Novel convenient method for the synthesis of N,N- bis(trimethylsilyloxy)enamines

Article abstract of DOI:10.1055/s-1998-2019

Both primary and secondary aliphatic nitro compounds 1 were found to react with two equivalents of bromotrimethylsilane in the presence of triethylamine followed by aqueous workup to give appropriate N,N- bis(trimethylsilyloxy)enamines 3 in good isolated yields. Products 3, starting from some secondary and/or sterically hindered compounds 1, are synthesized from the corresponding silyl nitronates 2.

Full text of DOI:10.1055/s-1998-2019

181
February 1998
SYNTHESIS
Novel Convenient Method for the Synthesis of N,N-Bis(trimethylsilyloxy)enamines
A. D. Dilman, A. A. Tishkov, I. M. Lyapkalo,* S. L. Ioffe,* Yu. A. Strelenko, V. A. Tartakovsky
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., 117913 Moscow, Russian Federation.
Fax: +7 (095) 1355328; E-mail: lyapkalo@cacr.ioc.ac.ru
Dedicated to Professor Dieter Seebach on occasion ofhis 60 th birthday.
Received 23 July 1997
Abstract: Both primary and secondary aliphatic nitro compounds 1
is necessary for further development in this field. We re-
port here a general method for the synthesis of BSENA 3
from the corresponding nitro compounds 1 using
Me3SiBr/Et3N in 1,2-dichloroethane (Scheme 1).
were found to react with two equivalents of bromotrimethylsilane in the
presence of triethylamine followed by aqueous workup to give appro-
priate N,N-bis(trimethylsilyloxy)enamines 3 in good isolated yields.
Products 3, starting from some secondary and/or sterically hindered
compounds 1, are synthesized from the corresponding silyl nitronates 2.
Key words: nitro compounds, bromotrimethylsilane, silylation, silyl
nitronates, N,N-bis(trimethylsilyloxy)enamines
Mono-silylation of aliphatic nitro compounds is well
known to afford trialkylsilyl nitronates1 which are used as
synthetic building blocks for new carbon–carbon bond
formation.1,2 However, double silylation of nitro com-
pounds has been scarcely investigated.
As late as 1986, Feger and Simchen obtained N,N-bis(tri-
alkylsilyloxy)enamines as a result of double silylation of
nitro compounds with powerful silylating reagents such as
trialkylsilyl triflates.3 It was found that unlike the typical
enamines, N,N-bis(trimethylsilyloxy)enamines (BSENA)
of general type 3 (Scheme 1) were not alkylated by alkyl
halides, but did interact smoothly with secondary aliphatic
amines in agreement with the pathway of SN2¢ substitu-
tion of OSiMe3 group to give a-aminooximes,3 i.e. they
behaved like b-C-electrophiles. Despite such unusual re-
activity, BSENA have not attracted the attention of other
investigators,4 presumably, because of their instability
andtendencytorearrangetobis(trimethylsilyl)a-hydroxy-
oxime derivatives3,5 under the action of CF3SO2OSiMe3
or Me2O·BF3.
Scheme 1
The reaction conditions are presented in Table 1. The syn-
thesis of target BSENA 3 is carried out, as a rule, without
isolation of the intermediate silyl nitronates 2. However,
when efforts were undertaken to silylate nitrocyclohexane
(1g) or sterically hindered 2-methyl-3-trimethylsilyloxy-
4-nitropentane (1f) with Me3SiBr/Et3N, the first step
(1 ® 2) did not occur at –30 or 20°C, respectively, while
raising the temperature resulted only in intractable mix-
tures of products.
Thus, a two-step procedure was elaborated for the synthe-
sis of BSENA 3f and 3g, which implies the preparation of
individual silyl nitronates 2f and 2g in the first step by
treatment of the starting nitro compounds 1f and 1g with
trimethylsilyl halides in the presence of DBU9 (Scheme
2). However, the second step requires the use of Me3SiBr/
Et3N in accordance with the general procedure (Table 1).
Recently we showed the possibility to generate some BSE-
NA as intermediates without the use of CF3SO2OSiMe3 as
silylating reagent.6,7 The resultant BSENA were used for
novel C–C6 and C–N8 bond formation, as well as in the syn-
thesis of functionalized a, b-unsaturated oximes.7
Although the chemistry of BSENA is promising, a simple The reaction conditions for the synthesis of 3 (tempera-
ture and time) depend on their stability, as well as on the
and reliable method of synthesis, enabling their isolation,
Table 1. Compounds 3a–g Prepared
Prod-
uct
R1
R2
Mol Ratio of
Reaction Conditions
1:Me3SiBr:Et3N
Yield
(%)
bp
(°C)/Torr
3a
3b
3c
3d
3e
3f
H
Me
(CH2)2CO2
H
H
H
Me
Me
CH2CO2Me
H
1:2.2:2.3
1:2.2:2.3
3 h at 0°C and 7 h at 20°C
3.5 h at 0°C and 40 h at 20°C
3.5 h at 0°C and 20 h at 20°C
48 h at –30°C
97 (87)d
92 (82)d
90b
39–40/0.4a
24–25/0.2
–
H 1:2.2:2.3
1:2.1:2.2
1:2.02:2.0
1:2.43:2.36c
1:1.11:1.26c
89 (80)d
71
29/0.25
H
39 h at 20°C
–
–
–
CH(OSiMe3)Pr-i
17 d at 20°Cc
62
60
-
3g
-(CH2)4
0.5 h at –35 °C and
20 h at –30°Cc
a Lit.3 bp 25 °C/0.05 Torr.
b Anal. calcd for C12H27NO2Si2: C, 47.18, H, 8.91; N, 4.58; Si, 18.39. Found: C, 47.35; H, 8.78; N, 4.41; Si, 18.66.
c For the step 2 ® 3, see Scheme 2.
d After distillation.

182
Papers
SYNTHESIS
Scheme 2
structure of starting 1. The synthesis of BSENA 3a–c, f bis(trimethylsilyloxy)enamines 3 were not so successful.
from la–c, f containing the fragment CH(NO2)Me could As a rule, silylation of intermediate silyl nitronates 2 to
be carried out at conventional temperature (Table 1). give the products 3 proceeds slowly.11 For example, when
Long exposure of silyl nitronate 2f to two-fold excess of silylating nitroethane (1a), or methyl 4-nitropentanoate
silylating reagent is necessary to obtain 3f successfully. It (1c), according to the NMR data, even reaction with four-
is noteworthy that second silylation occurs regioselective- fold excess of Me3SiCl/Et3N in acetonitrile during two
ly in the synthesis of 3a–c, f resulting exclusively in the weeks at 20°C does not afford acceptable conversion (90–
formation of terminal double bonds (see Schemes 1, 2, 95%) into 3a, c.
and Table 1). It should be emphasised that washing of the
Efforts were undertaken to accelerate the process of
resultant organic phase with dilute aqueous NaHSO4 to
formation of 3a, c by heating. However, it was found that
pH 2–3 is necessary for the successful isolation of stable
these compounds undergo further transformations, form-
BSENA 3a–c, f. On the contrary, spontaneous exothermic
ing finally the quaternary ammonium salts 6a, c (Scheme
decomposition of these products is possible during the
3).
concentration of the organic phase.
Unlike the compounds described above, the BSENA
3d, e, g are found to be unstable under the conditions of
silylation with Me3SiBr/Et3N at 0 to 20°C. For instance,
compounds 3d, g easily undergo 1,3-N ® C shift of the
OSiMe3 group, while the product 3e undergoes 1,4-elim-
ination of trimethylsilanol.7 So far, extremely mild condi-
tions (temperature about –30°C) are necessary to obtain
high yields of BSENA 3d, e, g (see Table 1). The com-
pounds 3d, e are formed exclusively as E-isomers.
The structures of 3a–g are established with the use of
NMR. In the cases of 3a, b, d, the NMR data are in good
agreement with those described earlier.3 The compounds
3c, e–g are obtained for the first time. Simplest BSENA
3a, b, d were purified by vacuum distillation. As a rule,
Scheme 3
the purity of undistilled products 3 is not less than 95%;
for 3c satisfactory microanalysis data are obtained. Indi-
vidual BSENA 3 can be stored at –30°C. Exception is
Products 6a, c are identified by desilylation and isolation
compound 3g that rearranges under these conditions to
of the stable crystalline N,N,N-triethyl-N-(2-hydroxyimi-
bis(trimethylsilyl) derivative of the a-hydroxycyclohex-
noalkyl)ammonium chlorides 7a,c whose structures
anone oxime 4g in 20 days. The structure of 4g was con-
were confirmed by microanalytical data. Besides, com-
firmed by NMR data and by desilylation resulting in the
pound 6c is characterized by NMR data.
known oxime 5g10 (Scheme 2).
We have shown earlier that BSENA 3b can be generated
as an intermediate from 1b by treatment with Me3SiCl/
Et3N.6 It seemed reasonable therefore to use the inexpen-
sive Me3SiCl in the presence of Et3N in acetonitrile for the
synthesis of BSENA 3 from nitro compounds 1. It ap-
peared possible, indeed, to obtain 3b as a result of silyla-
tion of 1b with two equivalents of Me3SiCl/Et3N in
NMR spectra were recorded on a Bruker AM-300 instrument. Chem-
ical shifts were measured relative to internal reference (d = 0) TMS
(1H, 13C and 29Si) and external reference (d = 0) MeNO2 (14N and
15N). The INEPT and SPT pulse sequences were used for 29Si and 15
N
signal observation.12 The assignment of 13C and 1H signals for 3g was
made by two-dimensional C–H and H–H correlations and by selec-
tive proton decoupling.
acetonitrile at 20°C followed by aqueous workup as de- Starting nitro compounds 1c,e13 and 2-methyl-4-nitropentan-3-ol14
were obtained according to known procedures. Freshly purified re-
scribed for 3a–c, f (see Experimental).
agents and solvents were used for the synthesis of BSENA 3 in a dry
argon atmosphere. Petroleum ether used refers to the fractions boil-
ing at 40–70°C.
Unfortunately, all attempts to extend the application of
Me3SiCl as silylating agent for the synthesis of other N,N-

February 1998
SYNTHESIS
DBU.HCl was filtered off in a dry atmosphere and washed with pe-
183
2-Methyl-3-trimethylsilyloxy-4-nitropentane (1f).
To a solution of 2-methyl-4-nitropentan-3-ol (2.18 g, 14.8 mmol) and troleum ether (2 ´ 10 mL). The combined filtrate was evaporated in
Et3N (1.96 g, 19.4 mmol) in ClCH2CH2Cl (15 mL) at –30°C was add- vacuo to afford 1.29 g (96%) of 2f as a yellowish oil.
ed the solution of Me3SiBr (2.9 g, 19.0 mmol) in ClCH2CH2Cl
Compound 2f:
(5 mL). The mixture was stirred for 20 h at 0 to 20°C, diluted with pe-
troleum ether (20 mL) and added to the two-phase mixture of petro-
1H NMR (CDCl3): d = 0.1 (s, 9 H, CHOSiMe3), 0.32 (s, 9 H,
3
3
NOSiMe3), 0.83 (d, 3 H, Me, J = 6.8 Hz), 0.95 (d, 3 H, Me, J =
6.6 Hz), 1.80 (m, 1 H, CHMe2), 1.88 (s, 3 H, MeC=N), 4.51 (d, 1 H,
CHOSiMe3, 3J = 8.1 Hz).
leum ether (50 mL) and ice-cold water (25 mL). The organic layer
was separated, washed with dil aq NaHSO4, H2O and dried (Na2SO4).
After evaporation of the volatile components in vacuo the residue was
distilled at 47–49°C/0.2 Torr to furnish 2.86 g (88%) of 1f (1:1 mix-
ture of two diastereomers); colourless liquid.
13C NMR (CDCl3): d = –0.5 (SiMe3), 0.3 (SiMe3), 11.9 (MeC=N),
17.8 (Me), 18.5 (Me), 32.7 (CHMe2), 74.3 (CHOSiMe3), 126.5
(C=N).
3
1H NMR (CDCl3): d = 0.08 and 0.09 (s, 9 H, SiMe3), 0.84 (d, J =
14N NMR (CDCI3): d = ca. –100 (Dv1/2 ca. 1000 Hz).
6.8 Hz), 0.92 (d, 3J = 6.8 Hz), 0.96 (d, 3J = 5.9 Hz) and 0.98 (d, 3J =
6.0 Hz) [6 H, Me2CH], 1.45 (d, 3J = 7.4 Hz) and 1.47 (d, 3J = 6.7 Hz)
[3 H, MeCHNO2], 1.65 and 1.78 (m, 1 H, CHMe2), 3.95 (dd, 3J = 9.0,
2.3 Hz) and 4.01 (dd, 3J = 7.4, 3.6 Hz) [1 H, CHOSiMe3], 4.56 (m, 1
H, CHNO2).
29Si NMR (CDCl3): d = 18.58 (CHOSiMe3), 23.94 (NOSiMe3).
To the crude silyl nitronate 2f were added successively at –5°C
ClCH2CH2Cl (3 mL), Et3N (1.05 g, 10.4 mmol), and a solution of
Me3SiBr (1.64 g, 10.7 mmol) in ClCH2CH2Cl (3 mL). The mixture
was kept with occasional stirring for 17 d at 20°C. The progress of the
reaction was monitored by 1H NMR. After consumption of silyl nitro-
nate 2f, the product 3f16 (1.04 g, 62% from 1f) was isolated as a yel-
lowish oil, according to the general procedure.
1H NMR (CDCl3): d = 0.09 (s, 9 H, CHOSiMe3), 0.21 (s, 18 H,
N(OSiMe3)2), 0.78 (d, 3 H, Me, 3J = 6.8 Hz), 0.96 (d, 3 H, Me, 3J =
6.9 Hz), 1.90 (m, 1 H, CHMe2), 4.19 (dd, 1 H, CHOSiMe3, 3J =
2.3 Hz, 4J = 1.0 Hz), 4.84 (d, 1 H, HA), 5.19 (s, 1 H, HB).
13C NMR (CDCl3): d = 0.1 (CHOSiMe3), 0.2 (N(OSiMe3)2), 14.2
(Me), 20.5 (Me), 31.8 (CHMe2), 74.0 (CHOSiMe3), 100.4 (CH2),
161.0 (C–N).
13C NMR (CDCl3): d = 0.1 and 0.2 (SiMe3), 11.8, 14.3, 16.2, 18.6,
19.0 and 20.5 (Me), 29.3 and 31.9 (CHMe2), 78.9 and 79.6
(CHOSiMe3), 84.8 and 87.7 (CHNO2).
14N NMR (CDCl3): d = 13.0 (Dn1/2 180 Hz).
29Si NMR (CDCl3): d = 18.70 and 18.80.
N,N-Bis(trimethylsilyloxy)enamines 3a–e; General Procedure:
To a solution of 1 (24 mmol) and Et3N in ClCH2CH2Cl (10 mL) was
added dropwise a solution of Me3SiBr in ClCH2CH2Cl (8 mL for 3a–
d, 12 mL for 3e) at 0°C for 3a–c or at –30°C for 3d,e (for the mol. ra-
tio of reagents see Table 1). The mixture was kept with occasional
stirring for the time indicated in Table 1 and added to the stirred two-
phase mixture of petroleum ether (twofold excess with respect to
ClCH2CH2Cl) and ice-cooled water (for 3a–c,f dilute aqueous
NaHSO415). The organic layer was separated, washed with H2O, dried
(Na2SO4), and evaporated in vacuo to provide the product 3 as a yel-
lowish liquid. Compounds 3a,b,d are obtained as colourless liquids
after purification in vacuo (Tables 1 and 2).
29Si NMR (CDCl3):
N(OSiMe3)2).
d =
17.22 (CHOSiMe3), 24.26 (br,17
N,N-Bis(trimethylsilyloxy)aminocyclohexene (3g):
To a solution of DBU (1.98 g, 13.0 mmol) in CH2Cl2 (8 mL) at 0°C
was added a solution of nitrocyclohexane (1.63 g, 12.6 mmol) in
CH2Cl2 (2 mL). After stirring for 5 min at 0 to 10°C the temperature
of the mixture was reduced to –70°C, and a solution of Me3SiBr (1.95
g, 12.7 mmol) in CH2Cl2 (2 mL) was slowly added. During 40 min the
temperature was allowed to raise to 10°C, and the volatile compo-
nents were removed in vacuo. The residual oil was treated with petro-
leum ether (30 mL), the resultant suspension was filtered in a dry
atmosphere, and the solvent was removed in vacuo to provide 2.41 g
(95%) of 2g, as a yellowish oil.18
2-[N,N-Bis(trimethylsilyloxy)]amino-3-trimethylsilyloxy-4-meth-
ylpent-1-ene (3f):
To a solution of 1f (1.01 g, 4.6 mmol) in CH2Cl2 (9 mL) at –5°C were
added successively DBU (0.84 g, 5.5 mmol) and a solution of
Me3SiCl (0.98 g, 9.1 mmol) in CH2Cl2 (5 mL). The resultant mixture
was stirred at 0–3°C for 30 min and evaporated in vacuo. The residual
oil was treated with petroleum ether (20 mL), the precipitate of
Table 2. NMR Data of Compounds 3a–e
Prod– 1H NMR (CDCl3/TMS)
13C NMR (CDCl3/TMS)
29Si NMR (CDCl3/TMS)
uct
d, J (Hz)
d
d
3aa
0.21 (s, 18 H, 2 SiMe3), 4.64 (d, 1 H, HA, 3J=8.0), 4.96
(d, 1 H, HB, 3J=15.2), 6.23 (dd, 1 H, CHN, 3J=l5.2, 8.0)
–0.1 (SiMe3), 102.3 (CH2), 148.6 (CHN)
24.43
3ba,b
3ca
0.20 (s, 18 H, 2 SiMe3), 1.88 (d, 3 H, Me, 4J=1.3), 4.53
0.2 (SiMe3), 13.8 (Me), 103.7 (CH2), 156.0 23.42
(C–N)
0.0 (SiMe3), 23.8, 33.1 (CH2), 51.4 (OMe), 24.23
(q, 1 H, HA, 4J=1.3), 4.92 (s, 1 H, HB)
0.20 (s, 18 H, 2 SiMe3), 2.60 (m, 4 H, CH2CH2), 3.67
(s, 3 H, OMe), 4.58 (t, 1 H, HA, 4J=1.1), 5.04 (s, 1 H; HB) 103.3 (=CH2), 158.0 (C–N), 173.2 (C=O)
3d
0.19 (s, 18 H, 2 SiMe3), 1.65 (dd, 3 H, Me, 3J=6.9,
4J=1.7), 5.53 (dq, 1 H, CH, 3J=13.4, 6.9), 6.01 (dq,
1 H, CHN, 3J=13.4, 4J=1.7)
0.21 (s, 18 H, 2 SiMe3), 3.05 (dd, 2 H, CH2, 3J=7.5,
4J=1.4), 3.69 (s, 3 H, MeO), 5.62 (dt, 1 H, CH, 3J=
13.6, 7.5), 6.09 (dt, 1 H, CHN, 3J=13.6, 4J=1.4)
–0.2 (SiMe3), 13.9 (Me), 117.3 (CH),
143.4 (CHN)
23.19
24.39
3e16
0.9 (SiMe3), 35.2 (CH2), 52.8 (MeO),
114.3 (CH), 145.9 (CHN), 172.4 (C=O)
a
b 15N NMR (CDCl3/MeNO2): d = –143.8 [N(OSiMe3)2].

184
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SYNTHESIS
The crude silyl nitronate 2g was dissolved in a mixture of
ClCH2CH2Cl (10 mL) and CH2Cl2 (3 mL). To this solution were suc-
cessively added Et3N (1.53 g, 15.1 mmol) and dropwise a solution of
Me3SiBr (2.03 g, 13.3 mmol) in ClCH2CH2Cl (2 mL) at –40°C. The
mixture was stirred for 30 min at –35°C and kept with occasional stir-
ring for 20 h at –30°C. The product 3g (2.35 g, 60% from 1g)19 was
isolated as a yellowish oil, following the general procedure.
1H NMR (CDCl3): d = 0.17 (s, 18 H, 2 SiMe3), 1.56 (m, 2 H, C4H2),
1.67 (m, 2 H, C5H2), 2.04 (m, 2 H, C3H2), 2.32 (m, 2 H, C6H2), 5.65
(tt, 1 H, C2H, 3J = 3.9 Hz, 4J = 1.5 Hz).
7.95 mmol) in MeCN (2 mL). The mixture was kept with occasional
stirring for 96 h at 24°C and for 96 h at 70–80°C. Theprogress of the
reaction was monitored by 1H NMR spectroscopy.20 The resultant
mixture was diluted with benzene (10 mL) and filtered in a dry at-
mosphere. The precipitate of Et3N·HCl was washed with benzene
(10 mL). The combined filtrate was evaporated carefully in vacuo to
afford 2.02 g (72%) of crude 6c as a moisture sensitive brown crystal-
line solid.
1H NMR (CDCl3): d = 0.22 (s, 9 H, SiMe3), 1.45 (t, 9 H, Me,
3J=7.3 Hz), 2.74 (m, 4 H, CH2CH2), 3.67 (s, 3 H, MeO), 3.68 (q, 6 H,
CH2, 3J=7.3 Hz), 4.56 (s, 2 H, CH2N).
13C NMR (CDCl3): d = –0.1 (SiMe3), 19.7 (C6H2), 22.3 (C4H2), 22.5
(C5H2), 24.0 (C3H2), 117.6 (C2H), 150.4 (C1–N).
29Si NMR (CDCl3): d = 22.36.
13C NMR (CDCl3): d = –0.7 (SiMe3), 8.3 (Me), 24.9 (CH2), 30.1
(CH2), 51.9 (MeO), 54.3 (CH2Me), 57.9 (CH2N), 155.9 (C=N), 173.2
(C=O).
14N NMR (CDCl3): d = –314 (Dn1/2 120 Hz, [–NEt3]+).
1-Trimethylsilyloxyimino-2-trimethylsilyloxycyclohexane (4g):
Product 3g (2.10 g, 7.7 mmol) disappeared completely in 20 d at
–30°C (NMR control). Distillation of the resultant oil (bp 109–110°C/
8 Torr) afforded 1.43 g (68%) of 4g as a colourless liquid.
29Si NMR (CDCl3): d = 28.6.
Further purification of the product 6c as given below failed due to
strong solubility in organic solvents.
1H NMR (CDCl3): d = 0.09 (s, 9 H, CHOSiMe3), 0.19 (s, 9 H,
NOSiMe3), 1.35 (m, 1 H, CH2), 1.52 (m, 2 H, CH2), 1.77 (m, 1 H,
CH2), 1.88 (m, 2 H, CH2), 2.07 (ddd, 1 H, CHAHBC=N, 2J = 13.8 Hz,
N,N,N-Triethyl-N-(4-methoxycarbonyl-2-hydroxyiminobutyl)-
ammonium Chloride (7c):
3
3J = 12.8 Hz and 5.4 Hz), 3.04 (dt, 1 H, CHAHBC=N, J = 3.8 Hz),
To a solution of 6c (1.76 g, 5.0 mmol) in distilled H2O (10 mL) was
added a small quantity of activated charcoal. After stirring for 12 h at
20°C, the mixture was filtered and evaporated in vacuo. The residue
was crystallized from acetone to furnish 1.05 g (75%) of 7c as colour-
less crystals; mp 142–145°C.
4.28 (t, 1 H, CH, 3J = 2.8 Hz).
13C NMR (CDCl3): d = 0.1 and 0.7 (SiMe3), 20.8, 22.1, 26.3 and 36.2
(CH2), 70.7 (CH), 165.0 (C=N).
29Si NMR (CDCl3): d = 17.24 (CHOSiMe3), 23.66 (NOSiMe3).
1H NMR (DMSO-d6): d = 1.28 (t, 9 H, Me, 3J = 7.2 Hz), 2.61 (m, 4
CH2CH2), 3.40 (q, 6 H, CH2, 3J=7.2 Hz), 3.63 (s, 3 H, MeO), 4.19 (s,
2 H, CH2N), 12.02 (s, 1 H, =NOH).
a-Hydroxycyclohexanone Oxime (5g):
A solution of 4 g (0.33 g, 1.2 mmol) and NH4F (0.06 g, 1.6 mmol) in
MeOH (6 mL) was stirred for 4 h at 20°C. The volatile components
were removed in vacuo, and the residue was crystallized from petro-
leum ether. Recrystallization from petroleum ether/benzene provided
0.11 g (71%) of 5 g, as colourless crystals; mp 102–105 °C (Lit.10 mp
104–106 °C).
13C NMR (DMSO-d6): d = 7.9 (Me), 24.2 (CH2), 29.0 (CH2), 51.5
(MeO), 52.8 (CH2Me), 57.0 (CH2N), 149.3 (C=N), 172.6 (C=O).
14N NMR (DMSO-d6): d = –314 (Dn1/2 64 Hz, [–NEt3]).
15N NMR (DMSO-d6, 100°C; SPT from CH2 at 4.19 ppm): d = –6.58
[t, 2J(15N, H) = 2.9 Hz, C=NOH].
Anal. Calcd for C12H25ClN2O3N2O3Cl: C, 51,33 ; H, 8.97; N, 9.98; Cl,
12.63. Found: C, 51.10; H, 9.03; N, 10.06; Cl, 12.66.
2-[N,N-Bis(trimethylsilyloxy)]aminopropene (3b); Typical Proce-
dure Using Chlorotrimethylsilane:
To a solution of Et3N (8.51 g, 84.3 mmol) and Me3SiCl (8.75 g, 80.6
mmol) in MeCN (18 mL) at 10°C was added Me2CHNO2 (3.26 g,
36.6 mmol). The temperature was allowed to rise to 20°C, and the
mixture was stirred for 70 h. The progress of the reaction was moni-
This work was performed at the Scientific Educational Centre for
young chemists and supported by Russian Foundation of Fundamental
Research (grant No. 96-03-32472). We thank Prof. Dr. D, Seebach
(Eidgenössische Technische Hochschule Zürich) for a gift of DBU.
1
tored by H NMR spectroscopy. Aqueous workup according to the
general procedure followed by distillation at 24–25°C/0.2 Torr pro-
vided 6.57 g (77%) of 3b as a colourless liquid.
(1) (a) Kashutina, M. V.; Ioffe, S. L.; Tartakovsky, V. A. Docl.
Akad. Nauk SSSR. 1974, 218, 109, 1974, 214-219, 607 (engl.
transl.); Chem. Abstr. 1975, 82, 43227.
(b) Torssell, K. B. G. Nitrile Oxides, Nitrones, and Nitronates
in Organic Synthesis; VCH: Weinheim, 1988.
(2) (a) Beck, A. K.; Seebach, D. Encyclopedia ofReagents for Or-
ganic Synthesis; Paquette, L, Ed.; Wiley: New York. 1995, 7, p
5270.
N,N,N-Triethyl-N-(2-hydroxyiminoethyl)ammonium Chloride (7a):
To a solution of Et3N (7.56 g, 74.9 mmol) and Me3SiCl (7.74 g, 71.3
mmol) in MeCN (10 mL) at 0–5°C was added a solution of EtNO2
(1.57 g, 20.9 mmol) in MeCN (2 mL) over 30 min. The mixture was
kept with occasional stirring for 90 h at 20°C and for 60 h at 50–60°C.
The progress of the reaction was monitored by 1H NMR spectrosco-
py. The volatile components were removed in vacuo, the crystalline
residue was dissolved in MeOH (200 mL) and kept for 96 h at 20°C.
After careful evaporation of the mixture in vacuo, CHCl3 (150 mL)
was added to the crystalline residue, the precipitate was filtered off,
washed with CHCl3 (3 ´ 70 mL) and dried in vacuo to provide 2.21 g
(54%) of 7a; colourless crystals; mp 200–205 °C (dec).
1H NMR (CD3OD): d = 1.35 (t, 9 H, Me, 3J = 7.2 Hz), 3.35 (q, 6 H,
CH2, 3J=7.2 Hz), 4.02 (d, 2 H, CH2, 3J = 6.3 Hz), 7.58 (t, 1 H, CH=N).
13C NMR (CD3OD): d = 8.9 (Me), 55.7 (CH2Me), 57.6 (CH2), 141.2
(C=N).
14N NMR (CD3OD): d = –316 (Dn1/2 68 Hz, [–NEt3]+).
Anal. Calcd for C8H19ClN2O: C, 49.35; H, 9.84; N, 14.39; Cl, 18.21.
Found: C, 49.18; H, 9.76; N, 14.22; Cl, 18.25.
(b) Kalinin, A. V.; Apasov, E. T.; Ioffe, S. L.; Kozjukov, V. P.;
Kozjukov, Vik. P. Izv. Akad. Nauk SSSR, Ser. Khim. 1985,
2635; 1985, 2442 (engl. transl.); Chem. Abstr. 1986, 105
191186.
(c) Marti, R. E.; Heinzer, J.; Seebach, D. Liebigs. Ann. Chem.
1995, 1193.
(3) Feger, H.; Simchen, G. Liebigs Ann. Chem. 1986, 1456.
(4) For the preparation, reactivity and synthetic application of
miscellaneous bis(Li-derivatives) of aliphatic nitro compounds,
see:
Marti, R. E.; Seebach, D. Encyclopedia ofReagentsfor Organic
Synthesis; Paquette, L., Ed.; Wiley: New York, 1995, 3, 1946
and 5, 3138.
(5) Feger, H.; Simchen, G. Lieb. Ann. Chem. 1986, 428.
(6) (a) Lyapkalo, I. M.; Ioffe, S. L.; Strelenko, Yu. A.; Tartakovsky,
V. A. Izv. Akad. Nauk, Ser. Khim. 1995, 1182; 1995, 44, 1142
(engl. transl.); Chem. Abstr. 1996, 124 56037.
N,N,N-Triethyl-N-(4-methoxycarbonyl-2-trimethylsilyloxyimi-
nobutyl)ammonium Chloride (6c):
To a solution of Et3N (2.97 g, 29.4 mmol) and Me3SiCl (3.27 g, 30.2
mmol) in MeCN (2 mL) at 0–5°C was added a solution of 1c (1.28 g,
(b) Dilman, A. D.; Lyapkalo, I. M.; Ioffe, S. L.; Strelenko, Yu.
A.; Tartakovsky, V. A. Mend. Commun. 1997, in press.

February 1998
SYNTHESIS
185
(7) Tishkov, A. A.; Lyapkalo, I. M.; Ioffe, S. L.; Strelenko, Yu. A.; (15) In the cases of 3a–c,f, the pH of the aqueous phase after the
Tartakovsky, V. A. Izv. Akad. Nauk. Ser. Khim. 1997, 210;
1997, 46, 205 (engl. transl.).
quenching must be 2–3.
(16) Contains ca. 5% of starting nitro compound according to H
1
(8) Makarenkova, L. M.; Ioffe, S. L.; Tartakovsky, V. A. 5th Rus-
NMR spectroscopy.
sian symposium on Structure and Reactivity of Organosilicon (17) Due to hindered inversion of nitrogen in 3f.
compounds; Irkutsk, 1996, Book ofAbstracts, p 63.
(9) Aizpurua, J. M.; Oiarbide, M.; Palomo, C. Tetrahedron Lett.
1987, 28, 5361.
(18) For 2g NMR data are in good agreement with those described
earlier:
Olah, G. A.; Gupta, B. G. B.; Malhotra, R. J. Org. Chem. 1979,
44, 4272.]
(10) Nenz, A.; Brichta, C.; Ribaldone, G.; Borsotti, G.; Gallinella, E.
Belgian Patent 635960, (Sicedison Societa per Azioni), 1964; (19) According to NMR data, the product 3g was contaminated with
Chem. Abstr. 1964, 61, 14553.
(11) On the contrary, the second silylation of nitroalkanes is con-
4g (7%) and unchanged 1g (ca. 5%); the yield of 3g was deter-
mined by 1H NMR spectroscopy.
siderably faster than the first with trialkylsilyl triflate as a silyl- (20) Hitherto unknown silyl nitronate 2c was identified as an inter-
ating reagent.5
mediate in solution:
(12) Morris, G. E.; Freeman, R. J. Am.. Chem. Soc. 1979, 101, 760.
(13) Bruson, H. A. U. S. Patent 2390918, (Resinous Products &
Chemical Co.), 1945; Chem. Abstr. 1946, 40, 2456.
(14) Kambe, S.; Yasuda, H. Bull. Chem. Soc. Jpn. 1968, 41, 1444.
1H NMR (CH3CN + CDCl3): d = 0.28 (s, 9 H, SiMe3), 1.97
(s, 3 H, Me), 2.56 (m, 4 H, CH2CH2), 3.64 (s, 3 H, OMe).
13C NMR (CH3CN + CDCl3): d = 0.2 (SiMe3), 17.2 (Me), 27.9
(CH2), 29.7 (CH2), 51.8 (OMe), 123.1 (C=N), 172.9 (C=O).
29Si NMR (CH3CN + CDCl3): d = 24.1.