Synthesis and characterization of dibenzodioxazasiladecines

Article abstract of DOI:10.1080/00397910701820608

The reaction of N-(2-hydroxymethylphenyl)salicylideneimine with sodium hydride in dry toluene at -4°C produces 1,9-remote dianion. The cyclization of this dianion with diorganodichlorosilanes affords dibenzodioxazasiladecines in good yields. The products

Full text of DOI:10.1080/00397910701820608

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Synthesis and Characterization of
Dibenzodioxazasiladecines
M. S. Singh a & Pratibha Singh a
a Faculty of Science, Department of Chemistry , Banaras Hindu University ,
Varanasi, India
Published online: 15 Feb 2008.
To cite this article: M. S. Singh & Pratibha Singh (2008) Synthesis and Characterization of
Dibenzodioxazasiladecines, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 38:5, 775-783, DOI: 10.1080/00397910701820608
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Synthetic Communicationsw, 38: 775–783, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701820608
Synthesis and Characterization
of Dibenzodioxazasiladecines
M. S. Singh and Pratibha Singh
Faculty of Science, Department of Chemistry, Banaras Hindu University,
Varanasi, India
Abstract: The reaction of N-(2-hydroxymethylphenyl)salicylideneimine with sodium
hydride in dry toluene at 248C produces 1,9-remote dianion. The cyclization of this
dianion with diorganodichlorosilanes affords dibenzodioxazasiladecines in good
yields. The products were characterized by satisfactory elemental analyses and
1
spectral (IR, H, 13C, and 29Si NMR and mass) studies.
Keywords: o-aminobenzyl alcohol, dianion, dibenzodioxazasiladecines, diorganodi-
chlorosilanes, electrophilic cyclizations
The development of chiral Schiff base ligands has received considerable interest
since Zhang et al.[1] and subsequently Irie et al.[2] reported significant success in
asymmetric epoxidation of unfunctionalized olefins by the chiral Mn(III)salen
Schiff base catalysts. Salen ligands give complexes, which also hold promise
in enantioselective cyclopropanation of styrenes, asymmetric aziridination of
olefins, asymmetric Diels–Alder cycloaddition, and enantioselective ring
opening of epoxides.[3] Schiff base ligands are considered privileged
ligands[4] because they are easily prepared by the condensation between
aldehydes and amines. Schiff base[5] ligands are able to coordinate metals
through imine nitrogen and another group, usually linked to the aldehyde.
When 2, equivalents of salicylaldehyde are combined with a diamine, a
Received September 10, 2007
Address correspondence to M. S. Singh, Faculty of Science, Department of
Chemistry, Banaras Hindu University, Varanasi 221 005, India. E-mail: mssinghbhu@
yahoo.co.in
775

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M. S. Singh and P. Singh
particular chelating Schiff base is produced. The so-called salen ligands with
four coordinating sites and two axial sites are very much like porphyrins.
Schiff bases have been used as precursors and intermediates for the
synthesis of a variety of organic compounds useful in analytical, medicinal,
polymer, and liquid-crystalline materials[6] or as ligands for complexation.
Monocyclic medium-ring heterocycles are an extremely important class of
compounds, which occur in a range of natural and synthetic products. Cyclo-
condensation reactions are recognized as worthwhile synthetic methods for
preparing heterocyclic compounds.[7] Increasing interest has been paid for
several years to the chemistry of heterocycles containing tin and silicon
because of their unique properties and potential biological activity.[8] Mono-
cyclic eight-membered silicon-containing[9] heterocycles have been prepared
by condensation reactions.[10] Chlorosilanes are synthetic intermediates in the
preparation of all classes of organosilicon compounds[11] and are used as pro-
tecting group for diols with varying chain length. Organosilicon complexes
with O, N donor ligands have been reported[12] and are widely used in
medicinal and pharmaceutical chemistry.[13] Strategies involving dianion
reactions[14–16] have become versatile tools in organic synthesis and have
developed as a powerful method for preparing various types of carbocyclic
and heterocyclic compounds. In our continuing studies on the synthesis of
new heterocyclic systems[17–19] using efficient intermolecular cyclization
reactions via the dianion intermediate, our aim is to broaden the range of
useful silaheterocycles, which may provide easy access to synthetic intermedi-
ates and therapeutic agents. A remarkable feature of this reaction is the con-
struction of oxygen–silicon bonds via a tandem process.
The reaction of equimolar amounts of salicylaldehyde and o-amino
benzyl alcohol in ethanol under reflux for 30 min according to the literature
method[20] afforded the corresponding N-(2-hydroxymethylphenyl)salicylide-
neimine (1). The structure of ligand (1) was established from its spectral and
1
analytical data. In its H NMR spectrum, one singlet at 13.05 ppm and one
singlet at 7.12 ppm exhibit for two unsymmetrical OH groups that are D2O
exchangeable, and the downfield signal of one of the -OH groups suggests
that there is intramolecular hydrogen bonding between this OH and the azo-
methine nitrogen. The azomethine proton comes at 8.61 ppm as a sharp
singlet. A multiplet in the range 6.93–7.53 ppm for aromatic protons and a
sharp singlet at 4.87 ppm for benzylic CH2 proton have been observed.
Our synthesis involves the initial formation of dianion (2) from sequential
deprotonations of the phenolic and benzylic -OH groups of ligand (1) by
sodium hydride in dry toluene. The 1,9-dianion thus generated attacks to a

Synthesis and Characterization of Dibenzodioxazasiladecines
777
variety of diorganodichlorosilanes, leading to the formation of compounds
3–10 (Scheme 1). The beauty of the reaction procedure resides in in situ
formation of remote dianion and further cyclization so that the multistep
reaction sequence is synchronized in a simple one-pot reaction. The dibenzo-
dioxazasiladecines are characterized on the basis of satisfactory elemental
analyses and spectral (IR, 1H, 13C, and 29Si NMR and mass) studies. The dis-
appearance of absorption band and signals corresponding to the -OH group in
both IR and proton magnetic resonance (PMR) spectra and appearance of a
new band in the region 1048–750 cm21 may be assigned to an Si-O
bond[21] suggesting the cyclic structure of prepared compounds. No
lowering of the n(C55N)[22] group in synthesized compounds is a further indi-
cation of no coordination of C55N to the silicon atom exhibiting a tetracoor-
1
dinated state, which is further supported by 29Si NMR chemical shifts. H
NMR spectra display a singlet at 8.61 ppm for azomethine proton, a
multiplet in the range 6.69–7.53 ppm for aromatic protons, a singlet around
4.86 ppm for benzylic CH2 proton, and singlets of silicon methyl in the
range 0.11–0.70 ppm. The signals for the vinyl and n-propyl protons were
visible in the expected regions. The alkyl groups attached to silicon display
single resonance for chemically equivalent protons and carbons. In addition,
the 13C NMR spectra supported the assigned structures. The upfield shifts
of the 29Si NMR signals of the compounds indicate the presence of tetracoor-
dinate[23] silicon in all the compounds. Mass spectroscopic data of the
compounds established their monomeric nature.
The newly synthesized silaheterocyclic rings gain rigidity because of the
presence of two benzene rings in their skeleton. In conclusion, a simple
workup, low consumption of solvent, fast reaction rates, mild reaction
condition, good yields, and selectivity of the reaction make this method a
very appealing and useful contribution to the preparation of a rare class of
silaheterocycles.
EXPERIMENTAL
Chemicals were obtained from Sigma-Aldrich, Merck, Fluka, and Lancaster
and are used as such without further purification. All solvents (analytical
Scheme 1. R ¼ R0 ¼ CH3, 3; R ¼ R0 ¼ Et, 4; R ¼ R0 ¼ Ph, 5; R ¼ H, R0 ¼ Me, 6;
R ¼ Et, R0 ¼ Me, 7; R ¼ CH ¼ CH2, R0 ¼ Me, 8; R ¼ Ph, R0 ¼ Me, 9; R ¼ n-Pr,
R0 ¼ Me, 10.

778
M. S. Singh and P. Singh
reagents (AR) or extrapure grade) used for spectroscopic and other physical
studies were further purified by literature methods.[24] All operations were
performed under a nitrogen atmosphere using standard glasswares. Infrared
spectra were recorded as KBr discs on a Jasco FT/IR-5300 spectropho-
tometer. Melting points were determined using a calibrated thermometer by
a Remi digital melting-point apparatus and are uncorrected. Elemental
analyses were performed by Central Drug Research Institute, Lucknow,
India. NMR (1H, 13C, and 29Si) spectra were recorded on a Jeol AL 300 instru-
ment. All chemical shifts were reported in parts per million relative to TMS as
an internal standard in CDCl3. Mass spectra were recorded at 70-eV ionizing
voltage on a Jeol SX-102 (FAB).
Synthesis of N-(2-Hydroxymethylphenyl)salicylideneimine 1
This ditopic ligand was first reported by Shyamal and Kale in 1980.[20]
To a stirred solution of o-aminobenzyl alcohol (5.66 g, 46 mmol) in
absolute ethanol (50 mL), an ethanolic (50 mL) solution of salicylaldehyde
(4.82 mL, 46 mmol) was added dropwise and refluxed for 30 min to get a
yellowish brown solution of ligand, which is checked by thin-layer chromato-
graphy (TLC). The solution was concentrated by rotavapor to get a yellow
solid, and the precipitate was recrystallized by dichloromethane to give 1.
Yield: 60%; mp 1218C. IR (KBr) cm21: 3400 (OH), 2908 (CH), 1618
1
(C55N). H NMR (300 MHz, CDCl3): d ¼ 13.05 (s, 1H, OH), 8.61 (s, 1H,
CH55N), 6.93–7.53 (m, 8H, ArH, & s, 1H, CH2OH), 4.87 (s, 2H, CH2).
13C NMR (75 MHz, CDCl3): d ¼ 61.40, 116.86, 117.56, 118.57, 119.36,
126.65, 127.20, 127.88, 128.40, 131.96, 132.99, 134.03, 146.19, 160.62,
162.74. MS: m/z (Mþ) 227. Anal. calcd. for C14H13NO2 (%): C, 73.99; H,
5.76; N, 6.16. Found: C, 73.95; H, 5.79; N, 6.19.
6,6-Dimethyl-8H-1,3-dioxa-7-aza-2-siladibenzo[d,h]cyclodecene (3)
General Procedure
A toluene solution (55 mL) of ligand (227 mg, 1 mmol) was added dropwise
to a stirred suspension of NaH (48 mg, 2 mmol) in dry toluene (5 mL) with
constant stirring at 248C for 4 h in an inert atmosphere. Dimethyldichlorosi-
lane (129 mg, 1 mmol) in dry toluene (5 mL) was added dropwise with
constant stirring to the yellowish brown solution of dianion generated in
situ, and the reaction mixture was stirred at room temperature for an additional
6 h. Completion of the reaction was checked by TLC. The reaction mixture
was evaporated under vacuum, and the residue was subjected to column
chromatography (diethylether) to give 3. Yield: 69%; mp 908C. IR (KBr)
1
cm21: 1618 (C55N), 804. H NMR (300 MHz, CDCl3): d ¼ 8.61 (s, 1H,

Synthesis and Characterization of Dibenzodioxazasiladecines
779
CH55N), 6.69–7.53 (m, 8H, ArH), 4.86 (s, 2H, CH2), 0.137 (s, 6H, CH3). 13
C
NMR (75 MHz, CDCl3): d ¼ 0.97, 61.48, 115.99, 117.17, 118.13, 119.09,
124.87, 126.97, 128.16, 128.61, 129.07, 132.29, 133.29, 13.4.39, 146.34,
160.91, 162.96. 29Si NMR (59.60 MHz, CDCl3): d ¼ 25.49. MS: m/z
(Mþ) 283. Anal. calcd. for C16H17NO2Si (%): C, 67.81; H, 6.04; N, 4.94.
Found: C, 67.79; H, 6.00; N, 4.90.
All other silaheterocycles (4–10) were also synthesized analogously as
mentioned previously. The spectral and analytical data for the compounds
4–10 are listed next.
6,6-Diethyl-8H-1,3-dioxa-7-aza-2-siladibenzo[d,h]cyclodecene (4)
The same procedure as for 3 with 227 mg (1 mmol) of N-(2-hydroxymethylphe-
nyl) salicylideneimine, 48 mg (2 mmol) of sodium hydride, and 157 mg
(1 mmol) of dichlorodiethylsilane afforded 4. Yield: 64%; mp 958C. IR
(KBr) cm21: 1620 (C55N), 870. 1H NMR (300 MHz, CDCl3): d ¼ 8.62
(s, 1H, CH55N), 6.69–7.53 (m, 8H, ArH), 4.87 (s, 2H, CH2), 0.95
(t, J ¼ 8.7 Hz, 6H, SiCH3), 0.55 (q, J ¼ 6.7 Hz, 4H, CH2). 13C NMR
(75 MHz, CDCl3): d ¼ 5.56, 6.70, 60.80, 116.27, 116.97, 118.16, 118.21,
126.06, 127.29, 131.37, 132.39, 133.43, 145.60, 160.03, 162.14. 29Si NMR
(59.60 MHz, CDCl3): d ¼ 23.58. MS: m/z (Mþ) 311. Anal. calcd. for
C18H21NO2Si (%): C, 69.42; H, 6.79; N, 4.49. Found: C, 69.39; H, 6.75; N, 4.43.
6,6-Diphenyl-8H-1,3-dioxa-7-aza-2-siladibenzo[d,h]cyclodecene (5)
The same procedure as for 3 with 227 mg (1 mmol) of N-(2-hydroxymethyl-
phenyl) salicylideneimine, 48 mg (2 mmol) of sodium hydride, and 253 mg
(1 mmol) of dichlorodiphenylsilane afforded 5. Yield: 72%; mp 1008C.
1
IR (KBr) cm21: 1618 (C55N), 804. H NMR (300 MHz, CDCl3): d ¼ 8.61
(s, 1H, CH55N), 6.71–7.60 (m, 18H, ArH), 4.87 (s, 2H, CH2). 13C NMR
(75 MHz, CDCl3): d ¼ 60.80, 115.29, 115.99, 116.27, 116.97, 118.16,
118.21, 119.09, 124.87, 126.06, 127.29, 131.37, 132.39, 133.43, 145.60,
160.03, 162.14. 29Si NMR (59.60 MHz, CDCl3): d ¼ 29.14. MS: m/z
(Mþ) 407. Anal. calcd. for C26H21NO2Si (%): C, 76.62; H, 5.19; N, 3.43.
Found: C, 76.58; H, 5.14; N, 3.38.
6-Methyl-8H-1,3-dioxa-7-aza-2-siladibenzo[d,h]cyclodecene (6)
Same procedure as for 3 with 227 mg (1 mmol) of N-(2-hydroxymethylphe-
nyl) salicylideneimine, 48 mg (2 mmol) of sodium hydride, and 115 mg
(1 mmol) of dichloromethylsilane afforded 6. Yield: 61%; mp 1108C. IR
(KBr) cm21: 1618 (C55N), 788. 1H NMR (300 MHz, CDCl3): d ¼ 8.61

780
M. S. Singh and P. Singh
(s, 1H, CH55N), 6.70–7.60 (m, 8H, ArH), 4.87 (s, 2H, CH2), 4.68 (s, 1H, SiH),
0.40 (s, 3H, SiCH3). 13C NMR (75 MHz, CDCl3): d ¼ 1.50, 61.80, 115.99,
116.97, 118.16, 119.09, 124.87, 126.06, 127.29, 131.37, 132.39, 133.43,
160.03, 162.14. 29Si NMR (59.60 MHz, CDCl3): d ¼ 212.68. MS: m/z
(Mþ) 269. Anal. calcd. for C15H15NO2Si (%): C, 66.88; H, 5.61; N, 5.20.
Found: C, 66.85; H, 5.59; N, 5.17.
6-Ethyl-6-methyl-8H-1,3-dioxa-7-aza-2-
siladibenzo[d,h]cyclodecene (7)
Same procedure as for 3 with 227 mg (1 mmol) of N-(2-hydroxymethylphe-
nyl) salicylideneimine, 48 mg (2 mmol) of sodium hydride, and 143 mg
(1 mmol) of dichloroethylmethylsilane afforded 7. Yield: 75%; mp 1608C.
1
IR (KBr) cm21: 1618 (C55N), 873. H NMR (300 MHz, CDCl3): d ¼ 8.61
(s, 1H, CH55N), 6.93–7.53 (m, 8H, ArH), 4.87 (s, 2H, CH2), 0.94
(t, J ¼ 8.8 Hz, 3H, SiCH3), 0.56 (q, J ¼ 6.8 Hz, 2H, CH2), 0.11 (s, 3H,
CH3). 13C NMR (75 MHz, CDCl3): d ¼ 1.59, 22.49, 30.45, 60.80, 116.27,
116.97, 118.16, 118.21, 126.06, 127.29, 131.37, 132.39, 133.43, 145.60,
160.03, 162.14. 29Si NMR (59.60 MHz, CDCl3): d ¼ 27.34. MS: m/z (Mþ)
297. Anal. calcd. for C17H19NO2Si (%): C, 68.65; H, 6.43; N, 4.70. Found:
C, 68.63; H, 6.39; N, 4.67.
6-Methyl-6-vinyl-8H-1,3-dioxa-7-aza-2-
siladibenzo[d,h]cyclodecene (8)
The same procedure as for 3 with 227 mg (1 mmol) of N-(2-hydroxymethyl-
phenyl) salicylideneimine, 48 mg (2 mmol) of sodium hydride, and 141 mg
(1 mmol) of dichloromethylvinylsilane afforded 8. Yield: 64%; mp 888C.
1
IR (KBr) cm21: 1616 (C55N), 758. H NMR (300 MHz, CDCl3): d ¼ 8.61
(s, 1H, CH55N), 6.71–7.53 (m, 8H, ArH), 5.90 (m, 3H, CH55CH2), 4.87
(s, 2H, CH2), 0.14 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): d ¼ 1.59,
62.52, 65.01, 116.58, 117.90, 118.62, 119.79, 127.67, 128.93, 129.47,
129.77, 129.97, 132.98, 133.67, 134.03, 135.01, 137.30, 147.29, 161.66,
163.81. 29Si NMR (59.60 MHz, CDCl3): d ¼ 23.36. MS: m/z (Mþ) 295.
Anal. calcd. for C17H17NO2Si (%): C, 69.12; H, 5.80; N, 4.74. Found: C,
69.09; H, 5.84; N, 4.77.
6-Methyl-6-phenyl-8H-1,3-dioxa-7-aza-2-
siladibenzo[d,h]cyclodecene (9)
Same procedure as for 3 with 227 mg (1 mmol) of N-(2-hydroxymethylphe-
nyl) salicylideneimine, 48 mg (2 mmol) of sodium hydride, and 191 mg

Synthesis and Characterization of Dibenzodioxazasiladecines
781
(1 mmol) of dichloromethylphenylsilane afforded 9. Yield: 60%; mp
1
1058C. IR (KBr) cm21: 1620 (C55N), 890. H NMR (300 MHz, CDCl3):
d ¼ 8.61 (s, 1H, CH55N), 6.25–7.89 (m, 13H, ArH), 4.87 (s, 2H, CH2),
0.77 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): d ¼ 2.50, 61.52, 116.58,
117.90, 118.66, 119.79, 126.06, 126.67, 128.58, 129.47, 129.77, 129.97,
132.98, 133.67, 134.03, 135.01, 137.30, 147.29, 161.66, 162.38. 29Si
NMR (59.60 MHz, CDCl3): d ¼ 27.56. MS: m/z (Mþ) 345. Anal. calcd.
for C21H19NO2Si (%): C, 73.01; H, 5.54; N, 4.05. Found: C, 73.05; H,
5.58; N, 4.09.
6-Methyl-6-propyl-8H-1,3-dioxa-7-aza-2-
siladibenzo[d,h]cyclodecene (10)
The same procedure as for 3 with 227 mg (1 mmol) of N-(2-hydroxymethyl-
phenyl) salicylideneimine, 48 mg (2 mmol) of sodium hydride, and 157 mg
(1 mmol) of dichloromethyl-n-propylsilane afforded 10. Yield: 71%; mp
1
828C. IR (KBr) cm21: 1620 (C55N), 800. H NMR (300 MHz, CDCl3):
d ¼ 8.61 (s, 1H, CH55N), 6.93–7.53 (m, 8H, ArH), 4.87 (s, 2H, CH2), 1.39
(sextet, 2H, CH2), 0.95 (t, J ¼ 8.7 Hz, 3H, CH3), 0.52 (t, J ¼ 8.6 Hz, 2H,
CH2), 0.10 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): d ¼ 0.97, 16.45,
17.85, 19.34, 61.80, 117.27, 117.96, 119.16, 127.06, 128.29, 128.80,
132.36, 133.39, 134.41, 146.57, 161.04, 163.12. 29Si NMR (59.60 MHz,
CDCl3): d ¼ 26.23. MS: m/z (Mþ) 311. Anal. calcd. for C18H21NO2Si
(%): C, 69.41; H, 6.79; N, 4.49. Found: C, 69.37; H, 6.75; N, 4.52.
ACKNOWLEDGMENTS
We are grateful for financial support from the Council of Scientific and Indus-
trial Research (CSIR) and Department of Science and Technology (DST),
New Delhi, India.
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