An efficient and practical synthesis of dibenzo[d,f][1,3]-dioxepines from 2,2'-dihydroxybiphenyl with terminal alkynes catalyzed by lewis acid TiCl 4

Article abstract of DOI:10.1002/cjoc.201190225

A synthetic strategy toward the cyclic addition of 2,2'-dihydroxybiphenyl to terminal alkynes has been developed using Lewis acid TiCl₄ as catalyst. The reactions generated dibenzo[d,f][1,3]dioxepines derivatives in good yields with excellent r

Full text of DOI:10.1002/cjoc.201190225

FULL PAPER
An Efficient and Practical Synthesis of Dibenzo[d,f][1,3]-
dioxepines from 2,2'-Dihydroxybiphenyl with Terminal
Alkynes Catalyzed by Lewis Acid TiCl4
Wu, Haishenga(吴海生)
Yang, Jina(杨进)
Wang, Lei*,a,b(王磊)
a Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, Shanghai 200032, China
A synthetic strategy toward the cyclic addition of 2,2'-dihydroxybiphenyl to terminal alkynes has been devel-
oped using Lewis acid TiCl4 as catalyst. The reactions generated dibenzo[d,f][1,3]dioxepines derivatives in good
yields with excellent regio-selectivity in the presence of catalytic amount of TiCl4 under mild reaction conditions.
Keywords cyclic addition, 2,2'-dihydroxybiphenyl, terminal alkynes, region-selectivity, Lewis acid, TiCl4
Introduction
Lewis acid as a catalyst for the preparation of
dibenzo(d,f)(1,3)dioxepines derivatives.17
Seven-membered oxygen-atom-containing heterocy-
cles are structural components of many natural products
and pharmaceuticals, such as 1,3-benzodioxoles,
dibenzo[d,f][1,3]-dioxepines and 12H-dibenzo[d,g]-
[1,3]-dioxocin derivatives.1 In fact, it has already dis-
covered that such structure is possible with their phar-
macology activeness in many biologically active natural
products.2 Alkynes are versatile building blocks in or-
ganic synthesis, addition of oxygen nucleophile to
non-activated alkynes is an important tool to construct a
carbon-oxygen bond.3 Several studies on the metal-
catalyzed addition reaction of O—H bonds of alcohols,4
carboxylic acids,5 phosphinic acids6 and water7 to al-
kynes have been recently reported in literature. Un-
doubtedly, addition of O—H bonds across the car-
bon-carbon triple bonds is one of the most interesting
and intriguing subjects in organic chemistry.
In continuation of our efforts in developing selective,
efficient, mild and new synthetic strategy to approach
these series of compounds, here we report the TiCl4
catalyzed cyclic addition reaction of 2,2'-dihydroxybi-
phenyl to terminal alkynes to establish the efficient and
simple catalytic system for the synthesis of
dibenzo[d,f][1,3]dioxepines (Scheme 1). It should be
noted that the reaction was carried out for the first time
using titanium(IV) chloride as a catalyst with high
chemo-selectivity for biphenol over alcohols, carboxylic
acids and water. In addition, the notable advantages of
this methodology are mild condition, short reaction time,
and good yields.
Scheme 1
Titanium(IV) halides are mild Lewis acid that could
be used as an efficient catalyst for a wild variety of or-
ganic reactions,8 among which TiCl4 is widely used in
many carbon-carbon and carbon-oxygen bond-forming
reactions, including the additions of allylsilane,9 al-
lyltin,10 propargylsilane11 to aldehydes, ketones and
α-keto esters. Furthermore, TiCl4 is also used in the car-
bocyclization of active methane compounds with alkyne
groups,12 Claisen rearrangements,13 Friedel-Crafts14 and
Baylis-Hillman15 reactions.
Until now, the common synthetic methods developed
for the dibenzo[d,f][1,3]dioxepines derivatives are fo-
cused on the condensation of biphenols with aldehydes
or ketones in the presence of various acidic catalysts.16
However, there have been only a few examples to use
Results and discussion
The dibenzo[d,f][1,3]dioxepines were synthesized by
the condensation of 2,2'-dihydroxybiphenyl with
phenylacetylene under very simple reaction conditions
in the presence of catalytic amount of TiCl4 (10 mol%)
while in the absence of any additive (Table 1, Entry 1).
The influence of solvent, catalyst, reaction temperature
and time on the reaction was also investigated and the
results are summarized in Table 1. As can be seen, the
*
E-mail: leiwang@chnu.edu.cn; Tel.: 0086-561-3802069; Fax: 0086-561-3090518
Received December 7, 2010; revised January 22, 2011; accepted March 24, 2011.
Project supported by the National Natural Science Foundation of China (No. 20972057).
Chin. J. Chem. 2011, 29, 1211— 1215
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Wu, Yang & Wang
FULL PAPER
yields were closed related to the reaction conditions,
such as solvent and catalyst. It was found that
ClCH2CH2Cl is the best solvent among the solvents
tested, the reaction underwent smoothly in ClCH2CH2Cl
and generated the desired product in 80% yield, while
DMF, CH3CN, THF and dioxane afforded trace amount
of the desired product. Moreover, using CH2Cl2,
BrCH2CH2Br, toluene or C2H5OH as solvents led to
slower reactions (Table 1, Entries 1—9). Among a vari-
ety of catalyst species examined, TiCl4 was found to be
the most effective one. When using Fe(III) salt, BiCl3,
Cu(OTf)2 and AlCl3 instead of TiCl4 as catalyst, their
efficiencies were lower than that of TiCl4 for the model
reaction (Table 1, Entries 10—16). It is important to
note that no cyclic addition product was isolated using
Fe(II) salt as catalyst (Table 1, Entries 17—19). This
clearly demonstrates an efficient Lewis acid is essential
for the formation of the intermediate and for the pro-
ceeding of the reaction. With respect to the catalyst
loading, when less than 10 mol% of TiCl4 was used, the
reaction did not complete, but a higher loading (＞10
mol%) of the catalyst gave a satisfactory results (Table 1,
Entries 20—21).
During the course of our further optimization of the
reaction conditions, the reactions generally completed in
a matter of hours, but the time, as expected, was in-
versely proportional to the temperature. A reaction tem-
perature of 80 ℃ for 1.0 h was found to be optimal
(Table 1, Entries 22—24). Thus, the optimized reaction
conditions for the reaction were found to be TiCl4 (10
mol%) in ClCH2CH2Cl at 80 ℃ for 1 h.
Having established the optimized reaction conditions,
we turned our attention to explore the scope of this pro-
tocol. The results are listed in Table 2. In most cases,
2,2'-dihydroxybiphenyl was reacted with a wide variety
of substituted phenylacetylene and afforded the corre-
sponding dibenzo[d,f][1,3]dioxepine in good yields
(Table 2). Substituted phenylacetylene containing elec-
tron-donating or electron-withdrawing groups on the
benzene rings reacted with 2,2'-dihydroxybiphenyl
smoothly under optimal reaction conditions and gener-
ated the desired products in moderate to good yields
(Table 2, Entries 2—11). Thus, the terminal aromatic
alkynes bearing both electron-withdrawing and electron-
donating groups are suitable substrates for this reaction.
Table 1 Optimization of the reaction conditionsa
Entry
1
Catalyst/mol%
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
Fe(acac)3 (10)
Fe(OTf)3 (10)
FeCl3 (10)
FeBr3 (10)
BiCl3 (10)
Cu(OTf)2 (10)
AlCl3 (10)
FeCl2 (10)
FeBr2 (10)
Fe(OAc)2 (10)
TiCl4 (5)
Solvent/(Temp./℃) Yieldb/%
ClCH2CH2Cl/80
DMF/110
80
Trace
Trace
Trace
Trace
67
2
3
Dioxane/100
4
CH3CN/80
5
THF/70
Table 2 TiCl4-catalyzed reaction of 2,2'-dihydroxybiphenyl
with terminal alkynesa
6
CH2Cl2/40
7
Toluene /110
52
8
BrCH2CH2Br/80
C2H5OH/78
65
9
43
10
11
12
13
14
15
16
17
18
19
20
21
22
23c
24d
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/80
ClCH2CH2Cl/60
ClCH2CH2Cl/60
ClCH2CH2Cl/60
NR
36
Entry
1
Alkyne
Product
Yieldb/%
80
51
47
42
33
62
NR
NR
NR
59
2
3
75
65
TiCl4 (15)
TiCl4 (10)
TiCl4 (10)
TiCl4 (10)
81
46
64
77
a
Reaction conditions: 2,2'-dihydroxybiphenyl (0.5 mmol),
phenylacetylene (1.0 mmol), Lewis acid (5—15 mol%) stirred in
solvent (2.0 mL) at the temperature indicated in Table 1 for 1 h.
c
d
b Isolated yield. Reaction was conducted for 4 h. Reaction was
conducted for 8 h.
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Chin. J. Chem. 2011, 29, 1211— 1215

An Efficient and Practical Synthesis of Dibenzo[d,f][1,3]dioxepines
Continued
electron-donating group, such as methoxy group on the
benzene ring showed lower reactivity than those with
electron-donating groups and middle or weak electron-
withdrawing groups (Table 2, Entry 6). It should be
noted that no desired product was obtained when the
reactions of terminal aliphatic alkyne, such as 1-hexyne
or 1-octyne, with 2,2'-dihydroxybiphenyl, and phenyl-
acetylene with 1,1'-bi-2-naphthol were carried out under
present reaction conditions. Overall, almost all reactions
were clean and afforded Markovnikov adducts selec-
tively and the target compounds were obtained in mod-
erate to good yields. The notable advantages of this
methodology are mild reaction conditions, short reaction
times and high yields of the desired products in com-
parison with known procedure.17b
The mechanism of the present addition of alkyne
with biphenol is considered to be similar to those of the
InCl3-catalyzed addition reaction of alkyne with biphe-
nol.17b A proposed mechanism is depicted in Scheme 2.
It involves the formation of a concerted six-membered
transition state to form intermediates 5 and 4, which was
formed by a Markovnikov addition of HCl derived from
the nucleophilic interaction between biphenol 1 and
TiCl4. The intermolecular nucleophilic addition of
compound 5 at 2-chloroalkene 4 and subsequent in-
tramolecular cyclization afforded the final product 3. On
the other hand, 2-chloroalkene 4 might generate a vinyl
cation that could react with intermediate 5 to afford the
final product 3.
Entry
Alkyne
Product
Yieldb/%
4
72
5
6
63
45
7
8
9
54
61
58
Scheme 2 Proposed reaction mechanism
10
11
54
56
Conclusion
In conclusion, TiCl4 has been demonstrated to be a
highly selective and efficient catalyst for the cyclic ad-
dition of 2,2'-dihydroxybiphenyl to a variety of terminal
alkynes. The reactions were performed smoothly to
generate the desired products in good yields under safe
experimental conditions. The notable advantages of this
methodology are mild condition, short reaction times,
and the procedure is simple and convenient. The method
offers one of the important motifs for synthesis of
a Reaction conditions: 2,2'-dihydroxybiphenyl (0.5 mmol), termi-
nal alkyne (1.0 mmol) and TiCl4 (0.05 mmol) were stirred in
ClCH2CH2Cl (2.0 mL) at 80 ℃ for 1 h. b Isolated yield.
In addition, we found that the electronic and steric effect
of phenylacetylene substituents had little impact on the
yields of the desired products. However, it is important
to note that substituted phenylacetylene with a strong
Chin. J. Chem. 2011, 29, 1211— 1215
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Wu, Yang & Wang
FULL PAPER
dibenzo[d,f][1,3]dioxepines, which are expected to be
promising starting materials to be converted to the re-
lated analogues of 1,3-benzodioxole-containing com-
pounds for their biological studies.
26.6. HRMS (ESI) calcd for C20H15BrO2 366.0255,
found 366.0252 ([M]＋).
6-(4-Chlorophenyl)-6-methyldibenzo[d,f][1,3]-
dioxepine 1H NMR (CDCl3, 400 MHz) δ: 7.61 (m,
2H), 7.50 (m, 2H), 7.33 (m, 2H), 7.26 (m, 4H), 6.95 (m,
2H), 1.90 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ: 151.4,
140.0, 134.1, 133.2, 128.7, 128.2, 128.1, 127.6, 125.3,
123.4, 115.4, 26.7. HRMS (ESI) calcd for C20H15ClO2
322.0761, found 322.0762 ([M]＋).
6-(4-Methoxyphenyl)-6-methyldibenzo[d,f][1,3]-
dioxepine17b 1H NMR (CDCl3, 400 MHz) δ: 7.57 (d,
J＝8.8 Hz, 2H), 7.50 (t, J＝9.3 Hz, 2H), 7.24 (t, J＝9.4
Hz, 4H), 6.95 (t, J＝9.2 Hz, 2H), 6.86 (d, J＝8.6 Hz,
2H), 3.78 (s, 3H), 1.92 (s, 3H); 13C NMR (CDCl3, 100
MHz) δ: 159.4, 151.7, 133.7, 133.3, 128.5, 128.1, 127.3,
125.1, 123.5, 116.0, 113.1, 55.2, 26.7.
6-(Biphenyl-4-yl)-6-methyldibenzo[d,f][1,3]dioxe-
pine 1H NMR (CDCl3, 400 MHz) δ: 7.80 (d, J＝8.1
Hz, 2H), 7.65 (t, J＝13.2 Hz, 4H), 7.24 (t, J＝8.8 Hz,
2H), 7.47 (t, J＝14.8 Hz, 2H), 7.38 (t, J＝14.7 Hz, 1H),
7.31—7.26 (m, 4H), 7.07 (t, J＝8.9 Hz, 2H), 2.01 (s,
3H); 13C NMR (CDCl3, 100 MHz) δ: 151.7, 140.9,
140.6, 140.4, 133.3, 128.7, 128.6, 128.2, 127.4, 127.1,
126.6, 126.5, 125.2, 123.5, 115.9, 26.9. HRMS (ESI)
calcd for C26H20O2 364.1463, found 364.1466 ([M]＋).
6-(2-Bromophenyl)-6-methyldibenzo[d,f][1,3]di-
oxepine 1H NMR (CDCl3, 400 MHz) δ: 7.83 (dd, J＝
7.9, 1.9 Hz, 1H), 7.71 (dd, J＝7.8, 1.3 Hz, 1H), 7.54—
7.49 (m, 2H), 7.29—7.25 (m, 5H), 7.21—7.14 (m, 4H),
2.11 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ: 151.6,
139.6, 135.0, 133.3, 129.7, 129.5, 128.7, 128.0, 127.2,
125.3, 123.1, 120.7, 115.1, 24.6. HRMS (ESI) calcd for
C20H15BrO2 366.0255, found 366.0261 ([M]＋).
Experimental
Physical measurements and materials
All 1H NMR and 13C NMR spectra were recorded on
a 400 MHz Bruker FT-NMR spectrometers. All chemi-
cal shifts are given as δ value with reference to tetrame-
thylsilane (TMS) as an internal standard. Products were
purified by flash chromatography on 230—400 mesh
silica gel, SiO2.
The chemicals and solvents were purchased from
commercial suppliers either from Aldrich, Fluka, USA
or Shanghai Chemical Company, China and were used
without purification prior to use.
Typical procedure for the synthesis of dibenzo[d,f]-
[1,3]dioxepines
To a solution of 2,2'-dihydroxybiphenyl (0.5 mmol)
and phenylacetylene (1.0 mmol) in ClCH2CH2Cl (2.0
mL) was added TiCl4 (0.05 mmol) in one portion. The
reaction mixture was heated to 80 ℃ for 1 h with stir-
ring under a nitrogen atmosphere. After cooling, the
reaction mixture was extracted with ethyl acetate and
the organic layer was dried over Na2SO4. Then, the or-
ganic solution was concentrated with a rotary evaporator,
and the residue was purified by column chromatography
on silica gel using cyclohexane/ethyl acetate (15∶1) as
eluent to provide pure 6-methyl-6-phenyldibenzo[d,f]-
[1,3]dioxepine in 80 % yield.
6-Methyl-6-phenyldibenzo[d,f][1,3]dioxepine17b
1H NMR (CDCl3, 400 MHz) δ: 7.69 (d, J＝6.6 Hz, 2H),
7.53—7.51 (m, 2H), 7.40—7.33 (m, 3H), 7.28—7.24 (m,
5H), 7.00—6.98 (m, 2H), 1.94 (s, 3H); 13C NMR
(CDCl3, 100 MHz) δ: 151.7, 141.4, 133.3, 128.6, 128.3,
128.2, 127.9, 126.0, 125.2, 123.5, 115.9, 26.8.
6-(4-tert-Butylphenyl)-6-methyldibenzo[d,f][1,3]-
dioxepine 1H NMR (CDCl3, 400 MHz) δ: 7.59 (d,
J＝8.4 Hz, 2H), 7.50—7.48 (m, 2H), 7.36 (d, J＝8.4 Hz,
2H), 7.24—7.20 (m, 4H), 7.01—6.97 (m, 2H), 1.90 (s,
3H), 1.31 (s, 9H); 13C NMR (CDCl3, 100 MHz) δ: 151.8,
151.0, 138.4, 133.3, 128.5, 128.1, 125.6, 125.1, 124.8,
123.6, 116.1, 34.5, 31.3, 27.0. HRMS (ESI) calcd for
C24H24O2 344.1776, found 344.1775 ([M]＋).
6-(4-Fluorophenyl)-6-methyldibenzo[d,f][1,3]di-
oxepine17b 1H NMR (CDCl3, 400 MHz) δ: 7.67—7.61
(m, 2H), 7.52—7.49 (m, 2H), 7.27—7.23 (m, 4H), 7.05—
7.00 (m, 2H), 6.96—6.92 (m, 2H), 1.91 (s, 3H); 13C NMR
(CDCl3, 100 MHz) δ: 162.6 (d, JC-F＝245.2 Hz), 151.5,
137.3 (d, JC-F＝3.1 Hz), 133.2, 128.6, 128.2, 128.0 (d,
JC-F＝8.2 Hz), 125.3, 123.4, 115.5, 114.7 (d, JC-F＝21.3
Hz), 26.8. HRMS (ESI) calcd for C20H15FO2 306.1056,
found 306.1052 ([M]＋).
6-Methyl-6-m-tolyldibenzo[d,f][1,3]dioxepine17b
1H NMR (CDCl3, 400 MHz) δ: 7.57—7.22 (m, 4H),
7.09—6.97 (m, 8H), 2.26 (s, 3H), 1.94 (s, 3H); 13C
NMR (CDCl3, 100 MHz) δ: 151.6, 141.0, 138.1, 133.3,
130.0, 129.2, 128.6, 128.2, 127.4, 123.1, 120.8, 116.1,
106.3, 26.9, 21.4.
6-Methyl-6-p-tolyldibenzo[d,f][1,3]dioxepine17b
1H NMR (CDCl3, 400 MHz) δ: 7.55 (d, J＝8.3 Hz, 2H),
7.49 (q, J＝9.4 Hz, 2H), 7.25—7.20 (m, 4H), 7.15 (d, J＝
8.1 Hz, 2H), 2.33 (s, 3H), 1.91 (s, 3H); 13C NMR
(CDCl3, 100 MHz) δ: 151.7, 138.4, 137.8, 133.3, 128.6,
128.5, 128.1, 125.9, 125.1, 123.5, 116.1, 26.9, 21.1.
6-(4-Bromophenyl)-6-methyldibenzo[d,f][1,3]-
dioxepine 1H NMR (CDCl3, 400 MHz) δ: 7.54—7.45
(m, 6H), 7.24—7.22 (m, 4H), 6.95—6.93 (m, 2H), 1.88 (s,
3H); 13C NMR (CDCl3, 100 MHz) δ: 151.3, 140.4, 133.1,
131.0, 128.6, 128.2, 127.8, 125.3, 123.3, 122.3, 115.3,
6-Methyl-6-o-tolyldibenzo[d,f][1,3]dioxepine17b
1H NMR (CDCl3, 400 MHz) δ: 7.62—7.37 (m, 4H),
7.21—6.75 (m, 8H), 2.31 (s, 3H), 1.90 (s, 3H); 13C
NMR (CDCl3, 100 MHz) δ: 151.6, 142.2, 134.5, 131.3,
130.6, 128.2, 128.2, 127.5, 127.0, 125.6, 120.2, 116.1,
103.6, 27.3, 19.1.
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An Efficient and Practical Synthesis of Dibenzo[d,f][1,3]dioxepines
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