Nickel-catalyzed decarbonylative addition of anhydrides to alkynes

Full text of DOI:10.1021/ja806569h

Published on Web 12/02/2008
Nickel-Catalyzed Decarbonylative Addition of Anhydrides to Alkynes
Yuichi Kajita, Takuya Kurahashi,* and Seijiro Matsubara*
Department of Material Chemistry, Graduate School of Engineering, Kyoto UniVersity, Kyoto 615-8510, Japan
Received August 19, 2008; E-mail: matsubar@orgrxn.mbox.media.kyoto-u.ac.jp; tkuraha@orgrxn.mbox.media.kyoto-u.ac.jp
Table 1. Nickel-Catalyzed Decarbonylative Addition of Phthalic
The transition metal-catalyzed insertion reaction of an unsaturated
carbon-carbon bond into a carbon-oxygen bond of an oxacyclic
compound is a useful transformation to prepare more complicated
oxacyclic compounds in a single step (Scheme 1). However, there
is no precedent for such a potentially valuable methodology. We
postulated that oxidative addition of cyclic anhydrides to nickel(0)
and subsequent decarbonylation are facile and might allow insertion
of alkynes. Thus, we attempted the decarbonylative addition of
phthalic anhydride to alkyne using nickel(0) catalyst to form
isocoumarin,1,2 which displays a wide range of biological activities.3
Our investigation began with an attempted addition of phthalic
anhydride (1a) to 4-octyne (2a) with 10 mol % of Ni(cod)2 and 40
mol % of PMe3 in refluxing acetonitrile (80 °C) for 12 h.4 However,
this resulted in low conversion of 1a and led to isocoumarin 3aa
in 12% yield (Table 1, entry 1).5 A detailed examination of the
reaction conditions revealed that, on addition of 20 mol % of ZnCl2,
the reaction proceeded smoothly to furnish 3aa in 96% isolated
yield (entry 2).6 Among the Lewis acids examined, ZnCl2 gave
the best yield of the product (entries 3-7). An addition of
quaternary ammonium salts was also found to be effective for the
reaction (entries 8-12). An electrostatic interaction between the
carbonyl moiety of 1a and the quaternary ammonium might behave
as a general Lewis acid.7
Anhydride to 4-Octynea
entry
additive
yield (%)b
entry
additive
yield (%)b
1
2
3
4
5
6
s
12
96
92
91
90
92
7
8
9
10
11
12
LiCl
76
54
72
67
65
52
ZnCl2
Zn(OTf)2
ZnBr2
ZnI2
Bu4NPF6
Bu4NCl
Bu4NOTf
Bu4NBr
Bu4NI
BPh3
a All reactions were carried out using Ni(cod)2 (10 mol %), PMe3 (40
mol %), additive (20 mol %), phthalic anhydride (0.5 mmol), and
4-octyne (0.6 mmol) in 2 mL of refluxing acetonitrile (80 °C). b Isolated
yields.
Table 2. Nickel-Catalyzed Decarbonylative Addition of Anhydrides
to 4-Octynea
With the optimized conditions in hand,8-10 we next investigated
the scope of the reaction using various anhydrides (Table 2). The
decarbonylative addition of maleic anhydride 1b to 4-octyne
provides R-pyrone 3ba in 87% yield (Table 2, entry1). The reaction
of 2,3-naphthalenedicarboxylic anhydride (1c) with 2a gave the
product 3ca in 82% yield (entry 2). Unsymmetrical anhydrides 1d
and 1e provide the corresponding products 3da and 3ea in 61%
and 53% yields, along with formation of the respective regioisomers
(entries 3 and 4). The addition of 1f to 2a proceeded smoothly to
provide 3fa in 94% yield (entry 5). The addition of diphenyl-
substituted maleic anhydride 1g to 4-octyne resulted in lower yield
(23%) even with prolonged reaction time (entry 6).
The addition reaction is also compatible with aryl-substituted
alkyne (Table 3, entry 1) and afforded the corresponding isocou-
marin 3ab in 87% yield. The reaction of 1a with unsymmetrical
alkynes such as 2c and 2d gave the products consisting of
regioisomers in a 1/1 ratio (entries 2 and 3). The addition of 1a to
2e, containing sterically hindered groups, gave adduct 3ae as a
major product with a regioselectivity ratio of 2/1 (entry 4). Bulky
and electron-rich trimethylsilyl-substituted alkynes such as 2f and
2g reacted with 1a to provide adducts with complete regiocontrol
in excellent yields (entries 5 and 6). Terminal alkynes, such as
1-octyne and phenylacetylene, failed to participate in the reaction,
presumably due to rapid oligomerization of alkynes.
A plausible reaction pathway to account for the formation of
isocoumarins 3 based on the observed results is outlined in Scheme
2. In view of the mechanism of the previously reported nickel-
catalyzed cross-coupling reaction of anhydrides with organometalic
reagents,11 it is reasonable to consider that the catalytic cycle of
a All reactions were carried out using Ni(cod)2 (10 mol %), PMe3 (40
mol %), ZnCl2 (20 mol %), 1 (0.5 mmol), and 2a in 2 mL of refluxing
acetonitrile (80 °C). b Isolated yields.
the present reaction should consist of oxidative addition of an
anhydride O-CO bond to nickel.12 Subsequent decarbonylation
and coordination of alkyne take place, in which the steric repulsive
interaction is minimal between the bulkier R1 and the PMe3 ligand
on the nickel, to give nickel(II) intermediate 4a. The alkyne would
then insert into the aryl-nickel bond to give nickelacycle 5, which
undergoes reductive elimination to give 3 and regenerates the
9
17226 J. AM. CHEM. SOC. 2008, 130, 17226–17227
10.1021/ja806569h CCC: $40.75
2008 American Chemical Society

C O M M U N I C A T I O N S
Table 3. Nickel-Catalyzed Decarbonylative Addition of Phthalic
group, which may generate electron-poor alkenylnickel through a
Anhydride to Alkynesa
conjugated system.5
i
In conclusion, the decarbonylative addition reaction of phthalic
anhydrides to alkynes is successfully demonstrated using a nickel
catalyst in association with a Lewis acid as a cocatalyst. Further
efforts to expand the scope of the chemistry and studies of the
detailed mechanism are currently underway in our laboratories.
Acknowledgment. This work was supported by Grants-in-Aid
for Young Scientist (B) (19750031) from the Ministry of Education,
Culture, Sports, Science, and Technology, Japan. T.K. also
acknowledges NOVARTIS Foundation (Japan) for the Promotion
of Science, and the Takeda Pharmaceutical Company Award in
Synthetic Organic Chemistry, Japan. We thank Mr. Okada and Mr.
Deuchi, Mettler-Toledo, for in situ IR analysis.
Supporting Information Available: Experimental procedures in-
cluding spectroscopic and analytical data of new compounds. This
material is available free of charge via the Internet at http://pubs.acs.org.
References
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a All reactions were carried out using Ni(cod)2 (10 mol %), PMe3 (40
mol %), 1a (0.5 mmol), and alkyne in 2 mL of refluxing acetonitrile (80
°C). b Isolated yields. c Ratio of regioisomers. d Only
a single
regioisomer was formed.
Scheme 1. Transition-Metal-Catalyzed Decarbonylative Addition of
Cyclic Anhydrides to Alkynes
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Scheme 2. Plausible Mechanism for the Nickel-Catalyzed
Decarbonylative Addition of Phthalic Anhydrides to Alkynes
(9) The reaction of 1a and 2a using air-stable trimethylphosphonium tetrafluo-
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the addition product and was completed in 36 h (Figure S2, Supporting
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starting nickel(0). In-situ IR spectra analysis demonstrated that the
stoichiometric reaction of Ni(cod)2/PMe3 with 1a and 2a without
ZnCl2 resulted in gradual consumption of 1a without formation of
3aa. Importantly, constant generation of 3aa was observed simul-
taneously on addition of ZnCl2 (Figure S1, Supporting Information).
These results imply that reductive elimination is specifically
promoted by the addition of ZnCl2. The origin of the effect of ZnCl2
is likely to result from the coordination of a Lewis acid to a carbonyl
JA806569H
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