Palladium-catalyzed cyclocarbonylation of arynes with methyl allyl carbonates: Selective synthesis of 1 H -inden-1-ones

Article abstract of DOI:10.1021/jo1003828

A selective protocol for the synthesis of 2-methylene-3-substituted-2,3- dihydro-1H-inden-1-ones and 2-benzylidene-2,3-dihydro-1H-inden-1-ones has been developed via palladium-catalyzed cyclocarbonylation reactions of arynes with allyl carbonates and carbon monooxide (CO). It is noteworthy that the selectivity of this new route is depended on both substrates and ligands.

Full text of DOI:10.1021/jo1003828

pubs.acs.org/joc
and industry.1-3 Among the most useful carbonylation
Palladium-Catalyzed Cyclocarbonylation of Arynes
with Methyl Allyl Carbonates: Selective Synthesis of
1H-Inden-1-ones
processes, transition metal-catalyzed cyclocarbonylation re-
actions are particularly interesting due to directly creating
carbocycles and heterocycles.1-3 Although benzyne chemi-
stry has been advanced recently due to the use of o-silyl
aryltriflates as the aryne precursors,3-7 only one paper has
been reported on the catalytic carbonylation of arynes to
date.3 In 2001, Chatani and Murai employed arynes as one of
the reaction partners to react with CO in the presence of Co,
Rh, or Pd catalysis. Particularly, they found that treatment
of arynes with CO and allyl acetates afforded the corre-
sponding 2-methylene-1H-inden-1-ones in moderate to good
yields (Scheme 1). On the other hand, inden-1-ones are
important frameworks found in numerous natural products
and pharmaceutically active compounds, as well as being
valuable intermediates in organic synthesis.8 As a continuing
interest in benzyne chemistry,7 we here report a novel
palladium-catalyzed cyclocarbonylation route to selectively
constructing inden-1-ones using o-silyl aryltriflates, methyl
allyl carbonates, and CO as the reaction partners (Scheme 1).
Shao-Feng Pi, Xu-Heng Yang, Xiao-Cheng Huang,
Yun Liang,* Guan-Nan Yang, Xiao-Hong Zhang, and
Jin-Heng Li*
Key Laboratory of Chemical Biology & Traditional Chinese
Medicine Research (Ministry of Education), Hunan Normal
University, Changsha 410081, China
jhli@hunnu.edu.cn; liangyun1972@126.com
Received March 1, 2010
(3) Chatani, N.; Kamitani, A.; Oshita, M.; Fukumoto, Y.; Murai, S.
J. Am. Chem. Soc. 2001, 123, 12686.
(4) For selected reviews, see: (a) Kessar, S. V. Comprehensive Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: New York, 1991;
A selective protocol for the synthesis of 2-methylene-3-
substituted-2,3-dihydro-1H-inden-1-ones and 2-benzyli-
dene-2,3-dihydro-1H-inden-1-ones has been developed
via palladium-catalyzed cyclocarbonylation reactions of
arynes with allyl carbonates and carbon monooxide
(CO). It is noteworthy that the selectivity of this new
route is depended on both substrates and ligands.
~
ꢀ
ꢀ
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Published on Web 04/07/2010
DOI: 10.1021/jo1003828
r
2010 American Chemical Society

Pi et al.
JOCNote
SCHEME 1
TABLE 1. Screening Conditionsa
yieldb (%)
entry
fluoride
ligand solvent T (°C) t (h)
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16c
17d
18
[(allyl)PdCl]2
PdCl2
Pd(OAc)2
Pd(PPh3)4
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
L1
L1
L1
L1
L2
L3
L4
L5
L6
L7
L1
L1
L1
L1
L1
L1
L1
L1
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
THF
80
80
80
80
80
80
80
80
80
80
100
50
rt
6
4
6
6
4
4
4
4
4
4
8
8
30
6
24
24
24
24
10
73
30
trace
trace
trace
We began our investigation with the reaction of
2-(trimethylsilyl)phenyl triflate (1a) (0.25 mmol) with cinna-
myl methyl carbonate (2a) (0.2 mmol) and CO (1 atm,
bubbling) in the presence of [allylPdCl]2, dppe, and CsF
(the reported conditions3). Unfortunately, a mixture of
products, including a trace amount of the target 1H-inden-
1-ones 3 and 4, was determined by GC-MS analysis. After a
series of trials, we were pleased to find that [allylPdCl]2
combined with PPh3 could give the desired 2-methylene-3-
phenyl-2,3-dihydro-1H-inden-1-one (3) in 10% yield along
with a trace amount of another product 4, (E)-2-benzylidene-
2,3-dihydro-1H-inden-1-one (entry 1, Table 1).9 Encouraged
by these results, the effect of Pd catalysis was examined
(entries 2-10). The results demonstrated that in the presence
of PPh3 ligand PdCl2 was the most efficient catalyst among
[allylPdCl]2, Pd(OAc)2, and Pd(PPh3)4 (entries 1-4). Treat-
ment of substrate 1a with carbonate 2a, CO, PdCl2, and PPh3
enhanced the yield of 3 sharply to 73% (entry 2). Interest-
ingly, PdCl2 combined with a more bulky ligand, P(o-tol)3,
selectively afforded another product 4 in 74% yield (entry 5).
However, the other ligands, such as PCy3, P(o-MeOC6H4)3,
dppm, dppe, and dppp, displayed lower selectivity, provid-
ing a mixture of products 3 and 4 in good total yields (entries
6-10). Subsequently, the reaction temperature effect was
tested in the presence of PdCl2 and PPh3, and the best results
were obtained at 80 °C (entries 2 and 11-13). Among the
solvents and fluorides examined, MeCN combined with CsF
was the most effective (entries 2 and 14-17). It was found
that the reaction could not take place without Pd catalysts
(entry 18). However, cinnamyl acetate, the reported effective
substrate,3 could not undergo the reaction with triflate 1a
and CO in the presence of PdCl2 and PPh3.
With the two optimal reaction conditions in hand, the o-silyl
aryltriflates and methyl allyl carbonates scope was explored for
selectively synthesizing 1H-inden-1-ones (Tables 2 and 3). As
shown in Table 2, 2-methylene-3-substituted-2,3-dihydro-1H-
inden-1-ones were selectively prepared from the reactions of
o-silyl aryltriflates (1) with methyl allyl carbonates (2) and CO
with useofthePdCl2/PPh3 system. Initially, a variety of methyl
allyl carbonates 2b-j were examined by reacting with triflate
1a and CO (Table 2, entries 1-9). The results demonstrated
that several functional groups, such as methyl, methoxy, and
chloro, on the aromatic ring at the terminal of allyl carbonates
2 were tolerated well, resulting in moderate yields (entries
1-5). Substrates 2b or 2c with a methyl group, for instance,
underwent the cyclocarbonylation reaction with triflate 1a and
trace trace
trace 74
25
24
36
48
40
27
64
35
38
18
52
17
25
28
trace
trace
trace
trace
80
80
80
80
80
toluene
MeCN
MeCN
MeCN
trace trace
trace trace
27
0
trace
0
aReaction conditions: 1a (0.25 mmol), 2a (0.2 mmol), [Pd] (5 mol %),
ligand (10 mol %), CsF (2 equiv), CO (1 atm, bubbled), and solvent
(2 mL). bIsolated yield. cn-Bu4NF (2 equiv) instead of CsF. dKF (2 equiv)
instead of CsF in the presence of 18-crown-6 (2 equiv).
CO in 65%, and 59% yields, respectively (entries 1 and 2).
Substrate 2f bearing a methyl group and a chloro group
successfully gave the desired product 9 in moderate yield
(entry 5). It was noted that 30% yield was achieved from the
reaction of methyl 3-(thiophen-2-yl)allyl carbonate (2g) with
triflate 1a and CO (entry 6). The optimal conditions were
found to be compatible with aliphatic and terminal allyl
carbonates 2h-j (entries 7-9). For example, treatment of
diene 2j with triflate 1a, CO, PdCl2 ,and PPh3 was carried
out smoothly in 55% yield (entry 9). We were pleased to
observe that a set of o-silyl aryltriflates 1b-e were suitable for
the reaction under the optimal conditions (entries 10-13), but
the bulky triflate 1c shifted the selectivity toward the (E)-2-
benzylidene product 16 (entry 11). It is noteworthy that the
unsymmetrical o-silyl aryltriflates 1b-e afford the correspond-
ing products regioselectively (entry 10-13). The results imply
that the carbonylation reaction takes place regioselectively at
the OTf position.
The synthesis of the (E)-2-benzylidene products9 was subse-
quently investigated in the presence of PdCl2 and P(o-tol)3, and
the results are summarized in Table 3. To our delight, moderate
yields of the 2-benzylidene products were still achieved from the
reactions of triflate 1a with allyl carbonates 2d, 2i, or 2k in the
presence of PdCl2 and P(o-tol)3 (entries 1-3). Two other o-silyl
aryltriflates 1c and 1e reacted with carbonate 2a and CO were
also examined under the same conditions, and the 2-benzyli-
dene products 16 and 21 were selectively prepared in 70% and
63%, respectively (entries 4 and 5).
(9) The constructions of the products are based upon the chemical shift of
the olefinic proton by comparison with the authoritative data, see: (a)
References 3 and 8. (b) Minatiti, A.; Zheng, X.; Buchwald, S. L. J. Org. Chem.
2007, 72, 9253.
We also tested the product 3 as a synthetic intermediate to
introduce a new group to this framework by the Heck
reaction (Scheme 2). In the presence of Pd(OAc)2, Ag2CO3,
J. Org. Chem. Vol. 75, No. 10, 2010 3485

Pi et al.
JOCNote
TABLE 2. PdCl2/PPh3-Catalyzed Carbonylation of o-Silyl
Aryltriflates (1) with Methyl Allyl Carbonates (2)a
TABLE 3. PdCl2/P(o-tol)3-Catalyzed Cycloarbonylation of o-Silyl
Aryltriflates (1) with Methyl Allyl Carbonates (2)a
aReaction conditions: 1 (0.25 mmol), 2 (0.2 mmol), PdCl2 (5 mol %),
P(o-tol)3 (10 mol %), CsF (2 equiv), CO (1 atm, bubbled), and MeCN
(2 mL) at 80 °C for 4 h.
SCHEME 2
A possible mechanism was proposed as outlined in
Scheme 3 on the basis of the present results and the reported
mechanism.3-8 Reaction of Pd(0) with allyl carbonate 2
affords the allylPd(II) intermediate B, followed by addition
of intermediate B to aryne A, which is generated in situ from
1 with CsF, gives intermediates C and/or D based on the
properties of both ligand and substrates.3 Insertion of CO
into intermediates C and D takes place to yield intermediates
E and F. The second cis-addition to the C-C double bond in
intermediates E and F leads to intermediates G and H.
Finally, reductive elimination of intermediates G and H
affords the products and regenerates the active Pd(0) species.
It is noteworthy that the steric hindrance effect of both
arynes and ligands has a fundamental influence on the
selectivity (intermediates I and J). In the presence of PPh3,
selectivity toward 2-methylene-1H-inden-1-ones may be that
secondary cabon in intermediate B is more active (stable)
than primary carbon, whereas P(o-tol)3 shifted the selectivity
toward 2-substituted-methylene-1H-inden-1-ones due to its
steric hindrance.
aReaction conditions: 1a (0.25 mmol), 2a (0.2 mmol), PdCl2
(5 mol %), PPh3 (10 mol %), CsF (2 equiv), CO (1 atm, bubbled),
and MeCN (2 mL) at 80 °C. bThe reaction time is given in parentheses.
d
cZ-/E-isomer =1:2.6. Product 16, (E)-2-benzylidene-5,7-di-tert-bu-
In summary, we have developed a new palladium-cata-
lyzed cyclocarboynlation protocol for selectively preparing
2-methylene-3-substituted-2,3-dihydro-1H-inden-1-ones and
tyl-2,3-dihydro-1H-inden-1-one, was obtained in 57% for 8 h.
and toluene, 3 was treated with iodobenzene smoothly to
afford a Heck/isomerization product 22, 2-benzyl-3-phenyl-
1H-inden-1-one, in 53% yield.10
(10) Pan, D.; Chen, A.; Su, Y.; Zhou, W.; Li, S.; Jia, W.; Xiao, J.; Liu, Q.;
Zhang, L.; Jiao, N. Angew. Chem., Int. Ed. 2008, 47, 4729.
3486 J. Org. Chem. Vol. 75, No. 10, 2010

Pi et al.
JOCNote
SCHEME 3. A Working Mechanism
(t, J = 8.0 Hz, 1H), 7.45 (t, J = 7.0 Hz, 1H), 7.33-7.26 (m, 4H),
7.12 (d, J = 7.0 Hz, 2H), 6.43 (d, J = 2.0 Hz, 1H), 5.44 (d, J = 1.5
Hz, 1H), 4.99 (s, 1H); 13C NMR (125 MHz, CDCl3) δ: 193.4,
153.5, 149.0, 142.3, 137.4, 135.4, 128.8, 128.3, 128.1, 127.1, 126.5,
124.2, 121.1, 49.1; IR (KBr, cm-1) 1679, 1654; LRMS (EI, 70 eV)
m/z (%) 220 (Mþ, 100), 191 (58), 165 (20), 115 (20).
Typical Experimental Procedure with the PdCl2/P(o-tol)3
System. Aryne 1 (0.25 mmol), allyl carbonat 2 (0.2 mmol), PdCl2
(5 mol %), P(o-tol)3 (10 mol %), CsF (2 equiv), and MeCN
(2 mL) were added to a two-necked flask in turn. Then, CO was
bubbled, and the solution was stirred at 80 °C for the indicated
time until complete consumption of starting material as mon-
itored by TLC and GC-MS analysis. After the reaction was
finished, the mixture was washed with brine, extracted with
diethyl ether, dried over anhydrous Na2SO4, and evaporated
under vacuum. The residue was purified by flash column
chromatography on silica gel (hexane/ethyl acetate) to afford
the desired product.
(E)-2-Benzylidene-2,3-dihydro-1H-inden-1-one (4):3 yellow
solid; mp 105.0-107.0 °C (uncorrected); H NMR (500 MHz,
CDCl3) δ 7.91 (d, J = 7.5 Hz, 1H), 7.68-7.60 (m, 4H), 7.55 (d,
J = 7.5 Hz, 1H), 7.48-7.34 (m, 4H), 4.05 (s, 2H); 13C NMR (125
MHz, CDCl3) δ 194.3, 149.6, 137.9, 135.3, 134.7, 134.6, 133.9,
130.7, 129.6, 128.9, 127.6, 126.1, 124.4, 32.4; IR (KBr, cm-1) 1732,
1715, 1650; LRMS (EI, 70 eV) m/z (%) 220 (Mþ, 65), 219 (100),
191 (43), 165 (13).
2-benzylidene-2,3-dihydro-1H-inden-1-ones. This work is the
first to demonstrate that the selectivity of cyclocarbonylation
between arynes and allyl carbonates can be controlled by
changing ligands. Most importantly, these products with
several functional groups can be employed as synthetic blocks
to synthesize this class of compounds with a new structural
feature readily for further elaboration.10
1
Experimental Section
Acknowledgment. We thank the Scientific Research Fund
of Hunan Provincial Education Department (Nos. 08B053
and 08A037), Opening Fund of Key Laboratory of Chemical
Biology and Traditional Chinese Medicine Research
(Ministry of Education of China; No. KLCBTCMR2008-
11), and New Century Excellent Talents in University (No.
NCET-06-0711) for financial support.
Typical Experimental Procedure with the PdCl2/PPh3 System.
Aryne 1 (0.25 mmol), allyl carbonate 2 (0.2 mmol), PdCl2
(5 mol %), PPh3 (10 mol %), CsF (2 equiv), and MeCN (2 mL)
were added to a two-necked flask in turn. Then, CO was bubbled,
and the solution was stirred at 80 °C for the indicated time until
complete consumption of starting material as monitored by TLC
and GC-MS analysis. After the reaction was finished, the mixture
was washed with brine, extracted with diethyl ether, dried over
anhydrous Na2SO4, and evaporated under vacuum. The residue
was purified by flash column chromatography on silica gel
(hexane/ethyl acetate) to afford the desired product.
Supporting Information Available: Analytical data and
spectra (1H and 13C NMR) for all the products 3-14 and
16-22 and typical procedure for the palladium-catalyzed cyclo-
carbonylation reaction. This material is available free of charge
via the Internet at http://pubs.acs.org.
2-Methylene-3-phenyl-2,3-dihydro-1H-inden-1-one (3):3 yellow
oil; 1H NMR (500 MHz, CDCl3) δ 7.92 (d, J = 7.5 Hz, 1H), 7.59
J. Org. Chem. Vol. 75, No. 10, 2010 3487