, J = 8.7 Hz); 7.67 (d, 2 H, CHAr
,
3J = 8.9 Hz); 8.18 (d, 2 H, CHAr, 3J = 8.9 Hz). 13C NMR
(CDCl3), δ: –0.3 and 0.2 (2 SiMe3); 45.8 (CH—Ar); 54.8 (OMe);
112.4 (OC=CH); 117.2 (CH=N); 113.9, 123.2, 126.2, and
128.7 (all CHAr); 131.9, 144.6, 147.1, and 158.5 (CAr); 149.1
(OC=CH). 29Si NMR (CDCl3), δ: 22.49 and 26.28 (2 SiMe3).
A mixture of trimethylsilyl 1ꢀmethoxycarbonylꢀ2,4ꢀdiphenylꢀ
4ꢀoxobutaneꢀ1ꢀaciꢀnitronate (3r) and trimethylsilyl 1ꢀmethoxyꢀ
carbonylꢀ2,4ꢀdiphenylꢀ4ꢀtrimethylsilyloxybutꢀ3ꢀeneꢀ1ꢀaciꢀnitroꢀ
nate (4r). Colorless oil, 3r : 4r = 1 : 2.7.
7.5 (NO2, ∆ν ≈ 700 Hz).
1/2
A mixture of N,Nꢀbis(trimethylsilyloxy)ꢀ1ꢀmethylideneꢀ2,4ꢀ
diphenylꢀ4ꢀ(trimethylsilyloxy)butꢀ3ꢀenylamine (13p) and triꢀ
methyl(4ꢀnitroꢀ1,3ꢀdiphenylpentꢀ1ꢀenyloxy)silane (2p). Triꢀ
methylsilyl triflate (0.6 mL, 3.5 mmol) was added to a solution
of γꢀnitro ketone 1p (285 mg, 1 mmol) in CH2Cl2 (3 mL) and
Et3N (0.6 mL, 4 mmol) at –40 °C for 2 min. The reaction
mixture was kept at –30 °C for one or two weeks and then
diluted with light petroleum (10 mL). Methanol (0.04 mL) was
added to the resulting emulsion at –30 °C and the resulting
1
Compound 4r. H NMR (CDCl3), δ: 0.14 and 0.32 (both s,
9 H each, 2 SiMe3); 3.85 (s, 3 H, OMe); 5.53 (d, 1 H, CH—Ph,
3J = 9.6 Hz); 5.69 (d, 1 H, CH=C, 3J = 9.6 Hz); 7.15—7.58 (m,
10 H, CHPh). 13C NMR (CDCl3), δ: –0.2 and 0.6 (2 SiMe3);
41.0 (CH—Ph); 52.5 (OMe); 107.0 (CH=CO); 122.2 (C=N);
126.2, 126.7, 127.6, 128.2, 128.3, and 128.4 (all CHPh); 138.7
and 140.3 (2 CPh); 152.2 (CH=CO); 162.5 (COOMe). 29Si NMR
(CDCl3), δ: 20.75 and 29.69 (2 SiMe3).

Silylation of γꢀnitro ketones
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
657
1
Compound 3r. H NMR (CDCl3), δ: 0.29 (s, 9 H, SiMe3);
(CDCl3), δ: 0.73—1.03 (m, 4 H, CH2); 1.92 (m, 1 H, CH); 3.82
(s, 3 H, OMe); 6.23 (s, 1 H, CH=CO); 6.90 (d, 2 H, CHAr, 3J =
8.5 Hz); 7.37 (d, 2 H, CHAr, 3J = 8.5 Hz); 7.46 (s, 1 H, C=CHO).
13C NMR (CDCl3), δ: 6.7 (CH2); 9.0 (CH); 55.4 (OMe); 102.9
(CH=CO); 114.3 and 126.9 (2 CHAr); 125.6 (C=CHO); 126.8
and 158.4 (2 CAr); 135.5 (C=CHO); 158.7 (CH=CO).
2
3
3.61 (dd, 1 H, CH2C=O, J = 16.5 Hz, J = 6.3 Hz); 3.81 (s,
3 H, OMe); 4.07 (dd, 1 H, CH2C=O, 2J = 16.5 Hz, 3J = 9.0 Hz);
4.87 (dd, 1 H, CH—Ph, J = 6.3 Hz, J = 9.0 Hz); 7.15—7.58
(m, 8 H, CHPh); 8.08 (d, 2 H, CHPh, J = 8.0 Hz). 13C NMR
3
3
3
(CDCl3), δ: –0.3 (SiMe3); 40.1 (CH2C=O); 40.3 (CH—Ph);
52.6 (OMe); 122.6 (C=N); 127.2, 128.0, 128.1, 128.5, 128.7,
and 133.3 (all CHPh); 136.6 and 139.0 (2 CPh); 162.7 (COOMe);
197.4 (CH2C=O). 29Si NMR (CDCl3), δ: 30.43 (SiMe3).
Desilylation of compounds 6, 7, and 9 with NH4F in MeOH
(general procedure). Crystalline NH4F (5 mg, 0.1 mmol) was
added to a solution of compound 6, 7, or 9 (1 mmol) in MeOH
(4.4 mL) at 0 °C. The reaction mixture was kept under the
conditions given in Table 2 and concentrated in vacuo. The
products were purified by recrystallization from MeOH or chroꢀ
matography on silica gel (yields are given in Table 2).
2ꢀ(4ꢀMethoxyphenyl)propenal oxime (10f), white crystals,
m.p. 65—67 °C (CH2Cl2—pentane). Found (%): C, 67.99;
H, 6.00; N, 7.67. C10H11NO2. Calculated (%): C, 67.78; H, 6.26;
N, 7.90. 1H NMR (CDCl3), δ: 3.81 (s, 3 H, OMe); 5.48 (s, 1 H,
CH2); 5.58 (s, 1 H, CH2); 6.89 (d, 2 H, CHAr, 3J = 8.5 Hz); 7.36
(d, 2 H, CHAr, 3J = 8.5 Hz); 7.55 (s, 1 H, CH=N); 8.01 (s, 1 H,
NOH). 13C NMR (CDCl3), δ: 55.4 (OMe); 113.7 and 129.6
(2 CHAr); 122.2 (CH2); 129.6 and 159.7 (2 CAr); 142.4 (C=CH2);
152.5 (CH=N).
2ꢀPhenylpropenal oxime (10h), white crystals, m.p.
105—107 °C (CH2Cl2—pentane) (cf. lit. data29: m.p. 103 °C
(MeOH)). H NMR (CDCl3), δ: 5.42 (s, 1 H, CH2); 5.50 (s,
1 H, CH2); 7.26 (br.s, 5 H, CHPh); 7.86 (s, 1 H, CH=N); 8.69 (s,
1 H, NOH). 13C NMR (CDCl3), δ: 123.0 (CH2); 128.2 (2 CHPh);
128.3 (CHPh); 137.4 (CPh); 143.1 (CH2=C); 151.5 (C=N).
4ꢀ(4ꢀMethoxyphenyl)ꢀ2ꢀphenylfuran (15a), white crystals,
m.p. 136—138 °C (MeOH) (cf. lit. data30: m.p. 132—134 °C
3ꢀAcetylꢀ2ꢀmethylꢀ4ꢀphenylfuran (15j), viscous colorless oil
1
(cf. Ref. 32). H NMR (CDCl3), δ: 2.05 (s, 3 H, Me); 2.57 (s,
3 H, MeCO); 7.29—7.39 (m, 5 H, CHPh); 7.37 (s, 1 H,
C=CHO). 13C NMR (CDCl3), δ: 14.5 (Me); 31.0 (MeCO);
122.3 (C=CO); 126.8 (C=CHO); 127.8, 128.5, and 129.3
(all CHPh); 132.5 (CPh); 138.1 (C=CHO); 158.7 (C=CO);
196.1 (C=O).
2,4ꢀDiphenylfuran (15l), white crystals, m.p. 110—111 °C
1
(MeOH) (cf. lit. data31: m.p. 109 °C). H NMR (CDCl3), δ:
6.92 (s, 1 H, CH=CO); 7.21—7.29 (m, 2 H, CHPh); 7.32—7.41
(m, 4 H, CHPh); 7.47—7.53 (m, 2 H, CHPh); 7.66—7.72 (m,
2 H, CHPh); 7.70 (s, 1 H, C=CHO). 13C NMR (CDCl3), δ:
104.1 (CH=CO); 124.0, 126.0, 127.3, 127.7, 128.8, and 129.0
(all CHPh); 128.5 (C=CHO); 130.8 and 132.5 (2 CPh); 138.0
(C=CHO); 155.0 (CH=CO).
4ꢀ(4ꢀChlorophenyl)ꢀ2ꢀphenylfuran (15m), white crystals, m.p.
133—134 °C (MeOH) (cf. lit. data30: m.p. 130 °C (MeOH)).
1H NMR (CDCl3), δ: 6.89 (s, 1 H, CH=CO); 7.22—7.47 (m,
7 H, CHPh and CHAr); 7.69 (m, 2 H, CHPh); 7.70 (s, 1 H,
C=CHO). 13C NMR (CDCl3), δ: 103.6 (CH=CO); 123.8, 126.9,
127.7, 128.7, and 128.9 (all CHAr and CHPh); 128.2 (C=CHO);
130.8, 131.0, and 133.1 (2 CAr and CPh); 137.9 (C=CHO); 153.2
(CH=CO).
1
4ꢀ(4ꢀNitrophenyl)ꢀ2ꢀphenylfuran (15n), yellow crystals, m.p.
166—167 °C (MeOH) (cf. lit. data30: m.p. 152 °C (MeOH)).
1H NMR ((CD3)2SO), δ: 7.34 (m, 1 H, CHPh); 7.47 (m, 2 H,
CHPh); 7.60 (s, 1 H, CH=CO); 7.76 (d, 2H, CHPh, 3J = 7.7 Hz);
1
3
3
(MeOH)). H NMR (CDCl3), δ: 3.85 (s, 3 H, OMe); 6.94 (s,
7.94 (d, 2 H, CHAr, J = 8.8 Hz); 8.26 (d, 2 H, CHAr, J =
8.8 Hz); 8.52 (s, 1 H, C=CHO). 13C NMR ((CD3)2SO), δ:
104.1 (CH=CO); 123.5, 124.0, 126.1, 127.9, and 128.8 (all CHAr
and CHPh); 126.1 (C=CHO); 141.4 (C=CHO); 129.6, 138.6,
and 146.0 (CPh and 2 CAr); 154.6 (CH=CO).
1 H, CH=CO); 6.96 (d, 2 H, CHAr, 3J = 8.8 Hz); 7.30 (m, 1 H,
3
CHPh); 7.37—7.53 (m, 4 H, CHPh); 7.71 (d, 2 H, CHAr, J =
8.8 Hz); 7.75 (s, 1 H, C=CHO). 13C NMR (CDCl3), δ: 55.4
(OMe); 104.2 (CH=CO); 114.4, 123.9, 127.1, 127.6, and 128.8
(all CHAr and CHPh); 125.1 (CAr); 128.1 (C=CHO); 130.8 (CPh);
137.2 (C=CHO); 154.8 (CH=CO); 158.9 (CAr).
Zꢀantiꢀ2ꢀ(4ꢀNitrophenyl)ꢀ4ꢀoxoꢀ4ꢀphenylbutꢀ2ꢀenal oxime
1
(8n), yellowish crystals, m.p. 149—151 °C (MeOH). H NMR
4ꢀ(4ꢀMethoxyphenyl)ꢀ2ꢀ(4ꢀtolyl)furan (15b), white crystals,
m.p. 135—137 °C (MeOH) (cf. lit. data30: m.p. 107 °C (MeOH)).
1H NMR (CDCl3), δ: 2.17 (s, 3 H, Me); 3.46 (s, 3 H, OMe); 6.78
(s, 1 H, CH=CO); 6.87 (d, 2 H, CHAr, 3J = 8.1 Hz); 7.07 (d, 2 H,
((CD3)2SO), δ: 7.40 (s, 1 H, CH=C); 7.56 (m, 2 H, CHPh); 7.68
(m, 1 H, CHPh); 7.81 (d, 2 H, CHAr, 3J = 8.5 Hz); 8.07 (d, 2 H,
3
3
CHPh, J = 7.7 Hz); 8.27 (d, 2 H, CHAr, J = 8.5 Hz); 8.83 (s,
1 H, CH=N); 11.99 (s, 1 H, OH). Irradiation of Ho of the
4ꢀNO2C6H4 group (δ 7.81) led to an increase in the intensities of
the signals at δ 7.40 (CH=C) and 8.27 (Hm of the 4ꢀNO2C6H4
group). Irradiation of the proton of the OH group (δ 11.99) led
to an increase in the intensity of the signal of CH=N at δ 8.83.
13C NMR ((CD3)2SO), δ: 122.9, 128.6, 128.8, 130.7 and 133.6
(CHAr and CHPh); 127.8 (CH=C); 137.6, 144.9, and 147.4 (2 CAr
and CPh); 146.1 (CH=C); 147.6 (CH=N); 190.2 (C=O).
3
3
CHAr, J = 8.1 Hz); 7.34 (d, 2 H, CHAr, J = 8.1 Hz); 7.48 (s,
3
1 H, C=CHO); 7.67 (d, 2 H, CHAr, J = 8.1 Hz). 13C NMR
(CDCl3), δ: 21.2 (Me); 55.1 (OMe); 104.1 (CH=CO); 114.8,
124.5, 127.5, and 129.7 (all CHAr); 125.8, 129.0, 137.5, and 159.7
(all CAr); 128.8 (C=CHO); 137.3 (C=CHO); 155.7 (CH=CO).
2,4ꢀBis(4ꢀmethoxyphenyl)furan (15c), white crystals, m.p.
188—189 °C (MeOH) (cf. lit. data31: m.p. 188—190 °C).
1H NMR (CDCl3), δ: 3.57 and 3.59 (both s, 3 H each, 2 OMe);
Methyl Eꢀantiꢀ2ꢀ(hydroxyiminomethyl)ꢀ4ꢀoxoꢀ4ꢀphenylbutꢀ
2ꢀenoate (8o), yellow crystals, m.p. 124—126 °C (MeOH).
Found (%): C, 61.60; H, 4.51; N, 5.83. C12H11NO4. Calcuꢀ
lated (%): C, 61.80; H, 4.75; N, 6.01. 1H NMR ((CD3)2CO), δ:
3.86 (s, 3 H, OMe); 7.16 (s, 1 H, CHBz); 7.50 (m, 2 H, CHPh);
7.61 (m, 1 H, CHPh); 7.94 (m, 2 H, CHPh); 7.96 (s, 1 H,
CH=N); 8.86 (br.s, 1 H, OH). Irradiation of the proton of the
CH=N group (δ 7.96) led to an increase in the intensity of the
signal of CHBz at δ 7.16. 13C NMR ((CD3)2CO), δ: 51.8 (OMe);
127.0 (CH=C); 128.7, 129.2, and 133.9 (all CHPh); 137.5 and
3
3
6.90 (d, 2 H, CHAr, J = 8.8 Hz); 6.93 (d, 2 H, CHAr, J =
8.8 Hz); 7.21 (s, 1 H, CH=CO); 7.47 (d, 2 H, CHAr, 3J =
8.8 Hz); 7.66 (d, 2 H, CHAr, 3J = 8.8 Hz); 7.75 (s, 1 H, C=CHO).
13C NMR (CDCl3), δ: 55.4 (2 OMe); 103.3 (CH=CO); 114.8,
114.9, 127.4, and 125.7 (all CHAr); 124.3, 125.5, 159.4, and
159.8 (all CAr); 128.5 (C=CHO); 155.1 (CH=CO).
2ꢀCyclopropylꢀ4ꢀ(4ꢀmethoxyphenyl)furan (15e), white
crystals, m.p. 119—122 °C (MeOH). Found (%): C, 78.06;
H, 6.70. C14H14O2. Calculated (%): C, 78.48; H, 6.59. 1H NMR

658
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Birin et al.
142.7 (CH=C and CPh); 148.2 (CH=N); 166.2 (COOMe);
188.4 (COPh).
8. A. A. Tishkov, I. M. Lyapkalo, S. L. Ioffe, Yu. A. Strelenko,
and V. A. Tartakovsky, Izv. Akad. Nauk, Ser. Khim., 1997,
210 [Russ. Chem. Bull., 1997, 46, 205 (Engl. Transl.)].
9. J. P. Guthrie, J. Cossar, and A. Klym, Can. J. Chem., 1987,
65, 2154.
10. R. G. Pearson and R. L. Dillon, J. Am. Chem. Soc., 1953,
75, 2439.
11. V. O. Smirnov, A. A. Tishkov, I. M. Lyapkalo, S. L. Ioffe,
V. V. Kachala, Yu. A. Strelenko, and V. A. Tartakovsky, Izv.
Akad. Nauk, Ser. Khim., 2001, 2324 [Russ. Chem. Bull., Int.
Ed., 2001, 50, 2433].
12. A. D. Dilman, A. A. Tishkov, I. M. Lyapkalo, V. V. Kachala,
S. L. Ioffe, Yu. A. Strelenko, and V. A. Tartakovsky, Syntheꢀ
sis, 1998, 181.
13. R. G. Kostyanovsky, G. K. Kadorkina, V. N. Voznesensky,
I. I. Chervin, M. Yu. Antipin, K. A. Lyssenko, E. V.
Vorontsov, V. I. Bakhmutov, and P. Rademacher, Mendeleev
Commun., 1996, 69.
14. A. A. Tishkov, A. D. Dilman, V. I. Faustov, A. A. Birukov,
K. S. Lysenko, P. A. Belyakov, S. L. Ioffe, Yu. A. Strelenko,
and M. Yu. Antipin, J. Am. Chem. Soc., 2002, 124, 11358.
15. V. F. Rudchenko, Chem. Rev., 1993, 93, 725.
16. C. L. Ioffe, M. V. Kashutina, V. M. Shitkin, A. Z.
Yankelevich, A. A. Levin, and V. A. Tartakovsky, Izv. Akad.
Nauk SSSR, Ser. Khim., 1972, 1341 [Bull. Acad. Sci. USSR,
Div. Chem. Sci., 1972, 21, 1292 (Engl. Transl.)].
17. A. D. Dilman, I. M. Lyapkalo, P. A. Belyakov, S. L. Ioffe,
Yu. A. Strelenko, and V. A. Tartakovsky, Izv. Akad. Nauk,
Ser. Khim., 2000, 1659 [Russ. Chem. Bull., Int. Ed., 2000,
49, 1649].
Zꢀ2ꢀ(4ꢀMethoxyphenyl)ꢀ4ꢀoxoꢀ4ꢀ(4ꢀtolyl)butꢀ2ꢀenonitrile
(17b). Tetrabutylammonium fluoride (0.3 mL, 0.2 mmol; a
0.73 M solution in THF) was added to a solution of dihydrofuran
6b (460 mg, 1 mmol) in CH2Cl2 (6 mL) at 0 °C. The reaction
mixture was kept at 20 °C for 24 h and then concentrated in
vacuo. The residue was recrystallized from a benzene—pentane
mixture (3 : 1). The product was obtained as yellow crystals in a
yield of 150 mg (54%), m.p. 154—156 °C (PhH—C5H12).
Found (%): C, 77.67; H, 5.25; N, 4.89. C18H15NO2. Calcuꢀ
lated (%): C, 77.96; H, 5.45; N, 5.05. MS (EI), m/z (Irel (%)):
277 [M]+ (95); 246 [M – OMe]+ (100). IR (KBr), ν/cm–1: 1655
1
(C=O); 2222 (CN). H NMR (CDCl3), δ: 2.44 (s, 3 H, Me);
3
3.88 (s, 3 H, OMe); 7.00 (d, 2 H, CHAr, J = 8.5 Hz); 7.32 (d,
2 H, CHAr, 3J = 7.9 Hz); 7.78 (d, 2 H, CHAr, 3J = 8.5 Hz); 7.80
3
(s, 1 H, CH=C); 7.94 (d, 2 H, CHAr, J = 7.9 Hz). 13C NMR
(CDCl3), δ: 21.8 (Me); 55.6 (OMe); 114.8, 128.7, 129.0, and
129.7 (all CHAr); 116.5 (CN); 124.1 (CH=C); 130.2 (CH=C);
125.0, 134.5, 145.0, and 162.4 (all CAr); 186.3 (C=O).
Eꢀ2ꢀ(4ꢀMethoxyphenyl)ꢀ4ꢀoxoꢀ4ꢀ(4ꢀtolyl)butꢀ2ꢀenonitrile
(Eꢀ17b). A solution of enenitrile (20 mg, 0.07 mmol) Zꢀ17b in
benzene (5 mL) was kept in a glass vessel in sunlight for one
week. Then the solvent was evaporated in vacuo and the residue
1
was analyzed by H NMR spectroscopy.
1
Compound Eꢀ17b. H NMR (CDCl3), δ: 2.41 (s, 3 H, Me);
3.78 (s, 3 H, OMe); 6.80 (d, 2 H, CHAr, 3J = 8.8 Hz); 7.25 (d, 2
3
H, CHAr, J = 8.8 Hz); 7.37 (s, 1 H, CH=C); 7.41 (d, 2 H,
CHAr, 3J = 8.1 Hz); 7.81 (d, 2 H, CHAr, 3J = 8.1 Hz).
The degree of conversion of Zꢀ17b into Eꢀ17b was 86%.
18. K. Nozaki, N. Sato, and H. Takaya, Bull. Chem. Soc. Jpn.,
1996, 1629.
19. (a) M. Largeron and M.ꢀB. Fleury, Tetrahedron Lett., 1991,
631; (b) H. Yamada, H. Yoshimura, and K. Tatsumi, Chem.
Pharm. Bull., 1982, 2647.
20. D. E. Warrall and C. J. Bradway, J. Am. Chem. Soc., 1936,
58, 1607.
21. A. A. Tishkov, V. O. Smirnov, M. V. Nefed´eva, I. M.
Lyapkalo, S. E. Semenov, S. L. Ioffe, Yu. A. Strelenko, and
V. A. Tartakovsky, Zh. Org. Khim., 2001, 37, 416 [Russ.
J. Org. Chem., 2001, 37, 390 (Engl. Transl.)].
The study was carried out at the Scientific and Educaꢀ
tional Center of the N. D. Zelinsky Institute of Organic
Chemistry of the Russian Academy of Sciences and the
Moscow Chemical Lyceum and was financially supported
by the Russian Foundation for Basic Research (Project
Nos. 03ꢀ98ꢀ33002 and 00ꢀ15ꢀ97455) and the Federal Tarꢀ
get Program "Integration" (Project Nos. A0082 and
B0062).
References
22. W. Davey and D. J. Tivey, J. Chem. Soc., 1958, 2276.
23. M. E. Kuehne and L. Foley, J. Org. Chem., 1965, 4280.
24. J. H. Nelson, P. N. Howells, G. C. DeLullo, G. L. Landen,
and R. A. Henry, J. Org. Chem., 1980, 1246.
25. E. P. Kohler and L. I. Smith, J. Am. Chem. Soc., 1922, 44, 624.
26. K. Watanabe, K. Miyazu, and K. Irie, Bull. Chem. Soc.,
1982, 55, 3212.
27. E. P. Kohler, J. Am. Chem. Soc., 1916, 38, 897.
28. E. P. Kohler, J. Am. Chem. Soc., 1924, 46, 1738.
29. P. Bravo, G. Gaudiano, C. Ticozzi, and A. UmaniꢀRonchi,
Gazz. Chim. Ital., 1969, 99, 549.
30. P. Molina, A. Lorenzo, and P. M. Fresenda, Synthesis,
1983, 49.
1. A. A. Tishkov, A. V. Kozintsev, I. M. Lyapkalo, S. L. Ioffe,
Yu. A. Strelenko, and V. A. Tartakovsky, Tetrahedron Lett.,
1999, 40, 5075.
2. V. A. Tartakovsky, S. L. Ioffe, A. D. Dilman, and A. A.
Tishkov, Izv. Akad. Nauk, Ser. Khim., 2001, 1850 [Russ.
Chem. Bull., Int. Ed., 2001, 50, 1936].
3. A. A. Tishkov, I. M. Lyapkalo, S. L. Ioffe, Yu. A. Strelenko,
and V. A. Tartakovsky, Eur. J. Org. Chem., 2000, 3229.
4. V. M. Danilenko, A. A. Tishkov, S. L. Ioffe, I. M. Lyapkalo,
Yu. A. Strelenko, and V. A. Tartakovsky, Synthesis, 2002, 635.
5. A. D. Dilman, A. A. Tishkov, I. M. Lyapkalo, V. V. Kachala,
S. L. Ioffe, Yu. A. Strelenko, and V. A. Tartakovsky, J. Chem.
Soc., Perkin Trans. 1, 2000, 2926.
31. I. Francesconi, A. Patel, and D. W. Boykin, Synthesis,
1999, 61.
6. A. A. Tishkov, I. M. Lyapkalo, S. L. Ioffe, Yu. A. Strelenko,
and V. A. Tartakovsky, Tetrahedron, 2001, 57, 2221.
7. (a) R. Noyori, S. Murata, and M. Suzuki, Tetrahedron, 1981,
37, 3899; (b) B. Mathieu and L. Ghosez, Tetrahedron Lett.,
1997, 38, 5497.
32. T. Kataoka, S. Watanabe, K. Yamamoto, M. Yoshimatsu,
G. Tanabe, and O. Muraoka, J. Org. Chem., 1998, 63, 6382.
Received August 1, 2002;
in revised form November 14, 2002