Organosilicon synthesis of isocyanates: III. Synthesis of aliphatic, carbocyclic, aromatic, and alkylaromatic isocyanatocatboxylic acid esters

Article abstract of DOI:10.1134/S1070363206070115

A series of aminoacid esters was prepared by treating the aminoacid suspensions in ethanol with thionyl chloride. Best conversion of aminoacid esters to corresponding isocyanates was achieved in the case of aromatic and carbocyclic aminoesters by phosgeneation of their N-silyl derivatives, and in the case of aliphatic and alkylaromatic aminoesters by phosgeneation of O-silyl or N,O-bissilylurethanes on their basis. In the last case additional step of esterification of the by-products isocyanatoalkylcarboxylic acid chlorides is required after phosgeneation. Unusual generation of cynnamates and intramolecular N→O-migration of trimethylsilyl group in the solutions of silylated alkylaromatic β-aminoacid esters were found. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S1070363206070115

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 7, pp. 1069 1080.
Original Russian Text A.V. Lebedev, A.B. Lebedeva, V.D. Sheludyakov, S.N. Ovcharuk, E.A. Kovaleva, O.L. Ustinova, 2006, published in Zhurnal
Obshchei Khimii, 2006, Vol. 76, No. 7, pp. 1118 1128.
Pleiades Publishing, Inc., 2006.
Organosilicon Synthesis of Isocyanates:
III.1 Synthesis of Aliphatic, Carbocyclic, Aromatic,
and Alkylaromatic Isocyanatocatboxylic Acid Esters
A. V. Lebedev, A. B. Lebedeva, V. D. Sheludyakov,
S. N. Ovcharuk, E. A. Kovaleva, and O. L. Ustinova
State Scientific and Research Institute of Chemistry and Technology of Organoelement Compounds,
sh. Entuziastov 38, Moscow, 111123 Russia
Received May 30, 2005
Abstract A series of aminoacid esters was prepared by treating the aminoacid suspensions in ethanol
with thionyl chloride. Best conversion of aminoacid esters to corresponding isocyanates was achieved in the
case of aromatic and carbocyclic aminoesters by phosgeneation of their N-silyl derivatives, and in the case of
aliphatic and alkylaromatic aminoesters by phosgeneation of O-silyl or N,O-bissilylurethanes on their basis.
In the last case additional step of esterification of the by-products isocyanatoalkylcarboxylic acid chlorides is
reqired after phosgeneation. Unusual generation of cynnamates and intramolecular N O-migration of tri-
methylsilyl group in the solutions of silylated alkylaromatic -aminoacid esters were found.
DOI: 10.1134/S1070363206070115
We have reported on the involvement of organo-
silicon derivatives to the synthesis of isocyanates of
the furan, thiophene, and polyfluorophenyl series [2],
and also for preparing aliphatic, carbocyclic, and
alkylaromatic isocyanates [1]. Developing these
studies of the isocyanate organosilicon synthesis we
investigated transformations of the aminoacid ester
silicon derivatives to corresponding isocyanates.
majority of -aminoacids exist as betaine form and
therefore they are poorly soluble in organic solvents.
The low solubility decreases significantly synthetic
performance of aminoacids. In this connection it
seemed interesting to convert the aminoacids into
esters having no betaine structure and therefore more
convenient for further synthetic purposes, in part, as
the precursors of new isocyanates.
Aminoacids for a long time attracted intently atten-
tion as the compounds having at least two reactive
functional groups and often as natural compounds.
Variety of these compounds increases continuously.
We have reported recently on the development of
convenient method for preparing a broad range of
previously unknown and hardly available -amino-
acids [3]. It seemed interesting to prepare new iso-
cyanates on the basis of -aminoacid esters. Synthesis
of the latter compounds is also actual because the
We found that such transformation of -aminoacids
can be easily carried out, in accordance with expecta-
tion, by treating them with 50 70% excess of thionyl
chloride in anhydrous ethanol [4]. This method is
more convenient and gives better results as compared
to the known aminoacid esterification with diazo-
methane, dialkyl sulfates, alcohols saturated with dry
hydrogen chloride [5], or alcohols and hydrogen
chloride in the presence of orthoformate [6]. Reaction
proceeds according to the following scheme.
R1C(R2)CH2COOH + SOCl2 + C2H5OH
R1C(R2)CH2COOC2H5,
SO2,
HCl
NH2
NH2 HCl
Ia Io
IIa IIo
R2 = H, R1 = C6H5 (a), 4-CH3OC6H4 (b), 4-(CH3)2CHOC6H4 (c), 4-C2H5O-3-CH3OC6H3 (d), 4-(CH3)2CHO-3-CH3OC6H3
(e), 4-(CH3)2CHCH2O-3-CH3OC6H3 (f), 4-CH3C6H4 (g), 2-ClC6H4 (h), 2-thenyl (i), (CH3)2CH (j), CH3(CH2)2 (k),
(CH3)2CHCH2 (l), CH3(CH2)3 (m), 3-pyridyl (n); R1 + R2 = (CH2)5 (o).
The corresponding ethyl ester hydrochlorides were
prepared similarly from 4 -aminophenylacetic acid III
and 4-(aminomethyl)cyclohexanecarboxylic acid IV.
Treating these compounds with concentrated NaOH
1
For communication II, see [1].
1069

1070
LEBEDEV et al.
solution at 0 5 C gave free aminoesters Va and Vb.
Yields, spectral characteristics and elemental analysis
data of free aminoesters and their hydrochlorides are
listed in Table 1.
Esterification of aromatic aminoacids proceeds
analogously to the above described. Using methanol
or ethanol as the alcohol component and neutralizing
hydrochlorides with aqueous solution of sodium hyd-
roxide at low temperature we prepared esters Vc Vj
from the corresponding aminoacids. In the case of
anthranylic acid and its derivatives a significant dilu-
tion of reaction mixture with ethanol and using of not
less than double excess of thionyl chloride is needed
for preparation of the aminoesters Vc, Vd, Vi, and Vl,
due to low solubility of these aminoacids in alcohols.
The -aminoacid ester hydrochlorides prepared are
viscous oil IIk or slightly hygroscopic solids IIa IIj,
IIl IIo with the broad (up to 40 C) range of melting
points, easily isolating in 97 99% purity. They are
well soluble in water, ethanol, chloroform, DMF,
DMSO, acetone, acetonitrile, and insoluble in ether
and toluene.
Silylation of aminoesters by treating with 20%
excess of hexamethyldisilazane at elevated tempera-
ture proceeds in high yields only in the case of aro-
matic aminoesters Va, Vc Vj and compound Vb.
Under these conditions the monosilylated derivatives
VIa to VIj are formed. At the action of phosgene 10%
excess used as 25% solution in toluene at 0 5 C and
subsequent distilling toluene off they form corres-
ponding isocyanates VIIa VIIj in high yields. The
formed compounds are easily isolated by vacuum
distillation.
From Table 1 it follows that the yields of amino
esters IIa IIm, IIo reach 90 95%. In the case of
aminoacid In the aminoester IIn HCl is also formed,
but competingly obtained aminoacid hydrochloride In
2HCl is so poorly soluble in ethanol that its esterifica-
tion results in formation of unseparable mixture of
salts In 2HCl and IIn HCl in 1:1 ratio. Pure amino-
ester salt IIn HCl can be isolated only when the reac-
tion is performed in semimicro scale.
(Me3Si)2NH
COCl2
RNH2
RNHSiMe3
VIa VIj
RN=C=O,
NH3
Me3SiCl,
HCl
Va Vj
VIIa VIIj
R = 4-C2H5OC(O)CH2C6H4 (a), (4-ethoxycarbonylcyclohexyl)methyl (b), 2-C2H5OC(O)C6H4 (c), 2-CH3OC(O)C6H4 (d),
3-C2H5OC(O)C6H4 (e), 3-CH3OC(O)C6H4 (f), 4-C2H5OC(O)C6H4 (g), 4-CH3OC(O)C6H4 (h), 2-CH3OC(O) 5-ClC6H3 (i),
2,5-[CH3OC(O)]2C6H3 (j).
Silylation of the aliphatic, carbocyclic, and alkyl-
aromatic - and -aminoacid ester hydrochlorides
proceeds markedly more difficultly. Treating the
hydrochlorides VIIIa VIIIe and IIj with 5% molar
excess of the equimolar mixture of hexamethyldisi-
lazane and triethylamine in boiling benzene (method
a) permits to prepare corresponding N-silyl deriva-
tives IXa IXe and IXl in 40 57% yield only. The
Table 1. Yields, 1H NMR spectral and elemental analysis data of hydrochlorides II and free aminoesters V
Found, % Calculated, %
Comp. Yield,
1H NMR spectrum in DMSO-d6, , ppm
Formula
no.
%
C
H
C
H
IIa
90 1.1 t (3H, CH3), 3.0 q (1H, CH2), 3.20 q (1H, CH2), 3.98 m
(2H, OCH2), 4.56 q (1H, CHN), 7.4 m (3Harom), 7.56 d
(2Harom), 8.75 s (3H, NH3)
C11H16ClNO2
IIb
IIc
93 1.2 t (3H, CH3), 3.05 q (1H, CH2), 3.20 q (1H, CH2), 3.77 s 55.43 6.96 C12H18ClNO3
(3H, OCH3), 4.02 q (2H, OCH2), 4.50 m (1H, CHN), 7.03 d
(2Harom), 7.50 d (2Harom), 8.41 s (3H, NH3)
95 1.2 t (3H, CH3), 1.32 d (6H, 2CH3), 3.05 q (1H, CH2), 58.37 7.66 C14H22ClNO3
3.20 q (1H, CH2), 4.02 q (2H, OCH2), 4.52 m (1H, CHN),
4.70 m (1H, OCH), 7.04 d (2Harom), 7.51 d (2Harom),
8.40 s (3H, NH3)
55.49 6.98
58.43 7.70
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ORGANOSILICON SYNTHESIS OF ISOCYANATES: III.
1071
Table 1. (Contd.)
Found, %
Calculated, %
Comp. Yield,
1H NMR spectrum in DMSO-d6, , ppm
Formula
no.
%
C
H
C
H
IId
95 1.2 t (3H, CH3), 1.33 t (3H, CH3), 2.87 q (1H, CH2), 3.01 q 55.30 7.26 C14H22ClNO4
(1H, CH2), 3.77 s (3H, OCH3), 4.05 m (4H, 2OCH2),
55.35 7.30
56.69 7.61
57.91 7.90
4.49 m (1H, CHN), 6.97 s (2Harom), 7.21 s (1Harom), 8.45 s
(3H, NH3)
95 1.2 t (3H, CH3), 1.29 d (6H, 2CH3), 2.88 q (1H, CH2), 56.63 7.62 C15H24ClNO4
2.99 q (1H, CH2), 3.77 s (3H, OCH3), 4.05 q (2H, OCH2),
4.50 m (1H, CHN), 4.71 m (1H, OCH), 6.97 d (2Harom),
7.22 s (1Harom), 8.43 s (3H, NH3)
95 1.01 d (6H, 2CH3), 1.21 t (3H, CH3), 2.00 m (1H, CH), 57.84 7.87 C16H26ClNO4
2.85 q (1H, CH2), 3.00 q (1H, CH2), 3.71 d (2H, OCH2),
3.76 s (3H, OCH3), 4.07 q (2H, OCH2), 4.48 m (1H, CHN),
6.97 s (2Harom), 7.23 s (1Harom), 8.43 s (3H, NH3)
IIe
IIf
IIg
IIh
IIi
93 1.10 t (3H, CH3), 2.30 s (3H, CH3), 2.94 q (1H, CH2), 59.20 7.47 C12H18ClNO2
3.16 q (1H, CH2), 4.00 q (2H, OCH2), 4.51 q (1H, CHN),
7.21 d (2Harom), 7.41 d (2Harom), 8.67 s (3H, NH3)
95 1.08 t (3H, CH3), 3.08 q (1H, CH2), 3.25 q (1H, CH2), 50.00 5.70 C11H15ClNO2
4.02 q (2H, OCH2), 4.99 t (1H, CHN), 7.41 m (2Harom),
7.51 d (1Harom), 7.83 d (1Harom), 8.89 s (3H, NH3)
90 1.12 t (3H, CH3), 3.01 q (1H, CH2), 3.16 q (1H, CH2), 45.86 6.02 C9H14ClNO2S
4.03 q (2H, OCH2), 4.89 q (1H, CHN), 7.06 q (1Harom),
7.24 d (1Harom), 7.57 d (1Harom), 8.60 br (3H, NH3)
92 0.88 d (6H, 2CH3), 1.20 t (3H, CH3), 1.95 m (1H, CH), 49.08 9.29 C8H18ClNO2
2.63 d (2H, CH2), 3.42 q (1H, CHN), 4.08 q (2H, OCH2),
8.30 s (3H, NH3)
95 0.98 t (3H, CH3), 1.32 t (3H, CH3), 1.45 m (2H, CH2), 49.06 9.30 C8H18ClNO2
1.72 m (2H, CH2), 2.77 q (1H, CH2), 2.89 q (1H, CH2),
3.71 m (1H, CHN), 4.26 q (2H, OCH2)
59.14 7.44
50.02 5.72
45.86 5.99
49.10 9.27
49.10 9.27
51.55 9.61
IIj
IIk
IIl
95 0.88 q (6H, 2CH3), 1.21 t (3H, CH3), 1.37 m (1H, CH2), 51.51 9.64 C9H20ClNO2
1.57 m (1H, CH2), 1.74 m (1H, CH), 2.62 q (1H, CH2),
2.79 q (1H, CH2), 3.43 m (1H, CHN), 4.12 q (2H, OCH2),
8.30 s (3H, NH3)
IIm 95 0.86 t (3H, CH3), 1.19 t (3H, CH3), 1.28 m (4H, 2CH2), 51.54 9.64 C9H20ClNO2
1.60 m (2H, CH2), 2.68 q (1H, CH2), 2.75 q (1H, CH2),
51.55 9.61
3.37 m (1H, CHN), 4.09 q (2H, OCH2), 8.26 s (3H, NH3)
IIn
50 1.24 t (3H, CH3), 3.38 m (2H, CH2), 4.21 q (2H, OCH2), 44.93 6.05 C10H16Cl2N2O2 44.96 6.04
5.21 m (1H, CHN), 8.28 t (1Harom), 8.87 d (1Harom), 8.99 d
HCla
(1Harom), 9.10 s (1Harom
)
IIo
90 1.20 t (3H, CH3), 1.32 m (1H, C6H11), 1.44 m (3H, C6H11),
1.66 m (2H, C6H11), 1.72 m (4H, C6H11), 2.74 s (2H, CH2),
4.10 q (2H, OCH2), 8.20 s (3H, NH3)
.
9.11 C10H20ClNO2
C10H13NO2
54.17 9.09
54 14
Va
95 1.16 t (3H, CH3), 3.4 s (2H, NH2), 4.04 q (2H, OCH2),
4.92 s (2H, CH2), 6.5 d (2Harom), 6.87 d (2Harom
)
1
H NMR spectrum was measured in D O.
2
yield can not be improved when trimethylchlorosilane
is used instead of hexamethyldisilazane because in
this case (procedure b) double amount of triethyl-
amine and solvent is needed. Besides, triethylamine
hydrochloride amorphous precipitate obtained in-
cludes reacting substances in its structure and hence
prevents their interaction. Using methylene chloride
instead of benzene favors crystallization of the
ammonium salt precipitate [7], but no increase in the
yield of silyl derivatives is observed. Combination of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

1072
LEBEDEV et al.
silylating systems with the initial treating with hexa-
methyldiailazane-triethylamine mixture, filtering pre-
cipitate off and subsequent treating it with tri-
methylchlorosilane-triethylamine mixture does not
increase yield of N-silyl derivatives IXa IXe, IXl,
and only for the alkylaromatic aminoester hydrochlo-
rides IIa IIc, IIg IIi and compound IIo 70 75%
yield of corresponding silylated aminoesters IXf IXk,
IXm may be achieved by using this combination.
Phosgeneation of silicon derivatives IXa IXm with
10% excess of phosgene used as 25% toluene solution
at 0 5 C and subsequent distilling toluene off
generates isocyanates Xa Xm in 55 60% yield.
a. (Me3Si)2NH/Et3N
or
b. Me3SiCl/2Et3N
COCl2
RNH2 HCl
RNHSiMe3
RN=C=O,
Me3SiCl,
HCl
Et3N HCl,
Xa Xe
VIIa VIIe
IXa IXe
NH3
(1) (Me3Si)2NH/Et3N,
(2) Me3SiCl/2Et3N
COCl2
IIa IIc, IIg IIj, IIo
IXf IXm
Xf Xm,
Me3SiCl,
HCl
Et3N HCl,
NH3
VIII X, XIV XVI, R = CH3OC(O)CH2 (a), CH3OC(O)(CH2)2 (b), CH3OC(O)CH(CH3) (c), C2H5OC(O)CH2 (d),
C2H5OC(O)(CH2)2 (e), C2H5OC(O)CH2CH(C6H5) (f), 4-CH3OC6H4CHCH2COOC2H5 (g), 4-(CH3)2CHOC6H4CHCH2
COOC2H5 (h), 4-CH3C6H4CHCH2COOC2H5 (i), 2-ClC6H4CHCH2COOC2H5 (j); R = XCHCH2COOC2H5, X = 2-thenyl
(k); R = (CH3)2CHCHCH2COOC2H5 (l), 1-[(ethoxycarbonyl)methyl]cyclohexyl (m).
Yields and physicochemical characteristics of pre-
pared compounds IX and X are listed in Table 2.
showed that they contain doubled resonance signals
of all hydrogen, carbon, and silicon atoms and that for
these compounds is characteristic the intramolecular
transannular interaction of Si with the carboxylic
group O atom. This interaction increases on dilution
1
Analysis of H, 13C, and 29Si NMR spectral data
of trimethylsilyl derivatives IXa IXl (Table 2)
1
Table 2. Yields, melting or boiling points, H NMR spectra and mass spectra of compoundsa VI, VII, IX XV, XVII,
XVIII, XXI, and XXII
mp, C or
Comp. Yield,
M+
(m/z)
bp,
C
1H NMR spectrum (CDCl3), , ppm
no.
%
(p, mm)
142 145 (3)
118 120 (1)
VIa
VIb
98
97
0.10 s (9H, 3CH3), 1.18 t (3H, CH3), 4.10 q (2H, OCH2), 4.85 br (1H, NH),
5.02 s (2H, CH2), 6.62 d (2Harom), 7.08 d (2Harom
)
0.05 s, 0.14 s (9H, 3CH3), 0.85 1.0 m (2H, CH2), 1.24 t (3H, CH3), 1.30 m (2H,
CH + NH), 1.35 1.48 m (2H, CH2), 1.85 d.d (2H, CH2), 2.0 m (2H, CH2),
2.21 t.t (1H, CH), 2.53 d (2H, CH2N), 4.10 q (2H, OCH2)
VIc
VId
VIe
VIf
VIg
VIh
VIi
97
97
97
96
97
96
95
95
98
118 120 (3)
100 103 (2)
120 122 (3)
125 130 (4)
45 47
125 130 (4)
16 18
101 103
237
223
237
223
237
223
257
281
VIj
VIIa
115 118 (3)
205 1.27 t (3H, CH3), 3.57 s (2H, CH2), 4.17 q (2H, OCH2), 7.03 d (2Harom),
7.24 d (2Harom
)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

ORGANOSILICON SYNTHESIS OF ISOCYANATES: III.
1073
Table 2. (Contd.)
mp, C or
bp,
(p, mm)
Comp. Yield,
M+
(m/z)
C
1H NMR spectrum (CDCl3), , ppm
no.
%
VIIb
93
119 121(3)
211 0.88 1.02 m (2H, CH2), 1.15 t (3H, CH3), 1.27 1.41 m (2H, CH2), 1.45 m (1H,
CH), 1.77 m (2H, CH2), 1.93 m (2H, CH2), 2.13 t.t (1H, CH), 3.09 d (2H,
CH2N), 4.02 q (2H, OCH2)
VIIc
VIId
VIIe
VIIf
95
95
95
94
29 31
191 1.41 t (3H, CH3), 4.42 q (2H, OCH2), 7.10 d (1Harom), 7.24 t (1Harom), 7.46 t
(1Harom), 8.00 d (1Harom
177 3.95 s (3H, OCH3), 7.11 d (1Harom), 7.24 t (1Harom), 7.46 t (1Harom), 8.00 d
(1Harom
191 1.37 t (3H, CH3), 4.37 q (2H, OCH2), 7.23 d (1Harom), 7.38 t (1Harom), 7.75 s
(1Harom), 7.86 d (1Harom
177 3.94 s (3H, OCH3), 7.23 d (1Harom), 7.37 t (1Harom), 7.74 s (1Harom), 7.85 d
(1Harom
191 1.38 t (3H, CH3), 4.36 q (2H, OCH2), 7.12 d (2Harom), 7.99 d (2Harom
)
47 50
)
112 115 (3)
35 38
)
)
VIIg
VIIh
VIIi
VIIj
94
94
88
84
27 29
50 52
160 163 (3)
115 117
)
177 3.90 s (3H, OCH3), 7.12 d (2Harom), 7.99 d (2Harom
211
)
235 3.91 s (3H, OCH3), 3.95 s (3H, OCH3), 7.71 s (1Harom), 7.82 d (1Harom), 8.02 d
(1Harom
)
IXa
IXc
51
57
60 64 (50)
50 53 (7)
161 0.044 s (9H, 3CH3), 1.40 br (1H, NH), 3.51 s (2H, CH2), 3.68 s (3H, OCH3)
175 0.046 s (9H, 3CH3), 1.34 d (3H, CH3), 1.44 br (1H, NH), 3.64 q (1H, CH),
3.74 s (3H, OCH3)
IXd
IXe
44
40
70
65 70 (50)
58 60 (9)
119 120 (1.5)
175 0.045 s (9H, 3CH3), 1.24 t (3H, CH3), 1.38 br (1H, NH), 3.48 s (2H, CH2),
4.17 q (2H, OCH2)
189 0.047 s (9H, 3CH3), 1.24 t (3H, CH3), 1.40 br (1H, NH), 2.47 t (2H, CH2),
3.08 t (2H, CH2), 4.07 q (2H, OCH2)
IXfb
265
295
323
279
299
271
0.04 s (9H, 3CH3), 1.15 br (1H, NH), 1.18 t (3H, CH3), 2.51 2.58 q (1H, CH2),
2.64 2.73 q (1H, CH2), 4.10 q (2H, OCH2), 4.38 br (1H, CH), 7.17 7.38
(5Harom
)
IXg
IXh
IXi
72
72
68
67
70
133 135 (1)
149 151 (1)
122 125 (1)
140 142 (1)
128 130 (1)
0.04 s (9H, 3CH3), 1.13 br (1H, NH), 1.19 t (3H, CH3), 2.50 2.58 q (1H, CH2),
2.68 2.75 q (1H, CH2), 3.88 s (3H, OCH3), 4.08 q (2H, OCH2), 4.40 br (1H,
CH), 6.83 d (2Harom), 7.36 d (2Harom
)
0.04 s (9H, 3CH3), 1.14 br (1H, NH), 1.20 t (3H, CH3), 1.32 d (6H, 2CH3),
2.52 2.60 q (1H, CH2), 2.69 2.76 q (1H, CH2), 3.88 s (3H, OCH3), 4.08 q (2H,
OCH2), 4.38 br (1H, CH), 4.80 m (1H, OCH), 6.85 d (2Harom), 7.38 d (2Harom
)
0.04 s (9H, 3CH3), 1.10 t (3H, CH3), 1.13 br (1H, NH), 2.28 s (3H, CH3),
2.47 2.54 q (1H, CH2), 2.63 2.69 q (1H, CH2), 4.08 q (2H, OCH2), 4.34 br (1H,
CH), 7.00 d (2Harom), 7.29 d (2Harom
)
IXj
IXk
0.03 s (9H, 3CH3), 1.08 t (3H, CH3), 1.14 br (1H, NH), 2.60 2.67 q (1H, CH2),
2.71 2.78 q (1H, CH2), 4.10 q (2H, OCH2), 4.81 br (1H, CH), 7.18 d (2Harom),
7.29 d (1Harom), 7.70 d (1Harom
)
0.03 s (9H, 3CH3), 1.14 br (1H, NH), 1.20 t (3H, CH3), 2.52 2.59 q (1H, CH2),
2.64 2.71 q (1H, CH2), 4.12 q (2H, OCH2), 4.71 br (1H, CH), 6.88 q (1Harom),
7.06 d (1Harom), 7.38 d (1Harom
)
IXl
60
75
85 90 (7)
231 0.048 s (9H, 3CH3), 0.98 d (6H, 2CH3), 1.22 t (3H, CH3), 1.41 br (1H, NH),
1.98 m (1H, CH), 2.65 d (2H, CH2), 3.44 q (1H, CHN), 4.08 q (2H, OCH2)
257 0.05 s (9H, 3CH3), 0.98 br (1H, NH), 1.23 t (3H, CH3), 1.30 1.62 m (10H,
5CH2), 2.40 s (2H, CH2), 4.09 q (2H, OCH2)
IXm
105 110 (1.5)
Xa
Xb
Xc
85
78
80
60 (12)
68 (3)
63 65 (3)
115 3.70 s (3H, OCH3), 3.95 s (2H, CH2)
129 2.56 t (2H, CH2), 3.55 t (2H, CH2N), 3.74 s (3H, OCH3)
129 1.42 d (3H, CH3), 3.77 s (3H, OCH3), 4.07 q (1H, CH)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

1074
LEBEDEV et al.
Table 2. (Contd.)
mp, C or
bp,
(p, mm)
Comp. Yield,
M+
(m/z)
C
1H NMR spectrum (CDCl3), , ppm
no.
%
Xd
Xe
Xf
80
77
82
60 (9)
80 (5)
113 117 (2)
129 1.30 t (3H, CH3), 3.91 s (2H, CH2), 4.27 q (2H, OCH2)
143 1.27 t (3H, CH3), 2.57 t (2H, CH2), 3.56 t (2H, CH2N), 4.17 q (2H, OCH2)
219 1.27 t (3H, CH3), 2.73 q (1H, CH2), 2.83 q (1H, CH2), 4.19 q (2H, OCH2),
5.13 q (1H, CH), 7.35 m (5Harom
249 1.27 t (3H, CH3), 2.72 q (1H, CH2), 2.82 q (1H, CH2), 3.90 s (3H, OCH3),
4.16 q (2H, OCH2), 5.08 q (1H, CHN), 7.16 d (2Harom), 7.38 d (2Harom
277 1.27 t (3H, CH3), 1.34 d (6H, 2CH3), 2.72 q (1H, CH2), 2.82 q (1H, CH2),
4.16 q (2H, OCH2), 4.82 m (1H, OCH), 5.08 q (1H, CHN), 7.16 d (2Harom),
)
Xg
Xh
77
75
126 128 (1)
136 139 (1)
)
7.38 d (2Harom
233 1.18 t (3H, CH3), 2.32 s (3H, CH3), 2.67 q (1H, CH2), 2.77 q (1H, CH2), 4.17 q
(2H, OCH2), 5.04 q (1H, CHN), 7.14 d (2Harom), 7.20 d (2Harom
253 1.17 t (3H, CH3), 2.80 q (1H, CH2), 2.89 q (1H, CH2), 4.19 q (2H, OCH2),
5.41 q (1H, CHN), 7.35 m (3Harom), 7.60 d (1Harom
225 1.28 t (3H, CH3), 2.73 q (1H, CH2), 2.84 q (1H, CH2), 4.20 q (2H, OCH2),
5.32 q (1H, CHN), 6.96 t (1Harom), 7.12 d (1Harom), 7.28 d (1Harom
185 1.00 d (6H, 2CH3), 1.26 t (3H, CH3), 2.00 m (1H, CH), 2.73 d (2H, CH2),
4.08 q (2H, OCH2), 4.14 t (1H, CHN)
211 1.17 m (1H, CH2), 1.25 t (3H, CH3), 1.35 1.67 m (7H, 4CH2), 1.82 d (2H,
CH2), 2.49 s (2H, CH2), 4.14 q (2H, OCH2)
)
Xi
79
68
72
55
96
117 119 (1)
132 134 (1)
123 125 (1)
82 84 (9)
)
Xj
)
Xk
Xl
)
Xm
110 115 (3)
XIa
XIb
161 0.053 s (9H, 3CH3), 1.40 br (1H, NH), 3.45 s (2H, CH2), 3.64 s (3H, OCH3)
175 0.056 s (9H, 3CH3), 1.28 d (3H, CH3), 1.44 br (1H, NH), 3.58 q (1H, CH),
3.70 s (3H, OCH3)
XId
XIe
XIfb
XIg
175 0.055 s (9H, 3CH3), 1.27 t (3H, CH3), 1.38 br (1H, NH), 3.41 s (2H, CH2),
4.14 q (2H, OCH2)
189 0.057 s (9H, 3CH3), 1.22 t (3H, CH3), 1.40 br (1H, NH), 2.43 t (2H, CH2),
3.03 t (2H, CH2), 4.12 q (2H, OCH2)
265 0.05 s (9H, 3CH3), 1.22 t (3H, CH3), 1.70 br (1H, NH), 2.65 d (2H, CH2),
4.08 q (2H, OCH2), 4.43 t (1H, CH), 7.17 7.38 (5Harom
)
295 0.05 s (9H, 3CH3), 1.23 t (3H, CH3), 1.68 br (1H, NH), 2.70 d (2H, CH2),
3.88 s (3H, OCH3), 4.12 q (2H, OCH2), 4.45 t (1H, CHN), 6.86 d (2Harom),
7.40 d (2Harom
)
XIh
XIi
323 0.05 s (9H, 3CH3), 1.24 t (3H, CH3), 1.34 d (6H, 2CH3), 1.72 br (1H, NH),
2.70 d (2H, CH2), 4.11 q (2H, OCH2), 4.43 t (1H, CHN), 4.76 m (1H, OCH),
6.88 d (2Harom), 7.41 d (2Harom
)
279 0.05 s (9H, 3CH3), 1.08 t (3H, CH3), 1.64 br (1H, NH), 2.24 s (3H, CH3),
2.64 d (1H, CH2), 4.06 q (2H, OCH2), 4.39 t (1H, CH), 7.04 d (2Harom), 7.32 d
(2Harom
)
XIj
XIk
299 0.05 s (9H, 3CH3), 1.08 t (3H, CH3), 1.70 br (1H, NH), 2.73 d (2H, CH2),
4.08 q (2H, OCH2), 4.85 t (1H, CH), 7.20 m (2Harom), 7.32 d (1Harom), 7.73 d
(1Harom
)
271 0.05 s (9H, 3CH3), 1.17 t (3H, CH3), 1.66 br (1H, NH), 2.66 d (2H, CH2),
4.10 q (2H, OCH2), 4.76 t (1H, CH), 6.94 t (1Harom), 7.10 d (1Harom), 7.41 d
(1Harom
)
XIl
231 0.058 s (9H, 3CH3), 1.0 d (6H, 2CH3), 1.19 t (3H, CH3), 1.41 br (1H, NH),
2.0 m (1H, CH), 2.68 d (2H, CH2), 3.47 q (1H, CHN), 4.10 q (2H, OCH2)
176 1.34 t (3H, CH3), 4.27 q (2H, OCH2), 6.45 d (1H, CH=), 7.35 m (3Harom),
7.54 t (2Harom), 7.70 d (1H, CH=)
XIIf
5
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

ORGANOSILICON SYNTHESIS OF ISOCYANATES: III.
1075
Table 2. (Contd.)
mp, C or
bp,
(p, mm)
Comp. Yield,
M+
(m/z)
C
1H NMR spectrum (CDCl3), , ppm
no.
%
XIIg
8
206 1.34 t (3H, CH3), 3.88 s (3H, OCH3), 4.27 q (2H, OCH2), 6.34 d (1H, CH=),
6.96 d (2Harom), 7.49 d (2Harom), 7.77 d (1H, CH=)
205
XIII
80 82
XIVa
XIVb
35
88
205 0.23 s (9H, 3CH3), 3.75 s (3H, OCH3), 3.96 d (2H, CH2), 5.18 br (1H, NH)
219 0.25 s (9H, 3CH3), 2.50 t (2H, CH2), 3.40 q (2H, CH2N), 3.70 s (3H, OCH3),
5.20 br (1H, NH)
XIVc
XIVd
XIVe
XIVf
XIVg
42
37
88
92
90
219 0.24 s (9H, 3CH3), 1.32 d (3H, CH3), 3.72 s (3H, OCH3), 3.92 q (1H, CH),
5.20 br (1H, NH)
219 0.23 s (9H, 3CH3), 1.27 t (3H, CH3), 3.89 d (2H, CH2), 4.20 q (2H, OCH2),
5.20 br (1H, NH)
233 0.25 s (9H, 3CH3), 1.25 t (3H, CH3), 2.50 t (2H, CH2), 3.40 q (2H, CH2N),
4.14 q (2H, OCH2) 5.19 br (1H, NH)
309 0.26 s (9H, 3CH3), 1.16 t (3H, CH3), 2.85 m (2H, CH2), 4.06 q (2H, OCH2),
5.11 q (1H, CH), 5.67 br (1H, NH), 7.24 7.36 m (5Harom
)
339 0.26 s (9H, 3CH3), 1.17 t (3H, CH3), 2.87 m (2H, CH2), 3.88 s (3H, OCH3),
4.08 q (2H, OCH2), 5.10 q (1H, CH), 5.70 br (1H, NH), 6.86 d (2Harom), 7.34 d
(2Harom
)
XIVh
XIVi
90
88
367 0.26 s (9H, 3CH3), 1.17 t (3H, CH3), 1.30 d (6H, 2CH3), 2.88 m (2H, CH2),
4.07 q (2H, OCH2), 4.80 m (1H, OCH), 5.10 q (1H, CH), 5.70 br (1H, NH),
6.86 d (2Harom), 7.34 d (2Harom
)
323 0.25 s (9H, 3CH3), 1.17 t (3H, CH3), 2.30 s (3H, CH3), 2.86 m (2H, CH2),
4.08 q (2H, OCH2), 5.11 q (1H, CH), 5.72 br (1H, NH), 6.95 d (2Harom), 7.30 d
(2Harom
343 0.28 s (9H, 3CH3), 1.18 t (3H, CH3), 2.94 m (2H, CH2), 4.08 q (2H, OCH2),
5.15 q (1H, CH), 5.80 br (1H, NH), 7.31 m (3Harom), 7.58 d (1Harom
315 0.25 s (9H, 3CH3), 1.18 t (3H, CH3), 2.86 m (2H, CH2), 4.10 q (2H, OCH2),
5.06 q (1H, CH), 5.70 br (1H, NH), 6.91 t (1Harom), 7.10 d (1Harom), 7.26 d
)
XIVj
92
90
)
XIVk
(1Harom
)
XVa
XVb
65
12
277 0.28 s (9H, 3CH3), 0.30 s (9H, 3CH3), 3.72 s (3H, OCH3), 3.90 s (2H, CH2)
291 0.29 s (9H, 3CH3), 0.31 s (9H, 3CH3), 2.46 t (2H, CH2), 3.34 t (2H, CH2N),
3.68 s (3H, OCH3)
XVc
XVd
XVe
XVf
XVg
58
63
12
8
291 0.28 s (9H, 3CH3), 0.30 s (9H, 3CH3), 1.30 d (3H, CH3), 3.70 s (3H, OCH3),
3.82 t (1H, CH)
291 0.27 s (9H, 3CH3), 0.29 s (9H, 3CH3), 1.24 t (3H, CH3), 3.86 s (2H, CH2),
4.15 q (2H, OCH2)
305 0.26 s (9H, 3CH3), 0.28 s (9H, 3CH3), 1.25 t (3H, CH3), 2.47 t (2H, CH2),
3.37 t (2H, CH2N), 4.12 q (2H, OCH2)
381 0.20 s (9H, 3CH3), 0.28 s (9H, 3CH3), 2.85 m (2H, CH2), 4.11 q (2H, OCH2),
4.98 t (1H, CHN), 7.24 7.36 m (5Harom
)
10
411 0.20 s (9H, 3CH3), 0.28 s (9H, 3CH3), 1.20 t (3H, CH3), 2.88 m (2H, CH2),
3.88 s (3H, OCH3), 4.13 q (2H, OCH2), 4.97 t (1H, CHN), 6.87 d (2Harom),
7.36 d (2Harom
)
XVh
XVi
10
12
439 0.20 s (9H, 3CH3), 0.28 s (9H, 3CH3), 1.20 t (3H, CH3), 1.32 d (6H, 2CH3),
2.89 m (2H, CH2), 4.11 q (2H, OCH2), 4.78 m (1H, OCH), 4.98 t (1H, CHN),
6.87 d (2Harom), 7.36 d (2Harom
)
395 0.20 s (9H, 3CH3), 0.28 s (9H, 3CH3), 1.20 t (3H, CH3), 2.32 s (3H, CH3),
2.88 m (2H, CH2), 4.10 q (2H, OCH2), 4.98 t (1H, CHN), 6.93 d (2Harom),
7.33 d (2Harom
)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

1076
LEBEDEV et al.
Table 2. (Contd.)
mp, C or
bp,
(p, mm)
Comp. Yield,
M+
(m/z)
C
1H NMR spectrum (CDCl3), , ppm
no.
%
XVj
8
415 0.22 s (9H, 3CH3), 0.29 s (9H, 3CH3), 1.22 t (3H, CH3), 2.96 m (2H, CH2),
4.12 q (2H, OCH2), 5.04 t (1H, CHN), 7.30 m (3Harom), 7.56 d (1Harom
)
XVk
10
387 0.20 s (9H, 3CH3), 0.28 s (9H, 3CH3), 1.21 t (3H, CH3), 2.90 m (2H, CH2),
4.12 q (2H, OCH2), 4.98 t (1H, CH), 6.89 t (1Harom), 7.08 d (1Harom), 7.24 d
(1Harom
)
XVII
30
35
20
15
12
80
68 70 (15)
68 70 (15)
75 80 (5)
63 65 (3)
119 3.81 s (2H, CH2)
119 3.93 s (2H, CH2)
133 3.14 t (2H, CH2), 3.64 t (2H, CH2N)
133 1.48 d (3H, CH3), 4.57 q (1H, CHN)
XVIIIa
XVIIIb
XVIIIc
XXI
130 133 (750) 137 3.37 s (3H, OCH3), 3.44 t (2H, CH2N), 3.49 t (2H, OCH2), 5.88 br (1H, NH)
115 117 (735) 101 3.40 t (2H, CH2N), 3.41 s (3H, OCH3), 3.52 t (2H, OCH2)
XXII
a
Elemental analysis data (C and H content) of all the individual compounds prepared were in good agreement with their empirical
b 13
formula.
C NMR spectrum (CDCl ), , ppm: 0.27 (3C, SiMe ), 14.22 (1C, CH ), 46.61 (1C, CH ), 53.39 (1C, CH), 60.26
3
C
3
3
2
29
(1C, OCH ), 126.05 (2C
3.70 (NSi).
), 126.72 (1C
), 128.30 (1C
), 146.40 (1C
), 171.54 (1C, C=O). Si (CDCl )
, ppm:
2
arom
arom
arom
arom
3
Si
c 13
C NMR spectrum (CDCl ), , ppm: 1.97 (3C, SiMe ), 14.22 (1C, CH ), 44.30 (1C, CH ), 52.71 (1C, CH), 60.27
3
C
3
3
2
29
(1C, OCH ), 126.10 (2C
), 127.20 (1C
), 128.61 (2C
), 146.42 (1C$sa 4do ), 171.96 (1C, NCO ). Si NMR spectrum
2
arom
arom
arom r m 2
(CDCl ),
, ppm: 7.38 (OSi).
3
Si
by CDCl3, and in 5 10% solutions in polar solvents
these compounds exist in an equlibrium with their
cyclic O-silyl tautomers XIa-m. The difference in the
frequency of proton resonance signals of CH or CH2
groups at the nitrogen atom in compounds IX and XI
is over 30 Hz that excludes absolutely a possibility of
the same time the resonance signal of the chiral center
protons due to the decrease in dipole moment of the
rigid structure XIf XIk is observed as a characteristic
triplet, while the higher dipole moment of the struc-
ture IXf IXk leads to revealing resonance of the CH
group proton as a broad signal. A polar solvent favors
the tautomeric transformation while in concentrated
solutions prevails structure IX (up to 90%). Tauto-
merism and ring strain in the isomers XI are probably
responsible for a gradual decomposition of com-
pounds IXe and IXj in diluted toluene solutions upon
handling so that cynnamates XIIf and XIIg obtained
in 5 8% amount according to NMR data, remain
intacted even after completing the phosgeneation.
1
appearing additional signals in H NMR spectra due
1
to spin coupling. Besides, in H NMR spectra of
alkylaromatic derivatives IXf IXk the CH2 group
resonance signal at the chiral center is observed as
two characteristic quartets, and in their rigidly fixed
tautomers XIf XIk degeneration of fine structure
leads to pseudoequivalence of the protons of CH2
group bound with asymmetric center, thus the usual
doublet of signals is observed in this group spectra. At
OSiMe3
R C(X) C OR
NH
Me3Si
IXa IXl
R C(X) C OR
NH
R CH=CHC(O)OR + [Me3SiNH2]
XIIf, XIIg
(Me3Si)2NH + NH3,
O
..
XIa XIl
R = H (a e), C6H5 (f), 4-CH3OC6H4 (g), 4-(CH3)2CHOC6H4 (h), 4-CH3C6H4 (i), 2-ClC6H4 (j), 2-thenyl (k), (CH3)2CH
(l); R1 = CH3 (a c), C2H5 (d l); X = H (a, d), CH2 (b, e l), CH3 (c).
It is known [8 16] that 1,3-(N,O)-migration of silyl
substituent is characteristic of silylamides, acetic and
trifluoroacetic acid hydrazide silicon derivatives, some
N-silylurethanes, N-trimethylsilylnitrocarbamates, and
also of the silicon-containing carbazic acid derivatives.
The 1,4- and 1,5-(N,O)-silatropic transformations of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

ORGANOSILICON SYNTHESIS OF ISOCYANATES: III.
1077
silylated aminoesters found by us can be regarded as
an example of far intramolecular donor-acceptor inter-
action of silicon and oxygen atoms.
the bisilylated carbamates XVa, XVc, and XVd
prevail. Their content in the reaction mixture falls to
the range of 58 65 mol%. In the case of -amino-
esters, mono-O-silyl urethanes XIVb, XIVe-XIVk
prevail: the content is 88 92 mol% that is caused
evidently by the increase in the basicity of their nitro-
gen atom as compared to the compounds XIVa,
XIVc, and XIVd because here the ester group is
located remotely and aromatic substituent is con-
jugated with NHCOOSiMe3 group. Probably by the
same reason N-siloxycarbonylation of -alanine ester
hydrochlorides and its aromatic derivatives results in
formation of known bis-trimethylsilylcarbamate XIII
[20] as a by-product. Because of high boiling points
of alkylaromatic isocyanatoesters Xf Xk their prepa-
ration by means of the corresponding urethane pyro-
lysis in the presence of phenyltrichlorosilane is im-
possible. Transformation of the obtained mixtures of
urerthans XIVa XIVk and XVa XVk to isocyanates
Xa Xk was carried out by treating with 10% excess
of phosgene used as 25% toluene solution at 0 C.
Under these conditions in the case of aliphatic amino-
esters the corresponding isocyanatocarboxylic acid
ester chlorides XVIIIa XVIIIc are formed as by-
products. In the case of glycine the substituted aziridine
XVII is additionally formed. Structures of all these
It has been reported previously [17 19] that silyla-
tion of aminoesters and their hydrochlorides proceeds
in high yield under the action of diethylaminotrime-
thylsilane. But yield of isocyanates Xa Xl in the reac-
tion of N-trimethylsilylaminoesters IXa IXl with
phosgene does not exceed 60% that can be probably
explained by side formation of insoluble amino esters
arising from the evolution of hydrogen chloride in the
reaction course [18]. Due to that the total yield of iso-
cyanates on an account of starting compounds II and
VIII even in the case of silylation with Et2NSiMe3
is far below 50%. Considering this situation we
studied the alternative two-stage approach to iso-
cyanates X which includes N-siloxycarbonylation of
amino ester hydrochlorides with the subsequent phos-
geneation of the urethanes obtained.
In the preceeding report [1] we have established
that amine hydrochlorides react with hexamethyldi-
silazane and CO2 to form a mixture of mono- and bi-
silylurethanes. Under the analogous conditions, ali-
phatic VIIIa VIIIe and alkylaromatic IIa IIc, IIg
IIi aminoester hydrochlorides react with hexamethyl-
disilazane CO2 system to generate quantitatively a
mixture of mono- (XIVa XIVk) and bi- (XVa XVk)
silylurethanes. The ratio of these compounds depends
on the electronic structure of starting aminoesters.
Thus, in the case of glycine and alanine derivatives
1
compounds were established on the basis of H NMR
and mass spectral data of isolated phosgeneation
products. Treating the byproducts XVIIIa XVIIIc
with methanol or ethanol in the presence of triethyl-
amine at 0 C lead to quantitative formation of iso-
cyanates Xa Xd in total yield reaching 85%.
VIIIa VIIIe, IIa IIc, IIg IIi + (Me3Si)2NH + CO2
Me3SiNHCOOSiMe3 + RNHCOOSiMe3
NH3
XIII
XIVa XIVk
25 C
Xa Xk
Me3SiCl,
CO2
R OH/Et3N
COCl2
+ RN(SiMe3)COOSiMe3
[RN(COCl)COOSiMe3]
Me3SiCl
XVa XVk
XVIa XVIk
O=C CH2
40 C
R1OSiMe3,
CO2
+ ClC(O) X N=C=O,
N C(O)Cl
XVII
XVIIIa XVIIIc
XIV XVI, R = CH3OC(O)CH2 (a), CH3OC(O)(CH2)2 (b), CH3OC(O)CH(CH3) (c), C2H5OC(O)CH2 (d), C2H5OC(O)
(CH2)2 (e), C2H5OC(O)CH2CH(C6H5) (f), 4-CH3OC6H4CHCH2COOC2H5 (g), 4-(CH3)2CHOC6H4CHCH2COOC2H5 (h),
4-CH3C6H4CHCH2COOC2H5 (i), 2-ClC6H4CHCH2COOC2H5 (j); R = XCHCH2COOC2H5, X = 2-thenyl (k). XVIII, X =
CH2 (a), (CH2)2 (b), CHCH3 (c). R = Me, Et.
Spectral characteristics and yields of compounds
X, XIV, XV, XVII, and XVIII are listed in the Table
2. It is evident that phosgeneation of a mixture of
urethanes XIV and XV proceeds through the inter-
mediate generation of carbaminoyl chlorides XVI.
Investigation of temperature effect on the phosgena-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 7 2006

1078
LEBEDEV et al.
tion products yield showed that careful slow increase
in temperature to 25 C and starting distillation of
volatile compounds only after the complete elimina-
tion of carbon dioxide leads to predominate formation
of isocyanates Xa Xk through elimination of tri-
methylchlorosilane and CO2 from the intermediates
XVIa XVIk. When the temperature growths fastly,
the carbamoyl chlorides XVIa XVIe decomposition
proceeds vigorously. In this case together with the tri-
methylchlorosilane elimination leading to formation
of isocyanates Xa Xe, elimination of methoxy- or
ethoxytrimethylsilane takes place which affords com-
pounds XVII and XVIIIa XVIIIc. In the case of
glycine derivatives their yield at 60 C reached 30%
and 35% respectively. Note that formation of iso-
cyanatocarboxylic acid chlorides of the type XVIII
was previously observed in the course of phosgenea-
tion of N-siloxycarbonylaminoacids trimethylsilyl
esters [21]. In our case their generation is the first
example of alkoxytrimethylsilane elimination with
the participation of ester group. Thus, N-siloxycar-
bonylation of aminoester hydrochlorides with the
subsequent phosgeneation of the formed O-silyl and
N,O-bis-silylurethanes is an effective method for
preparing isocyanatocarboxylic acid esters. It may be
extended on the synthesis of the other hardly available
isocyanates. We have reported [1] on the formation of
2-methoxyethylisocyanate in 60% yield by pyrolysis
of 3:7 mixture of urethanes XIX/XX in the presence
of PhSiCl3. Phosgeneation of the same mixture in
methylene chloride permitted to increase the iso-
cyanate XXII yield to 80%.
MeO(CH2)2NHCOOSiMe3 + MeO(CH2)2N(SiMe3)COOSiMe3
XIX
XX
COCl2
MeO(CH2)2NHC(O)Cl + MeO(CH2)2N=C=O.
HCl, CO2
Me3SiCl
XXI
XXII, 80%
Formation in small amount (8 12%) of carbamoyl
chloride XXI in the above reaction was unexpected.
Formally this substance may be regarded as the
product of urethane XIX transacylation. But elucida-
tion of real mechanism of its formation needs addi-
tional studies.
mixture, an additional amount of thionyl chloride
(1.5 mol per 1 mol of aminoacid) was added dropwise
and reaction mixture was refluxed additionally for
1 h. When no free aminoacid could be detected in the
analyzed sample, solvent was distilled off, 50 ml of
corresponding alcohol was added and aminoacid
hydrochloride obtained was precipitated by addition
of 350 450 ml of dry ether. The precipitate formed
was filtered off, washed with 150 ml of anhydrous
ether and dried at 50 C. Compounds IIa IIo were
obtained by this procedure. In the case of other
aminoacids the obtained hydrochloride was suspended
in 400 ml of toluene and treated at 0 C under vigo-
rous stirring with 100 ml of 38% aqueous sodium
hydroxide. Filtration of insoluble aminoesters or
evaporation of organic phase gave compounds Va Vj
in 90 92% yield. Aminoesters Va, Vb were addi-
tionally distilled in a vacuum. Boiling points 120
122 C (2 mm Hg) and 102 105 C (1 mm Hg),
respectively.
EXPERIMENTAL
1
The H NMR spectra were taken in CDCl3 on a
Bruker AM-360 spectrometer (360.14 MHz). Mass
spectra were obtained on a MAT-311A spectrometer
at the electron ionization energy 70 eV with direct
injection in the ion source.
Synthesis of -aminoacids ester hydrochlorides.
To a solution of 1 mol of aminoacid Ia Io, III or IV,
3- or 4-aminobenzoic acid in 750 ml of corresponding
absolute alcohol (methanol or ethanol) or to the sus-
pension of 1 mol of antranylic, 2-amino-4-chloroben-
zoic or aminoterephthalic acid in 1.7 l of alcohol
178.5 g (or 240 g in the case of aromatic ortho-
aminoacid) of freshly distilled thionyl chloride was
added at the initial temperature 50 C with the addition
rate providing slight boiling of reaction mixture. After
the addition was complete the resulting mixture was
refluxed for 2 h. A sample (about 0.5 ml) was taken,
solvent was evaporated from it and the aminoacid
Silylation of aromatic aminoacid esters. A mix-
ture of 1 mol of aminoester Va Vj, 96 g of hexa-
methyldisilazane and 2 3 drops of concentrated sul-
furic acid was gradually heated to 170 180 C, kept
for 30 min and distilled in a vacuum to give com-
pounds VIa VIj. For the ester VIb, n2D0 1.4572.
Silylation of aminoester hydrochlorides. To a
suspension of 1 mol of hydrochloride VIIIa VIIIe,
IIjin 400 ml of anhydrous benzene a mixture of 88 g
1
content in the residue was evaluated by means of H
NMR spectroscopy. If it still contained in the reaction
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ORGANOSILICON SYNTHESIS OF ISOCYANATES: III.
1079
of hexamethyldisilazane and 111 g of triethylamine
(method a) or a mixture of 119 g of trimethylchloro-
silane, 222 g of triethylamine and 400 ml of benzene
(method b) was added dropwise. After complete ad-
dition the reaction mixture was refluxed with stirring
for 2 h, then cooled, filtered from the salt precipitate,
and distilled in a vacuum to obtain compounds IXa
IXe, and IXl in 40 57% yield. The n2D0 values of
compounds are: IXa 1.4210, IXc 1.4230, IXd 1.2193,
IXe 1.4240.
urethanes XIVa k, XVa XVk in 99 100% yield on
the starting aminoester hydrochloride. In the case of
compounds XIVb, XVe XVk after volatile solvent
removing the residue was kept at 10 C for 120 h.
Liquid mixture of urethanes was separated by filtra-
tion from the crystals of carbamate XIII. The latter
was washed with cold hexane and distilled in a
vacuum.
Phosgeneation of aminoester based O-silyl and
N,O-bis-silylurethane mixture. A solution of a
mixture of urethanes XIVa XIVk, XVa XVk in
40 ml of toluene or a solution of 3:7 mixture of
urethanes XIX, XX in 40 ml of methylene chloride
(1 mol on per 1 mole of unsubstituted aminoester)
was added dropwise with stirring at 0 C to a solution
of 21.8 g of COCl2 in 80 ml of toluene or methylene
chloride (for a mixture of compounds XIX and XX).
After the addition was complete the reaction mixture
was slowly heated to 25 C, and kept to the end of
of CO2 evolution. Trimethylchlorosilane and solvent
were distilled off in a 50 mm Hg vacuum. Solvent
was removed from the residue, and the isocyanates
obtained were distilled in a 3 mm Hg vacuum. The
distillate was distilled once again to remove the
solvent admixture. In the case of isocyanates Xa Xe,
XXII a rectification column was used. Compounds
Xa Xk, XXI, and XXII were obtained by this pro-
cedure. In the case of isocyanates Xa Xe the isocya-
nates obtained contained 8 12% of by-products XVII
and XVIIIa XVIIIc. In some experiments after the
complete addition of a mixture of urethanes reaction
mixture was quickly heated to 40 C not allowing its
overburst, and the distillation of volatile products was
begun immediately. In these cases a significant
increase in the yield of by-products, compounds XVII
and XVIIIa XVIIIc was observed. These substances
were distilled in a vacuum together with the target
isocyanates Xa d. For the transformation of the by-
products to the target isocyanates their content in the
Two-stage silylation of aminoester hydrochlo-
rides. To a suspension of 1 mol of hydrochlorides IIa
IIc, IIg IIj, IIo in 400 ml of anhydrous benzene a
mixture of 88 g of hexamethyldisilazane and 111 g of
triethylamine was added dropwise with stirring. After
complete addition the reaction mixture was refluxed
with stirring for 2 h, then cooled, and the salt preci-
pitate was filtered off. Filtrate was treated dropwise
with a mixture of 72 g of trimethylchlorosilane, 67 g
of triethylamine, and 100 ml of benzene. Resulting
mixture was refluxed for 1 h, cooled, and the salt
precipitate was filtered off. Filtrate was distilled in a
vacuum to give compounds IXf IXk, IXm in 70
75% yield and silyl derivative IXl in 60% yield. The
n2D0 values for the compounds are: IXf 1.4860, IXm
1.4614.
Phosgeneation of the aminoester N-rimethylsilyl
derivatives. A solution of 0.2 mol of silylamine Va
Vj, IXa-IXm in 40 ml of toluene was added dropwise
with stirring at 0 C to a solution of 2.18 g of COCl2
in 80 ml of toluene. Complete dissolution of phos-
geneated compounds was if necessary achieved by the
addition of diethylene glycol dimethyl ether. When
the addition of reagent was complete, trimethylchlo-
rosilane and toluene were distiled off from the reac-
tion mixture until the temperature of the vapor
achieved 105 C. The residue was distilled in a
vacuum to remove toluene, diglime, and obtained
isocyanate. The last fraction was distilled again to
remove toluene and diglime. In the case of isoc-
yanates Xa Xe a rectification column was used.
Compounds VIIa VIIj, Xa Xm were obtained
analogously. The n2D0 values for the compounds: VIIa
1.5189, VIIb 1.4647, Xa 1.4230, Xf 1.5070, Xm
1.4643.
1
mixture was evaluated from H NMR spectral data. A
mixture of compounds Xa Xe, XVII, and XVIIIa
XVIIIc twice diluted with toluene was cooled to 0 C,
and cool alcohol (ethanol or methanol) triethylamine
mixture (equimolar to compound XVII and XVIIIa
XVIIIc content) was added to it. After the addition
was complete the resulting mixture was stirred for
30 min, filtered from the ammonium salt precipitate
and distilled in a vacuum to give pure isocyanate
Xa Xe.
N-Siloxylcarbonylation of aminoester hydro-
chlorides. A suspension of 2 mol of a compound
VIIIa VIIIe, IIa IIc, IIg IIi in a mixture of 200 g
of hexamethyldisilazane and 200 g of anhydrous
benzene or toluene was heated under CO2 flow for 5 h
at 80 90 C. After the completing the gas bubbling the
reaction mixture was cooled and the precipitate
formed was filtered off. The hexamethyldisilazane
excess and solvent were removed to give a mixture of
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