Aminomethylation of Thioureas with N,N-Dimethyl-1-(triethylsiloxy)methanamine, Involving Amino Group Exchange

Article abstract of DOI:10.1134/S1070428019110198

The O-triethylsilylated hemiaminal Et₃SiOCH₂NMe₂ readily transfers the Me₂NCH₂-group to various thioureas under mild conditions and without catalysts or co-reagents. In the reaction with PhNHC(=S)·NHPh, the initially formed mono-substituted derivative PhNHC(=S)NPhCH₂NMe₂ readily rearranges to produce the unsymmetrical thiourea PhNHC(=S)NMe₂ and hexahydro-1,3,5-triphenyl-1,3,5-triazine.

Full text of DOI:10.1134/S1070428019110198

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2019, Vol. 55, No. 11, pp. 1764–1771. © Pleiades Publishing, Ltd., 2019.
Aminomethylation of Thioureas
with N,N-Dimethyl-1-(triethylsiloxy)methanamine,
1
Involving Amino Group Exchange
a
a
a
a,
J. McMahon , H. K. Sharma , A. Metta-Magaña , and K. H. Pannell *
a
Department of Chemistry, The University of Texas at El Paso, El Paso, Texas, 79968 USA
e-mail: kpannell@utep.edu
*
Received June 13, 2019; revised July 10, 2019; accepted September 3, 2019
Abstract—The O-triethylsilylated hemiaminal Et
various thioureas under mild conditions and without catalysts or co-reagents. In the reaction with PhNHC(=S)·
NHPh, the initially formed mono-substituted derivative PhNHC(=S)NPhCH NMe readily rearranges to
produce the unsymmetrical thiourea PhNHC(=S)NMe and hexahydro-1,3,5-triphenyl-1,3,5-triazine.
3 2 2 2 2
SiOCH NMe readily transfers the Me NCH -group to
2
2
2
Keywords: O-silylated hemiaminal, aminomethylation, thioureas, thiourea rearrangements
DOI: 10.1134/S1070428019110198
Thioureas have long been studied as useful
synthons and bioactive materials [1], and their
aminomethylation reactions have received attention
The well-known Mannich reagent N,N,N',N'-
tetramethyldiaminomethane (Me NCH NMe ) has also
2
2
2
been shown to react with thiourea to form a similar
bis-Me NCH -substituted product that is a useful
[2]. For example, the reaction of the parent thiourea,
2
2
H N(C=S)NH , with paraformaldehyde and piperidine
has been shown to lead to both mono- and di-
substituted materials, as illustrated in reaction (1)
reagent for further reaction with primary amines to
form 1,3,5-triazinane-2-thiones [2]. However, this rea-
gent needs the presence of metal catalysts, e.g. Cu or
Sm, reaction (2) (Scheme 2) [2b].
2
2
(
Scheme 1) [2a].
Scheme 1.
S
S
S
NH
CH O
NH
CH O
N
N
H
NH2
N
N
N
N
(1)
H N
2
NH2
H
H
2
2
Scheme 2.
S
S
R
HN
N
(
Me N) CH
RNH2
2
2
2
(
2)
H N
2
NH2
SmCl3
Me N
N
N
NMe2
SmCl3
2
H
H
S
N
H
N,N-Dimethyl-1-trimethylsiloxymethanamine Me3·
Me NCH X, with excess N,N-dimethyl-1-trimethyl-
2 2
SiOCH NMe2 was first synthesized in 1981 by
silylmethan-amine to form diamines [reaction (3a)],
and with hydroaminosilane BuNHSiMe3 to
form hexahydro-1,3,5-tributyl-1,3,5-triazine [reaction
(3b)] [4]
2
the Mironov’s group [3] by the reaction of Me NSiMe3
2
with formaldehyde. The authors demonstrated
its reactions with halosilanes R SiX to form
3
1
This article is dedicated to many excellent Russian exponents and proponents of organosilicon chemistry, past, present, and future.
1
764

AMINOMETHYLATION OF THIOUREAS
1765
Me SiOCH NMe + Me SiX →
thiourea 2, regardless of the stoichiometry of the
reaction. Presumably, the restricted geometry of the
NH bonds in 4 accounts for this extra reactivity,
although precisely how is outside the scope of our
present study.
3
2
2
3
Me NCH NMe + Me SiOSiMe
(3a)
(3b)
2
2
2
3
3
3
Me SiOCH NMe + 3 Me SiNHBu →
3 2 2 3
(
BuNCH ) + 1.5 Me SiOSiMe
2 3 3 3
We earlier reported the utility of N,N-dimethyl-1-
triethylsiloxymethanamine Et SiOCH NMe (1) (an
The single crystal structure of 1,3-bis(N,N-
dimethylaminomethyl]-1,3-dihydro-2H-imidazole-2-
thione (7) is presented in Fig. 1. The molecule has a C
3
2
2
2
O-silylated hemiaminal) as a versatile and very efficient
aminomethylating reagent that requires neither cata-
lysts nor high temperatures [5–7]. Thus, compound 1
readily reacts with a range of EH, E = O, S, N, mate-
rials to form the corresponding E–CH NMe products
symmetry through the C=S bond, and the bond lengths
and angles are as expected. The crystal structure is
2
stabilized by hydrogen bonds (HBs) between N and
4
B
2
2
2
2
H
(2.850 Å) forming R (6) motifs, and generating
in high yield. For the corresponding E = P chemistry,
catalysts are required for efficient chemistry.
chains linked by this motif (Fig. 2). The 3-D
1
architecture is generated by the motif C (12) formed
2
1
by the bidentate interaction of S with two symmet-
We now report the utility of 1 for aminomethy-
lation of thioureas 2, 3, and 4, that results in new
previously unknown materials and surprising che-
mistry (Scheme 3).
4
A
rically equivalent H (2.876 Å).
The reaction between 1 and N,N-diphenylthiourea
(3) was more interesting and produced new chemistry
1
13
as opposed to simply new products. By H and
C
The reactions of compound 1 were studied in
dichloromethane without any catalytic reagent and
were fast and completed in a few hours at room
NMR monitoring we could observe the rapid
formation of a mono-aminomethylation product,
1
3
1
PhNH(C=S)PhNCH NMe (8). However, all attempts
2 2
temperature as determined by C and H NMR
monitoring. The reactions of both N,N-dimethyl-
thiourea (2) and 1,3-dihydroimidazole-2-thione (4)
were unremarkable and led initially to mono-
substitution in both cases to form compounds 5 and 6,
respectively, reactions (4) and (5) (Scheme 4). The
reaction of imidazole 4 continued in the presence of
excess 1 to form disubstituted product 7 (both 6 and 7
are new compounds). Contrary to the chemistry of 4,
we never observed a second substitution in the case of
to isolate this material resulted in the recovery of two
major products, the asymmetrical thiourea PhNH(C=S)·
NMe2 (9) [8], and hexahydro-1,3,5-triphenyl-1,3,5-
triazine (10) (Scheme 5). This chemistry represents a
new molecular rearrangement for such a structural unit.
If the initial reaction between compounds 1 and 3 is
monitored after the reaction to form 8 has gone to
completion, it can be seen that 8 is slowly converted to
9 and 10, even at room temperature. However, if the
Scheme 3.
S
S
S
HN
NH
MeHN
NHMe
PhHN
NHPh
2
3
4
Scheme 4.
S
S
1
(
4)
N
N
H
N
H
N
N
_Et
SiOH
3
H
2
5
S
S
S
Me N
2
1
1
NH
N
NMe2
N
NMe2
(5)
HN
_
HN
_
N
Et SiOH
3
Et SiOH
3
4
6
7
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 11 2019

1
766
McMAHON et al.
Fig. 1. Thermal ellipsoid rendering of molecule 7 (the
thermal ellipsoids are drawn at a 50% probability level and
hydrogens are drawn as spheres of arbitrary radii).
initially formed solution of 8 is heated to 60°C, the
transformation is complete within 40 min.
A plausible mechanism associated with this
transformation, involving an intramolecular base
substitution at the thiocarbonyl group by the strongly
basic Me N functionality, is outlined in Scheme 6.
2
Attempted isolation of triamine 8 using many
solvent systems to recrystallize the solid gave a
product that spectroscopically appeared to be pure.
Sometimes from such attempts, in addition to 9 and 10,
we isolated small amounts of a new aminomethanol,
PhHN(C=S)NPhCH OH (11), and could obtain a crys-
tal structure of this unusual material (Fig. 3).
Fig. 2. Views of (a) the chain formed via intermolecular
CH···N and CH···S HBs and (b) crystal packing of com-
pound 7, showing the central HB chain formed by CH···N
HBs and its interaction with neighboring chains through
CH···S HBs, and (c) lateral view of the same crystal
packing.
2
In the solid state, compound 11 forms an
intramolecular HB with the sulfur atom as acceptor
1
1
(
2.629 Å), while forming chains through the O -H···N
HBs (2.209 Å). At the same time, the C–N and C=S
bonds show no significant differentiation in com-
parison to 7, suggesting that the electronic factors are
similar. The presence of the phenyl group reduces the
conjugation of the nitrogen lone pair with the C−S
system, as shown by a comparison of the structure in
We surmised that 11 was formed by the hydrolysis
of 8 by residual water in our dried solvent systems and
thus attempted a treatment of 8 with water. This
experiment resulted in no identifiable products.
In another attempt to derivatize 8 we treated it with
MeI hoping to obtain a quaternary ammonium salt.
This reaction led only to the isolation of methyl
N,N'-diphenylcarbamimidothioate (13). After several
attempts to get suitable crystals, an acceptable structure
focus with that of the related compound [CH HN(C=S)·
3
NHCH OH] (12) [9]. The C–S bond distance of
2
1
1
.728(8) Å in 12 is considerably reduced compared to
.6870(11) and 1.678(3) Å for 7 and 11, respectively.
Furthermore, in the case of 12 the intra-molecular HB
is absent, indicating that it is probably the result of
steric interactions due to the phenyl rings in compound 11.
was solved in terms of R (Table 1), although with a
1
high R descriptor (Fig. 4). The structure data collected
1
at 100 K showed 4 symmetrically independent mole-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 11 2019

AMINOMETHYLATION OF THIOUREAS
1767
Table 1. Principal crystallographic parameters of compounds 7, 11, and 12
Parameter
7
11
12
Formula
MW
C
9
H
18
N
4
S
C
20HN
2
OS
14 14 2
C H N S
214.33
317.29
Orthorhombic
242.33
Monoclinic
P2 /c
Crystal system
Space group
Z
Monoclinic
C2/c
Pca2
1
1
4
4
16
8.6216(6)
15.5092(11)
38.094(3)
90
a, Å
8.2405(2)
11.6742(3)
11.8213(3)
90
18.932(3)
5.5591(8)
12.4216(18)
90
b, Å
c, Å
α, deg
β, deg
95.6500(10)
90
93.820
γ, deg
90
90
90
3
V, Å
1131.70(5)
13541
1307.3(3)
14194
5082.39
8701
Reflections used
R
int
0.0311
0.0418
0.1214
0.1195
2.79, 25.0
100(2)
R
1
[I > 2σ(I)]
0.0304
0.0414
q
min, qmax, deg
3.04, 30.99
100(2)
2.15, 28.28
298(2)
T, K
cules in an asymmetric unit cell for a total of 16 mole-
cules in the unit cell.
Secondly, the N–C bond distances to the central
carbon in salt 14 are statistically equivalent [1.340(6)
and 1.309(7) Å], indicating a significant amount of posi-
tive charge delocalization involving both N atoms. The
1
1
2
1
Examination of the N –C [1.366(9) Å] and N –C
1.288(9) Å] distances in compound 13 clearly reveals
[
1
1
2
3
2
values for the N –C –N angle [122(1)° and 125.5(5)° in
3 and 14, respectively] and C–S bond length [1.807(15)
distinctions between the sp -C–N and sp -C–N bond
lengths, whereas the Cphenyl–N bond lengths are equi-
valent: 1.413(8) and 1.425(9) Å, respectively. These
observations apply to all the 4 conformers in the
asymmetric unit. With respect to the packing, the NH
1
and 1.750(6) Å] are statistically not differentiable. The
N–Cphenyl distances in salt 14 are similar to those in the
neutral compound and, as might be expected, NH···N
HBs are replaced by NH···I interactions.
2
hydrogen forms HBs with the sp -C–N nitrogen of a
neighboring molecule, generating a chain of the type
Overall, the chemistry delineated in this article
·
··A···B···A···B···. The unit cell contains two different
shows that 1 is an efficient, low energy, Me NCH -
2
2
chains: one formed by conformers 1aa and 2ab
transfer agent to thioureas and requires no catalyst.
Additionally, it is clear that a significant new
chemistry is to be obtained by further investigation of
such simple materials. Scheme 7 illustrates the overall
chemistry of compound 8.
2
3
3
4
1
1
[
N ···H N–N (2.138 Å), N ···H N–N (2.238 Å)] and
8
5
5
the other, by conformers 3ac and 4ad [N ···H N–N
2.199 Å), N ···H N–N (2.261 Å)].
6
7
7
(
It is of interest to compare the neutral molecule 13
with its HI salt 14, reported in [10]. The first striking
difference is in the conformation adopted by the
charged compound (Fig. 4), where the two phenyl
groups appear to form a π-stacking motif, although the
phenyl rings are divergent rather than parallel.
EXPERIMENTAL
All manipulations were carried out under an argon
atmosphere using Schlenk or vacuum line techniques.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 11 2019

1
768
McMAHON et al.
Scheme 5. Chemical transformations in the reaction between 1 and PhNH(C=S)NHPh.
Ph
S
S
S
N
1
Δ
+
PhHN
NHPh
_
PhHN
N
NMe
2
PhHN
NMe2
Et SiOH
3
N
N
Ph
Ph
Ph
3
8
9
10
Scheme 6. Proposed mechanism for transformation of compound 8 to 10.
Ph
N
S
S
NMe2
S
x 3
NMe2
H C NPh
2
+
PhHN
PhHN
NMe2
PhHN
N
N
N
Ph
Ph
Ph
PhN
8
9
10
THF was distilled under nitrogen from benzophenone
ketyl prior to use. Hexane, benzene, and toluene were
dried over sodium metal and distilled before use.
bottom flask was charged with 0.22 g (1.16 mmol) of
Et SiOCH NMe and 0.06 g (0.57 mmol) of 1,3-dime-
3
2
2
thylthiourea in 5 mL dichloromethane. The solution
was stirred overnight at room temperature, and the
solvent and triethylsilanol were removed under
vacuum to obtain 1,2-dimethyl-1-[(dimethylamino)me-
thyl]thiourea MeNH(C=S)NMeCH NMe (5) as a
1
,3-Dimethylthiourea, 1,3-diphenylthiourea, and imi-
dazole-2-thiol were purchased from Sigma-Aldrich.
Et SiOCH NMe was synthesized by the reported method
3
2
2
[
11]. The NMR spectra were recorded on 300 MHz
2
2
Bruker spectrometer in CDCl . The SC-XRD analysis
colorless oil, yield 90%. The material is thermally
stable and does not undergo decomposition even on
heating at 70°C for 20 h. H NMR spectrum, δ, ppm:
3
of 7 was performed using a Bruker Venture Duo diff-
ractometer with a micro-source and a Photon 200 de-
tector, and the data for 11 were collected on a Bruker
APEX CCD diffractometer. Both structures were
solved using APEX3 crystallography software suite [12].
1
2.18 s (6H, CH ), 3.03 d (3H, CH , J 4.8 Hz), 3.32 s
3
3
1
3
(3H, CH ), 3.75 s (2H, CH ), 8.21 br.s (1H, NH).
C
3
2
NMR spectrum, δ, ppm: 32.2 (Me), 41.4 (Me), 42.1
(
Me), 76.4 (CH ), 186.6 (C=S).
2
Reaction of Et SiOCH NMe with 1,3-dimethyl-
3
2
2
thiourea. In a typical experiment, a 10 mL round-
Reaction of Et SiOCH NMe with imidazole-2-
3
2
2
thiol in a 1 : 1 molar ratio. A 20 mL round-bottom
flask was charged with 0.125 g (1.25 mmol) of imi-
dazole-2-thiol and 0.48 g (0.25 mmol) of 1 in 10 mL of
dichloromethane. The solution was stirred overnight at
room temperature. Volatiles were then removed under
vacuum to leave a brown solid, repeated recrys-
tallization of which from a mixture of hexane and
dichloromethane gave a 0.7 : 1.0 mixture of 1-(dime-
thylamino)imidazole-2-thiol (6) and 1,3-bis(dimethyl-
amino)imidazole-2-thiol (7).
1
-(N,N-Dimethylaminomethyl)-1,3-dihydro-2H-
1
imidazole-2-thione (6). H NMR spectrum, δ, ppm:
.33 s (6H, NMe ), 4.76 s (2H, CH ), 6.70 d (1H,
2
2
2
CH=CH, J 3.0 Hz), 6.82 d (1H, CH=CH, J 3.0 Hz),
1
3
1
0.59 br.s (1H, NH). C NMR spectrum, δ, ppm: 42.5
(
NMe ), 68.0 (CH ), 113.86, 118.1 (C=C), 161.4 (C=S).
2
2
1
,3-Bis(N,N-dimethylaminomethyl)-1,3-dihydro-
Fig. 3. Thermal ellipsoid rendering of molecule 11 (the
thermal ellipsoids are drawn at a 50% probability level and
hydrogens are drawn as spheres of arbitrary radii).
1
2
H-imidazole-2-thione (7). H NMR spectrum, δ, ppm:
2.37 s (6H, NMe ), 4.81 s (2H, CH ), 6.83 s (2H,
2
2
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 11 2019

AMINOMETHYLATION OF THIOUREAS
1769
(
a)
(b)
(
c)
(d)
Fig. 4. (a) Ortep view of molecule 13 at a 50% of probability level (shown is just one of the 4 structures in the asymmetric unit cell)
and (b) chains formed by interaction of the four conformers: (blue) conformer 1aa, (green) conformer 2ab, (yellow) conformer 3ac,
and (red) conformer 4ad. (c) Structure of HI salt 14 [6] and (d) side view of the HI salt.
1
3
CH=CH). C NMR spectrum, δ, ppm: 42.5 (NMe2),
The reaction between 1 and 1,3-diphenyl thiourea
in 2 : 1 molar ratio, too, resulted in exclusive formation
of 8; unexpectedly, no disubstituted product was
obtained. Due to the limited thermal stability of 8, we
6
4
8.8 (CH ), 116.9 (C=C), 163.7 (C=S). Found, %: C
8.75; H 8.13. Calculated, %: C 50.44; H 8.46.
2
Repeating the reaction of 1 with imidazole-2-thio in
: 2 molar ratio in dichloromethane gave a 1 : 2
mixture of compounds 6 and 7, but using a larger
excess of 1 (4-fold) gave compound 7 as a single
product (yield 85%).
1
could not perform its CHN analysis. H NMR spec-
1
trum, δ, ppm: 2.30 s (6H, NMe ), 4.40 s (2H, CH ),
2
2
1
3
7
.20–7.41 m (10H), 7.80 br.s (1H, NH). C NMR
spectrum, δ, ppm: 41.4 (Me), 41.9 (Me) 77.3 (CH ),
,
2
1
24.6, 125.1, 125.3, 127.5, 128.2, 128.5, 129.5, 139.5
Reaction of Et SiOCH NMe with 1,3-diphenyl-
thiourea. A 20 mL round-bottom flask was charged
3
2
2
(Ph), 184.7 (C=S).
with 0.165 g (0.88 mmol) of Et SiOCH NMe and
Thermal rearrangement of 1-[(dimethylamino)-
methyl]-1,2-diphenylthiourea (8). A Pyrex NMR
tube was charged with 0.183 g (0.64 mmol) of
3
2
2
0
.2 g (0.88 mmol) of 1,3-diphenylthiourea in 10 mL of
dichloromethane. The solution was stirred overnight
at room temperature, after which the solvent and
triethylsilanol were removed under vacuum to obtain
compound 8 in 0.3 mL of CDCl . The tube was sealed
3
under vacuum and immersed in an oil bath maintained
1
29
13
1
-[(dimethylamino)methyl]-1,2-diphenylthiourea Ph·
at 70°C. After 5 h, the H, Si and C NMR moni-
NH(C=S)NPhCH NMe (8), yield 80%. This new
toring showed a quantitative transformation of 8 to
2
2
material is thermally labile and undergoes slow trans-
formation even at room temperature.
1,1-dimethyl-3-phenylthiourea PhNH(C=S)NMe (9) [8]
2
and hexahydro-1,3,5-triphenyltriazine (PhNCH ) (10).
2
3
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 11 2019

1
770
McMAHON et al.
Scheme 7. Overall chemistry of 8.
Ph
Ph
NHPh
S
N
N
S
MeI
Δ
+
Me NCH I
PhN
Me N
S
+
2
2
N
PhN
NHPh
PhHN
NMe2
Ph
2
1
3
8
9
10
H O ?
2
NHPh
S
PhN
HO
1
1
Formation of N-hydroxymethyl-N,N-diphenyl-
mixture was stirred overnight at room temperature.
The solvent and triethylsilanol were removed under
vacuum overnight to isolate 1-[(dimethylamino)-
methyl]-1,2-dimethylurea MeNH(C=O)NMeCH NMe
thiourea PhNH(C=S)NPhCH OH (11). A 0.05 g of
2
thiourea 8 was dissolved in 1 mL of dichloromethane
in a screw cap vial and left in the refrigerator for a
2
2
week. A mixture of thioureas PhNH(C=S)NPhCH OH
as a colorless oil, yield 80% The material is thermally
stable and does not undergo significant decomposition
even on heating at 45°C for 2 days. H NMR spectrum,
2
(11), PhNH(C=S)NHPh, and compound 8 was
1
obtained as white crystals. Mechanical separation
permitted isolation of thiourea 11 which was subjected
to XRD analysis. H NMR spectrum, δ, ppm: 4.88 t
δ, ppm: 2.13 s (6H, CH ), 2.69 d (3H, CH , J 4.8 Hz),
3
3
1
2.87 s (3H, CH ), 3.51 s (2H, CH ), 6.31 br.s (1H,
3 2
1
3
(
(
1H, OH, J 9.0 Hz), 5.47 d (2H, CH ), 7.28–7.55 m
10H), 7.81 br.s (1H, NH). C NMR spectrum, δ,
NH). C NMR spectrum, δ, ppm: 26.8 (Me), 35.6
2
1
3
(Me), 41.5 (N-Me ), 73.9 (CH ), 160.6 (C=O).
2
2
ppm: 78.1 (CH ), 125.4, 125.8, 126.6, 127.4, 128.7,
2
A similar reaction between Et SiOCH NMe and
,3-diphenylurea in different molar ratios in
3
2
2
1
29.2, 138.2, 141.3 (Ph), 181.9 (C=S).
1
dichloromethane failed to yield any dimethylamino-
substituted product.
Reaction of 1-[(dimethylamino)methyl]-1,2-di-
phenylthiourea (8) with MeI. A 20 mL round-bottom
flask was charged with a solution of 0.24 g (1.27 mmol)
of 1 and 0.29 g (1.27 mmol) of 1,3-diphenylthiourea in
ACKNOWLEDGMENTS
1
0 mL of dichloromethane. The solution was stirred
This research was supported by the Welch Foundation
overnight at room temperature. Excess of MeI (1 mL)
was then added with a syringe to the reaction mixture.
After 15 min of stirring, a white solid started to
precipitate, and the reaction mixture was further stirred
for 2 h. The solvent and triethylsilanol were removed
under vacuum. The white solid was treated twice with
(
Grant AH-0546). J. M. acknowledges the Student Finance
England loan to cover the academic year 2017–2018 study
abroad from Newcastle University. We also acknowledge
the NSF MRI Program (CHE-1827875) for purchase of the
Bruker Venture and the Kresge Foundation for an NMR
maintenance endowment grant.
1
5 mL of hexane, the extract was filtered, and the
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
solvent was removed to obtain methyl N,N-diphenyl-
carbamimidothioate PhN=C(SMe)NHPh (13), yield
6
2% yield, mp 106°C (107°C [13]).
Reaction of Et SiOCH NMe with 1,3-dimethyl-
3
2
2
urea. In a typical experiment, a 10 mL round-bottom
flask was charged with 0.22 g (1.16 mmol) of
Et SiOCH NMe and 0.10 g (0.1.16 mmol) of 1,3-di-
1
. (a) Chaluvaraju, K.C. and Bhat, I.K., Int. J. Pharm.,
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