Gold-catalyzed naphthalene functionalization

Article abstract of DOI:10.3762/bjoc.7.77

The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one equiv of NaBAr'₄ (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO₂Et (R = H, Me) from N₂C(R)CO₂Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from the formal insertion of the carbene unit into the aromatic C-H bond or from its addition to a double bond. In addition, no byproducts derived from carbene coupling were observed.

Full text of DOI:10.3762/bjoc.7.77

Gold-catalyzed naphthalene functionalization
Pedro J. Pérez*, M. Mar Díaz-Requejo* and Iván Rivilla
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2011, 7, 653–657.
Laboratorio de Catálisis Homogénea, Departamento de Química y
Ciencia de los Materiales, Unidad Asociada al CSIC, Centro de
Investigación en Química Sostenible (CIQSO), Universidad de
Huelva, Campus de El Carmen 21007-Huelva, Spain
doi:10.3762/bjoc.7.77
Received: 31 March 2011
Accepted: 12 May 2011
Published: 23 May 2011
Email:
Pedro J. Pérez* - perez@dqcm.uhu.es; M. Mar Díaz-Requejo* -
mmdiaz@dqcm.uhu.es; Iván Rivilla - ivan.rivilla@dqcm.uhu.es
This article is part of the Thematic Series "Gold catalysis for organic
synthesis"
* Corresponding author
Guest Editor: F. D. Toste
Keywords:
© 2011 Pérez et al; licensee Beilstein-Institut.
License and terms: see end of document.
carbene insertion; copper catalysts; diazoacetates; gold catalysts;
naphthalene functionalization; selective insertion
Abstract
The complexes IPrMCl (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene, M = Cu, 1a; M = Au, 1b), in the presence of one
equiv of NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl), catalyze the transfer of carbene groups: C(R)CO2Et (R = H, Me) from
N2C(R)CO2Et to afford products that depend on the nature of the metal center. The copper-based catalyst yields exclusively a
cycloheptatriene derivative from the Buchner reaction, whereas the gold analog affords a mixture of products derived either from
the formal insertion of the carbene unit into the aromatic C–H bond or from its addition to a double bond. In addition, no byprod-
ucts derived from carbene coupling were observed.
Introduction
At the end of the nineteenth century, Buchner discovered [1] the rated and unsaturated substrates, including aromatics [3]. Thus,
thermal and photochemical route for the functionalization of the reaction of ethyl diazoacetate (EDA) with benzene in the
benzene using diazo compounds to provide a carbene moiety. presence of such catalysts at room temperature exclusively
The first step of this transformation consists of the addition of affords the cycloheptatriene product in quantitative yields. The
such a unit to the aromatic double bond to give a norcaradiene reaction, always referred to the intermolecular version, was later
intermediate that spontaneously undergoes ring opening to observed with other metal-based catalysts [4-6].
afford the more stable cycloheptatriene product (Scheme 1) [2].
Nearly one century later, Teyssié and co-workers discovered the The above transformation with rhodium-based catalysts [7,8]
potential of dirhodium tetraacetate and related Rh2(L-L)4 com- has also been investigated with naphthalene as a substrate. In
pounds as catalysts for the decomposition of diazo compounds this case, Teyssié and co-workers showed that it could be
and subsequent transfer of the carbene moiety to several satu- converted, using t-butyl diazoacetate, into norcaradiene type
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Beilstein J. Org. Chem. 2011, 7, 653–657.
Scheme 1: (a) The Buchner reaction of benzene and ethyl diazoacetate and (b) the Rh-catalyzed version. (c) Both pathways involve the formation of
norcaradiene intermediates.
derivatives, formed by the cyclopropanation of one of the C–H bond of benzene as well as the major product (Scheme 3).
double bonds of the naphthalene ring. Later, Müller and In this contribution, we report the results obtained from the
co-workers [9] showed the effect of a series of Rh2(L-L)4 in the analogous transformation using naphthalene as the substrate,
same transformation but with ethyl diazoacetate as the carbene with copper- and gold-based catalysts, not previously described
source. A mixture of the products (2a–d) arising from cyclopro- for the functionalization of such fused arenes.
panation, ring opening and the formal insertion of CHCO2Et
into the aromatic C–H bonds were observed, with 2a being by
far the major product (Scheme 2).
In the course of our research, focussed on the development of
group 11 metal-based catalysts for carbene transfer reactions
from diazo compounds [10], we found that the gold complex
IPrAuCl (1b) (IPr = 1,3-bis(diisopropylphenyl)imidazol-2-
ylidene) in the presence of one equiv of NaBAr'4 (Ar' = 3,5-
bis(trifluoromethyl)phenyl) induced the functionalization of
benzene with ethyl diazoacetate to give a mixture of a cyclohep-
tatriene and ethyl 2-phenylacetate [11], the latter being the
Scheme 3: The gold-catalyzed reaction of benzene and EDA.
result of the formal insertion of the CHCO2Et group into the
Scheme 2: The Buchner reaction applied to naphthalene. (a) Teyssié's system. (b) Müller's system.
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Beilstein J. Org. Chem. 2011, 7, 653–657.
Results and Discussion
Reaction of naphthalene and diazoacetates
catalyzed by IPrMCl (M = Cu, Au)
The selectivity observed is similar to that reported by Müller's
group with [Rh2(O2CC3F7)4] (60:22:18) [8]. However, in our
case the yield of products (EDA-based) was quantitative: prod-
ucts derived from dimerization of the diazo compound, i.e.,
diethyl fumarate and maleate, were not detected. The absence of
the fused cycloheptatriene 2d in our system is also noteworthy.
Substituted naphthalenes with OMe or Cl substituents at the
beta position were also employed as substrates, however, the
yields of the desired products were nearly negligible. The
former seemed to induce the insertion into the Me groups,
whereas in the latter case the aromatic reagent seemed deacti-
vated.
When dichloroethane solutions of naphthalene were treated
with ethyl diazoacetate in the presence of catalytic amounts
(5%) of a 1:1 mixture of IPrMCl (M = Cu, 1a; M = Au, 1b) and
NaBAr'4, the diazo compound was consumed after 24 h at
60 °C (no significant reaction was observed at room tempera-
ture or at 40 °C). NMR analysis of the crude reaction product
revealed that when 1a was used as the catalyst, only one com-
pound was formed, identified as ethyl 1a,7b-dihydro-1H-cyclo-
propa[a]naphthalene-1-carboxylate (2a), i.e., the product
derived from the direct cyclopropanation of the naphthalene
C–C double bond (Scheme 4a). By contrast, the use of the gold
catalyst IPrAuCl (1b) under the same reaction conditions gave a
mixture of three compounds, in ca. 65:20:15 ratio, that have
been identified as 2a, ethyl 2-(naphthalen-1-yl)acetate (2b) and
ethyl 2-(naphthalen-2-yl)acetate (2c). Compounds 2b and 2c,
respectively, are derived from the formal insertion of the
carbene group into a C–H bond of naphthalene (Scheme 4b).
We have expanded this reaction to ethyl 2-diazopropionate as
the diazo component. Following a similar protocol, naphtha-
lene was reacted in dichloroethane with ethyl 2-diazopropio-
nate in the presence of a 1:1 mixture of 1a,b and NaBAr'4 (5%
with respect to the diazo compound). Similarly to the previous
results, the fused norcaradiene 3a (Scheme 5) was exclusively
and quantitatively formed using the copper catalyst 1a, whilst
Scheme 4: The functionalization of naphthalene with ethyl diazoacetate catalyzed by the complexes (a) 1a and (b) 1b.
Scheme 5: The functionalization of naphthalene with ethyl 2-diazopropionate catalyzed by complexes 1a and 1b.
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Beilstein J. Org. Chem. 2011, 7, 653–657.
the use of 1b afforded a mixture of three products in a 60:20:20 Et2O:petroleum ether) gave a mixture of products. The prod-
ratio. The major product was identified as the 3a and the minor ucts 2a, 3b and 3c were identified by comparison with litera-
products have been characterized as the insertion products of ture data [17-19], and 2b and 2c were compared authentic
the carbene C(Me)CO2Et into the α- and β-C–H bonds of naph- samples obtained from commercial sources.
thalene, 3b and 3c, respectively. When other diazo reagents
such as Me3SiC(N2)CO2Et or PhC(N2)CO2Et were employed, Spectroscopic data for 3a: 1H NMR (400 MHz, CDCl3) δ
intractable mixtures of compounds, probably due to multiple 7.41–6.94 (m, 4H), 6.59 (d, 1H), 6.06 (dd, 1H), 4.23 (m, 2H),
insertions, were observed by NMR.
3.14 (d, J = 8.7 Hz, 1H), 2.72 (dd, J = 8.8 Hz, 1H), 1.26 (s, 3H),
1.29 (m, 3H); 13C NMR (101 MHz, CDCl3) δ 169.0 (CO2Et),
It is also worth mentioning that the above transformations do 146.4, 134.5, 133.4, 129.6, 128.5, 127.7, 126.6, 125.5
not compete with the formation of byproducts derived from the (aromatic), 63.1 (COCH2CH3), 39.6, 33.3, 31.2 (cyclopropyl),
catalytic dimerization of the diazo reagents, a common draw- 19.52 (CH3), 11.8 (COCH2CH3); MS m/z (%): 228 (70), 199
back in this methodology [2]. Despite of adding all the diazo (30), 182 (100).
compound in one portion at the beginning of the reaction, the
final reaction mixture only showed resonances due to the afore- Acknowledgements
mentioned insertion and addition products. This is at variance We wish to thank DGI (CTQ2008-00042BQU and Consolider
with other reported systems that required the use of slow addi- Ingenio 2010, Grant CSD2006-0003) and Junta de Andalucía
tion devices to diminish the formation of such byproducts.
(P07-FQM-02870) for funding.
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Conclusion
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