Novel catalytic CO2 incorporation reaction: Nickel-catalyzed regio- and stereoselective ring-closing carboxylation of bis-1,3-dienes

Article abstract of DOI:10.1021/ja026620c

Novel nickel-catalyzed carboxylation of bis-1,3-dienes using carbon dioxide (CO₂) was investigated. In the presence of catalytic amounts of Ni(acac)₂ and PPh₃, various bis-1,3-dienes smoothly reacted with CO₂ and an organozinc reagent (Et₂Zn, Me₂Zn, or Ph₂Zn) under mild conditions. This catalytic carboxylation process was accompanied by carbocyclization of bis-1,3-diene followed by alkylation by an organozinc reagent to afford cyclic carboxylic acid derivatives in high yields with high regio- and stereoselectivities. Copyright

Full text of DOI:10.1021/ja026620c

Published on Web 08/03/2002
Novel Catalytic CO2 Incorporation Reaction: Nickel-Catalyzed Regio- and
Stereoselective Ring-Closing Carboxylation of Bis-1,3-dienes
Masanori Takimoto and Miwako Mori*
Graduate School of Pharmaceutical Sciences, Hokkaido UniVersity, Sapporo 060-0812, Japan
Received April 21, 2002
Scheme 1. Ni-Catalyzed Ring-Closing Carboxylation of 1a
Development of transition-metal-catalyzed carbon dioxide (CO2)
incorporation reactions into organic molecules is an attractive
subject in synthetic organic chemistry.1 However, only a few
catalytic synthetic reactions have been reported.2 Among the
reported reactions, palladium- or nickel-catalyzed co-oligomeriza-
tion of 1,3-dienes with CO2, which proceeds via a bis-π-allyl
intermediate, is one of the first and most extensively studied
transition-metal-catalyzed CO2 fixation process.3-7 Despite the
potential usefulness of this reaction, it has rarely been used for the
synthesis of complex organic molecules, due in part to the low
selectivity. One practical solution to this problem might be to
conduct the reaction in intramolecular form.8 On the basis of this
concept, we have studied a nickel-promoted co-oligomerization of
bis-1,3-diene and CO2 and have found an efficient methodology
that utilizes an organozinc compound as a supplemental reagent
and enables a catalytic process with extra carbon-carbon bond
formation to be realized. In this communication, we report this novel
reaction, i.e., a highly regio- and stereoselective ring-closing
carboxylation of bis-1,3-dienes (eq 1).
a The product was isolated and characterized after treatment with
diazomethane.
Scheme 2. Determination of Stereochemistry of 2aa
a Reagents and conditions: (a) RuCl2(dCHPh)(PCy3)2 (5 mol %),
CH2Cl2, 6 h, 80%; (b) H2, Pd/C, AcOEt, rt, 6 h, 94%.
Scheme 3. Possible Reaction Mechanism
A reaction of symmetrical bis-1,3-diene 1a in the presence of a
nickel catalyst and Et2Zn was examined first (Scheme 1). To a
solution of Ni(cod)2 (20 mol %) and PPh3 (40 mol %) in THF were
added 1a and Et2Zn (4.5 equiv), and the mixture was stirred at 0
°C for 3 h under an atmosphere of CO2 (1 atm). Hydrolysis of the
resulting mixture followed by treatment with diazomethane afforded
2a in 75% yield as a sole product. The results of an NOE experiment
for 2a showed that the configuration of two side chains on the five-
membered ring was trans. The stereochemistry, which is concerned
with a methoxycarbonyl moiety, was determined by the coupling
1
constants of Ha in a H NMR spectrum of 3 that was prepared
from 2a by the procedures shown in Scheme 2. In this reaction, an
air-stable Ni(II) complex also can be used as a catalyst precursor
in place of Ni(cod)2. By using 5 mol % of Ni(acac)2 and 10 mol %
of PPh3, 2a was obtained in 72% yield (Scheme 1).
A possible reaction mechanism is shown in Scheme 3. The
reaction seems to start with oxidative cycloaddition of bis-diene
1a to an Ni(0) complex10 to produce bis-π-allylnickel complex 4,
and subsequent insertion of CO2 into the nickel-carbon bond
affords carboxylate 5.11 The role of Et2Zn in this reaction is probably
regeneration of a Ni(0) complex via a transmetalation process.12-15
Thus, complex 5 reacts with Et2Zn to provide ethylnickel complex
6, which can then easily undergo â-hydride elimination to afford
complex 7. Reductive elimination from 7 reproduces a Ni(0)
complex and provides carboxylate 8, which corresponds to ester
2a. In this case, the â-hydride elimination process (6 to 7) seems
to restrict the transfer of an ethyl group from Et2Zn to the product.
This possibility prompted us to examine organozinc reagents having
no â-hydrogen atom on their alkyl ligand.
The reaction of 1a with Me2Zn (4.5 equiv) and CO2 (1 atm) in
the presence of a nickel catalyst (10 mol %) afforded 9a in 94%
yield (Table 1, entry 1). The formation of 9a can be explained by
the reductive elimination from methylnickel complex 6′, which was
produced via a reaction course similar to that shown in Scheme 3.
Bis-diene 1b also underwent methylative carboxylation to afford
ester 9b in high yield (entry 2). Furthermore, phenylative ring-
* To whom correspondence should be addressed. E-mail: mori@
pharm.hokudai.ac.jp.
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J. AM. CHEM. SOC. 2002, 124, 10008-10009
10.1021/ja026620c CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
Table 1. Methylative or Phenylative Ring-Closing Carboxylationa
organozinc reagent. This reaction can be carried out easily under
mild conditions, and the yields and regio- and stereoselectivities
are generally high. Efforts to expand the scope of this reaction are
underway.
Acknowledgment. This work was supported in part by a Grant-
in-Aid for Scientific Research (No. 14771235) from the Ministry
of Education, Culture, Sports, Science and Technology, Japan,
which is gratefully acknowledged.
Supporting Information Available: Information on typical pro-
cedures for carboxylations, procedures for determination of the stere-
ochemistry, and spectral data for all new compounds (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
References
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10.8, 3.5 Hz) at 2.28 ppm. For the procedures to determine the
stereochemistry of other ring-closing carboxylation products, see Sup-
porting Information.
a All reactions were carried out in the presence of Ni(acac)2 (10 mol %
for entries 1 and 15 mol % for the other cases), PPh3 (2 equiv to nickel),
and organozinc (4.9 equiv for entry 3 and 4.5 equiv for the other cases)
under an atmosphere of CO2 (1 atm). b All products were isolated as methyl
esters after treatment with diazomethane.
closing carboxylation could be carried out in a regio- and stereo-
selective manner by the use of Ph2Zn instead of Me2Zn (entries 3
and 4).
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It is notable that this reaction was applicable to the reaction of
unsymmetrical bis-1,3-dienes with high selectivities. Methylative
carboxylation of bis-diene 1c or 1d, which possessed a methyl group
on a terminal carbon of one diene moiety, proceeded with
regioselective introduction of CO2 into the unsubstituted diene
moiety (not into the methyl-substituted one) to afford 9c or 9d
(Table 1, entries 5 and 6). The same selectivity was also found in
the reaction of 1e, which resulted in regio- and stereoselective
construction of a heterocyclic six-memberd ring (entry 7). Further-
more, the addition of a phenyl group also occurred in a stereose-
lective manner to afford 10c as a single diastereomer when
carboxylation of 1c was carried out with Ph2Zn (entry 8).16
In conclusion, we have developed a nickel-catalyzed ring-closing
carboxylation of bis-1,3-dienes, which proceeds via insertion of
CO2 into a bis-π-allylnickel intermediate followed by a transmeta-
lation process of the resulting cyclic nickel carboxylate with an
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(16) The 13C NMR spectrum of 10c indicated that 10c was obtained as a single
isomer (see Supporting Information). For detailed procedures to determine
the stereochemistry, see Supporting Information.
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