Synthesis of dendrimers with terminal formyl groups

Article abstract of DOI:10.1007/s11172-005-0076-z

A method for preparation of dendrons and dendrimers with formyl groups at the terminal aromatic rings, ether bonds in the branching blocks, and ester bonds in the core of the macromolecules is proposed. A way for the selective synthesis of p-hydroxymethylbenzaldehyde is described.

Full text of DOI:10.1007/s11172-005-0076-z

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Russian Chemical Bulletin, International Edition, Vol. 53, No. 9, pp. 2080—2085, September, 2004
Synthesis of dendrimers with terminal formyl groups
ꢀ
N. M. Loim and E. S. Kelbyscheva
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: loim@ineos.ac.ru
A method for preparation of dendrons and dendrimers with formyl groups at the terminal
aromatic rings, ether bonds in the branching blocks, and ester bonds in the core of the
macromolecules is proposed. A way for the selective synthesis of pꢀhydroxymethylbenzaldehyde
is described.
Key words: dendrimer, dendrimer branch, dendrimer core, formyl groups.
Chemistry of dendrimers is an actively developing area
of monodisperse polymeric compounds (both organic and
organoelement) with a cascade architecture. This area
opens new perspectives for developing substances, reꢀ
agents, and molecular devices to be used in different fields
of technology, materials science, organic synthesis, and
asymmetric catalysis.1—8
An important stage in the synthesis of dendrimers with
required properties and structures includes, in particular,
the controlled modification of the peripheral layer of a
molecule by the transformation of terminal functional
groups. These functions are, first of all, various amino
and hydroxyl groups of phenols and alcohols.9—13
Denrimers containing at the periphery ether and ester
groups and fragments of carboxylic acids, amides, acid
chlorides, and nitriles are also described.14—17 Unfortuꢀ
nately, many of these groups are poorly reactive, which
impedes their use for the modification of dendrimers. In
this work, we proposed an approach to the synthesis of
dendrimers with formyl groups at the periphery. High and
diverse reactivity of aldehydes makes it possible to modify
the nature of the terminal layer of dendrimers in a wide
range.
mine, would allow one to obtain benzylating agent 8
(Scheme 1).
Scheme 1
The approach to the synthesis of dendrimers containꢀ
ing formyl groups at the periphery is based on the syntheꢀ
sis of dendron 1 from 4ꢀhydroxymethylbenzaldehyde (2)
and 3,5ꢀdihydroxybenzyl alcohol (3). The latter is the
main building block in the convergent scheme of syntheꢀ
sis of dendrimers of the Frechet type using the Williamson
reaction.9,10
Although the synthesis and use of bifunctional comꢀ
pound 2 has been described,18,19 its yield, including that
in the reduction of teraphthalic aldehyde (4) with hydrides,
does not exceed 65%.18 Searching for a more efficient
method of the synthesis of 2, we studied a possibility of
the selective synthesis of monoacetal 5, whose subsequent
reduction and substitution of the OH group in 7 by broꢀ
Reagents and conditions: i. HOCH2CH2OH, benzene, TsOH;
ii. NaBH4, EtOH; iii. CBr4, PPh3, CH2Cl2.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1995—1999, September, 2004.
1066ꢀ5285/04/5309ꢀ2080 © 2004 Springer Science+Business Media, Inc.

Dendrimers with terminal formyl groups
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 9, September, 2004
2081
However, it turned out that the rate of formation of
diprotected derivative 6 substantially exceeds the rate of
the first step of the reaction with ethylene glycol, so that
monoacetal 5 is formed with an admixture of 10% comꢀ
pound 6 even when the 1 : 5 ratio of ethylene glycol to 4
is used.
Nevertheless, we succeeded to find a way for increasꢀ
ing the yield of 2 to 90—95% by the reduction of dialdeꢀ
hyde 4 using 0.25 equiv. NaBH4 in an EtOH—THF mixꢀ
ture at –5 °C (Scheme 2). For the bromination of
aldehydoalcohol 2 with a CBr4—PPh3 system, as well as
the bromination of its acetal 7, the yield of the target
pꢀbromomethylbenzaldehyde (8) is low, and a large
amount of byꢀproducts is mainly formed. A more sucꢀ
cessful method of hydroxyl group substitution by bromine
is the use of a mixture of PPh3 with Nꢀbromosuccinꢀ
imide (NBS).
formyl groups, viz., 3,5ꢀbis(4ꢀformylbenzyloxy)benzyl alꢀ
cohol (1) or methyl 3,5ꢀbis(4ꢀformylbenzyloxy)benzoate
(10) (Scheme 3).
Aforementioned difficulties in the synthesis and isolaꢀ
tion of compound 8 compelled us to search for a more
convenient reagent for constructing dendrimers of the
Frechet type with an ether bond between structural units.
We chose (4ꢀformylbenzyl) methanesulfonate (11), beꢀ
cause it possesses a better leaving group than the Br– anion.
We found that the reaction of methanesulfonate 11, which
is formed in high yield from alcohol 2, is an efficient
method for obtaining dendron 1. The overall yield of 11,
which is a key compound in the synthesis of formylꢀ
containing dendrimers via the scheme proposed by us, is
68% calculated to terephthalic aldehyde (Scheme 4).
In this work, we used benzeneꢀ1,3,5ꢀtricarboxylic
acid trischloride (12) as a core for the formation of
dendrimers.21 Its interaction with dendron 1 on refluxing
in benzene in the presence of excess DMAP affords a
dendrimer of first generation (13) with six terminal formyl
groups in 55% yield (Scheme 5).
Scheme 2
A dendrimer of zero generation (14) with three termiꢀ
nal formyl groups was synthesized similarly from acid
trischloride 12 and compound 2 (Scheme 6).
The data obtained indicate high purity and individual
character of dendrimers 13 and 14. They are solid white
and light yellow substances, respectively, well soluble in
СНСl3 and DMF but poorly soluble or virtually insoluble
in alcohols, benzene, and acetone. This fact was used to
isolate the reaction products from the starting compounds
that are easily soluble in acetone. Analytical TLC of isoꢀ
lated samples 13 and 14 (Rf in an AcOEt—CHCl3 (1 : 1)
system was 0.45 and 0.52, respectively) confirms the comꢀ
plete removal of compounds 1, 2, 12, and DMAP (Rf 0.75,
0.82, 0.85, and 0.05, respectively) and the absence of
i. 0.25 equiv. NaBH4, 90—95% yield; ii. CBr4/PPh3, 45% yield;
iii. NBS/PPh3, 65% yield.
The reaction of benzylating agent 8 with compound 3
or methyl 3,5ꢀdihydroxybenzoate (9) in acetone or DMF
in the presence of 18ꢀcrownꢀ6 and K2CO3 afforded the
corresponding dendron of zero generation with terminal
Scheme 3

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 9, September, 2004
Loim and Kelbyscheva
Scheme 4
Unlike direct methods of benzene ring formylation,
our procedure provides the complete and selective introꢀ
duction of the formyl group at the periphery of a dendrimer
resulting in macromolecules with a highly defined
structure.
The aboveꢀconsidered approach to the synthesis of
dendrimers with formyl groups at the periphery can natuꢀ
rally be used to construct cascade molecules with other
terminal functional groups and use other types of reacꢀ
tions for introducing fragments containing a funcꢀ
tional substituent. For example, the reaction of methyl
(pꢀbromomethylbenzoate) (15) with 3 produced dendron
(16) having ester groups at the periphery, whereas the
reaction of perfluorobenzaldehyde (17) with ester 9, unꢀ
der the conditions of nucleophilic aromatic substitution
rarely used in dendrimer synthesis, afforded methyl
3,5ꢀbis(4ꢀformylꢀ2,3,5,6ꢀtetrafluorophenyloxy)benzoate
(18), i.e., fluorinated analog of dendron 10, in 96% yield.
significant amounts of any other admixtures. The strucꢀ
tures of dendrimers 13 and 14 agree with the data of
elemental analysis and 1Н NMR spectra. The spectra conꢀ
tain a singlet signal at δ 8—9 ppm, indicating the presence
of three same substituents at the central aromatic ring in
both compounds. In the case of addition of only one or
two fragments of dendrons 1 and 2 to 12, two multiplets
with a ratio of 1 : 2 should be expected in this region of the
1H NMR spectra; however, they are not observed. Thus,
the degree of purity and individual character of dendrimers
13 and 14 is at least 95—97%.
Scheme 5
Scheme 6

Dendrimers with terminal formyl groups
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 9, September, 2004
2083
1 Н, ОН); 4.15 (m, АА´ВВ´, 4 Н, (СН2)2); 4.62 (s, 2 Н, СН2);
5.82 (s, 1 Н, СНО2); 7.30—7.50 (m, 4 Н, С6Н4). Found (%):
С, 66.72; Н, 6.57. С10Н12О3. Calculated (%): С, 66.65; Н, 6.71.
4ꢀBromomethylbenzaldehyde (8). A. Solutions of Ph3P
(1.63 g, 6.2 mmol) and CBr4 (2.03 g, 6.2 mmol) in anhydrous
THF (25 and 20 mL, respectively) were consequently added at
0 °С in an argon flow in the dark to a solution of alcohol 7 (0.9 g,
5 mmol) in anhydrous THF (20 mL). The reaction mixture was
stirred for 1 h at 0 °С and then for 8 h at room temperaꢀ
ture (~20 °C). After the solvent was removed, the residue was
purified by column chromatography on silica gel using an
AcOEt—hexane (1 : 3) mixture as an eluent. The yield of 8 was
0.3 g (25%), m.p. 102 °С (from hexane). 1Н NMR (acetoneꢀd6),
δ: 4.74 (s, 2 Н, СН2); 7.70—7.93 (q, 4 Н, Ph); 10.05 (s, 1 Н,
СНО). Found (%): С, 48.24; Н, 3.58. С8Н7BrO. Calculated (%):
С, 48.19; Н, 3.45.
B. Solutions of Ph3P (10.2 g, 39 mmol) and CBr4 (12.8 g,
39 mmol) in anhydrous THF (25 and 40 mL, respectively) were
consequently added at 0 °С in an argon flow in the dark to a
solution of hydroxymethylbenzaldehyde 2 (3.5 g, 26 mmol) in
anhydrous THF (20 mL). The reaction mixture was stirred for 1 h
at 0 °С and then for 24 h at room temperature (~20 °C). After
the solvent was removed, products were isolated by column
chromatography using an AcOEt—hexane (1 : 3) mixture as an
eluent. The yield of 8 was 2.3 g (45%), m.p. 102—103 °С (from
hexane).
C. A mixture of alcohol 2 (2 g, 15 mmol) and PPh3 (4.7 g,
18 mmol) in anhydrous CH2Cl2 (50 mL) was cooled to 0 °С, and
NBS (3.4 g, 19 mmol) in anhydrous CH2Cl2 (50 mL) was added
dropwise with stirring to the cooled solution. After 20 min,
water (100 mL) was added to the reaction mixture, and products
were extracted with CH2Cl2. After the solvent was removed, the
residue was treated with hot hexane (4×100 mL), the combined
solution was concentrated by evaporation to 100 mL, and crysꢀ
tals of 8 were separated. The yield was 1.9 g (65%), m.p.
102—102.5 °С.
4ꢀHydroxymethylbenzaldehyde (2). NaBH4 (1.7 g, 37 mmol)
was added at –5 °С with continuous stirring for 30 min to a
solution of dialdehyde 4 (20 g, 0.15 mol) in a mixture of 95%
EtOH (250 mL) and THF (350 mL). Then the mixture was
stirred for 6 h, while the temperature was maintained in an
interval of 0—2 °С. Then the reaction mixture was neutralized
with 2 M HCl to рН 5, the solvents were evaporated, water
(200 mL) was added to the residue, and products were extracted
with AcOEt. Combined organic extracts were dried with MgSO4,
and the solvent was evaporated. The yield of nonpurified prodꢀ
uct 2 was 19.1 g (94%). The product was purified by column
chromatography using an AcOEt—hexane (1 : 1) mixture of
solvents. The yield was 17.9 g (88%), m.p. 40 °С. TLC (eluent
AcOEt—CHCl3 (1 : 1)): Rf 0.82. 1Н NMR (acetoneꢀd6), δ: 4.50
(t, 1 Н, ОН, J = 5.7 Hz); 4.76 (d, 2 Н, СН2, J = 5.7 Hz);
7.60—7.90 (q, 4 Н, Ph); 10.03 (s, 1 Н, СНО). Found (%):
С, 70.69; Н, 5.94. С8Н8О2. Calculated (%): С, 70.58; Н, 5.92.
3,5ꢀDihydroxybenzyl alcohol (3). Compound 9 (10.3 g,
61 mmol) in anhydrous THF (100 mL) was added dropwise with
stirring to a suspension of LiAlH4 (7 g, 184 mmol) in anhydrous
THF (300 mL). After 12 h, ether (400 mL) was added to the
reaction mixture, and then a saturated solution of Na2SO4
(75 mL) was added dropwise. The mixture was neutralized with
15% НСl to pH 5.5, the solution was decanted, the residue was
dissolved in 15% НСl, and products were extracted with AcOEt.
Experimental
1
Н (solvent as the internal standard, δ from Me4Si) and 19F
(CF3COOH as the external standard) NMR spectra were reꢀ
corded on Bruker WPꢀ200 SY instruments with working freꢀ
quencies of 200.13 and 188.3 MHz, respectively. The reaction
courses and purity of products were monitored by analytical
TLC on Silufol UVꢀ245 plates (Czech Republic). Silica gel 60
(Merck) was used for column chromatography.
Commercial reagents 9, 12, and 17 (Aldrich) were used in
syntheses.
4ꢀ(1,3ꢀDioxolanꢀ2ꢀyl)benzaldehyde (5) and 1,4ꢀbis(1,3ꢀdiꢀ
oxolanꢀ2ꢀyl)benzene (6). A catalytic amount of TsOH was added
to a solution of terephthalic aldehyde 4 (2.0 g, 14.9 mmol) and
ethylene glycol (0.5 g, 7.45 mmol, 0.4 mL) in benzene (150 mL).
The mixture was refluxed with a Dean—Stark trap for 2 h. After
cooling, the reaction mixture was washed with a 15% solution of
NaHCO3 and a saturated solution of NaCl and dried with MgSO4
+ Na2SO4. The solvent was distilled off in vacuo, and the residue
was purified by column chromatography using a petroleum
ether—AcOEt (4 : 1) mixture as an eluent. Fractions of 4 (0.94 g),
monoacetal 5 (1.05 g, oil), and diacetal 6 (0.15 g, oil) were
consequently collected. 1Н NMR of compound 5 (acetoneꢀd6),
δ: 3.95—4.20 (m, 4 Н, (СН2)2); 5.84 (s, 1 Н, СНО2); 7.66—7.70
(m, 2 Н, BB´, C6H4); 7.92—7.96 (m, 2 Н, AA´, С6Н4); 10.07 (s,
1 Н, СНО); compound 6: 3.95—4.20 (m, 8 Н, 2 (СН2)2); 5.75
(s, 2 Н, 2 СНО2); 7.46 (s, 4 Н, С6Н4). Compound 5. Found (%):
С, 67.28; Н, 5.71. С10Н10О3. Calculated (%): С, 67.41; Н, 5.66.
Compound 6. Found (%) С, 64.92; Н, 6.30. С12Н14О4. Calcuꢀ
lated (%): С, 64.85; Н, 6.35.
4ꢀ(1,3ꢀDioxolanꢀ2ꢀyl)benzyl alcohol (7). NaBH4 (0.19 g,
1.5 mmol) was added with continuous stirring at room temperaꢀ
ture (~20 °C) for 30 min to a solution of monoacetal 5 (0.71 g,
4 mmol) in 95% EtOH (50 mL). After evaporation of EtOH, the
residue was dissolved in water, products were extracted with
AcOEt, volatile components were again evaporated, and the
residue was purified by column chromatography on silica gel
using an AcOEt—hexane (1 : 4) mixture as an eluent. The yield
of 7 (oil) was 0.43 g (60%). 1Н NMR (acetoneꢀd6), δ: 3.13 (br.s,

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Loim and Kelbyscheva
Combined organic solutions were concentrated to dryness, and
the residue was crystallized from an AcOEt—acetone (10 : 1)
mixture. The yield of 3 was 6 g (70%), m.p. 182 °С. 1Н NMR
(acetoneꢀd6), δ: 4.01 (t, 1 Н, ОН, J = 5.8 Hz); 4.38 (d, 2 Н,
СН2, J = 5.8 Hz); 6.13 (m, 1 Н, С6Н3); 6.26 (m, 2 Н, С6Н3);
8.04 (s, 2 Н, 2 ОН).
ane (2 : 1) mixture as an eluent. The yield of 1 was 0.87 g
(73.5%), m.p. 72 °С. TLC (eluent AcOEt—CHCl3 (1 : 1)):
Rf 0.75. 1Н NMR (acetoneꢀd6), δ: 4.57 (s, 4 H, CH2); 5.23 (s,
2 H, CH2OH); 6.60 (s, 1 H, С6Н3); 6.69 (s, 2 H, С6Н3);
7.68—7.94 (m, 8 Н, С6Н4); 10.04 (s, 2 Н, СНО). Found (%):
С, 73.46; Н, 5.30. С23Н20О5. Calculated (%): С, 73.38; Н, 5.37.
B. Dendron 1 was obtained by a similar procedure from 3
(0.65 g, 4.7 mmol) and mesylate 11 (2 g, 9.4 mmol). The yield
was 1.4 g (75%), m.p. 71—72 °С.
1,3,5ꢀTris[3,5ꢀbis(4ꢀformylbenzyloxy)benzyloxycarboꢀ
nyl]benzene (13). A solution of alcohol 1 (3.3 g, 8.8 mmol) and
DMAP (2.9 g, 23 mmol) in benzene (250 mL) was refluxed with
a Dean—Stark trap for 2 h and then cooled to ~20 °C. Acid
chloride 12 (0.7 g, 2.7 mmol) was added to the reaction mixture,
and refluxing was continued for 4 h. The precipitate was filtered
off, 5% HCl was added (рН 3), and products were extracted
with chloroform. A benzene solution was concentrated, 5% HCl
was added, and products were extracted with chloroform. Comꢀ
bined organic extracts were dried with MgSO4, the solvent was
evaporated, and the crystalline residue was washed with acetone
and kept in vacuo at 60—70 °С. The yield of 13 was 1.9 g (55%),
m.p. >300 °С; TLC (eluent AcOEt—CHCl3 (1 : 1)): Rf 0.45.
1Н NMR (CDCl3), δ: 5.11 (s, 12 H, CH2ОAr); 5.33 (s, 6 H,
CH2ОСО); 6.55 (s, 3H, С6Н3); 6.68 (s, 6 H, С6Н3); 7.54—7.84
(m, 24 H, С6Н4); 8.87 (s, 3 Н, С6Н3 ring); 9.97 (s, 6 Н, СНО).
Found (%): С, 72.77; Н, 4.78. С78Н60О18. Calculated (%):
С, 72.89; Н, 4.71.
1,3,5ꢀTris(4ꢀformylbenzyloxycarbonyl)benzene (14). Zeroꢀ
generation dendrimer 14 was obtained according to a procedure
described above from acid chloride 12 (1.0 g, 5.7 mmol), 2 (2.5 g,
18 mmol), and DMAP (5.9 g, 49 mmol) in benzene (250 mL).
Dendrimer 14 was isolated in 59% yield (1.9 g), m.p. >300 °С.
TLC (eluent AcOEt—CHCl3 (1 : 1)): Rf 0.52. 1Н NMR (CDCl3),
δ: 5.45 (s, 6 H, CH2); 7.60—7.86 (m, 12 H, С6Н4); 8.88 (s, 3 H,
С6Н3 ring); 10.10 (s, 3 H, CHO). Found (%): С, 70.34; Н, 4.18.
С33Н24О9. Calculated (%): С, 70.20; Н, 4.29.
3,5ꢀBis(4ꢀmethoxycarbonylbenzyloxy)benzyl alcohol (16).
Dendron 16 was obtained similarly to dendron 1 from 3 (0.71 g,
5.0 mmol) and bromide 15 (2.29 g, 10 mmol). The yield was
1.56 g (72%), m.p. 49—50 °С. 1Н NMR (acetoneꢀd6), δ: 3.87 (s,
6 Н, 2 Ме); 4.22 (t, 1 Н, НО, J = 5.2 Hz); 4.57 (d, 2 H,
НОCH2, J = 5.2 Hz); 5.19 (s, 4 H, 2 ОCH2); 6.56 (t, 1 H, С6Н3,
J = 2 Hz); 6.69 (d, 2 H, С6Н3, J = 2 Hz); 7.57—7.61 (m, 4 Н,
BB´, C6H4); 8.02—8.04 (m, 4 Н, АА´, C6H4). Found (%):
С, 68.52; Н, 5.47. С25Н24О7. Calculated (%): С, 68.80; Н, 5.54.
Methyl 3,5ꢀbis(4ꢀformylbenzyloxy)benzoate (10). К2СО3
(5.0 g, 36 mmol) and 18ꢀcrownꢀ6 (0.4 g, 1.6 mmol) were added
to a solution of ether 9 (1.4 g, 8 mmol) in anhydrous DMF
(25 mL). Then bromide 8 (4.2 g, 21 mmol) was added dropwise
with stirring, and the reaction mixture was kept for 4 h at
50—60 °С. The solvent was removed, water (100 mL) was added
to the residue, and products were extracted with AcOEt. Orꢀ
ganic extracts were dried with MgSO4, the solvent was evapoꢀ
rated, and the residue was purified with column chromatoꢀ
graphy using an AcOEt—hexane (2 : 1) mixture as an eluent.
The yield was 2.5 g (75%). 1Н NMR (acetoneꢀd6), δ: 4.02 (s,
3 H, CH3); 4.46 (s, 4 H, CH2); 6.53 (s, 1 H, С6Н3); 6.58 (s, 2 H,
С6Н3); 7.80—7.60 (m, 8 Н, С6Н4); 10.01 (s, 2 Н, СНО).
Found (%): С, 71.05; Н, 4.43. С24Н20О6. Calculated (%):
С, 71.26; Н, 4.49.
Methyl 3,5ꢀbis(4ꢀformylꢀ2,3,5,6ꢀtetrafluorophenyloxy)benꢀ
zoate (18). К2СО3 (5.52 g, 40 mmol) was added with stirring in
an argon flow to a solution of ester 9 (3.1 g, 18 mmol), aldehyde
17 (7.9 g, 40 mmol), and 18ꢀcrownꢀ6 (1.21 g, 4.5 mmol) in
anhydrous acetone (50 mL), maintaining the temperature of the
reaction mixture at 15—18 °С. After 2 h, the precipitate was
filtered off, the solvent was removed, water (200 mL) was added
to the residue, and products were extracted with AcOEt. Orꢀ
ganic extracts were dried with MgSO4, the solvent was evapoꢀ
rated, and the residue was purified by column chromatography
using an AcOEt—hexane (2 : 1) mixture as an eluent. The yield
was 8.98 g (96%), m.p. 137 °С. 1Н NMR (acetoneꢀd6), δ: 3.85
(s, 3 H, CH3); 7.46 (t, 1 H, С6Н3, J = 2 Hz); 7.54 (d, 2 Н, С6Н3,
J = 2 Hz); 10.31 (s, 2 Н, СНО). 19F NMR, δ: 65.61 (dd, 4 F,
J = 8 and 19.5 Hz); 74.51 (dd, 4 F, J = 9.3 and 19.7 Hz).
Found (%): С, 51.05; Н, 1.43; F, 28.92. C22H8F8O6. Calcuꢀ
lated (%): С, 50.79; Н, 1.55; F, 29.21.
(4ꢀFormylbenzyl) methanesulfonate (11). Anhydrous CH2Cl2
(200 mL) was added to a solution of alcohol 2 (17.8 g, 0.13 mol)
in Et3N ((36.6 mL, 0.26 mol). The reaction mixture was cooled
to –5 °С, and MeSO2Cl (15.3 mL, 0.20 mol) in anhydrous
CH2Cl2 (50 mL) was added dropwise. The reaction was carried
out for 15 min, after which the reaction mixture was treated with
water (2×200 mL), a saturated solution of NaHCO3 (200 mL),
and a saturated solution of NaCl. The organic layer was dried
with MgSO4. After the solvent was removed, compound 11 was
isolated in 95% yield (26.6 g), m.p. 58—59 °С. 1Н NMR (acꢀ
etoneꢀd6), δ: 3.34 (s, 3 H, CH3); 5.56 (s, 2 H, CH2); 7.85—8.13
(m, 4 Н, С6Н4); 10.23 (s, 1 Н, СНО). Found (%): С, 50.48;
Н, 4.87. C9H10O4S. Calculated (%): С, 50.45; Н, 4.71.
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Received April 7, 2004;
in revised form August 23, 2004