Dioxazoles, a new mild nitrene transfer reagent in gold catalysis: Highly efficient synthesis of functionalized oxazoles

Article abstract of DOI:10.1039/c6cc02776h

A gold-catalyzed regioselective [3+2] cycloaddition of ynamides with 1,4,2-dioxazoles was developed and offers a novel approach to obtain highly functionalized oxazoles under mild reaction conditions. 1,4,2-Dioxazole was found to act as an efficient N-acyl nitrene equivalent to trigger a facile generation of α-imino gold-carbene intermediate through the elimination of a ketone.

Full text of DOI:10.1039/c6cc02776h

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DOI: 10.1039/C6CC02776H
Graphic abstract:
R3
cat. LAu+
EWG
R2
O
N
O
O
R1
N
+
rt, or 50-80 oC, in DCE
[3+2] cycloaddition
N
R1
N
R2
R3
EWG
36 examples with up to 99% yield
new reagents for the generation of α-imino gold-carbene high efficiency
√
√
√
regioselective and wide functional group tolerance
gram scale
√
Abstract: Gold-catalyzed regioselective [3+2] cycloaddition of ynamides with
1,4,2-dioxazoles offers an efficient approach to functionalized oxazoles under mild
reaction conditions.
1

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DOI: 10.1039/C6CC02776H
Journal Name
COMMUNICATION
Dioxazoles, A New Mild Nitrene Transfer Reagent in Gold Catalysis:
Highly Efficient Synthesis of Functionalized Oxazoles
Received 00th January 20xx,
Accepted 00th January 20xx
†
†
Ming Chen, Ning Sun, Haoyi Chen and Yuanhong Liu *
DOI: 10.1039/x0xx00000x
www.rsc.org/
catalyzed synthesis of N-acyl sulfoximines and sulfimides at
room temperature via ruthenium N-acyl nitrene
intermediate using dioxazolone
as the nitrene precursors.[12]
More recently, Chang and others[13] revealed that the
substrates could also be used as amidating reagents in
metal-catalyzed C-H amidation reactions, in which metal-
nitrene complex is proposed to be involved (Scheme 1). During
our continuous work on gold-catalyzed oxidative reactions, we
hypothesized that these five-membered heterocycles might be
employed as a nucleophilic nitrene equivalent to trigger an
A gold-catalyzed regioselective [3+2] cycloaddition of ynamides
with 1,4,2-dioxazoles has been developed, which offers a novel
approach to highly functionalized oxazoles under mild reaction
conditions. 1,4,2-Dioxazole was found to act as an efficient N-acyl
nitrene equivalent to trigger a facile generation of -imino gold-
carbene intermediate through the elimination of a ketone.
a
a
a-c
In recent years, gold-carbene mediated reactions have
attracted considerable attention since they serve as promising
intermediates in the synthesis of various types of carbo- or
efficient generation of -imine gold-carbene species through
heterocycles.[1] Compared with

-carbonyl gold carbenes,[2]
nucleophilic attack of the gold-activated alkyne followed by
expulsion of a leaving group. In this design, no metal-nitrene
complex is formed, which is different from other metal-
catalyzed reactions shown in above. Herein, we describe a
novel reactivity of dioxazole derivatives, which acts as a new
type of nitrene transfer reagent and undergoes gold-catalyzed
[3+2] cycloaddition with ynamides leading to a facile synthesis
of highly functionalized oxazoles.[6b-d]
generations and reactions of -imino gold carbenes have less
been explored.[3] These highly reactive gold-species are mainly
accessed through gold-catalyzed nitrene transfer to alkynes
using azides as the nitrene equivalent reported by Toste,[4a]
Gagosz,[4b] Zhang[4c-e] and others.[4] Recently, 2H-azirines,[5] N-
iminopyridium ylides,[6] isoxazoles,[7] benzoisoxazoles[8] and
triazapentalene[9] have also been used as nitrene equivalents.
Despite the impressive progress, the development of new
To test our hypothesis, we initially investigated the reactions
of mesylamide-derived ynamide 1a with three different types
of dioxazole derivatives 2a-2c in the presence of 5 mol%
methods for the generation of
-imino gold carbenes that
utilization of less reactive/sensitive nitrene transfer reagents
with high chemo- and regioselectivities under milder reaction
conditions is still highly desired. 1,4,2-Dioxazol-5-one
carbonate of hydroxamic acids, and its derivative of 1,4,2-
dioxazol-5-thione , were found in 1968 to undergo thermal or
a, a cyclic
Previous work: 1,4,2-dioxazolone derivatives used as N-acyl nitrene precursors
O
O
S
O
b
O
O
O
O
O
O
R
N
photo-induced decomposition leading to highly reactive N-acyl
N
N
N
nitrene intermediates via elimination of CO2 or SO2.[10] 1,4,2-
R
R
R
N-acyl nitrene
a
c
b
Dioxazole
c decomposed similarly at elevated temperatures
(above 150 oC) into isocyanates and ketones.[11] These
attractive and easily accessible heterocyclic compounds are
potentially useful as the N-acyl nitrene precursors in place of
hazardous acyl azides, which may produce the N-acyl nitrene
or N-acyl nitrenoid intermediates under mild reaction
conditions such as in the presence of a metal catalyst. Recently,
Bolm et al. described an elegant light-induced ruthenium-
Chang and
Jiao et al:
cat. Ru, h
cat. Rh, or Co
DG
Bolm et al:
O
O
S
DG
O
R1
R2
N
R
O
[M]
N
R
NH
S
R1
R2
metal-catalyzed amidation
metal-nitrene
O
R
This work: gold-catalyzed nitrene transfer to the alkynes
Y
Y
Y
O
O
O
O
O
O
O
N
R
N
R
N
R
N
cat. Au
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032. E-
mail: yhliu@sioc.ac.cn
R
+
Y
O
LAu+
LAu+
-imino gold carbene
LAu
[+] These authors contributed equally to this work.
Y = C=O, S=O, C(Me)2
Electronic Supplementary Information (ESI) available: CCDC 1455247, 1450076 and
1455246. For ESI and crystallographic data in CIF or other electronic format. See
DOI: 10.1039/x0xx00000x
Scheme 1. Metal-catalyzed reactions involing nitrene equivalents of 1,4-2-
dioxazolone derivatives and the design of gold-catalyzed nitrene transfer reactions
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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Journal Name
Johnphos(MeCN)AuSbF6 (catalyst
temperature. However, in the case of dioxazolone 2a, a non- reactions proceeded very well DwOiI:th10.103to9/sCy6l,CC0p27a7r6aH-
clean reaction mixture was resulted with significant remaining bromobenzenesulfonyl (Bs) and stronger electron-
of 2a, possibly the rapid self-reaction of ynamide occurred withdrawing para-nitrobenzenesulfonyl (p-Ns) moiety,
under gold-catalyzed conditions.[14] No desired cyclization furnishing 3c
3e in 72-86% yields. More electron-rich ynamide
A) in DCE at room withdrawing groups on nitrogen were first exVaimewiAnreticdle. OTnlhinee
a
-
product was observed also in the case of dioxathiazole 2b with an oxazolidine group also afforded the corresponding
(Table 1, entries 1-2). Considering the lower nucleophilicity of oxazole 3f in 89% yield. N-aryl mesylamide, whenever bearing
2a and 2b, we reasoned that employing more nucleophilic an electron-neutral, electron-deficient CF3, or electron-rich
dioxazole might be feasible for the successful transformation. MeO substituent on its aromatic ring, tolerated well in this
Gratifyingly, employing dioxazole 2c led to the desired 4- reaction, leading to 3b and 3g-3h in 96-99% yields. N-benzyl
amino-oxazole 3a in 92% yield within 2 h (entry 3). The results mesylamide was also suitable to provide 3i in 85% yield. Next,
implied that an efficient [3+2] cycloaddition of ynamide with the effect of R1 group on the alkyne terminus was examined.
dioxazole took place, and the self-reaction of yanmide was For aryl substituted alkynes, a wide range of functionalities
mostly suppressed. A similar reaction outcome was found such as F, Cl, CF3, Me and MeO on aromatic rings were
when
(IPrAu(MeCN)SbF6) or
(IPr 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) partial of the product precipitated during the reaction process
N-heterocyclic
carbene
gold(I)
complex
B
compatible, furnishing 3j-3n in good to high yields. It was
C
(IPrAuNTf2)[15] was used as the catalyst noted that when p-MeO-substituted aryl alkyne was used,
=
(entries 4-5). Various commonly used gold catalysts also at room temperature, which appeared to interfere with the
o
catalyze the desired cyclization efficiently, furnishing 3a in reaction process. Then a higher reaction temperature (50 C)
lower yields of 72-87% (entries 6-8). The reaction could also be was required to achieve a better conversion. Ynamide with an
performed smoothly in the solvents of DCM, THF, toluene or 1,3,5(10)-estratrien-3-ol-17-one derivative also reacted
CH3CN (entries 9-12). No reaction was observed catalyzed by efficiently to produce the oxazole 3o in 97% yield. 1-Naphthyl
IPrAuCl or AgNTf2 alone or in the absence of any catalyst and 2-thienyl-substituted alkynes converted into the
(entries 13-15).
corresponding 3p and 3q in excellent yields. Cyclohexenyl-
Encouraged by these results, we next investigated the substituted alkyne transformed to the corresponding 3r in
substrate scope of the reaction. The scope of ynamides was
first investigated using dioxazole 2c as the reaction partner
under the reaction conditions given in Table 1, entry 5. The
Table 2. Scope of ynamides.[a]
results are shown in Table 2. The effects of the electron-
Ph
EWG
5 mol% IPrAuNTf2
DCE, rt
O
O
N
O
N
R1
N
+
R2
Table 1. Optimization of reaction conditions.
R1
N
Ph
EWG
Ph
R2
Ph
1
2c (1.2 equiv)
3
Y
Ms
N
Me
catalyst (5 mol%)
solvent, rt
O
N
O
O
N
Ph
Ph
+
Ph
3b, EWG = Ms, 5 h, 96%
3c, EWG = Ts, 3 h, 72%
3d, EWG = Bs, 5 h, 86%
3e, EWG = p-Ns, 5 h, 77%
Ph
3a
N
O
N
O
N
O
N
Ph
Ms
N
Me
O
2 (1.2 equiv)
1a
Ph
N
Ph
N
Ph
p-CF3C6H4
3g, 5 h, 96%
N
Ms
EWG
O
Ph
+SbF6
O
+SbF6
Ar
tBu
tBu
O
3f, 4 h, 89%
N
N
N
Ar
P
Au NCMe
S
Ar
Ar
O
O
O
O
O
O
Ph
Ph
Ph
Au
Au
N
N
N
Ph
Ph
Ph
NTf2
O
N
O
N
NCMe
O
N
3j, X = F, 4 h, 89%
3k, X = Cl, 3 h, 85%
3l, X = CF3, 9 h, 83%
3m, X = Me, 3 h, 88%
B
C
2a
2b
2c
A
Ar = 2,6-(iPr)2C6H3
Ph
N
Ms
Bn
Ph
N
Ms
N
Me
Ms
p-MeOC6H4
entry
substrate
catalyst
solvent
time (h)
yield (%)[a]
3h, 5 h, 99%
3i, 3 h, 85%
X
-
-
1
2
3
4
2a
2b
2c
2c
A
A
DCE
DCE
DCE
DCE
3 h
3 h
2 h
2 h
Ph
Ph
Ph
A
B
C
92
O
O
N
O
N
N
90
H
H
N
Me
95
2c
2c
2c
2c
2c
5
DCE
DCE
DCE
DCE
DCM
THF
2 h
2 h
3 h
3 h
3 h
3 h
3 h
3 h
3 h
3 h
12 h
N
Ms
N
Ms
Ms
Me
Me
85
6
PPh3AuNTf2
H
PPh3AuSbF6
7
87
MeO
3o, 2 h, 97%[c]
O
3n, 4 h, 71%[b]
8
PPh3AuOTf
72
3p, 3 h, 88%
91
9
C
C
Ph
Ph
Ph
Ph
86
10
11
12
13
14
15
2c
2c
2c
2c
2c
2c
toluene
MeCN
DCE
88
C
O
S
N
O
N
O
N
O
N
92
C
N
N
R
N
Ms
N
Ph
-(99)
-(98)
-(99)
Ms
Ms
IPrAuCl
AgNTf2
none
Ms
Me
Me
Me
DCE
3s, R = Ph, 6 h, 70%
3t, R = Bu, 5 h, 30%
3q, 5 h, 94%
3r, 4 h, 50%[b]
DCE
3u, 2 h, 89%
[a] Isolated yields. Ms = methanesulfonyl. The yileds of recovered 1a are shown in
parentheses.
[a] Isolated yields. Ts = toluene-4-sulfonyl, Bs = para-bromobenzenesulfonyl. p-Ns =
para-nitrobenzenesulfonyl. [b] 50 oC. [c] 80 oC.
2 | J. Name., 2012, 00, 1-3
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COMMUNICATION
moderate yield. Alkyl-substituted alkynes such as benzyl- or Alkyl-substituted dioxazoles such as methyl, cyclohexyl or even
View Article Online
cyclopropyl-substituted one underwent the reaction smoothly bulky adamantyl turned out to be alsoDpOeI:r1fe0.c1t03s9u/Cb6stCrCa0te27s76tHo
to give 3s and 3u in 70% and 89% yields, respectively. However, afford 3zf-3zh in 71-96% yields. It was noted that in the case of
a pentyl-substituted ynamide afforded 3t only in 30% yield. No 3zf, dioxazole 2n was used instead of 3,5,5-trimethyl-1,4,2-
alkene product derived from 1,2-C-H insertion of gold-carbene dioxazole since it is not convenient to prepare the latter with a
intermediate was observed in these cases. The results lower boiling point. Oxazoles constitute important classes of
indicated that intramolecular nucleophilic attack of N-acyl natural products, drugs, and biologically active substances.
group to gold-carbene is much faster than 1,2-C-H insertion These compounds are commonly prepared by cyclization of an
due to the ease of aromatization.
acyclic precursors or ring derivatization. However, construction
The scope of dioxazoles was also investigated using ynamide of oxazoles through convergent and one-pot methods from
1a as the reaction partner. Due to the lower solubility of the readily available substrates is still limited.[16] Our method
products in DCE, all the reactions were carried out at 80 oC. provided a mild and efficient route to these compounds.
Under this reaction condition, we were pleased to see that the
To demonstrate the practicality of our method, a gram scale
reactions were quite general with substituted dioxazoles, since reaction was performed. It was found that using only 2 mol%
aryl, heteroaryl, alkenyl as well as alkyl substituted one were of IPrAuNTf2, the reaction of 1a with dioxazole 2c at 5 mmol
all suitable for this reaction, leading to the highly scale delivered oxazole 3a in high yield of 89% (Scheme 2).
functionalized oxazoles in good to excellent yields. The reaction
efficiency was affected by the nature of aryl substituents: p-
FC6H4 (3v, 90%), p-ClC6H4 (3w, 93%), p-CF3C6H4 (3x, 77%), p-
MeOC6H4 (3y, 92%). Sterically encumbered o-Me-substituted
aryl dioxazole reacted efficiently to afford 3z in 90% yield,
suggesting the steric hindrance had little effect on the reaction
course. Heteroaryl-substituted dioxazoles, such as pyridyl,
Ph
Ms
Me
2 mol% IPrAuNTf2
O
N
O
O
+
Ph
N
N
DCE, rt, 6 h
Ph
N
Ph
Ms
5 mmol scale
2c
Me
3a, 89%, 1.47 g
1a, 1.05 g
1.2 equiv
furanyl and thienyl-substituted one transformed to 3za
-
3zc
Scheme 2. Gram scale synthesis of 3a.
successfully in 75-95% yields. High product yields were also
observed in 2-naphthyl or alkenyl-substituted dioxazoles.
The reaction can be extended to other activated alkynes. As
shown in Scheme 3, gold-catalyzed reactions of alkynyl ester
or alkynyl ketone with 2c afforded functionalized oxazole
or
4
6
5
Table 3. Scope of dioxazoles.[a]
7
in 51% and 50% yields, respectively. However, when
terminal alkyne such as phenylacetylene was used, no clean
reaction was observed.
R3
Ms
N
Me
5 mol% IPrAuNTf2
O
N
O
Ph
R
+
O
DCE, 80 o
C
R3
N
Ph
N
Ms
Ph
Me
1a
2 (1.2 equiv)
3
1.2 equiv 2c
5 mol% IPrAuNTf2
O
N
O
R
Cl
Ph
DCE, 80 oC, 24 h
O
Ph
N
R
Me
4 or 5
3v, R = F, 4 h, 90%
3w, R = Cl, 5 h, 93%
3x, R = CF3, 5 h, 77%
3y, R = MeO, 4 h, 92%
R = OEt, 6, 51%
R = Ph, 7, 50%
O
N
O
N
O
N
Scheme 3. Reactions of dioxazole with activated alkynes.
Ph
N
Ms
Ph
N
Me
Ph
N
Ms
Me
Ms
Me
We propose the following reaction mechanism for this novel
3z, 3 h, 90%
3za, 5 h, 75%
transformation (Scheme 4). Initially, dioxazole
2 attacks on the
gold-coordinated ynamide or 8’ regioselectively at the
carbon adjacent to the nitrogen due to the polarity of the
8
Ph
O
O
S
ynamide to afford iminium ion intermediate 10. Subsequently,
N
O
N
O
N
ring fragmentation of 10 generates
-imino gold-carbene 11
O
N
with concomitant elimination of acetone. In fact, acetone was
formed quantatively and could be detected in the crude
reaction mixture.[17] Intermediate 11 may prefer an E-form of
C=N bond due to the steric repulsion between R3 substituent
on dioxazole with amino moiety,[6a] resulting a cis orientation
of N-acyl group with gold-carbene. Nucleophilic attack of the
acyl oxygen in 11 to gold-carbene[18] followed by elimination of
Ph
N
Me
Ph
N
Me
Ph
N
Me
Ms
Ms
Ms
Ph
N
Me
Ms
3zb, 3 h, 95%
3zc, 2 h, 95%
3zd, 2 h, 97%
3ze, 2 h, 97%
Me
O
N
O
N
O
N
O
O
N
the gold catalyst leads to the oxazole products 3. The reaction
Ph
N
Me
Ph
N
Me
Ph
N
Ms
Me
Ms
Ms
Me
pathway involving the formation of N-acylaziridine via gold-
nitrene followed by cyclization is unlikely, since the oxazole
with different regioselectivity would possibly be resulted.[6b,19]
3zf, rt, 10 h, 71%
2n
3zh, 3 h, 96%
3zg, 3 h, 94%
[a] Isolated yields.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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2
3
4
For reviews, see: a) J. Xiao and X. Li, Angew. Chem., Int. Ed.,
2011, 50, 7226; b) L. Zhang, Acc. Chem. Res., 201Vi4ew, 4A7rti,c8le7O7n;line
R1
Ms
DOI: 10.1039/C6CC02776H
O
O
N+
For a review, see: P. W. Davies and M. Garzón, Asian J. Org.
Chem., 2015, 4, 694.
O
O
O
R2
R3
R3
N
O
8'
LAu
N
+
N
R3
R1
LAu+
2
Ms
a) D. J. Gorin, N. R. Davis and F. D. Toste, J. Am. Chem. Soc.,
2005, 127, 11260; b) A. Wetzel and F. Gagosz, Angew., Chem.
Int. Ed., 2011, 50, 7354; c) B. Lu, Y. Luo, L. Liu, L. Ye, Y. Wang
and L. Zhang, Angew. Chem., Int. Ed., 2011, 50, 8358; d) Y.
Xiao and L. Zhang, Org. Lett., 2012, 14, 4662; e) Z.-Y. Yan, Y.
Xiao and L. Zhang, Angew. Chem., Int. Ed., 2012, 51, 8624; f)
Y. Tokimizu, S. Oishi, N. Fujii and H. Ohno, Org. Lett., 2014,
16, 3138; g) Y. Wu, L. Zhu, Y. Yu, X. Luo, and X. Huang, J. Org.
Chem., 2015, 80, 11407.
1
R1
N
Ms
R1
N
N Ms
R2
R2
LAu+
R2
AuL
10
LAu+
9
8
R3
R3
R3
+
O
O
R1
N
N
O
N
R1
N Ms
R2
LAu+
R1
N
Ms
O
N Ms
R2
AuL
LAu+
R2
5
6
a) A. Prechter, G. Henrion, P. Faudot dit Bel and F. Gagosz,
Angew. Chem., Int. Ed., 2014, 53, 4959; b) L. Zhu, Y. Yu, Z.
Mao and X. Huang, Org. Lett., 2015, 17, 30.
11
12
3
a) C. Li and L. Zhang, Org. Lett., 2011, 13, 1738; b) P. W.
Davies, A. Cremonesi and L. Dumitrescu, Angew. Chem., Int.
Ed., 2011, 50, 8931; c) E. Chatzopoulou and P. W. Davies,
Chem. Commun., 2013, 49, 8617; d) A. D. Gillie, R. J. Redd
and P. W. Davies, Adv. Synth. Catal., 2016, 358, 226. In the
reactions of Ref. 6b-d, oxazoles were formed via gold-
catalyzed [3+2] cycloaddition of pyridine-N-aminides with
ynamides or alkynyl indoles. e) H.-H. Hung, Y.-C. Liao and R.-S.
Liu, J. Org. Chem., 2013, 78, 7970.
A. Zhou, Q. He, C. Shu, Y. Yu, S. Liu, T. Zhao, W. Zhang, X. Lu
and L. Ye, Chem. Sci., 2015, 6, 1265.
H. Jin, L. Huang, J. Xie, M. Rudolph, F. Rominger and A. S. K.
Hashmi, Angew. Chem., Int. Ed., 2016, 55, 794.
J. González, J. Santamaría, Á. L. Suárez-Sobrino, and A.
Ballesterosa, Adv. Synth. Catal. 2016, DOI: 10.1002/adsc.
201600022.
Scheme 4. Possible reaction mechanism
To understand the reaction mechanism, we also tried to
trap the α-imino gold-carbene intermediate via an
intramolecular cyclization of dioxazole-ynamide 13, since the
C-O bond formation can be avoided in such case. To our
delight, 13 cyclized efficiently to give the fused indole
derivative 15[15] in 70% yield (Scheme 5). The results indicated
that the α-imino gold-carbene 14 was likely generated in the
process, which could be trapped by N-aryl ring followed by
deauration to furnish the cyclized product.
7
8
9
O
H
Ts
N
O
10 J. Sauer and K. K. Mayer, Tetrahedron Lett., 1968, 9, 319.
11 H. Nouira, K. Inoue, H. Hattori, T. Okawa and T. Mukaiyama,
Bull. Chem. Soc. Jpn., 1967, 40, 664.
12 V. Bizet, L. Buglioni and C. Bolm, Angew. Chem., Int. Ed.,
2014, 53, 5639.
O
N
5 mol% IPrAuNTf2
THF, rt, 5 h
N
S
S
Ts
N
13
15, 70%
Ph
cyclization
and deauration
13 a) Y. Park, K. T. Park, J. G. Kim and S. Chang, J. Am. Chem.
Soc., 2015, 137, 4534; b) J. Park and S. Chang, Angew. Chem.,
Int. Ed., 2015, 54, 14103; c) Y. Liang, Y. Liang, C. Tang, Y. Yuan
and N. Jiao, Chem.-Eur. J., 2015, 21, 16395.
O
Ts
N
N
Au+L
S
acetone
14
14 S. Kramer, Y. Odabachian, J. Overgaard, M. Rottländer, F.
Scheme 5. Trapping of α-imino gold-carbene intermediate
Gagosz and T. Skrydstrup, Angew. Chem., Int. Ed., 2011, 50
5090.
,
15 CCDC-1455247 (IPrAuNTf2), 1450076 (3b) and 1455246 (16
)
In summary, we have disclosed that 1,4,2-dioxazole can be
used as an efficient nitrene equivalent in gold-catalyzed
nitrene transfer reactions to ynamides. The reaction proceeds
under mild reaction conditions to afford highly functionalized
oxazoles in good to excellent yields via likely the formation of
contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif
.
16 For selected papers, see: a) C. Wan, J. Zhang, S. Wang, J. Fan
and Z. Wang, Org. Lett., 2010, 12, 2338; b) C. Lalli, J. M.
Bouma, D. Bonne, G. Masson and J. Zhu, Chem.-Eur. J., 2011,
17, 880; c) W. He, C. Li and L. Zhang, J. Am. Chem. Soc., 2011,
133, 8482; d) Y. Luo, K. Ji, Y. Li and L. Zhang, J. Am. Chem.
Soc., 2012, 134, 17412; e) Ref. 6b-d. For Ru/Cu-catalyzed
reaction of 1,4,2-dioxazol-5-ones with terminal alkynes to
oxazoles, see: f) C. Zhong, B. Tang, P. Yin, Y. Chen and L. He, J.
Org. Chem., 2012, 77, 4271.
an -imino gold carbene intermediate followed by cyclization.
This method offers several advantages such as easily accessible
starting materials, high regioselectivity, wide functional group
compatibility and high efficiency. Further investigations on the
detailed reaction mechanism and application of this chemistry
are in progress.
We thank the National Natural Science Foundation of China
(Grant Nos. 21421091, 21372244, 21572256) for financial
support.
17 See supporting information.
18 a) S. Kramer and T. Skrydstrup, Angew. Chem. Int. Ed. 2012,
51, 4681; b) X. Huang, B. Peng, M. Luparia, L. F. R. Gomes, L.
F. Veiros, and N. Maulide, Angew. Chem. Int. Ed., 2012, 51
8886.
19 H. Li and R. P. Hsung, Org. Lett., 2009, 11, 4462.
,
Notes and references
1
For reviews, see: a) “Gold Carbenes”: L. Zhang, in
Contemporary Carbene Chemistry (Eds. R. A. Moss, M. P.
Doyle), Wiley, Hoboken, 2013, pp. 526; b) Y. Wang, M. E.
Muratore and A. M. Echavarren, Chem.-Eur. J., 2015, 21
,
7332.
4 | J. Name., 2012, 00, 1-3
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