2,2-Dimethyl-3-[(4-methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-benzoxazasilole: synthesis, properties, and structure

Article abstract of DOI:10.1007/s11172-021-3097-3

2,2-Dimethyl-3-[(4-methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-benzoxazasilole was synthesized by the reaction of N-(2-hydroxyphenyl)-4-methylbenzenesulfonamide with dimethyl-dichlorosilane or N, N-bis(dimethylamino)dimethylsilane in 68 and 96% yield, respectively. The structure of the new compound was assigned using NMR and IR spectroscopy and confirmed by X-ray diffraction. In the crystal, the silole molecules are linked to each other by short O?H-C contacts (～2.6 ?) between the oxygen atoms of the bicyclic moiety and the methyl hydrogen atoms of adjacent molecules.

Full text of DOI:10.1007/s11172-021-3097-3

386
Russian Chemical Bulletin, International Edition, Vol. 70, No. 2, pp. 386—390, February, 2021
2
,2-Dimethyl-3-[(4-methylphenyl)sulfonyl]-2,3-dihydro-
1
,3,2-benzoxazasilole: synthesis, properties, and structure
A. Yu. Nikonov, I. V. Sterkhova, and N. F. Lazareva
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,
1
ul. Favorskogo, 664033 Irkutsk, Russian Federation.
E-mail: nataly_lazareva@irioch.irk.ru
2
,2-Dimethyl-3-[(4-methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-benzoxazasilole was syn-
thesized by the reaction of N-(2-hydroxyphenyl)-4-methylbenzenesulfonamide with dimethyl-
dichlorosilane or N,N-bis(dimethylamino)dimethylsilane in 68 and 96% yield, respectively.
The structure of the new compound was assigned using NMR and IR spectroscopy and con-
firmed by X-ray diffraction. In the crystal, the silole molecules are linked to each other by short
O∙∙∙H—C contacts (~2.6 Å) between the oxygen atoms of the bicyclic moiety and the methyl
hydrogen atoms of adjacent molecules.
Key words: N-(2-hydroxyphenyl)-4-methylbenzenesulfonamide, silylation, 2,2-dimethyl-
3
-[(4-methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-benzoxazasilole, hydrolysis, alcoholysis, X-ray
diffraction.
Sulfonic acid amides RSO NR´R (R, R´, Rʺ = Alk,
Recently, we synthesized N-{[2-(trimethylsilyl)oxy]-
phenyl}-4-methylphenyl- and N-{[2-(trimethylsilyl)oxy]-
phenyl}-4-chlorophenylsulfonamides and investigated
their structures. As part of our continuing research, we
synthesized 2,2-dimethyl-3-[(4-methylphenyl)sulfonyl]-
2,3-dihydro-1,3,2-benzoxazasilole (1), determined its
structure, and investigated selected properties.
2
Ar, Hetaryl) are widely used in synthetic organic and
medicinal chemistry.1 para-Aminobenzenesulfonamide
derivatives have been commonly applied in medical prac-
tice as antibacterial agents since the mid-20th century.
Investigations showed that compounds containing the
—6
3
2
SO N group exhibit a wide range of biological activities.
2
In particular, these compounds possess antibacterial,
antiviral, antifungal, anti-inflammatory, antituberculosis,
antimalarial, antiprotozoal, and anticoagulant proper-
N-(2-Hydroxyphenyl)-4-methylbenzenesulfonamide
reacts with dimethyldichlorosilane in dichloromethane
at room temperature in the presence of triethylamine
as a hydrogen chloride acceptor (Scheme 1) to form
7
—16
ties.
In recent years, sulfonic acid amides were found
to have antitumor activity due to their ability to inhibit
2
1
,2-dimethyl-3-[(4-methylphenyl)sulfonyl]-2,3-dihydro-
tubulin polymerization.1
7—19
The biological activity of
,3,2-benzoxazasilole (1) in 68% yield (method A).
sulfonamides is largely determined by their ability to form
non-covalent bonds (hydrogen and halogen bonds, com-
plexation with metal sites of proteases, π-bonding with
aromatic donors, etc.).2
Scheme 1
0—23
The silyl modification of organic compounds is
widely used in synthetic, medicinal, and analytical
chemistry. The introduction of trialkylsilyl groups R Si
3
as efficient, easily removable protecting groups has re-
ceived great attention to series of O- and N-nucleo-
2
4—27
28
philes.
The Si/C bioisosterism, which is of both
theoretical interest and practical importance for the
development of medicinal chemistry, is less known. It
is worth noting that the bioisosteric replacement of the
carbon moiety in the molecule with a silicon-containing
group can lead to the enhancement of the therapeutic
effect and a decrease in toxicity of the compound.2
Silicon-containing sulfonamides are poorly studied.
Variations of the experimental conditions (the sol-
vent and the hydrogen chloride acceptor) did not lead
to an increase in the yield of the target product. The
main problem is that the largest loss of the product oc-
curs in the step of its isolation from the reaction mixture.
An alternative method of synthesis (method B) is more
9—31
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 386—390, February, 2021.
066-5285/21/7002-0386 © 2021 Springer Science+Business Media LLC
1

1
,3,2-Benzoxazasilole derivative
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 2, February, 2021
387
Compounds 1 and 2 have very similar geometric pa-
С(10)
rameters of the five-membered heterocycle. The Si—O and
O(2)
C(11)
Si—N distances in the heterocycle of
C(6)
С(5)
O
compound 1 are 1.683 and 1.789 Å,
respectively. The O—Si—N, Si—
N—C, and C—O—Si bond angles
are 91.18°, 110.49°, and 113.11°,
respectively. The differences in the
geometric parameters of compounds
Si(1)
Me
Si
С(7)
С(8)
Me
Me
S(1)
N(1)
N
O(1)
O
С(9)
С(12)
С(14)
С(15)
С(4) O(3)
С(3)
1
and 2 are at most 0.06 Å and 0.5°.
In the crystal, the molecules of com-
pound 1 are linked to each other by short CH···O contacts
2.638 and 2.681 Å) between the hydrogen atoms of SiMe2
2
С(13)
C(1)
С(2)
(
groups and the oxygen atoms of adjacent molecules (Fig. 2).
Compound 1 is extremely hygroscopic and is easily
hydrolyzed by atmospheric moisture. The mild hydrolysis
of this compound with atmospheric moisture leads to the
opening of the heterocycle at the Si—N bond to form the
corresponding silanole, N-[2-(hydroxydimethylsilyloxy)
phenyl]-4-methylphenylsulfonamide (3) (Scheme 2).
The resulting silanole is a yellowish powdered compound
soluble in aromatic hydrocarbons, chloroform, and aceto-
nitrile. Unfortunately, we failed to obtain crystals of com-
pound 3 suitable for X-ray diffraction. Both the hydroly-
sis of compound 1 in a solvent using an equimolar amount
of water and the storage of the solid sample within a week
lead to the decomposition of silanole 3 into N-(2-hydr-
oxyphenyl)-4-methylphenylsulfonamide and polysiloxanes
of unidentified structure. The storage of a solution of
compound 3 in acetonitrile above molecular sieves 4 Å re-
sulted in the formation of N,N´-[(1,1,3,3-tetramethyldisil-
oxane-1,3-diyl)bis(oxy-2,1-phenylene]bis(4-methylphenyl-
sulfonamide) (4) as the condensation product (see Scheme 2).
The reaction of compound 1 with tert-butanol was
accompanied by the Si—N bond cleavage and gave the
corresponding N-{2-[tert-butoxy(dimethyl)silyloxy]phen-
yl}-4-methylphenylsulfonamide 5 (see Scheme 2).
Fig. 1. Molecular structure of compound 1 with displacement
ellipsoids drawn at the 50% probability level.
efficient and allows the preparation of compound 1 in
nearly quantitative yield (96%). This method is based
on the reaction of N-(2-hydroxyphenyl)-4-methyl-
benzenesulfonamide with N,N-bis(dimethylamino)di-
methylsilane (see Scheme 1). The reaction occurs at
reflux in toluene within 6—8 h. The completion of the
reaction is evidenced by the cessation of the release of
dimethylamine from the reaction mixture (litmus paper).
The structure of compound 1 was assigned using IR
and NMR spectroscopy and confirmed by X-ray diffrac-
tion. The molecular structure of compound 1 is shown in
Fig. 1. Selected structural parameters are given in Table 1.
There is one molecule of compound 1 per asymmetric
unit. No structural analogs of compound 1 are avaialable
in the Cambridge Crystallographic Data Centre. 3-Acetyl-
2
,2-dimethyl-2,3-dihydro-1,3,2-benzoxazasilole (2), which
3
3
was synthesized in our recent research, is structurally
most similar to compound 1.
Table 1. Selected bond lengths (d), bond angles (ω), and torsion angles (ϕ) in molecule 1
Bond
d/Å
Bond angle
ω/deg
Torsion angle
ϕ/deg
Si(1)—O(1)
Si(1)—N(1)
Si(1)—C(10)
Si(1)—C(11)
S(1)—O(2)
S(1)—O(3)
S(1)—N(1)
S(1)—C(5)
O(1)—C(12)
N(1)—C(4)
C(1)—C(2)
C(2)—C(3)
C(3)—C(4)
C(8)—C(9)
1.683(1)
1.789(1)
1.839(2)
1.839(2)
1.442(1)
1.438 (1)
1.629(1)
1.761(1)
1.377(2)
1.424(2)
1.390(2)
1.402(2)
1.387(2)
1.505(2)
O(1)—Si(1)—N(1)
O(1)—Si(1)—C(10)
N(1)—Si(1)—C(10)
O(1)—Si(1)—C(11)
N(1)—Si(1)—C(11)
C(10)—Si(1)—C(11)
C(12)—O(1)—Si(1)
O(3)—S(1)—O(2)
O(2)—S(1)—N(1)
O(3)—S(1)—N(1)
O(3)—S(1)—C(5)
O(2)—S(1)—C(5)
N(1)—S(1)—C(5)
C(4)—N(1)—S(1)
91.2(1)
111.2(1)
113.9(1)
113.6 (1)
110.5(1)
114.3(1)
113.1(1)
119.7(1)
103.7(1)
109.9(1)
108.2(1)
109.0(1)
105.5(1)
125.3(1)
N(1)—Si(1)—O(1)—C(12)
C(10)—Si(1)—O(1)—C(12)
O(3)—S(1)—N(1)—C(4)
C(11)—Si(1)—O(1)—C(12)
O(2)—S(1)—N(1)—C(4)
C(5)—S(1)—N(1)—C(4)
O(3)—S(1)—N(1)—Si(1)
O(2)—S(1)—N(1)—Si(1)
C(5)—S(1)—N(1)—Si(1)
O(1)—Si(1)—N(1)—C(4)
C(10)—Si(1)—N(1)—C(4)
C(1)—C(2)—C(3)—C(4)
C(11)—Si(1)—N(1)—C(4)
O(1)—Si(1)—N(1)—S(1)
–1.3(1)
–117.7(1)
46.6(1)
111.7(1)
175.6(1)
–69.8(1)
–138.3(1)
–9.2(1)
105.4(1)
2.0(1)
115.9(1)
–0.4(2)
–113.8(1)
–173.8(1)

3
88
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 2, February, 2021
Nikonov et al.
2
.681
2
.638
.638
2
2
.681
Fig. 2. Short intermolecular contacts in the crystal of compound 1.
Scheme 2
To conclude, the reaction of N-(2-hydroxyphenyl)-4-
methylbenzenesulfonamide with N,N-bis(dimethylamino)-
dimethylsilane allows the synthesis of 2,2-dimethyl-3-[(4-
methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-benzoxaza-
silole (1) in nearly quantitative yield (96%). This reaction
with dimethyldichlorosilane affords the target product in
much lower yield (68%). The structure of 2,2-dimethyl-
λ = 0.71073 Å) using the φ- and ω-scanning technique. The
structure was solved by direct methods using the SHELX program
3
9
package. An absorption correction was applied with the
SADABS program. All nonhydrogen atoms were refined with
anisotropic displacement parameters using the SHELX program
3
9
package. Crystallographic data for molecule 1 were deposited
with the Cambridge Crystallographic Data Centre (www.ccdc.
cam.ac.uk/data_request/cif, CCDC 1947409).
3
-[(4-methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-benzox-
The X-ray crystallographic data for compound 1:
azasilole was confirmed by NMR and IR spectroscopy and
X-ray diffraction. The further investigation of the proper-
ties of polyfunctional 2,2-dimethyl-3-[(4-methylphenyl)-
sulfonyl]-2,3-dihydro-1,3,2-benzoxazasilole and its ana-
logs holds promise for the following reasons. First, com-
pounds containing a Si—N bond are commonly applied
C15H17NO SSi, M = 319.44, colorless prismatic crystals,
3
0.40×0.50×0.50 mm. The crystal belongs to the monoclinic
system, space group P2 /c; θmin/θ
= 2.67/30.21; T = 100 K,
1
max
a = 12.642(2) Å, b = 8.743(2) Å, c = 13.729(3) Å; β = 90.38(1)°,
3
3
V = 1517.3(5) Å , Z = 4, d
= 1.398 g cm , F(000) = 760; the
calc
–
1
absorption coefficient μ = 0.301 mm ; a total of 66798 reflec-
tions, of which 4459 reflections were unique; 193 refined param-
3
4—36
37,38
in organic synthesis
and materials science.
eters; R = 4.43, R = 0.052 (for all reflections); goodness of fit
w
Second, compounds containing the sulfonamide group
2
–3
based on F is 1.047; Δρ /Δρ
= 0.708/–0.851 e Å ; the
max
min
exhibit a wide range of biological activities.7
—16
2
2
2
–1
weighting scheme w = [σ (F0 ) + (0.0392P) + 1.3952P]
,
2
2
where P = (F0 + 2Fc )/3.
N-(2-Hydroxyphenyl)-4-methylphenylsulfonamide was syn-
thesized by a procedure described in our previous study.33
N,N-Bis(dimethylamino)dimethylsilane was synthesized by
Experimental
4
0
The NMR spectra were recorded on a Bruker DPX-400
a method described in the literature. The solvents and reagents
1
13
29
41
spectrometer ( H, 400.1 MHz; C, 100.6 MHz; Si, 79.5 MHz)
were prepared by standard procedures before use.
in CDCl using HMDS and cyclohexane as the internal standard.
2,2-Dimethyl-3-[(4-methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-
3
The IR spectra of amide 1 were measured as KBr pellets on
a Varian 3100 FT-IR spectrophotometer. A single crystal of com-
pound 1 was obtained by the crystallization from a benzene—
hexane mixture (5 : 1). The X-ray diffraction data were col-
lected on a Bruker D8 Venture diffractometer (Mo-Kα radiation,
benzoxazasilole (1). Method A. A solution of Me SiCl (1.29 g,
2 2
0.01 mol) in CH Cl (15 mL) was slowly added dropwise to
2
2
a vigorously stirred solution of N-(2-hydroxyphenyl)-4-methyl-
phenylsulfonamide (2.63 g, 0.01 mol) in dichloromethane
(150 mL) in the presence of triethylamine (5 g, excess). The

1
,3,2-Benzoxazasilole derivative
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 2, February, 2021
389
resulting reaction mixture was heated with stirring on a water
bath at 60 °C for 18 h. The solvent was removed from the reaction
mixture on a rotary evaporator, and then benzene (50 mL) was
added. After the cooling, the precipitate of triethylamine hydro-
chloride that formed was filtered off, washed with benzene, and
combined with the filtrate. The filtrate was concentrated to dry-
ness. According to the NMR spectrum, the resulting product was
a mixture of compound 1 and triethylamine hydrochloride.
Compound 1 was isolated by the recrystallization from a benz-
ene—hexane mixture (5 : 1). The yield was 2.17 g (68%), com-
130.08, 136.56, 144.49, 149.42 (2 Ar). 29Si NMR, δ: –6.96.
Found (%): C, 57.83; H, 6.86; N, 3.48. C19H27NO SSi. Calcul-
4
ated (%): C, 57.98; H, 6.92; N, 3.56.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 18-33-
0
0368-mol_a). The main results were obtained using
equipment of the Baikal Analytical Center for Collective
Use of the Siberian Branch of the Russian Academy of
Sciences.
1
pound 1 decomposes at a temperature above 152 °C. H NMR
(
(
CDCl ), δ: 0.75 (s, 6 H, Me Si); 2.39 (s, 3 H, Me); 6.69—7.86
3 2
m, 8 H, HAr). C NMR, δ: 0.92 (Me Si); 26.99 (Me); 113.79,
1
3
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2
1
1
21.06, 123.10, 127.25, 127.44, 129.58, 129.92, 136.69, 144.31,
2
9
49.15 (2 Ar). Si NMR (CDCl ), δ: 25.89. Found (%): C, 56.21;
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3
H, 5.19; N, 4.52. C15H17NO SSi. Calculated (%): C, 56.40;
3
H, 5.36; N, 4.38.
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Method B. A mixture of N-(2-hydroxyphenyl)-4-methyl-
benzenesulfonamide (2.63 g, 0.01 mol) and N,N-bis(dimethyl-
amino)dimethylsilane (1.46 g) in toluene (50 mL) was heated
until dimethylamine ceased to be released (litmus paper). The
solution was concentrated to 4/5 of the initial volume. The
crystals that formed were washed with pentane and dried in vacuo.
The yield was 3.07 g (96%). The spectral characteristics are
identical to those reported above.
N-(2-{[Hydroxy(dimethyl)silyl]oxy}phenyl)-4-methylphenyl-
sulfonamide (3). Compound 1 (0.32 g, 0.001 mol) was kept in an
open vessel for 36 h at room temperature, after which a yellow-
ish amorphous powder was obtained. The product was washed
with cold diethyl ether and dried in vacuo. The yield was 0.34 g
1
(
~100%), compound 3 decomposes at 196 °C. H NMR, δ: 0.37
(
s, 6 H, Me Si); 2.39 (s, 3 H, Me); 6.92—7.69 (m, 8 H, HAr);
2
1
3
5
.92 (br.s, 1 H, NH); 8.34 (br.s, 1 H, SiOH). C NMR, δ: 1.32
(
Me Si); 26.82 (Me); 113.56, 119.84, 122.97, 127.46, 127.75,
2
2
9
1
29.64, 130.12, 136.78, 144.62, 149.59 (2 Ar). Si NMR, δ:
–
9.72. Found (%): C, 53.62; H, 5.27; N, 4.35. C15H19NO SSi.
4
Calculated (%): C, 53.39; H, 5.68; N, 4.15.
N,N´-[(1,1,3,3-Tetramethyldisiloxane-1,3-diyl)bis(oxy-2,1-
phenylene)]bis(4-methylphenylsulfonamide) (4). Molecular sieves
4
0
Å (1 g) were added to a solution of compound 3 (0.32 g,
.001 mol) in acetone (25 mL). The mixture was stirred for 48 h
at room temperature. Then the solvent was removed. Attempts
to crystallize the resulting viscous product failed. The yield was
1
0
.31 g (~100%). H NMR, δ: 0.39 (s, 12 H, Me Si); 2.40 (s, 6 H,
2
Me); 6.24 (br.s, 2 H, 2 NH); 6.90—7.74 (m, 16 H, HAr).
1
3
C NMR, δ: 2.56 (Me Si); 26.86 (Me); 113.58, 119.92,
2
1
23.04, 127.48, 127.86, 129.72, 130.25, 136.79, 144.68, 150.12
(
4 Ar). 29Si NMR, δ: 7.84. Found (%): C, 54.93; H, 5.65;
N, 4.47. C30H36N O S Si . Calculated (%): C, 54.85; H, 5.52;
N, 4.26.
2
7
2
2
N-{2-[tert-Butoxy(dimethyl)silyloxy]phenyl}-4-methyl-
phenylsulfonamide (5). A solution of tert-butanol (0.15 g,
0
.002 mol) in CH Cl (5 mL) was added dropwise to a solution
2 2
of compound 1 (0.64 g, 0.002 mol) in CH Cl (15 mL). The
2
2
reaction mixture was refluxed for 4 h. The solvent was removed
in vacuo, and the residue (opalescent viscous substance) was
stored in vacuo for 3 h and then analyzed. The yield was 0.78 g
1
(
~100%). H NMR, δ: 0.32 (s, 6 H, Me Si); 1.27 (s, 9 H, Me C);
2
3
2
.40 (s, 3 H, Me); 4.32 (br.s, 1 H, NH); 6.74—7.69 (m, 8 H,
1
3
HAr). C NMR, δ: –1.56 (Me Si); 26.58 (Me); 32.37 (Me C);
7
2
3
8.64 (C—Me ); 113.70, 119.65, 122.56, 127.39, 127.72, 129.40,
3

3
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Nikonov et al.
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