Convenient synthesis of benzene-1,3,5-tricarbaldehyde and congeners

Article abstract of DOI:10.1080/00397910601033435

A convenient synthesis of benzene-1,3,5-tricarbaldehyde was developed as well as benzaldehyde derivatives carrying one or two latent aldehyde groups. The asymmetric derivatives may serve as versatile scaffolds for the synthesis of sectorial dendrimers and multifunctional molecules. Copyright Taylor & Francis Group, LLC.

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Convenient Synthesis of
Benzene‐1,3,5‐tricarbaldehyde and
Congeners
Erik Tullberg a & Torbjörn Frejd a
a Department of Organic Chemistry, Lund University, Lund, Sweden
Published online: 25 Jul 2007.
To cite this article: Erik Tullberg & Torbjörn Frejd (2007) Convenient Synthesis of
Benzene‐1,3,5‐tricarbaldehyde and Congeners, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 37:2, 237-245, DOI: 10.1080/00397910601033435
To link to this article: http://dx.doi.org/10.1080/00397910601033435
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Synthetic Communicationsw, 37: 237–245, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601033435
Convenient Synthesis of Benzene-1,3,5-
tricarbaldehyde and Congeners
¨
Erik Tullberg and Torbjorn Frejd
Department of Organic Chemistry, Lund University, Lund, Sweden
Abstract: A convenient synthesis of benzene-1,3,5-tricarbaldehyde was developed as
well as benzaldehyde derivatives carrying one or two latent aldehyde groups. The
asymmetric derivatives may serve as versatile scaffolds for the synthesis of sectorial
dendrimers and multifunctional molecules.
Keywords: aldehydes, diols, lithiation, oxidations, reductions
INTRODUCTION
Aromatic aldehydes carrying more than one carbaldehyde group have been
used extensively as starting materials for the synthesis of more complex
molecules.[1,2] We have used them as starting materials for the synthesis of
phenyl 1,3-bis- and 1,3,5-tris-alanine derivatives as well as some dendrimers
and ferrocene analogs.[3,4]
Selective reactions of one of several identical functional groups in the
same molecule are always plagued by more or less statistical distributions
of products. Easily available starting materials carrying differentiated latent
functional groups would therefore be interesting candidates for the synthesis
of more advanced sectorial compounds. One such class of compounds are
sectorial dendrimers.[5] Compound 1 would provide a versatile starting
material for the synthesis of such compounds (Fig. 1).
In this article, we present the synthesis of 1 and of related C2- and
C3-symmetric derivatives.
Received in Poland May 22, 2006
Address correspondence to Torbjorn Frejd, Department of Organic Chemistry,
¨
Lund University, P.O. Box 124, SE-221 00, Lund, Sweden. E-mail: torbjorn.frejd@
organic.lu.se
237

238
E. Tullberg and T. Frejd
Figure 1. Benzaldehyde derivative with two latent aldehyde groups 1 and general
multifunctional derivative (MFD) thereof.
RESULTS AND DISCUSSION
Compound 1 possesses a carbaldehyde functionality, a hydroxymethyl group,
and a silyl ether. When the carbaldehyde group has been functionalized,
another carbaldehyde group can be brought forth by mild tetrapropylammo-
nium perruthenate (TPAP) oxidation of the remaining hydroxymethyl
group. Once this second carbaldehyde group has been functionalized, a
third carbaldehyde group may be liberated under mild conditions from the
silyl ether.[6] Alternatively, the hydroxymethyl group may be transformed
into a suitable alcohol derivative followed by deprotection of the silyl ether
to afford a further hydroxymethyl group amendable for continued transform-
ation. Combinations of these two strategies are of course also possible. Thus,
multifunctional derivatives (MFDs) would be created in a stepwise fashion
from the functionalization on an aldehyde, an alcohol, or any functional
group that can be derived from these two types of functional groups.
The synthesis of 1 was achieved in three steps from commercially available
diethyl-5-hydroxymethyl isophtalate. Thus, this compound was silylated in
good yield to give diester 2, which was reduced with LiAlH4 to diol 3 in
excellent yield. Compound 1 was obtained by oxidation of 3 with TPAP and
1 equivalent of N-methylmorpholine-N-oxide (NMO) with concomitant
formation of 4. Compounds 1, 4, and unreacted 3 were easily separated by
column chromatography (Scheme 1).
Initially we thought we might access 1 from diol 6 obtained from the
reduction of the corresponding diester 5. Reduction of diester 5 according
to literature procedure[7] was unsatisfactory in our hands because of concomi-
tant deiodination, resulting in the formation of 3,5-benzene dimethanol.
Substituting LiAlH4 for DIBAL-H in refluxing dichloromethane solved this
problem.[8] Silylation of 6 using 1 equivalent of TBDMSCl resulted in
monosilyation to give 7. However, all attempts failed at formylation of this
compound via metal–halogen exchange, followed by quenching with DMF
to give 1 (Scheme 2).
Carboxylation by quenching of the lithiation mixture with solid carbon
dioxide was also attempted without success. To elucidate the reason for this

Benzene-1,3,5-tricarbaldehyde
239
Scheme 1. Synthesis of compound 1. Reagents and conditions: i) LiAlH4, THF,
˚
reflux, 1 h, 94%; ii) TPAP, NMO, molecular sieves 4A, CH2Cl2, rt, 12 h, 1: 62%,
4: 19%.
apparent lack of reactivity, the reaction was quenched with CD3OD. 13C NMR
analysis of the crude product revealed that metal–halogen exchange had been
successful on account of the disappearance of the 13C-I signal at 94.6 ppm.
Careful chromatographic workup of the residue resulted in the isolation of
8, in 19% yield, presumably via a Wurtz-type coupling. Lochmann et al.
Scheme 2. Attempted synthesis of 1 via formylation of 7. Reagents and conditions:
i) Dibal-H, CH2Cl2, reflux, 1 h, 91%; ii) NaH, TBDMSCl, THF, rt, 12 h, 29%;
iii) a) n BuLi, THF, 2788C; b) DMF, THF, 2788C; iv) a) n BuLi, THF, 2788C; b)
d4-methanol, THF, 2788C.

240
E. Tullberg and T. Frejd
observed that the proportion of Wurtz product increased upon the addition of
alkoxides to a mixture of bromobenzene and n-BuLi in THF.[9] Therefore we
may assume that the alkoxide of 7 may be more than an innocent bystander in
this reaction. Mass analysis of further unpure fractions suggested that a
mixture of products had been formed where the iodo-substituent had been
replaced by a hydrogen or a deuterium.
Finally, we addressed the synthesis of benzene-1,3,5-tricarbaldehyde 9.
Previous syntheses of this compound were unsatisfactory in our hands. The
high-pressure hydrogenation of trimesic acid described by Nagayama et al. is
problematic because of limited autoclave batch size and a tedious workup of
bulb-to-bulb distillationand careful chromatographicseparation.[10] Procedures
in which the corresponding trialkyl-1,3,5-trimesoates are reduced to the corre-
sponding triol followed by oxidation to 9 necessarily involve reactive and toxic
chemicals and are complicated by the low solubility of the intermediate triol in
organic solvents.[11,12] Oxidation of readily available 1,3,5-trisbromomethyl
benzene under Sommelet conditions resulted in poor yields.[13] We
could avoid these problems by NMO oxidation of 1,3,5-trisbromomethyl
benzene.[14] Compound 9 was isolated from the reaction mixture in a reasonable
yield (47%) via a simple series of filtrations (Scheme 3).
CONCLUSION
As a result of this work, we have synthesized two aldehydes, 1 and 4, with
properties amendable to the stepwise selective buildup of complex MFDs,
and we have found a milder and more efficient synthesis of benzene-1,3,5-tri-
carbaldehyde 9.
EXPERIMENTAL
General Information
All reagents were used as delivered without further purification. Chromato-
˚
graphic workup was performed with Matrex 60-A 35 to 70-mesh silica.
Thin-layer chromatography (TLC) analyses were performed on Merck
silica-gel 60–coated aluminium plates. NMR spectra were recorded on a
Scheme 3. Synthesis of benzene-1,3,5-tricarbaldehyde.

Benzene-1,3,5-tricarbaldehyde
241
Bruker ARX 400 instrument or a Bruker ARX 300 instrument. Melting points
were measured on a Gallenkamp melting-point apparatus MFB-595 and are
uncorrected. IR spectra were recorded on a Shimadzu FTIR-8300 instrument,
and mass spectra were recorded on a Jeol SX-102 mass spectrometer. Micro-
analysis was performed by H. Kolbe Mikroanalytisches Laboratorium,
Mu¨hlheim an der Ruhr, Germany.
5-Hydroxymethyl-isophtalic acid diethyl ester 2 was purchased from
Aldrich and used without further purification. Ethyl acetate and heptane
were supplied by Fluka. Petroleum ether (bp 60–808C) was supplied by
VWR Prolabo.
5-(tert-Butyl-dimethyl-silanyloxymethyl)-isophtalic Acid Diethyl
Ester (2)
Imidazole (1.63 g, 23.9 mmol) and TBDMSCl (2.15 g, 14.3 mmol) were
added to a stirred solution of diethyl-5-hydroxymethyl isophtalate (3.00 g,
12 mmol) in DMF (20 ml). The mixture was stirred overnight at rt and then
diluted with ethyl ether (50 ml). The organic phase was washed with water
(3 ꢀ 50 ml), dried over Na2SO4, and filtered, and the solvents were
removed under reduced pressure. The residue was purified by column chrom-
atography (SiO2, petroleum ether–EtOAc gradient elution 50:1 to 5:1) to
remove excess tert-butyl-dimethylsilanol. The title compound 2 was isolated
as a clear oil (3.6 g, 81%). IR (NaCl, film): 2930, 2903, 1726, 1369,
1230 cm21
.
1H NMR (300 MHz, CDCl3): d ¼ 8.57 (s, 1H, Ar-H), 8.21
(s, 2H, Ar-H), 4.83 (s, 2H, Ar-CH2), 4.41 (q, 4H, J ¼ 7.14 Hz, J ¼ 6.5 Hz,
O-CH2-), 1.44 (t, 6H, J ¼ 6.5 Hz, CH3-), 0.97 [s, 9H, (CH3)3C], 0.06 [s,
6H, (CH3)2Si]. 13C NMR (75 MHz, CDCl3): d ¼ 166.1, 142.6, 131.3, 131.1,
129.4, 64.2, 61.5, 26.1, 18.6, 14.5, 25.0. HRMS (FABþ) m/z þ1 calculated
for C19H31O5Si: 367.1941. Found: 367.1941. Anal. calc. for C19H30O5Si:
C, 62.26; H, 8.25. Found: C, 62.34; H, 8.17.
[3-(tert-Butyl-dimethylsilanyloxymethyl)-5-hydroxymethyl-
phenyl]-methanol (3)
A solution of 2 (1.1 g, 3.0 mmol) in dry THF (10 ml) was added dropwise to a
stirred slurry of lithium aluminium hydride (228 mg, 6.1 mmol) in dry THF
(5 ml) at 08C over a period of 30 min. The dark slurry thus obtained was
heated to reflux for 1 h, left to cool, and then quenched by careful addition
of a solution of EtOAc (1.3 ml) in THF (20%). The mixture was stirred at rt
for an hour, and then aqueous Na2SO4 (sat., 1.3 ml) was added. The
mixture was left to stir overnight. The slurry was then filtered through a
glass frit, and the precipitate was washed thoroughly with EtOAc. The
solution was dried with Na2SO4 and filtered, and the solvents were removed

242
E. Tullberg and T. Frejd
under reduced pressure. The title compound 3 was isolated as a clear oil and
was used in the next step without further purification (0.8 g, 94%). IR (NaCl,
1
film): 3333, 2854, 1373, 1254 cm21. H NMR (300 MHz, CDCl3): d ¼ 7.26
(s, 3H, Ar-H), 4.87 (s, 2H, Ar-CH2), 4.75 (s, 4H, ArCH2), 0.95 [s, 9H,
(CH3)3C], 0.11 [s, 6H, (CH3)2Si]. 13C NMR (75 MHz, CDCl3): d ¼ 142.1,
141.4, 124.3, 124.1, 65.2, 65.0, 26.1, 18.6, 25.0. HRMS (FABþ) m/z 21
calculated for C15H25O3Si: 281.1578. Found: 281.1574. Anal. calc. for
C15H26O3Si: C, 63.78; H, 9.28. Found: C, 63.88; H, 9.36.
3-(tert-Butyl-dimethyl-silanyloxymethyl)-5-hydroxymethyl-
benzaldehyde (1) and 5-(tert-Butyl-dimethyl-silanyloxymethyl)-
benzene-1,3-dicarbaldehyde (4)
TPAP (11 mg, 3.2 ꢀ 1025 mol), NMO (83 mg, 0.70 mmol), and crushed
˚
molecular sieves 4A (200 mg) were added to a stirred solution of 3 (200 mg,
0.708 mmol) in dichloromethane (5 ml). The black slurry was stirred vigor-
ously at rt overnight. TLC analysis (heptane–EtOAc 1:1) showed that two
new products had been formed with Rf 0.82 and 0.53 respectively. The slurry
was then filtered through a pad consisting of a layer of Celite over silica and
washed thoroughly with dichloromethane. The solvent was then removed
under reduced pressure, and the residue was purified by column chromato-
graphy (SiO2, heptane–EtOAc 10 : 1). Product 4 ¼ Rf 0.82 (heptane, EtOAc
1:1) was isolated as a clear oil (38 mg, 19%). IR (NaCl, film): 2928, 2858,
1
1701, 1373, 1254 cm21. H NMR (300 MHz, CDCl3): d ¼ 10.12 [s, 2H,
CHO], 8.26 (s, 1H, Ar-H), 8.11 (s, 2H, Ar-H), 4.87 (s, 2H, Ar-CH2-), 0.96
(s, 9H, (CH3)3C), 0.12 [s, 6H, (CH3)2Si]. 13C NMR (75 MHz, CDCl3):
d ¼ 191.4, 144.4, 137.3, 132.2, 129.9, 64.0, 26.1, 18.7, 25.0. HRMS
(FABþ) m/z -1 calculated for C15H21O3Si: 277.1265. Found: 277.1273.
Anal. calc. for C15H22O3Si: C, 64.71; H, 7.96. Found: C, 64.79; H, 7.91.
Product 1 ¼ Rf 0.53 (heptane, EtOAc 1:1) was isolated as a clear oil
(125 mg, 62%). IR (NaCl, film): 3410, 2858, 1701, 1365, 1254 cm21
.
1H NMR (300 MHz, CDCl3): d ¼ 10.02 (s, 1H, CHO), 7.77 (s, 2H, Ar-H),
7.61 (s, 1H, Ar-H), 4.81 (s, 2H, Ar-CH2), 4.79 (s, 2H, Ar-CH2-), 0.95 [s, 9H,
(CH3)3C], 0.11 [s, 6H, (CH3)2Si]. 13C NMR (75 MHz, CDCl3): d ¼ 192.4,
143.1, 142.0, 136.8, 130.4, 126.6, 126.5, 64.7, 64.3, 26.0, 18.5, 25.2. HRMS
(FABþ) m/z -1 calculated for C15H23O3Si: 279.1422. Found: 279.1421.
Anal. calc. for C15H24O3Si: C, 64.24; H, 8.63. Found: C, 64.08; H, 8.52.
3-Hydroxymethyl-5-iodo-phenyl-methanol (5)
A solution of DIBAL-H 1 M in dichloromethane (50 ml, 50 mmol) was added
to a stirred solution of 5-iodo-isophthalic acid dimethyl ester[7] (2.7 g,
9.0 mmol) in dry dichloromethane (50 ml) at 2308C over a period of

Benzene-1,3,5-tricarbaldehyde
243
30 min. The reaction mixture was then heated at reflux for 6 h and then stirred
at rt overnight. The brown reaction mixture was then quenched by careful
addition of EtOH (100 ml), and a white precipitate formed. The slurry was
filtered, and the filtercake was triturated with hot ethanol (3 ꢀ 100 ml).
Silica (6 g) was added to the filtrate, and the solvents were removed under
reduced pressure. The solid residue thus absorbed on silica was purified by
column chromatography (SiO2, petroleum ether–EtOAc 1:1) to give the
title compound 5 as a white powder (2.00 g, 91%), mp: 105.3–106.38C. IR
(KBr): 3333, 3244, 2895, 1600 cm21 1H NMR (300 MHz, CDCl3):
.
d ¼ 7.65 (s, 2H, Ar-H), 7.33 (s, 1H, Ar-H), 4.67 (s, 4H, Ar-CH2). 13C NMR
(75 MHz, DMSO-d6): d ¼ 145.2, 133.3, 123.9, 94.5, 62.2. HRMS (FABþ)
m/z calculated for C8H9IO2: 263.9647. Found: 263.9627. Anal. calc. for
C8H9IO2: C, 36.39; H, 3.44. Found: C, 36.49, H, 3.28.
[3-(tert-Butyl-dimethyl-silanyloxymethyl)-5-iodo-phenyl]-methanol (7)
NaH 60% in mineral oil (150 mg, 3.75 mmol) was added to a stirred solution of
6 (0.8 g, 3.13 mmol) in dry THF (5 ml) at 08C. When the gas evolution had
ceased, TBDMSCl (470 mg, 3.13 mmol) was added in one portion. The
solution was stirred at rt overnight and diluted with diethyl ether (10 ml),
and water (10 ml) was added carefully to destroy residual NaH. The aqueous
phase was extracted with diethyl ether (3 ꢀ 20 ml), the combined organic
phases were dried over Na2SO4 and filtered, and the solvents were removed
under reduced pressure. The residue was purified by column chromatography
(SiO2, petroleum ether–EtOAc 1:1) to give the title compound 7 as a clear oil
1
(0.35 g, 29%). IR (NaCl, film): 3364, 2942, 1358, 1249 cm21. H NMR
(300 MHz, CDCl3): d ¼ 7.59 (s, 2H, Ar-H), 7.26 (s, 1H, Ar-H), 4.74 (s, 2H,
Ar-CH2), 4.64 (s, 2H, Ar-CH2). 13C NMR (75 MHz, CDCl3): d ¼ 144.2,
143.2, 134.5, 134.4, 123.8, 94.6, 64.7, 64.2, 26.2, 18.6, 25.0. HRMS
(FABþ) m/z 2 1 calculated for C14H22IO2Si: 377.0439. Found: 377.0454.
[3-Butyl-5-(tert-butyl-dimethyl-silanyloxymethyl)-phenyl]-
methanol (8)
NaH 60% in mineral oil (32 mg, 0.79 mmol) was added to a solution of
7 (200 mg, 0.529 mmol) in dry THF (5 ml) at 08C. When the gas evolution
had ceased, the slightly yellow slurry was cooled to 2788C, then n-BuLi
(2.5 M in hexanes) (0.4 ml, 1.0 mmol) was slowly added to the slurry via a
syringe. The slurry turned bright yellow, and stirring was continued at
2788C for a further 2 h, by which time the slurry had darkened somewhat.
The mixture was then quenched with CD3OD (0.5 ml), precooled to
2788C, and left to stir and reach rt overnight. Water (5 ml) was carefully
added to the slurry to destroy residual NaH, and the mixture was extracted

244
E. Tullberg and T. Frejd
with diethyl ether (3 ꢀ 10 ml). The combined organic phases were dried over
Na2SO4, and the solvent was removed under reduced pressure to afford a
yellow oil, 178 mg. Upon TLC analysis (petroleum ether–EtOAc, 5:1 and
3:1), this oil was found to contain a mixture of at least three products.
Crude product NMR analysis showed no C-I signal. The products correspond-
ing to the two most intense spots were separated by careful column chromato-
graphy (SiO2, petroleum ether–EtOAc, 10:1). Only the title compound 8
could be isolated in acceptable purity as a clear oil (19% of mixture on
comparing with the crude product, NMR spectrum). IR (NaCl) film: 3342,
2942, 2871, 1468, 1249 cm21
.
1H NMR (400 MHz, CDCl3): d ¼ 7.13
(s, 1H, Ar-H), 7.07 (s, 2H, Ar-H), 4.72 (s, 2H, Ar-CH2), 4.66 (s, 2H, Ar-
CH2), 2.61 (t, 2H, J ¼ 7.6 Hz, Ar-CH2-C3H7), 1.63–1.57 (m, 2H, Ar-CH2-
C2-C2H5), 1.42–1.28 (m, 2H, Ar-C2H4-CH2-CH3), 0.94–0.88 [m, 12 H,
C(CH3)3, Ar-C3H6-C3], 0.10 [s, 6H, (CH3)2Si]. 13C NMR (100 MHz,
CDCl3): d ¼ 141.5, 141.9, 141.0, 126.0, 125.8, 122.3, 65.8, 65.2, 35.8, 33.8,
26.2, 22.6, 18.6, 14.2, 25.0. HRMS (FABþ) m/z 21 calculated for
C18H31O2Si: 307.2099. Found: 307.2087.
Benzene-1,3,5-tricarbaldehyde (9)
The title compound was synthesized according to literature methodology for
the synthesis of benzaldehyde from benzyl bromide.[15]
N-methyl-morpholine oxide (1 g, 8.4 mmol) and crushed molecular
sieves (10 g) were added to a stirred solution of 1,3,5-tris-bromomethyl-
benzene (0.5 g, 1.4 mmol) in acetonitrile (50 ml).
Caution: 1,3,5-tris-Bromomethyl-benzene is a very potent irritant.
Always use gloves when handling this compound. It was synthesized
according to literature procedure.[14]
The resulting slurry was heated to reflux and stirred vigorously overnight
and then left to cool. The slurry was then filtered through a pad of silica,
followed by rinsing with EtOAc. Silica (1.5 g) was added to the filtrate, and
the solvents were removed under reduced pressure. The solid residue
absorbed on silica was placed on a short column and eluted with heptane–
ethylacetate 1 : 1 (200 ml). The solvents were removed under reduced
pressure to afford the title compound 9 (0.11 g, 47%). The melting point
1
163–1658C (lit. 164–1658C) and H NMR data of the compound were in
accordance with literature data.[11,16]
ACKNOWLEDGMENTS
The authors thank the Swedish Science Council, the Royal Physiographic
Society in Lund, and the Lund, University Research School of Medicinal
Sciences for financial support.

Benzene-1,3,5-tricarbaldehyde
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