Sequential Au(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates

Article abstract of DOI:10.3762/bjoc.7.74

The gold(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates provides 1H-isochromene derivatives in good yields. The reaction follows a catalytic sequence of gold carbene formation/water O-H insertion/alcohol-alkyne cyclization. The gold(I) complex is the only catalyst in each of these steps.

Full text of DOI:10.3762/bjoc.7.74

Sequential Au(I)-catalyzed reaction of water with
o-acetylenyl-substituted phenyldiazoacetates
Lei Zhou, Yizhou Liu, Yan Zhang and Jianbo Wang*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2011, 7, 631–637.
Beijing National Laboratory of Molecular Sciences (BNLMS), Key
Laboratory of Bioorganic Chemistry and Molecular Engineering of
Ministry of Education, College of Chemistry, Peking University, Beijing
100871, China
doi:10.3762/bjoc.7.74
Received: 29 March 2011
Accepted: 09 May 2011
Published: 18 May 2011
Email:
Jianbo Wang* - wangjb@pku.edu.cn
This article is part of the Thematic Series "Gold catalysis for organic
synthesis".
* Corresponding author
Guest Editor: F. D. Toste
Keywords:
alkyne; carbene O–H insertion; cyclization; diazo compounds; gold
© 2011 Zhou et al; licensee Beilstein-Institut.
License and terms: see end of document.
catalysis; 1H-isochromene
Abstract
The gold(I)-catalyzed reaction of water with o-acetylenyl-substituted phenyldiazoacetates provides 1H-isochromene derivatives in
good yields. The reaction follows a catalytic sequence of gold carbene formation/water O–H insertion/alcohol-alkyne cyclization.
The gold(I) complex is the only catalyst in each of these steps.
Introduction
Transition metal carbene complexes are versatile intermediates example of carbene transfer from ethyl diazoacetate (EDA)
and can undergo diverse transformations, including X–H (X = using (IPr)AuCl. The subsequent generation of a gold carbene
C, O, S, N, etc.) insertions, cyclopropanations, ylide formation, was followed by insertion into a phenyl C–H bond, an O–H
and 1,2-migrations [1-5]. Among the various methods to bond, or an N–H bond [6]. Similar reactions were also reported
generate metal carbene complexes, transition metal-catalyzed by Dias and co-workers with a gold(I) ethylene complex [7].
decomposition of diazo compounds is the most straightforward Although the scope of those studies was limited to ethyl diazo-
and is highly reliable. Various transition metals have been acetate, the examples therein demonstrated that gold complexes
found to decompose diazo compounds and then transfer a can be used as efficient catalysts in carbene transfer reactions
carbene unit to saturated or unsaturated organic substrates [3]. with diazo compounds.
However, compared to the other group 11 metals, i.e., copper
and silver, there are only a few reports on gold-catalyzed On the other hand, the development of reaction systems in
carbene transfer reactions of diazo compounds [6-20]. In 2005, which a single catalyst mediates two or more different reac-
Díaz-Requejo, Nolan, Pérez and co-workers reported the first tions in a selective manner has become an emerging area of
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Beilstein J. Org. Chem. 2011, 7, 631–637.
research [21-28]. This type of sequential or concurrent catalysis
is particularly appealing in view of the requirements of green
chemical processes in the fine chemical industry. In this
context, we have previously reported the copper(I)-catalyzed
reaction of amines with o-acetylenyl-substituted phenyldiazo-
acetates, which leads to a Cu(I)-catalyzed tandem N–H inser-
tion/hydroamination of an alkyne [29]. Subsequently, we have
tried to extend this reaction by replacing the amine component
with water, and we expected that similar tandem reaction would
occur. Copper is a good catalyst for the decomposition of diazo
Scheme 1: Gold(I)-catalyzed insertion/cyclization of o-acetylenyl-
substituted phenyldiazoacetates providing 1H-isochromene deriva-
tives.
compounds and the subsequent insertion of water. However, Results and Discussion
we have found that it is not a suitable catalyst for the At the onset of this investigation, o-acetylenyl-substituted
alcohol–alkyne cyclization. Since gold complexes are well- phenyldiazoacetate 1a was selected as the model substrate. In a
known for their efficacy in activating alkynes, we reasoned that preliminary experiment, 1a was treated with CuI catalyst in a
a concurrent catalysis based on gold-catalyzed reaction of diazo mixture of CH3CN and H2O (v:v = 1:1) (Table 1). As expected,
compounds and alkynes might be possible [30]. Herein we only the water insertion product 4a was obtained as the major
report such a catalytic system, namely a gold(I)-catalyzed inser- product and in high yield (91%) (Table 1, entry 1). Since
tion/cyclization cascade by reacting water with o-acetylenyl- previous reports have shown that silver [32-34] and gold [35-
substituted phenyldiazoacetates. The reaction affords 38] complexes are efficient catalysts for alcohol–alkyne cycliza-
1H-isochromene derivatives in good yields (Scheme 1) [31]. tion, we then proceeded to examine other catalysts viz. AgOTf,
Table 1: Optimization of reaction conditions with phenyldiazoacetate 1aa.
Yield
(2a + 3a)b
Entry
Catalyst
Solvent
T/°C
2a:3a
4a, Yield
1
CuI
H2O:CH3CN (1:1)
H2O:CH3CN (1:1)
H2O:CH3CN (1:1)
H2O:CH3CN (1:1)
H2O:CH3CN (1:1)
H2O:CH3CN (1:1)
H2O:CH3CN (1:1)
H2O:CH3CN (1:1)
H2O:CH3CN (1:3)
H2O:CH3CN (3:1)
H2O
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
100
60
40
0%
—
91%
<10%
trace
trace
trace
80%
15%
0%
2
AgOTf
0%
—
3
AgF/PCy3
NaAuCl4
AuCl
trace
0%
—
4
—
5
0%
—
6
(PPh3)AuCl
(PMe3)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
(IPr)AuCl
8%
—
7
10%
95%
25%
57%
54%
0%
—
8
1:1
2:3
1:1.3
1:2
0
9
61%
11%
0%
10
11
12c
13
14
15
16
17
18
CH3CN
41%
0%
H2O:DMF (1:1)
H2O:NMP (1:1)
H2O:toluene (1:1)
H2O:DMF (1:1)
H2O:DMF (1:1)
H2O:DMF (1:1)
90%
0%
4:1
—
trace
0%
19%
57%
66%
48%
1:1
3:1
5:1
5:1
0%
0%
0%
aAll the reactions were carried out using 0.2 mmol phenyldiazoacetate 1a with 3 mol % of catalyst in 1 mL solvent for 24 h. bYield and ratio of 2a and
3a were measured by 1H NMR. c1 mmol of water was added.
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Beilstein J. Org. Chem. 2011, 7, 631–637.
AgF/PCy3, NaAuCl4 and AuCl (Table 1, entries 2–5). How- (v:v = 1:1) was used as the solvent, the ratio of 2a:3a increased
ever, these metal complexes were not efficient catalysts for the to 4:1, with slightly diminished overall yield. The reaction with
decomposition of diazo compounds, and a large amount of NMP or toluene as the co-solvent gave poor yields of desired
starting materials remained. However, when 1a was treated with products (Table 1, entries 14,15). Finally, the effect of tempera-
(PPh3)AuCl in a mixture of CH3CN and H2O, product 4a was ture was evaluated: The reaction gave diminished yields when
obtained in 80% yield, along with the minor cyclization pro- carried out at a temperature higher or lower than 80 °C
duct 2a (8%) (Table 1, entry 6). Encouraged by this result, elec- (Table 1, entries 16–18).
tron-rich ligand coordinated gold complexes (PMe3)AuCl and
(IPr)AuCl were examined (Table 1, entries 7 and 8). It was With the optimized reaction conditions in hand, a series of
found that (IPr)AuCl was an efficient catalyst for both carbene substituted diazo compounds 1a–f were prepared, and their
transfer and cyclization. Product 2a from 6-endo-dig cycliza- reactions with water in the presence of (IPr)AuCl in aqueous
tion and product 3a from 5-exo-dig cyclization were both DMF were investigated. As shown in Table 2, all the reactions
obtained in nearly equal amounts in combined yield of 95%. gave isochromene derivatives as the major products. In the reac-
Next, we examined the effect of the ratio of CH3CN and H2O tion of diazo compounds 1e and 1f with water, only 6-endo-dig
with (IPr)AuCl as catalyst: A ratio of 1:1 (v:v) afforded the best cyclization products 2e and 2f were isolated as the sole product
results (Table 1, entries 9–12). It is worth noting that the reac- in yields of 69% and 75%, respectively. Functional groups such
tion also occurred in pure water to afford the cyclization prod- as bromo and hydroxy groups were tolerated under the present
ucts, 2a and 3a, in moderate yield (Table 1, entry 11). Next, the catalytic systems. When diazo compound 1g (R’ = H) was
effect of different co-solvents, such as DMF, NMP employed as the substrate, none of the cyclization product was
(N-methylpyrrolidone) and toluene, was investigated (Table 1, detected and the water insertion product 4g was obtained in
entries 13–15). Interestingly, when a mixture of H2O and DMF 81% yield.
Table 2: Gold(I)-catalyzed cascade insertion/cyclization of water with various substituted phenyldiazoacetatesa.
Entry
Substrate
Yield of 2b
Yield of 3b
1
2a, 70%
3a, 15%
1a
2
2b, 64%
3b, 31%
1b
3
2c, 67%
3c, 22%
1c
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Beilstein J. Org. Chem. 2011, 7, 631–637.
Table 2: Gold(I)-catalyzed cascade insertion/cyclization of water with various substituted phenyldiazoacetatesa. (continued)
4
5
2d, 82%
2e, 69%
3d, <10%
3e, Trace
1d
1e
6
2f, 75%
2g, 0%
3f, Trace
3g, 0%
1f
7c
1g
aAll the reactions were carried out using 0.5 mmol phenyldiazoacetate 1 with 3 mol % of (IPr)AuCl catalyst in 2 mL solvent for 24 h. bIsolated yield.
cOnly the water insertion product methyl 2-(2-ethynylphenyl)-2-hydroxyacetate (4g) was isolated as the major product in a yield of 81%.
A tentative mechanism for this gold(I)-catalyzed cascade inser-
tion/cyclization is proposed in Scheme 2. Decomposition of
diazo compound 1 by (IPr)AuCl generates gold carbene species
A, which inserts into the O–H bond of H2O to form the
chelating intermediate B. Subsequently, 6-endo-dig attack of
the Au(I)-activated triple bond affords the vinylgold intermedi-
ate C, which is protonated to give the final product 2 with
regeneration of the catalyst. This mechanism is supported by the
fact that when 4a was subjected to the gold(I)-catalyzed reac-
tion under identical conditions 2a and 3a were obtained in
similar yields.
Conclusion
In summary, we have developed a cascade insertion/cyclization
of water with o-acetylenyl-substituted phenyldiazoacetates
catalyzed by a single Au(I) catalyst. This tandem process
provides a novel and straightforward method to synthesize
isochromene derivatives. Isochromene and its derivatives
frequently occur as structural units in natural products and ex-
hibit interesting biological activities such as antibiotic prop-
erties [39-51]. Moreover, this study further demonstrates the
Scheme 2: Tentative mechanism.
possibility to incorporate gold-catalyzed reaction of diazo com-
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Beilstein J. Org. Chem. 2011, 7, 631–637.
pounds with various other gold-catalyzed transformations. 7.64–7.62 (m, 1H), 7.39–7.35 (m, 1H), 7.30–7.19 (m, 4H),
Further studies to broaden the scope of these reactions are 7.11–7.09 (m, 1H), 6.27 (s, 1H), 5.87 (s, 1H), 3.76 (s, 3H);
currently underway.
13C NMR (100 MHz, CDCl3) δ 170.1, 151.5, 135.5, 133.5,
131.4, 130.1, 129.9, 129.1, 127.3, 127.2, 125.9, 125.5,
124.2, 106.0, 77.2, 52.5; MS (70 eV) m/z (%): 344 (41,
Experimental
General. For chromatography, 200–300 mesh silica gel 79Br) [M+], 285 (100), 206 (36), 178 (96), 151 (17);
(Qingdao, China) was employed. 1H NMR and 13C NMR HRMS–ESI (m/z): [M + H]+ calcd for C17H14BrO3, 345.0120;
spectra were recorded on Varian 300 or Bruker ARX 400 found, 345.0125.
spectrometer in CDCl3 solution and chemical shifts are reported
in parts per million (δ) relative to internal standard TMS (0 Methyl 3-(2-bromobenzylidene)-1,3-dihydroisobenzofuran-
ppm). Mass spectra were obtained on a VG ZAB-HS mass 1-carboxylate (3b). 1H NMR (400 MHz, CDCl3) δ 8.36–8.34
spectrometer. Diazo compounds were prepared according to our (m, 1H), 7.66 (d, J = 8.0 Hz, 1H), 7.58–7.52 (m, 2H), 7.41–7.39
previous reported procedures. Unless otherwise noted, materials (m, 2H), 7.34–7.29 (m, 1H), 7.03–7.01 (m, 1H), 6.42 (s, 1H),
obtained from commercial suppliers were used without further 6.05 (s, 1H), 3.82 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
purification.
168.9, 155.9, 136.6, 134.9, 134.2, 132.6, 130.0, 129.5, 129.4,
127.3, 127.0, 123.0, 122.1, 96.1, 82.6, 52.8; MS (70 eV) m/z
General procedure for the gold(I)-catalyzed cascade inser- (%): 344 (13, 79Br) [M+], 285 (100), 206 (32), 178 (67), 151
tion/cyclization reaction. Distilled water (0.5 mL) was added (14); HRMS–ESI (m/z): [M + H]+ calcd for C17H14BrO3,
to a solution of complex 1 (0.5 mmol) and (IPr)AuCl (3 mol %, 345.0120; found, 345.0127.
9.3 mg) in DMF (1.5 mL) at room temperature under a N2
atmosphere. The reaction mixture was stirred for 24 h at 80 °C. Methyl 3-(3-bromophenyl)-1H-isochromene-1-carboxylate
After the mixture cooled to room temperature, it was diluted (2c). 1H NMR (400 MHz, CDCl3) δ 7.96–7.95 (m, 1H),
with ether and water. The aqueous phase was extracted with 7.72–7.71 (m, 1H), 7.49–7.47 (m, 1H), 7.32–7.25 (m, 4H),
Et2O (2 × 10 mL) and the combined organic extracts were 7.11–7.09 (m, 1H), 6.37 (s, 1H), 5.86 (s, 1H), 3.71 (s, 3H);
washed with brine (1 × 10 mL), dried over Na2SO4, and 13C NMR (100 MHz, CDCl3) δ 170.1, 151.3, 136.1, 131.8,
concentrated. Purification by column chromatography on silica 129.8, 129.1, 128.6, 127.1, 126.2, 125.7, 124.2, 124.1,
gel afforded products 2 and 3.
122.6, 101.4, 76.2, 52.6; MS (70 eV) m/z (%): 344 (34,
79Br) [M+], 285 (100), 206 (35), 178 (82), 151 (14);
Ethyl 3-phenyl-1H-isochromene-1-carboxylate (2a). HRMS–ESI (m/z): [M + H]+ calcd for C17H14BrO3, 345.0120;
1H NMR (400 MHz, CDCl3) δ 7.81 (d, J = 6.8 Hz, 2H), found, 345.0117.
7.41–7.35 (m, 3H), 7.28–7.20 (m, 3H), 7.09 (d, J = 7.6 Hz, 1H),
6.36 (s, 1H), 5.83 (s, 1H), 4.15 (m, 2H), 1.19 (t, J = 7.2 Hz, Methyl 3-(3-bromobenzylidene)-1,3-dihydroisobenzofuran-
3H); 13C NMR (100 MHz, CDCl3) δ 170.0, 153.0, 134.2, 130.6, 1-carboxylate (3c). 1H NMR (400 MHz, CDCl3) δ 7.94–7.93
129.18, 129.16, 128.4, 126.7, 126.2, 126.0, 125.8, 124.1, 100.5, (m, 1H), 7.68–7.66 (m, 1H), 7.55–7.52 (m, 2H), 7.45–7.38 (m,
76.6, 61.7, 14.2; MS (70 eV) m/z (%): 280 (29) [M+], 207 2H), 7.30–7.27 (m, 1H), 7.22–7.17 (m, 1H), 6.07 (s, 1H), 5.92
(100), 178 (47), 152 (8); HRMS–ESI (m/z): [M + H]+ calcd for (s, 1H), 3.82 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 168.9,
C18H17O3, 281.1172; found, 281.1168.
155.7, 137.8, 136.8, 134.0, 130.8, 129.8, 129.47, 129.44, 128.5,
126.7, 122.5, 122.2, 120.1, 96.4, 82.6, 52.8; MS (70 eV) m/z
Ethyl 3-benzylidene-1,3-dihydroisobenzofuran-1-carboxy- (%): 344 (28, 79Br) [M+], 285 (100), 206 (34), 178 (50), 151
late (3a). 1H NMR (400 MHz, CDCl3) δ 7.81 (d, J = 7.2 Hz, (19); HRMS–ESI (m/z): [M + H]+ calcd for C17H14BrO3,
2H), 7.75–7.55 (m, 1H), 7.53–7.51 (m, 1H), 7.41–7.32 (m, 4H), 345.0120; found, 345.0126.
7.18–7.17 (m, 1H), 6.03 (s, 1H), 6.00 (s, 1H), 4.33–4.23 (m,
2H), 1.31 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ Methyl 3-p-tolyl-1H-isochromene-1-carboxylate (2d).
168.8, 154.8, 136.8, 135.8, 134.6, 129.4, 129.1, 128.5, 128.4, 1H NMR (400 MHz, CDCl3) δ 7.69 (d, J = 8.4 Hz, 2H),
125.9, 122.3, 120.1, 97.9, 82.6, 62.0, 14.3; MS (70 eV) m/z (%): 7.25–7.17 (m, 5H), 7.05 (d, J = 6.8 Hz, 1H), 6.31 (s, 1H), 5.83
280 (11) [M+], 264 (8), 207 (100), 191 (13), 178 (43); (s, 1H), 3.67 (s, 3H), 2.36 (s, 3H); 13C NMR (100 MHz,
HRMS–ESI (m/z): [M + H]+ calcd for C18H17O3, 281.1172; CDCl3) δ 170.4, 153.1, 139.2, 131.4, 130.7, 129.17, 129.15,
found, 281.1166.
126.5, 126.2, 125.76, 125.71, 123.9, 99.7, 76.5, 52.5, 21.4; MS
(70 eV) m/z (%): 280 (17) [M+], 221 (100), 207 (7), 178 (27);
Methyl 3-(2-bromophenyl)-1H-isochromene-1-carboxylate HRMS–ESI (m/z): [M + H]+ calcd for C18H17O3, 287.1172;
(2b). 1H NMR (400 MHz, CDCl3) δ 7.89–7.86 (m, 1H), found, 281.1168.
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Beilstein J. Org. Chem. 2011, 7, 631–637.
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Methyl 3-(2-hydroxyethyl)-1H-isochromene-1-carboxylate
(2e). 1H NMR (400 MHz, CDCl3) δ 7.26–7.15 (m, 3H), 6.92 (d,
J = 7.2 Hz, 1H), 5.74 (s, 1H), 5.70 (s, 1H), 4.09–4.07 (m, 1H),
3.78–3.64 (m, 2H), 3.69 (s, 3H), 2.51–2.47 (m, 2H); 13C NMR
(100 MHz, CDCl3) δ 171.4, 154.0, 130.1, 129.3, 126.5, 126.4,
124.4, 123.2, 102.9, 76.1, 59.7, 52.9, 37.5; MS (70 eV) m/z (%):
234 (2) [M+], 192 (8), 175 (100), 145 (28), 133 (77);
HRMS–ESI (m/z): [M + H]+ calcd for C13H15O4, 235.0964;
found, 235.0960.
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1H), 5.67 (s, 1H), 5.58 (s, 1H), 3.68 (s, 3H), 2.77 (t , J = 7.6
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Acknowledgements
The project is supported by Natural Science Foundation of
China (Grant No. 20902005, 20832002, 20772003, 20821062),
National Basic Research Program of China (973 Program, No.
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