Synthesis of oxazole and furan derivatives via Rh2(OAc)4-catalyzed C≡X bond insertion of cyclic 2-diazo-1,3-diketones with nitriles and arylacetylenes

Article abstract of DOI:10.1080/00397911.2018.1473441

A convenient and efficient procedure for the synthesis of 2-substituted-6,7-dihydrobenzo[d]oxazol-4(5H)-ones and 2-aryl-6,7-dihydrobenzofuran-4(5H)-ones through a Rh₂(OAc)₄-catalyzed C≡X (X = N, C) insertion of cyclic 2-diazo-1,3-diketones with nitriles and aromatic alkynes has been developed. This reaction uses readily available starting materials and stable cyclic 2-diazo-1,3-diketone compounds, with desired products formed in good to high yields. A tentative mechanism involving a C≡X bond insertion and 1,5-dipolar electrocyclization/ring opening and cyclization sequence for this reaction is proposed.

Full text of DOI:10.1080/00397911.2018.1473441

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
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ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Synthesis of oxazole and furan derivatives
via Rh2(OAc)4-catalyzed C≡X bond insertion of
cyclic 2-diazo-1,3-diketones with nitriles and
arylacetylenes
Chenli Fan, Xinwei He, Yin Zuo & Yongjia Shang
To cite this article: Chenli Fan, Xinwei He, Yin Zuo & Yongjia Shang (2018): Synthesis of oxazole
and furan derivatives via Rh2(OAc)4-catalyzed C≡X bond insertion of cyclic 2-diazo-1,3-diketones
with nitriles and arylacetylenes, Synthetic Communications, DOI: 10.1080/00397911.2018.1473441
To link to this article: https://doi.org/10.1080/00397911.2018.1473441
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SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2018.1473441
Synthesis of oxazole and furan derivatives via
Rh2(OAc)4-catalyzed CꢀX bond insertion of cyclic
2-diazo-1,3-diketones with nitriles and arylacetylenes
Chenli Fana,b, Xinwei Heb, Yin Zuob, and Yongjia Shangb
b
aDepartment of Material Engineering, Wuhu Institute of Technology, Wuhu, P.R. China; Key Laboratory
of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials
(State Key Laboratory Cultivation Base), College of Chemistry and Materials Science, Anhui Normal
University, Wuhu, P.R. China
ABSTRACT
ARTICLE HISTORY
Received 25 January 2018 24
September 2018
A convenient and efficient procedure for the synthesis of 2-substituted-
6,7-dihydrobenzo[d]oxazol-4(5H)-ones and 2-aryl-6,7-dihydrobenzo-
furan-4(5H)-ones through a Rh2(OAc)4-catalyzed CꢀX (X ¼ N, C) inser-
tion of cyclic 2-diazo-1,3-diketones with nitriles and aromatic alkynes
has been developed. This reaction uses readily available starting mate-
rials and stable cyclic 2-diazo-1,3-diketone compounds, with desired
products formed in good to high yields. A tentative mechanism
involving a CꢀX bond insertion and 1,5-dipolar electrocyclization/ring
opening and cyclization sequence for this reaction is proposed.
KEYWORDS
Cyclic 2-diazo-1,3-diketone;
electrocyclization; furans;
insertion; oxazoles
GRAPHICAL ABSTRACT
Introduction
Oxazoles and furans represent an important class of heterocycles because they occur in
a multitude of natural products and possess a broad spectrum of biological properties
in medicinal chemistry.[1] They are also regarded as privileged heterocyclic motifs
in numerous synthetic intermediates and pharmaceuticals. Consequently, many new
methods, including the intramolecular cyclization of preformed precursors,[2] transi-
tional metal-catalyzed [3 þ 2] cycloaddition of a-carbonyl diazocompounds with nitriles
CONTACT Xinwei He
Education, Anhui Laboratory of Molecule-Based Materials (State Key Laboratory Cultivation Base), College of Chemistry
and Materials Science, Anhui Normal University, Wuhu 241000, P.R. China; Yongjia Shang shyj@mail.ahnu.edu.cn
xinweihe@mail.ahnu.edu.cn
Key Laboratory of Functional Molecular Solids, Ministry of
Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials
(State Key Laboratory Cultivation Base), College of Chemistry and Materials Science, Anhui Normal University, Wuhu
241000, P.R. China.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2018 Taylor & Francis Group, LLC

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C. FAN ET AL.
Scheme 1. Synthesis of oxazoles or furans via Rh2(OAc)4-catalyzed reaction of cyclic 2-diazo-1,3-
diketones with nitriles and arylacetylenes.
or alkynes,[3,4] cyclization of N-sulfonyl propargylamides,[5] one-step bimolecular annu-
lation,[6] and Michael addition,[7] have been widely developed to form oxazoles
and furans.
The rich chemistry of diazo compounds has been extensively explored and has found
useful applications in organic synthesis.[8] Transition metal-catalyzed reactions of diazo
compounds could generate metal-carbene species that could undergo diverse conversions,
such as addition,[9] insertion,[10] rearrangement,[11] 1,3-dipolar cycloaddition,[12] cycliza-
tion reactions,[13] as well as other reactions.[14–16] Cyclic 2-diazo-1,3-diketones are stable
diazo compounds and polar substrates with high dipole moments; they are easily obtained
from arylsulfonyl azides and cyclic 1,3-diketones under mild conditions. Recently, several
new reactions of cyclic 2-diazo-1,3-diketones, including Wolff rearrangement,[17–19]
1,3-dipolar cycloadditions,[20] and other reactions,[21] have been developed.
During our ongoing studies on transition metal-catalyzed the reactions of cyclic 2-
diazo-1,3-diketones,[22] we found that oxazoles and furans could be efficiently prepared
by a Rh-catalyzed CꢀX insertion and intramolecular1,5-dipolar electrocyclization/ring
opening and cyclization of cyclic 2-diazo-1,3-diketones with nitriles and arylacetylenes,
respectively. In this study, we report an efficient synthetic pathway to 2-substituted-6,7-
dihydrobenzo[d]oxazol-4(5H)-ones and 2-aryl-6,7-dihydrobenzofuran-4(5H)-ones via a
Rh2(OAc)4-catalyzed CꢀX insertion/1,5-dipolar electrocyclization under mild conditions
in good to high yields (Scheme 1).
Results and discussion
Initially, 2-diazocyclohexane-1,3-dione 1a and acetonitrile 2a served as the model
substrates to optimize the reaction conditions, and the results were given in Table 1. It
was found that the reaction yield was significantly improved when the Rh-catalysts were
used in acetone as solvent (Table 1, entries 1–7), and Rh2(OAc)4 gave a better yield
(Table 1, entry 3). Several other solvents, including dimethylformamide (DMF), tetra-
hydrofuran (THF), CH2Cl2, methanol, ethanol, toluene, 1,4-dioxane, 1,2-dichloroethane
(DCE), and water, were screened, but inferior yields were obtained (Table 1, entries
8–17). Thus, in this reaction, acetonitrile was used as a solvent and as one of the reac-
tants (Table 2, entry 17). In addition, the effect of temperature and reaction time were
also investigated (Table 1, entries 18–23). In this reaction, the yield could not be
improved by increasing the reaction time to 6 h (Table 1, entry 19). Moreover, decreas-
ing or increasing the reaction temperature and the amount of catalyst were detrimental
to the yield (Table 1, entries 20–22, 23–25). Therefore, the optimum reaction conditions

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3
Table 1. Optimization of the reaction conditions.a
Entry
Catalyst
CuI
Rh(PPh3)3Cl
Rh2(OAc)4
DABCO
Solvent
Temp. (ꢁC)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
CH3OH
DCE
H2O
CH2Cl2
THF
EtOH
Toluene
DMF
1,4-dioxane
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
r.t.
40
80
60
60
60
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
2
6
4
4
4
4
4
4
Trace
52
75
Trace
17
Trace
26
nano-Au/SiO2
FeCl3
Pd(OAc)2
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
Rh2(OAc)4
32
9
Trace
Trace
Trace
37
Trace
16
Trace
43
87
68
87
Trace
68
42
10
11
12
13
14
15
16
17
18
19
20
21
22
23c
24d
25e
69
76
63
MeCN
MeCN
aReaction conditions: 2-diazocyclohexane-1,3-dione 1a (0.5 mmol), acetonitrile 2a (0.5 mmol), solvent
(2 mL), Rh2(OAc)4 (1 mol%).
bIsolated yield.
cThe amount of catalyst was 0.5 mol%.
dThe amount of catalyst was 2 mol%.
eThe amount of catalyst was 5 mol%.
resulting in an 87% yield of 2-methyl-6,7-dihydrobenzo[d]oxazol-4(5H)-one (3a) were
1 mol% of Rh2(OAc)4, 4 h reaction time, and 60 ꢁC reaction temperature.
Next, we explored the scope and limitations of this method (Table 2). Various cyclic
2-diazo-1,3-diketones 1 and nitriles 2 were subjected to the optimized reaction condi-
tions, and a series of oxazoles were obtained in good to excellent yields. With cyclic 2-
diazo-1,3-diketones 1, both alkyl and aryl nitriles participated in the reaction well, with
alkyl nitriles giving relatively higher yields of the products. A variety of functional
groups in the examined substituted aryl nitriles 2d–j were well tolerated to give good
yields of the desired products (4d–j), regardless of their electronic nature or steric hin-
drance. Particularly, when the benzene ring of nitrile 2 had a strongly electron-donating
group (e.g., OCH3) or electron-withdrawing group (e.g., Br), desired products in good
yields were also obtained. When 2-methylbenzonitrile (2e) was used, the desired product
4e was obtained in an 80% yield. Different cyclic 2-diazo-1,3-diketones 1 were then
examined. Compared with 1a, the desired products were obtained in lower yields when
R2 was methyl (1c) or when R1, R2 were both methyl (1b). When other cyclic 2-diazo-
1,3-diketones were used for this reaction, such as 5-diazo-2,2-dimethyl-1,3-dioxane-4,6-
dione (1d) and 2-diazocyclopentane-1,3-dione (1e), no desired product was obtained.

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C. FAN ET AL.
Table 2. Synthesis of oxazole derivatives via Rh2(OAc)4-catalyzed CꢀN insertion of cyclic 2-diazo-1,3-diketone
and nitriles.a
aReaction conditions: cyclic 2-diazo-1,3-diketones 1 (0.5 mmol), nitriles 2 (2 mL), Rh2(OAc)4 (1 mol %), 60 ꢁC, 4 h. Yields
are given for the isolated products after chromatography.
The structure of products 4n and 4q were unambiguously confirmed by X-ray crystallo-
graphic analysis.
Based on the information obtained while screening the reaction conditions, we then
selected phenylacetylene (3a) as the dipolarophile to react with 2-diazocyclohexane-1,3-
dione (1a), yielding the expected major isolated product 6,7-dihydrobenzofuran-4(5H)-
one 5a in 76% yield in the presence of 1 mol% Rh2(OAc)4 in DMF at 60 ꢁC for 4 h
(Table 3, entry 4). Next, we utilized Rh2(OAc)4 as the catalyst to screen the solvent,
temperature, and reaction time. The experimental results showed that the optimal reac-
tion conditions were with 1,4-dioxane as the solvent at 60 ꢁC for 4 h (Table 3, entry 10).
Using the optimized reaction conditions, we then investigated the scope of the
reaction of diazo-1,3-diketones 1 and terminal alkynes 3. As summarized in Table 4,
various diazo-1,3-diketones 1 and arylacetylenes 3 were smoothly transformed into the
corresponding target products 5 in good to high yields. For arylacetylenes 3, the benzene
ring bearing electron-donating groups (e.g., CH3, OCH3) or electron-withdrawing
groups (e.g., Cl, Br, F) at the 2- or 4-position gave satisfactory yields. Compared with

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Table 3. The optimal reaction conditions of Rh2(OAc)4-catalyzed CꢀC insertion of cyclic 2-diazo-1,3-
diketone and phenylacetylene.a
Entry
Solvent
H2O
THF
MeCN
DMF
DCE
acetone
EtOH
MeOH
Temp. (ꢁC)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
60
60
60
60
60
60
60
60
60
60
r.t.
40
60
80
60
60
60
4
4
4
4
4
4
4
4
4
4
6
6
6
6
2
6
6
Trace
15
41
76
36
33
37
35
46
83
32
55
83
62
47
69
76
9
CH2Cl2
10
11
12
13
14
15
16c
17d
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
aReaction conditions: 2-diazocyclohexane-1,3-dione 1a (0.5 mmol), phenylacetylene 3a (0.5 mmol),
solvent (2 mL), Rh2(OAc)4 (1 mol%).
bIsolated yield.
cThe amount of catalyst was 0.5 mol%.
dThe amount of catalyst was 2 mol%.
Table 4. Rh2(OAc)4-catalyzed CꢀC insertion for the formation of 2-aryl-6,7-dihydrobenzofuran-4(5H)-one derivatives.a
aReaction conditions: cyclic 2-diazo-1,3-diketones 1 (0.5 mmol), terminal alkynes 3 (0.5 mmol), 1,4-dioxane (2 mL),
Rh2(OAc)4 (1 mol%), 60 ꢁC, 4 h. Yields are given for the isolated products after chromatography.

6
C. FAN ET AL.
Scheme 2. Proposed reaction mechanism for the formation of oxazoles 4 or furans 5.
arylacetylenes, when an aliphatic terminal alkyne, such as hept-1-yne, was used for this
reaction, no desired product was obtained, illustrating that the conjugation effect of the
aromatic ring can promote the reactivity of the terminal alkyne. The structure of the
products 5b was unambiguously confirmed by X-ray crystallographic analysis.
Based on these experimental results and those from previous studies,[22c,23] a possible
mechanism for the formation of 2-substituted-6,7-dihydrobenzo [d]oxazol-4(5H)-ones or
2-aryl-6,7-dihydrobenzofuran-4(5H)-ones is depicted in Scheme 2. First, cyclic diazo-
1,3-diketones 1 reacted with Rh2(OAc)4 to generate the Rh-carbene A with the release
of N2. In path (a), the nitrogen atom of nitriles 2 underwent insertion into the Rh ¼ C
bond of the Rh-carbene A to produce the intermediate B and generate the metal
catalyst. Finally, the 1,5-dipolar electrocyclization of intermediate C, which was the res-
onance of intermediate B, would deliver the desired product 4. Otherwise, in path (b),
the Rh-carbene A was then trapped by the triple bond of arylacetylene 3 to give inter-
mediate D, which may give the cyclopropenation intermediate E followed by a ring
cleavage and a cyclization. Finally, the intermediate E probably underwent direct ring
opening and cyclization to give corresponding furans 5.
Experimental section
General procedure for the synthesis of 2-substituted-6,7-dihydrobenzo[d]oxazol-
4(5H)-ones 4. To a stirred solution of diazo-1,3-diketones 1 (0.5 mmol) in nitriles 2
(2 mL) was added Rh2(OAc)4 (0.005 mmol). The reaction mixture was heated in an oil
bath at 60 ꢁC for 6 h. After the reaction was complete, the mixture was cooled to room
temperature, diluted with CH2Cl2 (3 ꢂ 10 mL), and washed with water. Organic layers
were combined, dried over Na2SO4, filtered, and evaporated under vacuum. The residue
was further purified by flash column chromatography on silica gel (200–300 mesh) with
ethyl acetate and petroleum ether (1:5–1:6, v/v) as the eluting solvent to give the desired
products 4.
2-Methyl-6,7-dihydrobenzo[d]oxazol-4(5H)-one (4a). Yield: 66 mg (87%); White
1
liquid. H NMR (CDCl3, 300 MHz): d 2.85 (t, J ¼ 6.0 Hz, 2H), 2.48 (t, J ¼ 6.3 Hz, 2H),
2.43 (s, 3H), 2.11–2.18 (m, 2H); 13C NMR (75 MHz, CDCl3): d 191.5, 164.0, 161.5,
134.3, 37.6, 22.3, 22.1, 13.8. IR (KBr): ꢀ 1688, 1614, 1593, 1398, 1209, 1058, 1016, 893,
578, 420 cmꢃ1. HRMS (ESI) calcd for [C8H9O2N þ H]þ 152.0705, found 152.0706.
General procedure for the synthesis of 2-aryl-6,7-dihydrobenzofuran-4(5H)-ones 5.
To a stirred solution of diazo-1,3-diketones 1 (0.5 mmol) and arylacetylenes 3

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7
(0.5 mmol) in 1,4-dioxane (2 mL), Rh2(OAc)4 (0.005 mmol) was added. The reaction
mixture was heated in an oil bath at 60 ꢁC for 4 h. After the reaction was complete, the
mixture was cooled to room temperature, diluted with CH2Cl2 (3 ꢂ 10 mL), and washed
with water. Organic layers were combined, dried over Na2SO4, filtered, and evaporated
under vacuum. The residue was further purified by flash column chromatography on
silica gel (200–300 mesh) with ethyl acetate and petroleum ether (1:6–1:8, v/v) as the
eluting solvent to give the desired products 5.
2-Phenyl-6,7-dihydrobenzofuran-4(5H)-one (5a). Yield: 90 mg (85%); White solid;
mp 112–114 ꢁC. 1H NMR (CDCl3, 300 MHz): d 7.63 (d, J ¼ 7.5 Hz, 2H), 7.39
(t, J ¼ 7.5 Hz, 2H), 7.25-7.31 (m, 1H), 6.88 (s, 1H), 2.95 (t, J ¼ 6.3 Hz, 2H), 2.52 (t,
J ¼ 6.3 Hz, 2H), 2.17-2.25 (m, 2H); 13C NMR (75 MHz, CDCl3) d 194.7, 166.7, 154.3,
129.7, 128.7, 128.0, 123.9, 122.9, 100.8, 37.6, 23.4, 22.5. IR (KBr) ꢀ 3053, 2945, 1668,
1450, 1436, 1411, 1359, 1238, 1220, 1186, 1136, 1001, 921, 844, 765, 729, 692, 412 cmꢃ1
.
HRMS (ESI) calcd for [C14H12O2 þ H]þ 213.0916, found 213.0915.
Conclusions
In conclusion, we explored the Rh2-catalyzed reaction of diazo-1,3-diketones with the
CꢀX (X ¼ N or C) triple bond, which results in the formation of 2-substituted-6,7-
dihydrobenzo[d]oxazol-4(5H)-ones and 2-aryl-6,7-dihydrobenzofuran-4(5H)-ones in
good to excellent yields. This method showed advantages such as readily available
starting materials, mild, ligand-free reaction conditions and wide substrate scope, and
with N2 as the only by-product to give advanced structures with high atom economy.
Funding
The work was partially supported by the National Natural Science Foundation of China (Nos.
21772001, 21372008), the Natural Science Foundation of Education Administration of Anhui
Province (No. KJ2016A267), the Special and Excellent Research Fund of Anhui Normal
University, and the Doctoral Scientific Research Foundation of Anhui Normal University
(No. 2016XJJ110).
References
€
[1] (a) Richard, C.; Frank, S.; Paul, H.; Bjorn, Å. Direct Preparation of 4-Carboethoxy-1,3-
Oxazoles. Tetrahedron Lett. 1991, 32, 17–20. (b) Richard, D. C.; Mark, T.; Anthony, R. G.;
€
Paul, H.; Bjorn, Å. Rhodium-Catalyzed Heterocycloaddition Route to 1,3-Oxazoles as
Building Blocks in Natural Products Synthesis. Tetrahedron. 1993, 49, 5445–5449. (c)
Padwa, A.; Straub, C. S. Synthesis of Furo[3,4-c]Furans Using a Rhodium(II)-Catalyzed
Cyclization/Diels ꢃ Alder Cycloaddition Sequence. J. Org. Chem. 2003, 68, 227–239. (d)
Gulevich, A. V.; Dudnik, A. S.; Chernyak, N.; Gevorgyan, V. Transition Metal-Mediated
Synthesis of Monocyclic Aromatic Heterocycles. Chem. Rev. 2013, 113, 3084–3213.
[2] (a) Senadi, G. C.; Hu, W. P.; Hsiao, J. S.; Vandavasi, J. K.; Chen, C. Y.; Wang, J. J. Facile,
Selective, and Regiocontrolled Synthesis of Oxazolines and Oxazoles Mediated by ZnI2 and
FeCl3. Org. Lett. 2012, 14, 4478–5581. (b) Hashmi, A. S. K.; Schuster, A. M.; Schmuck, M.;
Rominger, F. Gold-Catalyzed Cyclization of Nonterminal Propargylic Amides to
Substituted Alkylideneoxazolines and –Oxazines. Eur. J. Org. Chem. 2011, 2011,
4595–4602. (c) Hashmi, A. S. K.; Jaimes, M. C. B.; Schuster, A. M.; Rominger, F. From

8
C. FAN ET AL.
Propargylic Amides to Functionalized Oxazoles: domino Gold Catalysis/Oxidation by
Dioxygen. J. Org. Chem. 2012, 77, 6394–6408.
[3] (a) Kim, H.-S.; Lee, J.-Y.; Koh, Y. K.; Kwon, I.-C.; Choi, J.-H.; Suk, J. Y.; Lee, Y. R.
Rhodium Catalyzed Reactions of Cyclic 2-Diazo-1,3-Dicarbonyl Compounds with Nitriles.
€
Bull. Korean Chem. Soc. 1997, 18, 1222–1225. (b) Richard, C.; Frank, S.; Paul, H.; Bjorn,
Å. Functionalized Oxazoles from Rhodiumi-Catalyzed Reaction of Dimethyl
Diazomalonate with Nitriles. Tetrahedron Lett. 1986, 27, 5559–5562.
[4] (a) Hossain, M. L.; Ye, F.; Zhang, Y.; Wang, J. Cu(I)-Catalyzed Reaction of Diazo
Compounds with Terminal Alkynes: A Direct Synthesis of Trisubstituted Furans.
Tetrahedron. 2014, 70, 6957–6962. (b) Pang, W.; Zhu, S.; Xin, Y.; Jiang, H.; Zhu, S.
Rh2(OAc)4 Catalyzed Formation of Fluorine-Containing Polysubstituted Furans from
Diazocompounds and Aromatic Alkynes. Tetrahedron. 2010, 66, 1261–1266. (c) Xia, L.;
Lee, Y. R. Regioselective Synthesis of Highly Functionalized Furans through the RuII-
Catalyzed [3 þ 2] Cycloaddition of Diazodicarbonyl Compounds. Eur. J. Org. Chem. 2014,
2014, 3430–3442. (d) Kinder, F. R.; Padwa, A. Preparation of Oxygenated Heterocycles via
the Cyclization Reaction of a-Diazo Substituted Alkynes. Tetrahedron Lett. 1990, 31,
6835–6838. (e) Padwa, A.; Kinder, F. R. Rhodium(II)-Catalyzed Cyclization of 2-Alkynyl
2-Diazo-3-Oxobutanoates as a Method for Synthesizing Substituted Furans. J. Org. Chem.
2010, 24, 28.
[5] (a) Yu, X.; Xin, X.; Wan, B.; Li, X. Base-Catalyzed Cyclization of N-Sulfonyl
Propargylamides to Sulfonylmethyl-Substituted Oxazoles via Sulfonyl Migration. J. Org.
Chem. 2013, 78, 4895–4904. (b) Hu, Y.; Yi, R.; Wu, F.; Wan, B. Synthesis of
Functionalized Oxazoles via Silver-Catalyzed Cyclization of Propargylamides and
Allenylamides. J. Org. Chem. 2013, 78, 7714–7726. (c) Hu, Y. C.; Yi, R. X.; Wang, C. X.;
Xin, X. Y.; Wu, F.; Wan, B. S. From Propargylamides to Oxazole Derivatives: NIS-
Mediated Cyclization and Further Oxidation by Dioxygen. J. Org. Chem. 2014, 79,
3052–3059. (d) Gao, X.-H.; Qian, P.-C.; Zhang, X.-G.; Deng, C.-L. FeBr3-Catalyzed
Tandem Reaction of N-Propargylamides with Disulfides or Diselenides for the Synthesis of
Oxazole Derivatives. Synlett. 2016, 27, 1110–1115.
[6] (a) Kuwano, R.; Kameyama, N.; Ikeda, R. Catalytic Asymmetric Hydrogenation of N-Boc-
Imidazoles and Oxazoles. J. Am. Chem. Soc. 2011, 133, 7312–7315. (b) Xu, Z. J.; Zhang,
C.; Jiao, N. Synthesis of Oxazoles through Copper-Mediated Aerobic Oxidative
Dehydrogenative Annulation and Oxygenation of Aldehydes and Amines. Angew. Chem.
Int. Ed. 2012, 51, 11367–11370. (c) Saito, A.; Taniguchi, A.; Kambara, Y. Hanzawa.; Y,
Metal-Free [2 þ 2þ1] Annulation of Alkynes, Nitriles, and Oxygen Atoms: Iodine(III)-
Mediated Synthesis of Highly Substituted Oxazoles. Org. Lett. 2013, 15, 2672–2675. (d)
Ritson, D. J.; Spiteri, C.; Moses, J. E. A Silver-Mediated One-Step Synthesis of Oxazoles.
J. Org. Chem. 2011, 76, 3519–3522.
[7] (a) Song, L.; Li, X.; Xing, C.; Li, D.; Zhu, S.; Deng, H.; Shao, M. Fluorine-Containing
Furan Derivatives from the Michael Addition of Ethyl 4,4,4-Trifluoro-3-Oxobutanoate
with b-Nitrostyrenes. Synlett. 2010, 5, 830–834. (b) Sousa, J. L. C.; Talhi, O.; Rocha,
D. H. A.; Pinto, D. C. G. A.; Almeida, P.; F. A.; Bachari, K.; Kirsch, G.; Silva, A. M. S.
One-Pot Synthesis of Novel Highly Functionalized Furan-Based Polyphenolics. Synlett.
2015, 26, 2724–2729.
[8] (a) Zhang, Y.; Wang, J.-B. Recent Development of Reactions with a-Diazocarbonyl
Compounds as Nucleophiles. Chem. Commun. 2009, 2009, 5350–5361. (b) Zhang, Z.-H.;
Wang, J.-B. Recent Studies on the Reactions of a-Diazocarbonyl Compounds. Tetrahedron.
2008, 64, 6577–6605. (c) Zhao, X.; Zhang, Y.; Wang, J.-B. Recent Developments in
Copper-Catalyzed Reactions of Diazo Compounds. Chem. Commun. (Camb.) 2012, 48,
10162–10173.
[9] (a) Briones, J. F.; Davies, H. M. L. Gold(I)-Catalyzed Asymmetric Cyclopropenation of
Internal Alkynes. J. Am. Chem. Soc. 2012, 134, 11916–11919. (b) Qin, C.-M.; Boyarskikh,
V.; Hansen, J. H.; Hardcastle, K. I.; Musaev, D. G.; Davies, H. M. L. D2-Symmetric
Dirhodium Catalyst Derived from a 1,2,2-Triarylcyclopropanecarboxylate Ligand: design,

R
SYNTHETIC COMMUNICATIONSV
9
Synthesis and Application. J. Am. Chem. Soc. 2011, 133, 19198–19204. (c) Dudognon, Y.;
Presset, M.; Rodriguez, J.; Coquerel, Y.; Bugaut, X.; Constantieux, T. Addition of Silylated
Nucleophiles to a-Oxoketenes. Chem. Commun. (Camb.) 2016, 52, 3010–3013.
[10] (a) Kischkewitz, M.; Daniliuc, C.-G.; Studer, A. 3. Alkylperoxy-3-Cyano-Oxindoles from
2-Cyano-2-Diazo-N-Phenyl-Acetamides via Cyclizing Carbene Insertion and Subsequent
ꢀ
Radical Oxidation. Org. Lett. 2016, 18, 1206–1209. (b) Hyde, S.; Veliks, J.; Liegault, B.;
Grassi, D.; Taillefer, M.; Gouverneur, V. V. Copper-Catalyzed Insertion into
Heteroatom–Hydrogen Bonds with Trifluorodiazoalkanes. Angew. Chem. Int. Ed. 2016, 55,
3785–3789.
[11] (a) So, S. S.; Mattson, A. E. Urea Activation of a-Nitrodiazoesters: An Organocatalytic
Approach to N–H Insertion Reactions. J. Am. Chem. Soc. 2012, 134, 8798–8801. (b)
Hansen, J. H.; Gergg, T. M.; Ovalles, S. R.; Autschbach, J.; Davies, H. M. L. On the
Mechanism and Selectivity of the Combined C ꢃ H Activation/Cope Rearrangement. J.
Am. Chem. Soc. 2011, 133, 5076–5085. (c) Huang, Z.; Wang, C.; Tokunaga, E.; Sumii, Y.;
Shibata, N. Stereoselective Synthesis of b-Lactam-Triflones under Catalyst-Free Conditions.
Org. Lett. 2015, 17, 5610–5613.
[12] (a) Lian, Y.-J.; Miller, L. C.; Born, S.; Sarpong, R.; Davies, H. M. L. Catalyst-Controlled
Formal [4 þ 3] Cycloaddition Applied to the Total Synthesis of (þ)-Barekoxide and
(ꢃ)-Barekol. J. Am. Chem. Soc. 2010, 132, 12422–12425. (b) Chattopadhyay, B.;
Gevorgyan, V. Rh-Catalyzed Transannulation of N-Tosyl-1,2,3-Triazoles with Terminal
Alkynes. Org. Lett. 2011, 13, 3746–3749. (c) Xing, Y. P.; Sheng, G. R.; Wang, J.; Lu, P.;
Wang, Y. G. Preparation of Triazoloindoles via Tandem Copper Catalysis and Their
Utility as a-Imino Rhodium Carbene Precursors. Org. Lett. 2014, 16, 1244–1247. (d) Ren,
A. N.; Lang, B.; Lin, J. L.; Lu, P.; Wang, Y. G. 4-Diazoisochroman-3-Imines: A Class of
Metal Carbene Precursors for the Synthesis of Isochromene Derivatives. J. Org. Chem.
2017, 82, 10953–10959.
[13] Schwartz, B. D.; Denton, J. R.; Lian, Y.; Davies, H. M. L.; Williams, C. M. Asymmetric
[4 þ 3] Cycloadditions between Vinylcarbenoids and Dienes: application to the Total
Synthesis of the Natural Product (ꢃ)-5-Epi-Vibsanin E. J. Am. Chem. Soc. 2009, 131,
8329–8332.
[14] (a) Mondal, S.; Nechab, M.; Campolo, D.; Vanthuyne, N.; Bertrand, M. P. Copper
Carbenoid, Reactant and Catalyst for One-Pot Diazo Ester Coupling Cascade
Rearrangement of Enediynes: formation of Two Contiguous Tetrasubstituted Stereocenters.
Adv. Synth. Catal. 2012, 354, 1987–2000. (b) Jadhav, A. M.; Pagar, V. V.; Liu, R.-S.
Development
of
a
Povarov
Reaction/Carbene
Generation
Sequence
for
Alkenyldiazocarbonyl Compounds. Angew. Chem. Int. Ed. 2012, 51, 11809–11813. (c) Xu,
X.-F.; Zavalij, P. Y.; Hu, W.-H.; Doyle, M. P. Vinylogous Reactivity of Enol Diazoacetates
with Donor–Acceptor Substituted Hydrazones. synthesis of Substituted Pyrazole
Derivatives. J. Org. Chem. 2013, 78, 1583–1588.
[15] (a) Basso, A.; Banfi, L.; Garbarino, S.; Riva, R. Ketene Three-Component Reaction: A
Metal-Free Multicomponent Approach to Stereodefined Captodative Olefins. Angew.
Chem. Int. Ed. 2013, 52, 2096–2099. (b) Zhou, C.-Y.; Wang, J.-C.; Wei, J.-H.; Xu, Z.-J.;
Guo, Z.; Low, K.-H.; Che, C.-M. Dirhodium Carboxylates Catalyzed Enantioselective
Coupling Reactions of a-Diazophosphonates, Anilines, and Electron-Deficient Aldehydes.
Angew. Chem. Int. Ed. 2012, 51, 11376–11380.
[16] (a) Hu, M.-Y.; Ni, C.-F.; Hu, J.-B. Copper-Mediated Trifluoromethylation of a-Diazo
Esters with TMSCF3: The Important Role of Water as a Promoter. J. Am. Chem. Soc.
2012, 134, 15257–15260. (b) Wu, Y.; Sun, P.; Zhang, K.; Yang, T.; Yao, H.; Lin, A.
Rh(III)-Catalyzed Redox-Neutral Annulation of pPrimary Benzamides with Diazo
Compounds: Approach to Isoquinolinones. J. Org. Chem. 2016, 81, 2166–2173. (c) Mishra,
N. K.; Choi, M.; Jo, H.; Oh, Y.; Sharma, S.; Han, S. H.; Jeong, T.; Han, S.; Lee, S.-Y.; Kim,
I. S. Direct C–H Alkylation and Indole Formation of Anilines with Diazo Compounds
under Rhodium Catalysis. Chem. Commun. 2015, 51, 17229–17232. (d) Hu, F.; Xia, Y.; Ye,
F.; Liu, Z.; Ma, C.; Zhang, Y.; Wang, J. Rhodium(III)-Catalyzed Ortho Alkenylation of

10
C. FAN ET AL.
N-Phenoxyacetamides with N-Tosylhydrazones or Diazoesters through C-H Activation.
Angew. Chem. Int. Ed. Engl. 2014, 53, 1364–1367.
[17] (a) Presset, M.; Coquerel, Y.; Rodriguez, J. Microwave-Assisted Wolff Rearrangement
of Cyclic 2-Diazo-1,3-Diketones: An Eco-Compatible Route to a-Carbonylated
Cycloalkanones. J. Org. Chem. 2009, 74, 415–441. (b) Presset, M.; Coquerel, Y.; Rodriguez,
J. Microwave-Assisted Domino and Multicomponent Reactions with Cyclic Acylketenes:
expeditious Syntheses of Oxazinones and Oxazindiones. Org. Lett. 2009, 11, 5706–5709.
(c) Galvez, J.; Castillo, J.-C.; Quiroga, J.; Rajzmann, M.; Rodriguez, J.; Coquerel, Y.
Divergent Chemo-, Regio-, and Diastereoselective Normal Electron-Demand Povarov-Type
Reactions with a-Oxo-Ketene Dienophiles. Org. Lett. 2014, 16, 4126–4129.
[18] (a) Castillo, J.-C.; Presset, M.; Abonia, R.; Coquerel, Y. Rodriguez, J., Microwave-Aassisted
Domino Benzannulation of a-Oxo Ketenes: Preparation of 1,3-Dihydro-2H-1,5-
Benzodiazepin-2-Ones. Eur. J. Org. Chem. 2012, 2012, 2338–2345. (b) Mohanan, K.;
Presset, M.; Mailhol, D.; Coquerel, Y.; Rodriguez, J. Catalyst- and Halogen-free
Regioselective Friedel–Crafts a-Ketoacylations. Chem.-Eur. J. 2012, 18, 9217–9220. (c)
Boddaert, T.; Coquerel, Y.; Rodriguez, J. Combination of Rearrangement with Metallic and
Organic Catalyses – a Step- and Atom-Economical Approach to a-Spiroactones and
-Lactams. Eur. J. Org. Chem. 2011, 2011, 5061–5070. (d) Boddaert, T.; Coquerel, Y.;
Rodriguez, J. Expeditious Divergent Synthetic Approach to Polycyclic Terpene-like
Molecules. Chemistry. 2011, 17, 2048–2051.
[19] (a) Presset, M.; Coquerel, Y.; Rodriguez, J. Periselectivity Switch of Acylketenes in
Cycloadditions with 1-Azadienes: Microwave-Assisted Diastereoselective Domino Three-
Component Synthesis of a-Spiro-d-Lactams. Org. Lett. 2010, 12, 4212–4215. (b) Presset,
M.; Mohanan, K.; Hamann, M.; Coquerel, Y.; Rodriguez, J. 1,3-Dipolar Cycloaddition of
Hydrazones with a-Oxo-Ketenes:
A
Three-Component Stereoselective Entry to
Pyrazolidinones and an Original Class of Spirooxindoles. Org. Lett. 2011, 13, 4124–4127.
(c) Castillo, J.-C.; Quiroga, J.; Rodriguez, J.; Coquerel, Y. Time-Efficient Synthesis of
Pyrido[2,3-d]Pyrimidinones via a-Oxoketenes. Eur. J. Org. Chem. 2016, 2016, 1994–1999.
[20] (a) Kim, H.-S.; Lee, J.-Y.; Koh, Y. K.; Kwon, I.-C.; Choi, J.-H.; Suk, J. Y.; Lee, Y. R.
Rhodium Catalyzed Reactions of Cyclic 2-Diazo-1,3-Dicarbonyl Compounds with Nitriles.
Bull. Korean Chem. Soc. 1997, 18, 1222–1225. (b) Xia, L.; Lee, Y. R. Regioselective
Synthesis of Highly Functionalized Furans through the RuII-Catalyzed [3 þ 2]
Cycloaddition of Diazodicarbonyl Compounds. Eur. J. Org. Chem. 2014, 2014, 3430–3442.
(c) Magar, K. B. S.; Lee, Y. R.; Kim, S. H. Efficient One-Pot Synthesis of Biologically
Interesting Diverse Furo[2,3-b]Pyran-6-Ones by Rhodium(II)-Catalyzed Cascade Reactions
of Diazo Compound with Ethynyl Compounds. Tetrahedron. 2013, 69, 9294–9302.
[21] (a) Shi, J.; Zhou, J.; Yan, Y.; Jia, J.; Liu, X.; Song, H.; Xu, H. E.; Yi, W. One-Pot Cascade
Synthesis of N-Methoxyisoquinolinediones via Rh(III)-Catalyzed Carbenoid Insertion C–H
Activation/Cyclization. Chem. Commun. 2015, 51, 668–671. (b) Dudognon, Y.; Presset, M.;
Rodriguez, J.; Coquerel, Y.; Bugaut, X.; Constantieux, T. Addition of Silylated Nucleophiles
to a-Oxoketenes. Chem. Commun. 2016, 52, 3010–3013. (c) Sharma, S.; Han, S. H.; Han,
S.; Ji, W.; Oh, J.; Lee, S.-Y.; Oh, J. S.; Jung, Y. H.; Kim, I. S. Rh(III)-Catalyzed Direct
Coupling of Azobenzenes with a-Diazo Esters: facile Synthesis of Cinnolin-3(2H)-Ones.
Org. Lett. 2015, 17, 2852–2855.
[22] (a) Yang, C.; He, X.; Zhang, L.; Han, G.; Zuo, Y.; Shang, Y. Synthesis of Isocoumarins from
Cyclic 2-Diazo-1,3-Diketones and Benzoic Acids via Rh(III)-Catalyzed C–H Activation and
Esterification. J. Org. Chem. 2017, 82, 2081–2088. (b) He, X.; Zhou, Y.; Shang, Y.; Yang,
C. Zuo, Y. Synthesis of 2-Arylimino-6,7-Dihydrobenzo[d][1,3]Oxathiol-4(5H)-Ones via
Rh2(OAc)4-Catalyzed Reactions of Cyclic 2-Diazo-1,3-Diketones with Aryl Isothiocyanates.
ACS Omega. 2016, 1, 1277–1283. (c) He, X.; Yu, Z.; Zuo, Y.; Yang, C.; Shang, Y. Direct
Carboxamidation of Cyclic 2-Diazo-1,3-Diketones by Rh2(OAc)4-Catalyzed Isocyanide
Insertion-Hydrolysis. Org. Biomol. Chem. 2017, 15, 7127–7130. (d) He, X.; Zhou, Y.;
Shang, Y.; Yang, C.; Zuo, Y. Y. Rh(III)-Catalyzed C-H Activation/Intramolecular

R
SYNTHETIC COMMUNICATIONSV
11
Cyclization: access to N-Acyl-2,3-Dihydro-1H-Carbazol-4(9H)-Ones from Cyclic 2-Diazo-1,
3-Diketones and N-Arylamides. ACS Omega. 2016, 1, 1277–8516.
[23] (a) Chupraov, S.; Kwok, S. W.; Fokin, V. V. Transannulation of 1-Sulfonyl-1,2,3-Triazoles
with Heterocumulenes. J. Am. Chem. Soc. 2013, 135, 4652–4655. (b) Nikolaev, V. A.;
ꢀ
Ivanov, A. V.; Rodina, L. L.; Mloston, G. Less Reactive Dipoles of Diazodicarbonyl
Compounds in Reaction with Cycloaliphatic Thioketones – First Evidence for the 1,3-
Oxathiole–Thiocarbonyl Ylide Interconversion. Beilst. J. Org. Chem. 2013, 9, 2751–2761.
ꢀ
(c) Mloston, G.; Heimgartner, H. Synthesis of Five-Membered Sulfur-Heterocycles via 1,5-
Dipolar Electrocyclization of Thiocarbonyl Ylides and Related Processes. Current Org.
Chem. 2011, 15, 675. (d) Shao, Z.-H.; Zhang, H.-B. N-Tosylhydrazones: Versatile Reagents
for Metal-Catalyzed and Metal-Free Cross-Coupling Reactions. Chem. Soc. Rev. 2012, 41,
560–572.