Chemospecific intramolecular buchner reaction catalyzed by copper(II) acetylacetonate

Article abstract of DOI:10.1002/cctc.201400014

A chemospecific intramolecular Buchner reaction of N-benzyl-2-cyano-2- diazoacetamides catalyzed by inexpensive copper(II) acetylacetonate (acac) has been achieved to synthesize a variety of 9-aza-1-cyanobicyclo[5.3.0]deca-2,4,6- trien-10-ones, 5,7-bicyclic products. The methodology involves sole chemoselectivity, an inexpensive metal catalyst, broad substrate scope, and moderate to excellent yields. Cheap as copper: Copper(II) acetylacetonate is an efficient catalyst in the intramolecular Buchner reaction of N-benzyl-2-cyano-2-diazoacetamides for the chemospecific synthesis of 9-aza-1-cyanobicyclo[5.3.0]deca-2,4,6-trien-10-one derivatives in moderate to excellent yields with a broad substrate scope.

Full text of DOI:10.1002/cctc.201400014

CHEMCATCHEM
FULL PAPERS
DOI: 10.1002/cctc.201400014
Chemospecific Intramolecular Buchner Reaction Catalyzed
by Copper(II) Acetylacetonate
Shanyan Mo and Jiaxi Xu*[a]
A chemospecific intramolecular Buchner reaction of N-benzyl-
2-cyano-2-diazoacetamides catalyzed by inexpensive copper(II)
acetylacetonate (acac) has been achieved to synthesize a varie-
ty of 9-aza-1-cyanobicyclo[5.3.0]deca-2,4,6-trien-10-ones, 5,7-bi-
cyclic products. The methodology involves sole chemoselectivi-
ty, an inexpensive metal catalyst, broad substrate scope, and
moderate to excellent yields.
Introduction
The Buchner reaction, a two-stage reaction of the addition of
a carbene to an aromatic ring and the ring expansion, is an ef-
ficient method to synthesize cyclohepta-1,3,5-triene deriva-
tives. Although intramolecular Buchner reactions, especially,
the intramolecular Buchner reactions of 2-substituted
N-benzyl-2-diazoacetamides for the synthesis of 9-azabicyclo-
[5.3.0]deca-2,4,6-trien-10-ones (5,7-bicyclic products), have
been extensively studied,[1] 2-nonsubstituted,[2] 2-acetyl,[2j,3]
2-methoxycarbonyl,[2j,3c,4] and 2-aryl[5] substituted N-benzyl-2-di-
azoacetamides A generally gave rise to the corresponding
5,7-bicyclic products B, always accompanied by the aromatic
and aliphatic CÀH insertion products, such as b-lactams C,
g-lactams D, and d-lactams E, even as major products, with Rh
catalysts (Scheme 1). It has been reported that the a-substi-
tuents,[2b,3c,6] the ligands in the catalysts,[2b,7] and even the reac-
tion conditions[2b] (e.g., the reaction temperature and solvents)
have great effects on the chemo- and regioselectivities, and ef-
forts have been devoted to achieve high chemoselectivity to
obtain the desired products, such as C, D, and E, respective-
ly.[2–7] However, to the best of our knowledge, the specific che-
moselectivity towards the Buchner reaction for the preparation
of B has not been realized in these reactions until now.
Recently, Charette et al.[8] and Nani and Reisman[9] achieved
chemospecific intermolecular and intramolecular cyclopropa-
nations of 2-diazo-2-cyanoacetyl compounds. In their reactions,
the cyano group plays a crucial role in the sole chemoselectivi-
ty. The metal carbenoids derived from a-diazo-b-ketonitriles
adopt an out-of-plane conformation, so they are more electro-
philic than those derived from a-diazo-b-nitro/acyl acetamides
and tend to undergo cyclopropanation rather than the CÀH in-
sertion.[2b] However, the cyano group is less sterically bulky,
which minimizes the destabilizing nonbonding interactions be-
tween the metal carbenoid and the arene/alkene
moiety in the cyclopropanation transition-sate struc-
ture.
In the Buchner reactions studied previously, RhII
catalysts were the most efficient, universal, and
widely used metal catalysts.[2–7] However, they are
very expensive and not abundant in the Earth.[10]
Some relatively cheaper metal catalysts, such as
Au,[11] Ru,[12] and Ag,[13] have also been used in the
catalysis of the reaction, but with limited application.
Cu salts are one class of the most inexpensive metal
catalysts and have been applied in carbene-related
reactions with excellent catalytic performance.[14]
Moreover, CuII catalysts provide better selectivity for
the cyclopropanation than the CÀH insertion, even in
the systems in which the CÀH insertion is geometrically favor-
able.[9,15] As cyclopropanation is the first stage of the Buchner
reaction, the use of CuII catalysts in the Buchner reaction may
probably improve their yields to make the reactions economi-
cal and practical.
Scheme 1. Reactions of substituted N-benzyl-2-diazoacetamides.
[a] S. Mo, Prof. Dr. J. Xu
State Key Laboratory of Chemical Resource Engineering
Department of Organic Chemistry, Faculty of Science
Beijing University of Chemical Technology
100029, No.15, Northern 3rd Ring Road East, Beijing (P.R. China)
Fax: (+86)10-64435565
Herein, we present an inexpensive Cu(acac)2-catalyzed and
chemospecific intramolecular Buchner reaction of N-benzyl-2-
cyano-2-diazoacetamides with a wide substrate scope. The re-
E-mail: jxxu@mail.buct.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201400014.
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 1679 – 1683 1679

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
action displays the following advantages: 1) sole chemoselec-
tivity—only Buchner reaction products are obtained; 2) only
a nonprecious metal catalyst Cu(acac)2 is used; 3) wide sub-
strate scope—various functional groups are tolerated on the
aromatic group in the substrates.
point, we decided to further optimize the reaction conditions
with this cheap catalyst.[18] If we increased the catalyst loading,
the yield reached 94%, but the reaction time did not decrease
(Table 1, entries 9–12). To perform the reaction more efficiently,
we changed to a solvent mixture of toluene and 1,2-dichloro-
ethane (DCE) with a higher boiling point, which resulted in the
successful reduction of the reaction time to only 0.5 h with
a good yield (Table 1, entries 13 and 14). Other cheap CuII cata-
lysts cupric acetate hydrate and cupric chloride dihydrate also
catalyzed the reaction very well (Table 1, entries 15 and 16). Fi-
nally, 5 mol% Cu(acac)2 and DCE were selected as the opti-
mized conditions and used in the following studies.
Results and Discussion
N,N-Dibenzyl-2-cyano-2-diazoacetamide (1a) was prepared
from N,N-dibenzyl-2-cyanoacetamide and triflic azide in the
presence of triethylamine[16] and selected as a model to opti-
mize the reaction conditions (Table 1). In all explored solvents,
only the desired Buchner reaction product, the 5,7-bicyclic
Various N-alkyl-N-benzyl-2-cyano-2-diazoacetamides 1 were
prepared from the corresponding secondary amines[19] and cy-
anoacetic acid and investigated under the optimized
product
9-aza-9-benzyl-1-cyanobicyclo[5.3.0]deca-2,4,6-trien-
reaction conditions. All reactions proceeded smoothly
Table 1. Optimization of catalysts and solvents.
under the optimized reaction conditions to afford the
Buchner reaction products
2
chemospecifically
except for 1r with an N-naphthalen-2-ylmethyl in-
stead of N-benzyl groups, which stopped at the first
stage of the Buchner reaction to give the cyclopropa-
nation product 3r (Table 2, entry 18). The results are
summarized in Table 2. The diazoamide 1a produced
the desired product 2a in the highest yield because
the same two benzyl groups were on the amide
(Table 2, entry 1). Even for N-benzyl-diazoamides 1a–f
with benzyl, primary, secondary, and tertiary alkyl
groups on the nitrogen atom of the amide (Table 2,
entries 1–6), only Buchner reaction products were ob-
tained in all cases. No carbene CÀH insertion product
on the benzylic, primary, secondary, or tertiary CÀH
bond was observed, regardless of if the N-alkyl group
is straight or branched, linear or cyclic, primary, sec-
ondary, tertiary, or the even more active benzylic
group. However, higher yields were achieved if the
N-alkyl groups were more sterically bulky. This can be
rationalized by the preferred stable conformation of
the metal carbene amide intermediates I (Figure 1).
In the Newman projection of the intermediates, if R1
is more bulky, conformation I is more favorable than
II, in which two bulky groups exist in the gauche po-
sition because of steric hindrance.[2a] Conformation I
is the reactive conformation that leads to the Buch-
Entry
Solvent
Catalyst
Catalyst loading [%]
t [h]
Yield [%][a]
1
2
3
4
5
6
7
8
toluene
benzene
DCM
CHCl3
DCE
DCM
DCM
DCM
DCM
DCM
DCM
DCM
toluene
DCE
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
1
1
1
1
0.5
0.5
0.5
0.5
0.5
40
0.5
48
48
48
48
48
0.5
0.5
0.5
0.5
69
69
70
61
68
59
63
trace[d]
60
69
79
94
90
1
[b]
Rh2(cap)4
Rh2(oct)4
0.5
0.5
1
0.5
1
2
5
5
5
Co(TDMPP)[c]
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(OAc)2·H2O
CuCl2·2H2O
9
10
11
12
13
14
15
16
90
87
86
DCE
DCE
5
5
[a] Isolated yield after column chromatography on silica gel. All reactions were per-
formed on a 1 mmol scale in 10 mL of solvent. Diazo compound 1a was dissolved in
5 mL of solvent and added dropwise with a syringe over 40 min. [b] Dirhodium(II) cap-
rolactamate. [c] Cobalt(II) meso-tetrakis(4-methoxyphenyl)porphyrin. [d] Most of the
diazo compound 1a was recovered.
10-one (2a), was obtained with slightly different yields under
the catalysis of Rh2(OAc)4 (Table 1, entries 1–5). The catalyst dir-
hodium(II) caprolactamate [Rh2(cap)4] with an electron-donat-
ing ligand resulted in a decrease in the reaction rate, which re-
quired a longer reaction time (Table 1, entry 6). However, differ-
ent Rh catalysts did not show a clear difference in either che-
moselectivity or yield (Table 1, entries 6 and 7). This phenom-
enon is different from that reported,[2b,7] in which the
chemoselectivity depends clearly on the ligands coordinated
to Rh. The inexpensive catalyst Co(TDMPP) [TDMPP=tris(2,6-di-
methoxyphenly)phosphine] did a poor job in the reaction
(Table 1, entry 8). Cupric(II) acetoacetate [Cu(acac)2], a very
cheap and easy-to-prepare catalyst,[17] showed a good result
Figure 1. Explanation of the chemospecificity: a) Cyano group and carbenoid
are in-plane, carbonyl group and carbenoid are out-of-plane; b) p–p Stack-
ing stabilizes conformation I.
and gave rise to the desired product in 60% yield with only
0.5 mol% catalyst loading. Therefore, from an economic view-
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 1679 – 1683 1680

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
not proceed to the second stage of the standard
Buchner reaction (Table 2, entry 18).
Table 2. Intramolecular Buchner reaction of N-benzyl-2-cyano-2-diazoacetamides cata-
lyzed by Cu(acac)2.
It has been observed that the steric effect of the
N-alkyl group does not influence the chemoselectivi-
ty at all. The chemospecificity was observed in all
cases even if R1 was a less bulky group, such as
methyl, n-propyl, and n-butyl groups. It is proposed
that, compared to carbenes with other electron-with-
drawing groups (e.g. acetyl and methoxycarbonyl
groups), a-cyanocarbenes possess a particular elec-
trophilicity, which is more preferable for the cyclopro-
panation because the cyano moiety adopts in an in-
plane conformation and is less sterically hin-
dered,[11c,d] whereas a-acetyl and methoxycarbonyl
carbenes exist in an out-of-plane conformation. In ad-
dition, the p–p stacking interaction between the
cyano and phenyl groups may play an important role
to stabilize conformation I to result in the formation
of the Buchner products chemospecifically. In our
opinion, the p–p stacking interaction should play
a more significant effect than steric hindrance in the
stabilization of conformation I because the steric hin-
drance of the N-alkyl groups only impacts the yield
rather than the chemoselectivity (Figure 1).
Entry R1, R2
Product(s)
Yield [%][a]
1
Bn, H
2a
2b
2c
2d
2e
2 f
2g
2h
2i
2j
2k
2l
2m
2n
2o
90
35
67
70
71
80
58
31
81
82
86
51
86
46
71
2
Me, H
3
Cy, H
4
nPr, H
5
nBu, H
6
tBu, H
7
8
9
10
11
12
13
14
15
tBu, 4-Me
tBu, 4-OMe
tBu, 4-F
tBu, 4-Cl
tBu, 4-Br
tBu, 4-CF3
tBu, 4-CO2Me
Cy, 4-CN
tBu, 4-NO2
16
17
tBu, 3-Cl
tBu, 2-Cl
64[b]
If we consider the intramolecular Buchner reaction
mechanism, we proposed that 2-cyano-2-diazo-
amides 1 first generate copper carbene intermediates
I by the release of nitrogen under the catalysis of Cu-
(acac)2. The intermediate I undergoes an intramolecu-
lar cyclopropanation through the addition of the
copper carbene to the benzene ring in the benzyl
group to afford 3-alkyl-2-oxo-benzo[e]-3-azabicyclo-
[3.1.0]hexane-1-carbonitriles 3, which further undergo
a ring expansion to give rise to the final Buchner re-
action products 2 (Scheme 2). The first stage of the
Buchner reaction is an electrophilic addition reaction
of the metal carbene to the aromatic ring. Padwa
and co-workers found that aromatic rings with
a higher electron density were more accessible.[2b]
2q
3r
86
tBu, (R2C6H4 =naphth-1-
yl)
18
90
[a] Isolated yield. All reactions were performed under the optimized conditions.
[b] Two products 2pa and 2pb were obtained in a 1:3 ratio after silica gel column
chromatography.
ner reaction. As a result, N-benzyl-N-tert-butyl-2-cyano-2-diazo-
acetamide (1 f) defeats other N-alkyl-N-benzyl-2-cyano-2-diazo-
acetamides in yield, except for N,N-dibenzyl-2-cyano-2-diazoa-
cetamide (1a), which has two of the same N-benzyl groups.
Therefore, an N-tert-butyl group is used as the N-protecting
group to obtain higher yields for most of other substrates 1g–
m and 1o–r (Table 2, entries 7–13 and 15–18). Diazoamides
1g–o that have various substituents at the para position of
benzyl group were studied. The substrates with both electron-
withdrawing and electron-donating groups work well to afford
only Buchner reaction products 2g–o (Table 2, entries 7–15).
For the ortho-substituted substrate 1q, only one product 2q
was generated (Table 2, entry 17). However, the meta-substitut-
ed substrate 1p produced two regioisomeric products 2pa
and 2pb with a low regioselectivity (1:3; Table 2, entry 16). The
N-naphthalen-2-ylmethyl substrate 1r only generated the cy-
clopropanation product 3r in an excellent yield instead of the
5,7-bicyclic product, which indicates that this substrate does
However, in our case, we did not observe the same trend for
the yield. The electronic effect has an unclear influence on the
yield, and the cyclopropanation product 3r was obtained in
our reactions. The results suggest that the cyclopropanation
step is the rate-determining step in Padwa’s experiments but
not in ours. The ring-expansion step could be the rate-deter-
mining step in our case.
After success in the synthesis of 5,7-bicyclic products by the
Buchner reaction and understanding the reaction mechanism,
we attempted to extend the reaction to prepare 6,7- and 7,7-
bicyclic products (Scheme 3). N-tert-Butyl-2-cyano-2-diazo-N-(2-
phenylethyl/3-phenylpropyl)acetamides (1s and 1t) were pre-
pared and subjected to the reaction. The results indicate that
the 6,7-bicyclic product, 10-aza-10-tert-butyl-1-cyanobicyclo-
[5.4.0]undeca-2,4,6-trien-8-one (2s), was successfully construct-
ed in a moderate yield (50%),[20] but the 7,7-bicyclic ring failed
possibly because of the long distance between the aromatic
ring and the cyano group, which resulted in a weak p–p stack-
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 1679 – 1683 1681

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
also suitable for the synthesis of 10-aza-1-cyanobicyclo-
[5.4.0]undeca-2,4,6-trien-11-one, the 6,7-bicyclic product. The
current method is an economic, chemospecific, and green ver-
sion of the intramolecular Buchner reaction that can be used
to prepare 9-aza-1-cyanobicyclo[5.3.0]deca-2,4,6-trien-10-one-1-
carboxylic acid derivatives chemospecifically through the trans-
formation of the cyano group.
Acknowledgements
This work was supported in part by The National Basic Research
Program of China (No. 2013CB328905) and the National Natural
Science Foundation of China (Nos. 21372025 and 21172017).
Keywords: copper
· fused-ring systems · homogeneous
catalysis · nitrogen heterocycles · ring expansion
Scheme 2. Proposed mechanism for the Cu(acac)2-catalyzed intramolecular
Buchner reaction.
[1] J. J. Li, Name reactions, 4th ed., Springer, Berlin, 2009, pp. 78–79; and
references cited therein.
[2] a) M. P. Doyle, M. S. Shanklin, H. Q. Pho, Tetrahedron Lett. 1988, 29,
2639–2642; b) A. Padwa, D. J. Austin, A. T. Price, M. A. Semones, M. P.
Doyle, M. N. Protopopova, W. R. Winchester, A. Tran, J. Am. Chem. Soc.
1993, 115, 8669–8680; c) C. A. Merlic, A. L. Zechman, M. M. Miller, J. Am.
Chem. Soc. 2001, 123, 11101–11102; d) M. P. Doyle, M. Yan, I. M. Phillips,
D. J. Timmons, Adv. Synth. Catal. 2002, 344, 91–95; e) M. P. Doyle, W. H.
Hu, A. G. H. Wee, Z. Y. Wang, S. C. Duncan, Org. Lett. 2003, 5, 407–410;
f) Z. H. Qu, W. F. Shi, X. L. Jin, J. B. Wang, Chin. J. Org. Chem. 2003, 23,
988–995; g) Z. L. Chen, Z. Y. Chen, Y. Z. Jiang, W. H. Hu, Synlett 2004,
1763–1764; h) Z. L. Chen, Z. Y. Chen, Y. Z. Jiang, W. H. Hu, Tetrahedron
2005, 61, 1579–1586; i) W. J. Liu, Z. L. Chen, Z. Y. Chen, W. H. Hu, Tetra-
hedron: Asymmetry 2005, 16, 1693–1698; j) C. P. Park, A. Nagle, C. H.
Yoon, C. L. Chen, K. W. Jung, J. Org. Chem. 2009, 74, 6231–6236; k) J. X.
Wang, B. Stefane, D. Jaber, J. A. I. Smith, C. Vickery, M. Diop, H. O.
Sintim, Angew. Chem. Int. Ed. 2010, 49, 3964–3968; Angew. Chem. 2010,
122, 4056–4060; l) V. K.-Y. Lo, Z. Guo, M. K.-W. Choi, W.-Y. Yu, J.-S.
Huang, C.-M. Che, J. Am. Chem. Soc. 2012, 134, 7588–7591.
[3] a) F. Zaragoza, G. Zahn, J. Prakt. Chem. 1995, 337, 292–298; b) F. Zara-
goza, Tetrahedron 1995, 51, 8829–8834; c) C. H. Yoon, A. Nagle, C.
Chen, D. Gandhi, K. W. Jung, Org. Lett. 2003, 5, 2259–2262.
[4] a) D. L. Whitehouse, K. H. Nelson, S. N. Savinov, R. S. Lowe, D. J. Austin,
Bioorg. Med. Chem. 1998, 6, 1273–1282; b) C. J. Moody, S. Miah, A. M. Z.
Slawin, D. J. Mansfield, I. C. Richards, J. Chem. Soc. Perkin Trans. 1 1988,
4067–4075.
Scheme 3. Extension of the substrate scope.
ing interaction and more difficulty for the Buchner reaction to
occur for diazoamide 1t.
Finally, we tried to convert the cyano group into other func-
tional groups. The cyano group was converted to a carboxylic
acid methyl ester in 89% yield after treatment with KOH in
methanol (Scheme 4). This strategy provides a chemospecific
protocol to access 1-alkoxycarbonyl-substituted 5,7-bicyclic
products, whereas the direct metal catalysis of 2-alkoxycarbon-
yl-N-benzyl-2-diazoacetamides results in mixed products (Sche-
me 1).[2j,3c,4]
[5] J. Yang, H. Song, X. Xiao, J. Wang, Y. Qin, Org. Lett. 2006, 8, 2187–2190.
[6] a) H. M. L. Davies, R. E. J. Beckwith, Chem. Rev. 2003, 103, 2861–2903;
b) H. M. L. Davies, E. G. Antoulinakis, J. Organomet. Chem. 2001, 617–
618, 47–55; c) M. P. Doyle, M. S. Shanklin, S. M. Oon, H. Q. Pho, F. R. van
de Heide, W. R. Veal, J. Org. Chem. 1988, 53, 3384–3386; d) A. G. H.
Wee, B. Liu, L. Zhang, J. Org. Chem. 1992, 57, 4404–4414; e) C. H. Yoon,
M. J. Zaworotko, B. Moulton, K. W. Jung, Org. Lett. 2001, 3, 3539–3542;
f) P. M. P. Gois, C. A. M. Afonso, Eur. J. Org. Chem. 2003, 3798–3810;
g) P. M. P. Gois, C. A. M. Afonso, Eur. J. Org. Chem. 2004, 3773–3788.
[7] a) S. Miah, A. M. Z. Slawin, C. J. Moody, S. M. Sheehan, J. P. M. Marino, A.
Semones, A. Padwa, I. C. Richards, Tetrahedron 1996, 52, 2489–2514;
b) C. J. Moody, S. Miah, A. M. Z. Slawin, D. J. Mansfield, I. C. Richards, Tet-
rahedron 1998, 54, 9689–9700; c) M. Prein, P. J. Manley, A. Padwa, Tetra-
hedron 1997, 53, 7777–7794; d) M. P. Doyle, J. Tauton, H. Q. Pho, Tetra-
hedron Lett. 1989, 30, 5397–5400.
[8] V. N. G. Lindsay, D. Fiset, P. J. Gritsch, S. Azzi, A. B. Charette, J. Am. Chem.
Soc. 2013, 135, 1463–1470.
[9] R. R. Nani, S. E. Reisman, J. Am. Chem. Soc. 2013, 135, 7304–7311.
[10] M. P. Doyle, J. Org. Chem. 2006, 71, 9253–9260.
[11] I. Rivilla, B. P. Gomez-Emeterio, M. R. Fructos, M. M. Diaz-Requejo, P. J.
Perez, Organometallics 2011, 30, 2855–2860.
[12] B. R. Galan, M. Gembicky, P. M. Dominiak, J. B. Keister, S. T. Diver, J. Am.
Chem. Soc. 2005, 127, 15702–15702.
Scheme 4. Transformation of the cyano group to a methoxycarbonyl group.
Conclusions
We realized the chemospecific intramolecular Buchner reaction
of N-benzyl-2-cyano-2-diazoacetamides catalyzed by inexpen-
sive copper(II) acetylacetonate to afford 9-aza-1-cyanobicyclo-
[5.3.0]deca-2,4,6-trien-10-ones, the 5,7-bicyclic products, in
moderate to excellent yields. The reaction is accessible to
a broad substrate scope, regardless of the benzyl groups with
various electron-withdrawing and -donating groups. Even the
cyanodiazoacetamide that bears an N-2-phenylethyl group is
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 1679 – 1683 1682

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
[13] C. J. Lovely, R. G. Browning, V. Badarinarayana, H. V. R. Dias, Tetrahedron
Lett. 2005, 46, 2453–2455.
[14] a) M. P. Doyle, R. Duffy, M. Ratnikov, L. Zhou, Chem. Rev. 2010, 110, 704–
724; b) X. Zhao, Y. Zhang, J.-B. Wang, Chem. Commun. 2012, 48, 10162–
10173.
[15] a) D. H. Rogers, J. C. Morris, F. S. Roden, B. Frey, G. R. King, F.-W. Rus-
skanmp, R. A. Bell, L. N. Mander, Pure Appl. Chem. 1996, 68, 515–522;
b) S. Levin, R. R. Nani, S. E. Reisman, Org. Lett. 2010, 12, 780–783; c) S.
Levin, R. R. Nani, S. E. Reisman, J. Am. Chem. Soc. 2011, 133, 774–776.
[16] D. Marcoux, S. Azzi, A. B. Charette, J. Am. Chem. Soc. 2009, 131, 6970–
6972.
Ref. [11]. However, in our case, both Cu and Rh catalysts show the
same chemospecificity (the Buchner reaction) and very close yields for
the same kind of metal complexes.
[19] J. X. Xu, R. C. Wang, Arkivoc 2010, (9), 293–299.
[20] In the intramolecular cyclopropanation of a-diazo-b-ketonitriles pub-
lished by Reisman et al., their reactions did not lead to the ring open-
ing of the cyclopropane derivatives. However, after we analyzed the
NMR spectra of 21h in their paper and compared it with our spectra,
we found that their compound 21h corresponds to 2s in this text, and
21d should also be a ring-opening product. See Ref. [9].
[17] a) L. David, C. Craciun, O. Cozar, V. Chis, C. Agut, D. Rusu, M. Rusu, J.
Mol. Struct. 2001, 563–564, 573–578; b) J. P. Muena, M. Villagran, J. Cos-
tamagna, M. Aguirre, J. Coord. Chem. 2008, 61, 479–489.
[18] Cu catalysts can improve the selectivity for cyclopropanation (the first
stage of the Buchner reaction) compared with Rh catalysts, see
Received: January 7, 2014
Published online on April 3, 2014
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 1679 – 1683 1683