Fe(III)-catalyzed trityl benzyl ether formation and disproportionation cascade reactions to yield benzaldehydes

Article abstract of DOI:10.1016/j.tet.2015.07.040

During investigating water-compatible Lewis acids catalyzed etherifications using alcohols as alkylating reagents directly, we developed Fe(III)-catalyzed trityl benzyl ether formations irradiated by microwave. Then an in situ trityl benzyl ether formation and disproportionation cascade reaction was achieved to yield the benzaldehyde products with good functional group tolerances under neat conditions at relative higher temperatures. The substituent effects of the substrates on the etherification and disproportionation were explored by changing the substitutions on benzyl alcohols and triarylmethanols using chemical kinetic plots methods and the mechanism of the transformation was studied by crossover experiments. The etherification and disproportionation cascade process could be conveniently scaled up in laboratory without losing much efficiency.

Full text of DOI:10.1016/j.tet.2015.07.040

Tetrahedron 71 (2015) 6744e6748
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Fe(III)-catalyzed trityl benzyl ether formation and
disproportionation cascade reactions to yield benzaldehydes
,
,
,
,
,b
Xiaoyu Wang a b, Chuan Du a b, Hui Shi a b, Yadong Pang a b, Shengfei Jin a
,
Yuqian Hou a b, Yanshi Wang a b, Xiaoshi Peng a b, Jianyong Xiao b, Yang Liu a,
,
,
,
Yongxiang Liu a , Maosheng Cheng
,
b,
a,b,
*
*
a Key Laboratory of Structure-Based Drug Design and Discovery (Shenyang Pharmaceutical University), Ministry of Education,
Shenyang 110016, PR China
b Institute of Drug Research in Medicine Capital of China, Benxi 117000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 May 2015
Received in revised form 10 July 2015
Accepted 14 July 2015
Available online 18 July 2015
During investigating water-compatible Lewis acids catalyzed etherifications using alcohols as alkylating
reagents directly, we developed Fe(III)-catalyzed trityl benzyl ether formations irradiated by microwave.
Then an in situ trityl benzyl ether formation and disproportionation cascade reaction was achieved to
yield the benzaldehyde products with good functional group tolerances under neat conditions at relative
higher temperatures. The substituent effects of the substrates on the etherification and disproportion-
ation were explored by changing the substitutions on benzyl alcohols and triarylmethanols using
chemical kinetic plots methods and the mechanism of the transformation was studied by crossover
experiments. The etherification and disproportionation cascade process could be conveniently scaled up
in laboratory without losing much efficiency.
Keywords:
Iron
Trityl benzyl ether
Disproportionation
Benzaldehyde
Mechanism
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
laboratory and industry in view of sustainable chemistry. Despite
the numerous transformations based on the sustainable metal
Selective oxidation of primary alcohols, especially benzyl alco-
hols into benzaldehydes is a fundamental and indispensable
transformation in organic synthesis. Generally, the oxidation of
benzyl alcohols to benzaldehydes in laboratory is completed by
several methods, involving the use of stoichiometric amounts of
inorganic oxidants such as manganese1 and chromium salts,2 ac-
tivated DMSO-mediated Swern oxidation,3 hypervalent iodine
based reagents,4 TPAP/NMO oxidative system,5 TEMPO oxidation,6
molecular oxygen with transition-metal catalysts7 and so on.
Nowadays, it has become a routine procedure to achieve the se-
lective oxidation of benzyl alcohols in laboratory.
As many environmental issues are recognized and the supply of
most useful metal ores is being exhausted,8 less toxic and costly
earth-abundant metals, such as sodium, potassium, calcium, alu-
minium, titanium and iron based green catalysts have attracted
much attention9 and should be preferably chosen as reagents in
derived catalysts that have been developed so far,10 many limita-
tions are still present in this area of research and these remaining
challenges will provide many opportunities for researchers.
2. Results and discussion
As part of our research on the investigation of water-compatible
Lewis acids catalyzed methods of etherification using alcohols as
alkylating reagents, we compared the sustainable metal iron11 with
precious metal gold in the formation of trityl benzyl ether 3 from
benzyl alcohol 1 and triphenylmethanol 2, developed in our group
previously.12 Interestingly, we found that when 0.05 mol
%
Ph3PAuNTf2 was used as catalyst, the ether 3 could be generated in
92% yield, however, no product could be detected at the same ca-
talysis loading of FeCl3$6H2O. Increasing the catalyst loading of
FeCl3$6H2O to 10 mol % results in complete consumption of the
starting materials and furnished the product 3 in a yield of 87%
despite lower temperature compared to Ph3PAuNTf2 conditions
(Scheme 1).
* Corresponding authors. Tel.: þ86 2445864056; e-mail addresses: yongxiang.
liu@syphu.edu.cn (Y. Liu), mscheng@syphu.edu.cn (M. Cheng).
http://dx.doi.org/10.1016/j.tet.2015.07.040
0040-4020/Ó 2015 Elsevier Ltd. All rights reserved.

X. Wang et al. / Tetrahedron 71 (2015) 6744e6748
6745
Scheme 1. Au(I) and Fe(III)-catalyzed formation of trityl benzyl ether 3.
This promising result promoted us to examine the scope of the
Fe(III)-catalyzed etherification. To our delight, all the selected
substrates gave moderate to excellent yields under the standard
conditions (3ae3p, Fig. 1). The etherification had good tolerance of
functional groups and those substrates with electron-donating,
electron-withdrawing or halogen groups could give good yields.
Unexpected results were obtained as we raised the temperature
of reaction between benzyl alcohol 1 and triphenylmethanol 2 from
45 ꢀC to 55 ꢀC under microwave irradiation. We observed that the
benzaldehyde 4 and triphenylmethane were isolated exclusively
instead of the corresponding ether 3 as shown in Scheme 2, in-
dicating that a disproportionation of the ether13 occurred under the
catalysis of FeCl3$6H2O. To test this hypothesis, we performed some
controlled experiments. We heated the intermediate 3 in the ab-
sence of FeCl3$6H2O and found no benzaldehyde. We also treated
benzyl alcohol with FeCl3$6H2O under oxygen atmosphere and
trace amount of benzaldehyde could be detected, which excluded
the possibility of formation of the benzaldehyde from cleavage of
trityl ether and sequent oxidation of the benzyl alcohol.14 To further
exclude the influence of oxygen, the reaction was also carried out at
nitrogen atmosphere and the benzaldehyde product still could be
yielded (Scheme 2). The reaction was also examined in classical
heating oil baths to afford the product efficiently only consuming
much longer reaction time (more than 24 h). It was noteworthy that
the reaction could proceed smoothly under neat conditions and the
triphenylmethanol could be readily renewed from the by-product
triphenylmethane in one step.15 This one-pot sequence provides
us a robust and alternative Fe(III)-catalyzed strategy to prepare
benzaldehydes via trityl benzyl ether formation and
disproportionation.
Scheme 2. Fe(III)-catalyzed formation of benzaldehyde and controlled experiments.
With these results in hand, we further optimized and in-
vestigated the etherification and disproportionation cascade re-
action by employing substituted benzyl alcohols. In all cases, no
additional solvents were required in the oxidation and the reaction
profiles were so clean that the crude product could be subjected to
the silica gel column chromatography directly. The benzyl alcohols
with electron donating substituents on the phenyl ring could be
transformed to the corresponding benzaldehydes in excellent
yields (4ae4e, Fig. 2). The substrates with electron-withdrawing
groups resulted in a slight decrease in efficiency (4f and 4g,
Fig. 2). The 2-bromosubstituted substrates were chosen consider-
ing that the benzaldehydes with halogens could be utilized as im-
portant synthetic intermediates.16 Satisfactory results were
obtained in all the selected bromosubstituted substrates (4he4o,
Fig. 2). More sensitive aromatic aldehydes such as thiophene-2-
carbaldehyde could also be synthesized but with a relatively
lower yield due to the generation of some unidentifiable impurities
(4p, Fig. 2).
The substituent effects of the substrates on the etherification
and disproportionation were explored by changing the
Fig. 1. Scope of Fe(III)-catalyzed formation of trityl benzyl ethers.
Fig. 2. Scope of Fe(III)-catalyzed disproportionation of trityl benzyl ethers.

6746
X. Wang et al. / Tetrahedron 71 (2015) 6744e6748
substitutions on benzyl alcohols or triarylmethanols. First, we
chose 1, 1e and 1n as the substrates to perform the reaction at 45 ꢀC
for 1 h at a 5 mol % loading of catalyst by using triphenylmethanol
as the alkylating reagent. The etherification reactions were moni-
tored every ten minutes and the isolated yields of 3, 3e and 3n were
plotted versus the time; thus providing the corresponding kinetic
plots a and b in Scheme 3. The plots of disproportionation were
described using the same procedure but with temperature in-
creased to 55 ꢀC. Comparing the two plots, we observed that the
substituent effects of benzyl alcohols have consistent influence on
the etherification and disproportionation. The richer the electron
density of the aromatic system is, the faster the reactions proceed.
To probe the mechanism of this disproportionation, we pre-
pared the ether 3s with the methoxyl substitution on one phenyl
ring of trityl group17 and 3t deuterated on the benzyl position.18
Under standard conditions, this substrate underwent a deuterium
crossover. The corresponding benzaldehydes 4e and deuterated
benzaldehyde 4e0 were detected together with non-crossover
products triarylmethanes 50, 6 and crossover products 5, 60 assis-
ted by NMR technique (Scheme 5). These results indicated that the
hydride transfer might occur in an intermolecular manner in the
disproportionation when the oxygen of substrates was coordinated
with iron.
Scheme 5. Mechanism determination by crossover experiments.
3. Conclusions
In summary, we described a sustainable Fe(III)-catalyzed trityl
benzyl etherification formation and disproportionation cascade
reaction to produce benzaldehydes in gram scales under neat
conditions. The influence of the substitutions of the triphenylme-
thanols and benzyl alcohols was examined by using designed
substrates. The reaction mechanistically involves in situ formation
and the following disproportionation of trityl benzyl ethers. This
procedure provides a robust and environmentally compatible route
to synthesize gram quantities of substituted benzaldehydes in
a laboratory setting.
Scheme 3. Influences of electron effects on the etherification and disproportionation.
a Plot of etherification of benzyl alcohols 1, 1e and 1n with triphenylmethanol. b Plot of
disproportionation of benzyl alcohols 1, 1e and 1n (for 1e, the temperature was 50 ꢀC).
c
Plot of etherification of triphenylmethanol 2, tri(4-methoxyphenyl)methanol 2q and
d
tri(4-chlorophenyl)methanol 2r with benzyl alcohol. Plot of disproportionation of
triarylmethanols 2, 2q and 2r.
4. Experimental section
4.1. General information
To complement the study of benzyl alcohol substitution we set
out to examine the substituent effects of triarylmethanols by uti-
lizing triphenyl-methanol 2, tri(4-methoxyphenyl)methanol 2q
and tri(4-chlorophenyl)methanol 2r, which were reacted with
benzyl alcohol 1 under the standard conditions. As shown in
Scheme 3, the substituent effects of 2, 2q and 2r on the ether-
ification and disproportionation reactions were totally opposite.
The tri(4-methoxyphenyl)methanol 2q underwent fastest in the
formation of ether (c in Scheme 3). On the contrary, the dispro-
portionation of 2q became very difficult and the benzaldehyde 4
could not be detected after 1 h at 55 ꢀC (d in Scheme 3). We also
attempted to increase the temperature to 80 ꢀC, but the ether-
ification and disproportionation of 2q remained unsuccessful.
We wished to explore the feasibility of performing the reaction
on larger scale. We found that the etherification and dispropor-
tionation cascade reaction could be conveniently scaled up to 2 g
without losing much efficiency by elevating the temperature from
55 ꢀC to 65 ꢀC. This allows the gram-scale synthesis of benzalde-
hyde derivatives in laboratory (Scheme 4).
Reagents were obtained commercially and used without further
purification. TLC analysis of reaction mixtures was performed on
Dynamicadsorbents silica gel F-254 TLC plates. Flash chromatog-
raphy was carried out on Zeoprep 60 (200e300 mesh) silica gel. 1H
and 13C NMR spectra were recorded with Bruker Avance-III 600
spectrometers and referenced to CDCl3 and DMSO-d6. HR-ESI-MS
were recorded on a Bruker SolariX 7.0T instrument. IR spectra
were recorded on a Bruker IFS 55 spectrometer. Melting points
were tested on Thomas Hoover capillary melting point apparatus.
Microwave reactions were performed on CEM discover microwave
reactor.
4.2. General procedures for the synthesis of trityl benzyl
ethers
The benzyl alcohols substrates (1ae1p) (0.2 mmol), FeCl3$6H2O
(0.002 mmol, 5.4 mg) and triphenylmethanol 2 (0.2 mmol, 52 mg)
were mixed in a dried vessel. Then the reaction was irradiated
under the microwave at 45 ꢀC for 1 h. The crude mixture was pu-
rified by a flash column chromatography to give the trityl benzyl
ethers (3ae3p).
4.2.1. (((3-Methylbenzyl)oxy)methanetriyl)tribenzene (3b). White
solid in 84% yield (EtOAc/petroleum ether¼1:200): Mp
Scheme 4. Gram-scale synthesis of benzaldehyde.
76.4e77.8 ꢀC; 1H NMR (600 MHz, CDCl3)
d 7.62e7.55 (m, 6H), 7.36

X. Wang et al. / Tetrahedron 71 (2015) 6744e6748
6747
(t, J¼7.7 Hz, 6H), 7.31e7.26 (m, 5H), 7.23 (s, 1H), 7.14 (d, J¼7.0 Hz,
1H), 4.20 (s, 2H), 2.41 (s, 3H); 13C NMR (150 MHz, CDCl3)
144.37,
139.24, 138.02, 128.95, 128.39, 128.04, 127.91, 127.20, 124.26, 87.15,
65.96, 21.70; IR (thin film, cmꢁ1) 3085, 3057, 3031, 2865, 2345,1818,
1609, 1595, 1490, 1448, 1371, 1220, 1001; HRMS (ESI): Calcd for
116.00, 115.45, 115.43, 115.23, 115.07, 87.04, 64.69; IR (thin film,
cmꢁ1) 3060, 3019, 2923, 2853, 1957, 1605, 1599, 1580, 1466, 1445,
1227, 1148, 1111, 1086, 1029, 900; HRMS (ESI): Calcd for
d
C26H20BrFKO 485.029010, Found 485.031314.
C
27H24NaO 387.171936, Found 387.172068.
4.2.8. (((2-Bromo-4-fluorobenzyl)oxy)methanetriyl)tribenzene
(3n). White solid in 71% yield (EtOAc/petroleum ether¼1:200): Mp
4.2.2. (((4-(tert-Butyl)benzyl)oxy)methanetriyl)tribenzene
167.5e168.2 ꢀC; 1H NMR (600 MHz, CDCl3)
d
7.73 (dd, J¼8.5, 6.2 Hz,
(3c). White solid in 86% yield (EtOAc/petroleum ether¼1:200): Mp
1H), 7.52e7.48 (m, 6H), 7.32 (t, J¼7.6 Hz, 6H), 7.25e7.27 (m, 5H),
116.7e117.3 ꢀC; 1H NMR (600 MHz, CDCl3)
d 7.58e7.55 (m, 6H),
7.09 (td, J¼8.4, 2.6 Hz, 1H), 4.20 (s, 2H); 13C NMR (150 MHz, CDCl3)
7.44e7.40 (m, 2H), 7.37 (d, J¼8.4 Hz, 2H), 7.34 (t, J¼7.6 Hz, 6H),
d 162.46, 160.81, 144.01, 134.60, 134.57, 129.69, 129.64, 128.88,
7.29e7.26 (m, 3H), 4.19 (s, 2H), 1.37 (s, 9H); 13C NMR (150 MHz,
128.14, 127.41, 122.20, 122.14, 119.77, 119.61, 114.68, 114.54, 87.60,
CDCl3)
d
150.19, 144.41, 136.37, 128.97, 128.03, 127.18, 126.91, 125.37,
65.20; IR (thin film, cmꢁ1) 3452, 2921, 2851, 1958, 1641, 1596, 1493,
87.06, 65.64, 34.71, 31.62. IR (thin film, cmꢁ1) 3421, 2958, 2920,
1958, 1596, 1489, 1448, 1218, 1031; HRMS (ESI): Calcd for C30H30KO
445.192800, Found 445.192824.
1447, 1225, 1078, 809; HRMS (ESI): Calcd for
485.029810, Found 485.031314.
C26H20BrFKO
4.2.9. (((2-Bromo-5-chlorobenzyl)oxy)methanetriyl)tribenzene
4.2.3. (((2-Bromo-4-methylbenzyl)oxy)methanetriyl)tribenzene
(3o). White solid in 73% yield (EtOAc/petroleum ether¼1:200): Mp
(3h). White solid in 83% yield (EtOAc/petroleum ether¼1:150): Mp
128.8e130.2 ꢀC; 1H NMR (600 MHz, CDCl3)
d
7.76 (d, J¼2.6 Hz, 1H),
109.2e110.4 ꢀC; 1H NMR (600 MHz, CDCl3)
d
7.66 (d, J¼7.8 Hz, 1H),
7.49e7.51 (m, 6H), 7.38 (d, J¼8.4 Hz, 1H), 7.32e7.35 (m, 6H),
7.55e7.50 (m, 6H), 7.33 (t, J¼7.6 Hz, 7H), 7.25e7.27 (m, 3H), 7.19 (d,
7.26e7.27 (m, 3H), 7.11 (dd, J¼8.4, 2.6 Hz, 1H), 4.20 (s, 2H); 13C NMR
J¼7.6 Hz, 1H), 4.20 (s, 2H), 2.33 (s, 3H); 13C NMR (150 MHz, CDCl3)
(150 MHz, CDCl3)
d 143.84, 140.48, 133.77, 133.38, 128.85, 128.53,
d
144.19, 138.66, 135.58, 132.92, 128.93, 128.54, 128.35, 128.08,
128.20, 127.47, 119.75, 87.75, 65.41; IR (thin film, cmꢁ1) 3452, 3059,
2921, 2851, 1958, 1641, 1596, 1493, 1447, 1225, 1078; HRMS (ESI):
Calcd For C26H20BrClNaO 485.027790, Found 485.027826.
127.31, 122.18, 87.40, 65.58, 20.95; IR (thin film, cmꢁ1) 3420, 3059,
3020, 2922, 2851, 2254, 1489, 1447, 1081, 1036; HRMS (ESI): Calcd
For C27H23BrNaO 465.082167, Found 465.082448.
4.2.10. 2-((Trityloxy)methyl)thiophene (3p). White solid in 78%
yield (EtOAc/petroleum ether¼1:150): Mp 89.4e90.5 ꢀC; 1H NMR
4.2.4. 4-Bromo-2-methoxy-5-((trityloxy)methyl)phenol (3j). White
solid in 82% yield (EtOAc/petroleum ether¼1:50): Mp
(600 MHz, DMSO-d6)
d
7.50 (d, J¼5.0 Hz, 1H), 7.43 (d, J¼7.9 Hz, 6H),
160.1e161.9 ꢀC; 1H NMR (600 MHz, CDCl3)
d
7.51 (d, J¼7.4 Hz, 6H),
7.37 (t, J¼7.7 Hz, 6H), 7.29 (t, J¼7.2 Hz, 3H), 7.01e6.97 (m, 1H), 6.96
7.35 (s, 1H), 7.31e7.34 (m, 6H), 7.24 (d, J¼7.3 Hz, 3H), 6.96 (s, 1H),
(s, 1H), 4.22 (s, 2H); 13C NMR (150 MHz, DMSO-d6)
d
143.44, 141.01,
5.57 (s, 1H), 4.11 (s, 2H), 3.88 (s, 3H); 13C NMR (150 MHz, CDCl3)
128.11, 128.05, 127.20, 126.78, 125.54, 125.13, 86.68, 61.01; IR (thin
film, cmꢁ1) 3058, 3032, 2864, 1961, 1596, 1490, 1448, 1376, 1338,
1218, 1180, 1150, 1066, 1032; HRMS (ESI): Calcd for C24H20NaOS
379.112707, Found 379.113021.
d
146.21, 145.17, 144.16, 131.60, 128.94, 128.08, 127.29, 114.99, 114.85,
111.28, 87.40, 65.37, 56.48; IR (thin film, cmꢁ1) 3508, 3058, 3029,
2928, 2851, 1958, 1640, 1579, 1500, 1448, 1280, 1202, 1153, 1031;
HRMS (ESI): Calcd for
497.072277.
C27H23BrNaO3 497.071364, Found
4.2.11. 4,40,400-((Benzyloxy)methanetriyl)tris(methoxybenzene)
(3q). White solid in 92% yield (EtOAc/petroleum ether¼1:80): Mp
4.2.5. (((2-Bromo-4,5-dimethoxybenzyl)oxy)methanetriyl)tribenz-
142.5e144.3 ꢀC; 1H NMR (600 MHz, DMSO-d6)
d
7.35 (d, J¼4.3 Hz,
ene (3k). White solid in 88% yield (EtOAc/petroleum ether¼1:80):
4H), 7.33e7.29 (m, 6H), 7.27 (dt, J¼8.7, 4.3 Hz, 1H), 6.90 (d, J¼8.8 Hz,
Mp 115.7e117.5 ꢀC; 1H NMR (600 MHz, CDCl3)
d
7.51 (d, J¼7.4 Hz,
6H), 4.07 (s, 2H), 3.73 (s, 9H); 13C NMR (150 MHz, DMSO-d6)
6H), 7.32 (t, J¼7.6 Hz, 7H), 7.27 (s, 2H), 7.25 (d, J¼7.5 Hz, 2H), 7.22 (s,
d 157.98, 138.77, 136.26, 129.31, 128.30, 127.09, 126.65, 113.23, 85.57,
1H), 6.96 (s, 1H), 4.19 (s, 2H), 3.92 (s, 3H), 3.86 (s, 3H); 13C NMR
64.78, 55.00; IR (thin film, cmꢁ1) 3031, 2996, 2952, 2928, 2901,
2832, 2046, 1916, 1607, 1580, 1505, 1465, 1454, 1442, 1415, 1379,
1302, 1246, 1175, 1153, 1086, 1063, 1027; HRMS (ESI): Calcd for
(150 MHz, CDCl3)
d 148.70, 148.57, 144.18, 130.79, 129.90, 128.91,
128.11, 127.36, 115.42, 112.32, 111.96, 87.49, 65.48, 56.41, 56.29; IR
(thin film, cmꢁ1) 3421, 3072, 3024, 2921, 2851, 1958, 1659, 1632,
1050, 1448, 1266, 1211, 1159, 1031; HRMS (ESI): Calcd for
C29H28NaO4 463.187980, Found 463.188392.
C
28H25BrNaO3 511.086708, Found 511.087927.
4.2.12. 4,40,400-((Benzyloxy)methanetriyl)tris(chlorobenzene)
(3r). White solid in 77% yield (EtOAc/petroleum ether¼1:200): Mp
4.2.6. 5-Bromo-6-((trityloxy)methyl)benzo[d][1,3]dioxole
146.0e147.8 ꢀC; 1H NMR (600 MHz, DMSO-d6)
d 7.46e7.41 (m, 12H),
(3l). White solid in 82% yield (EtOAc/petroleum ether¼1:100): Mp
7.38e7.33 (m, 4H), 7.31e7.27 (m, 1H), 4.09 (s, 2H); 13C NMR
110.9e112.0 ꢀC; 1H NMR (600 MHz, CDCl3)
d
7.52e7.48 (m, 6H),
(150 MHz, DMSO-d6) d 141.90,137.89,132.25,129.95,128.36,128.25,
7.31e7.33 (m, 6H), 7.27 (s, 2H), 7.26e7.24 (m, 2H), 6.94 (s, 1H), 5.99
127.38, 126.88, 85.35, 65.35; IR (thin film, cmꢁ1) 3067, 3029, 2899,
2866, 1607, 1588, 1487, 1453, 1402, 1378, 1306, 1245, 1219, 1175,
1156, 1093, 1066, 1013; HRMS (ESI): Calcd for C26H19Cl3NaO
475.039369, Found 475.039101.
(s, 2H), 4.13 (s, 2H); 13C NMR (150 MHz, CDCl3)
d
144.08, 128.90,
128.12, 127.35, 112.61, 108.98, 101.84, 87.49, 65.64; IR (thin film,
cmꢁ1) 3420, 3071, 3023, 2923, 2851, 2253, 1632, 1503, 1487, 1448,
1421, 1263, 1238, 1119, 1051; HRMS (ESI): Calcd for C27H21BrNaO3
495.056524, Found 495.056627.
4.2.13. (((4-Methoxybenzyl)oxy)(4methoxyphenyl)methylene)dib-
enzene (3s). White solid in 93% yield (EtOAc/petroleum
ether¼1:100): Mp 77.4e78.1 ꢀC; 1H NMR (600 MHz, CDCl3)
4.2.7. (((2-Bromo-5-fluorobenzyl)oxy)methanetriyl)tribenzene
(3m). White solid in 74% yield (EtOAc/petroleum ether¼1:200):
d
7.58e7.54 (m, 4H), 7.46e7.42 (m, 2H), 7.34 (t, J¼7.8 Hz, 6H),
Mp 124.3e125.5 ꢀC; 1H NMR (600 MHz, DMSO-d6)
d
7.59 (dd, J¼8.8,
7.25e7.27 (m, 2H), 6.95e6.91 (m, 2H), 6.90e6.87 (m, 2H), 4.14 (s,
5.3 Hz, 1H), 7.49 (dd, J¼9.6, 3.1 Hz, 1H), 7.45 (dd, J¼8.4, 1.1 Hz, 6H),
7.38 (t, J¼7.8 Hz, 6H), 7.29 (t, J¼7.3 Hz, 3H), 7.13 (td, J¼8.5, 3.1 Hz,
2H), 3.84 (s, 3H), 3.82 (s, 3H); 13C NMR (150 MHz, CDCl3)
d
158.97,
158.72, 144.89, 136.13, 131.50, 130.58, 128.68, 128.00, 127.03, 113.87,
113.28, 86.78, 65.54, 55.45, 55.39; IR (thin film, cmꢁ1) 3434, 3057,
3032, 2999, 2953, 2931, 2865, 2835, 2549, 2490, 2051, 1961, 1737,
1H), 4.12 (s, 2H); 13C NMR (150 MHz, DMSO-d6)
d 162.37, 160.75,
143.26, 139.96, 139.91, 133.88, 133.82, 128.13, 128.09, 127.32, 116.15,

6748
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1611, 1585, 1512, 1463, 1446, 1300, 1249, 1176, 1153; HRMS (ESI):
Calcd for C28H26NaO3 433.174722, Found 433.177415.
4.2.14. 2d-(((4-Methoxybenzyl)oxy)methanetriyl)tribenzene
(3t). White solid in 90% yield (EtOAc/petroleum ether¼1:100): Mp
129.2e131.3 ꢀC; 1H NMR (600 MHz, CDCl3)
d 7.51e7,52 (m, 6H),
7.29e7.32 (m, 8H), 7.23e7.25 (m, 3H), 6.91e6.87 (m, 2H), 3.82 (s,
3H); 13C NMR (150 MHz, CDCl3)
159.03, 144.44, 131.31, 128.95,
128.75, 128.02, 127.18, 113.90, 87.07, 55.48; IR (thin film, cmꢁ1
d
4. (a) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155e4156; (b) Wirth, T.
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)
3421, 3072, 3024, 2958, 2934, 2836, 2187, 2083, 1892, 1611, 1581,
1511, 1490, 1461, 1445, 1298, 1239, 1071, 1031; HRMS (ESI): Calcd for
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C
27H22D2NaO2 405.178204, Found 405.179404.
4.3. General procedures for the synthesis of benzaldehydes
The benzyl alcohols substrates (1ae1p) (0.2 mmol), FeCl3$6H2O
(0.002 mmol, 5.4 mg) and triphenylmethanol 2 (0.2 mmol, 52 mg)
were mixed in a dried vessel. Then the reaction was irradiated
under the microwave at 55 ꢀC for 1 h. The crude mixture was pu-
rified by a flash column chromatography to afford the benzalde-
hydes (4ae4p).
7. (a) Vasant, R.; Pankaj, A. C.; Vijay, S. C. Catal. Commun. 2003, 171e175; (b)
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4.4. General procedures for the plotting of kinetic curves in
Scheme 3
ꢀ
1530e1537; (e) Pascanu, V.; Gomez, A. B.; Ayats, C.; Platero-Prats, A. E.; Carson,
ꢁ
ꢁ
F.; Su, J.; Yao, Q.; Pericas, M. A.; Zou, X.; Martín-Matute, B. ACS Catal. 2015, 5,
472e479.
To a dried vessel the substituted benzyl alcohols (1, 1e and 1n)
(0.2 mmol), FeCl3$6H2O (0.002 mmol, 5.4 mg) and triarylmethanol
(2, 2q and 2r) (0.2 mmol) were added. Then the reaction was ir-
radiated under the microwave at 45 ꢀC or 60 ꢀC for 10 min, 20 min,
30 min, 40 min, 50 min and 60 min respectively. And then the
products were isolated by a flash column chromatography to get
the yields. Each yield experiment was performed for three times
and the average values of the yields were used. The yield curves
were obtained by plotting the average yields versus time.
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Acknowledgements
~
Chem., Int. Ed. 2008, 47, 3317e3321; (d) Correa, A.; Mancheno, O. G.; Bolm, C.
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Chem. Soc. Rev. 2008, 37, 1108e1117; (e) Sherry, B. D.; Furstner, A. Acc. Chem. Res.
This work is supported by the National Natural Science Foun-
dation of China (Grants 21202103), the Natural Science Foundation
of Liaoning Province of China (Grants 2014020080) and Liaoning
Province Education Administration of China (Grants L2014386). We
also thank the program for innovative research team of the Ministry
of Education and program for Liaoning innovative research team in
university. We acknowledged Prof. Ping Gong (Shenyang Pharma-
ceutical University) for facilities support and Mr. Patrick Michael
Barbour (University of Colorado at Boulder) for advise in the
manuscript preparation.
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Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2015.07.040
References and notes
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