Gold-Catalyzed Formal [4+1]/[4+3] Cycloadditions of Diazo Esters with Triazines

Article abstract of DOI:10.1002/anie.201606139

Reported herein is the unprecedented gold-catalyzed formal [4+1]/[4+3] cycloadditions of diazo esters with hexahydro-1,3,4-triazines, thus providing five- and seven-membered heterocycles in moderate to high yields under mild reaction conditions. These reactions feature the use of a gold complex to accomplish the diverse annulations and the first example of the involvement of a gold metallo-enolcarbene in a cycloaddition. It is also the first utilization of stable triazines as formal dipolar adducts in the carbene-involved cycloadditions. Mechanistic investigations reveal that the triazines reacted directly, rather than as formaldimine precursors, in the reaction process.

Full text of DOI:10.1002/anie.201606139

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201606139
German Edition: DOI: 10.1002/ange.201606139
Heterocycles
Gold-Catalyzed Formal [4+1]/[4+3] Cycloadditions of Diazo Esters
with Triazines
Chenghao Zhu, Guangyang Xu, and Jiangtao Sun*
Abstract: Reported herein is the unprecedented gold-catalyzed
formal [4+1]/[4+3] cycloadditions of diazo esters with
hexahydro-1,3,4-triazines, thus providing five- and seven-
membered heterocycles in moderate to high yields under
mild reaction conditions. These reactions feature the use of
a gold complex to accomplish the diverse annulations and the
first example of the involvement of a gold metallo-enolcarbene
in a cycloaddition. It is also the first utilization of stable
triazines as formal dipolar adducts in the carbene-involved
cycloadditions. Mechanistic investigations reveal that the
triazines reacted directly, rather than as formaldimine precur-
sors, in the reaction process.
T
ransition-metal-catalyzed cycloadditions of diazocarbonyl
precursors with dipolar adducts are powerful tools for the
rapid construction of diverse scaffolds, and diazo compounds
can serve as one- to three-carbon synthons in various [n+m]
[
1]
annulations. In particular, the rhodium- and copper-cata-
lyzed cycloadditions have been extensively studied by the
groups of Doyle, Davies, and others. In contrast, the use
of gold complexes in such reactions remains less well
[
2]
[3]
[4]
[
5]
[6]
Scheme 1. Previous reports and our approach. LA=Lewis acid,
Si=silyl protecting group.
investigated. Recently, the groups of Liu, Davies, and
[7]
others described several novel gold-catalyzed cycloaddi-
tions, thus demonstrating totally different reactivity and
selectivity compared to other metals. Nevertheless, the
unique catalytic activity of gold complexes prompted chem-
ists to discover novel reactions which do not occur for
additions between diazo esters and hexahydro-1,3,5-triazines
(Scheme 1b). Notably, different from Krischeꢀs protocols, in
which the triazines acted as active imine/iminium intermedi-
ates undergoing nucleophilic attack by a nucleophilic allylru-
thenium complex for various aminomethylations, we herein
employ these triazines as formal dipolar adducts under gold
catalysis to realize the synthesis of five- and seven-membered
heterocycles.
[
8,9]
others,
complexity.
thus providing efficient ways towards molecular
[10]
Recently, Krische and co-workers developed a series of
novel ruthenium-catalyzed hydroaminomethylations by using
hexahydro-1,3,5-triazines as precursors of N-aryl formaldi-
[
11]
mines (Scheme 1a). Just recently, following their efforts on
developing novel aminations, Huang and co-workers de-
scribed an elegant palladium-catalyzed formal insertion of
carbenoids into aminals by CÀN bond activation, thus
Initially, the triazine 1a and phenyl diazoacetate (2a)
were utilized as model substrates to achieve the optimal
reaction conditions (Table 1). The application of gold com-
plexes (5 mol%) as the catalyst was first examined. When the
reactions were performed in dichloromethane at 608C, the
use of IPrAuCl, PPh AuCl, (C F ) PAuCl, Xantphos(AuCl) ,
affording an efficient approach towards diamino acid esters
[
12]
with quaternary carbon centers. Inspired by these pioneer-
ing reports, and in continuation of our ongoing research
3
6
5
3
2
[13]
interests in gold-carbene-mediated transformations,
we
XPhosAuCl, and JohnPhosAuCl all gave 3a in quite low yield
within 12 hours (entries 1–6). The use of tBuXPhosAuCl
provided 3a in 55% yield (entry 7), which improves to 68%
yield in toluene (entry 8) and 81% yield in tetrahydrofuran
report herein the unprecedented formal [4+1]/[4+3] cyclo-
[*] C. Zhu, G. Xu, Prof. Dr. J. Sun
(entry 9). However, a reduced catalyst loading resulted in
Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology
School of Pharmaceutical Engineering & Life Science
Changzhou University, 1 Gehu Road, 213164 Changzhou (China)
E-mail: jtsun@cczu.edu.cn
moderate yield (entry 10) and almost no 3a was detected at
room temperature (entry 11). Moreover, rhodium complexes
such as [Rh (Oct) ] and [Rh (esp) ] were also examined, but
2
4
2
2
jtsun08@gmail.com
gave low conversion (entries 12 and 13).
With the optimal reaction conditions in hand, we next set
out to investigate the scope with respect to the substrates
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201606139.
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
[
a]
Table 1: Selected optimization.
Table 2: Substrate scope for gold-catalyzed formal [4+1] cyclo-
additions.
[
a,b]
[
b]
Entry
Catalyst (mol%)
IPrAuCl (5)
Solvent
T [8C]
t [h]
Yield [%]
1
2
3
4
5
6
7
8
9
CH Cl2
60
60
60
60
60
60
60
60
60
60
25
25
25
12
12
12
12
12
12
12
12
12
24
24
1
<5
<5
<5
<5
<5
15
55
68
81
57
2
Ph PAuCl (5)
CH Cl2
3
2
(C F ) PAuCl (5)
CH Cl2
6
5
3
2
Xantphos(AuCl) (5)
CH Cl2
2
2
XPhosAuCl (5)
CH Cl2
2
JohnPhosAuCl (5)
tBuXPhosAuCl (5)
tBuXPhosAuCl (5)
tBuXPhosAuCl (5)
tBuXPhosAuCl (2)
tBuXPhosAuCl (5)
[Rh (OAc) ] (1)
CH Cl2
2
CH Cl2
2
toluene
THF
THF
10
11
12
13
THF
<5
33
22
CH Cl2
2
4
2
[Rh (esp) ] (1)
CH Cl2
1
2
2
2
[
a] Reactions were performed with 1a (0.25 mmol) and 2a (0.3 mmol) in
solvent (5 mL) in the presence of either gold or rhodium complexes.
b] Yields of isolated products.
[
(
Table 2). A wide range of donor/acceptor diazo esters,
including aryl diazoacetates (2a–h), alkyl diazoacetate (2j),
vinyl diazoacetates (2k–m), cyclic diazo compounds (2n and
2
o), and acceptor/acceptor diazoesters (2p and 2q) were
evaluated. Generally, highly substituted imidazolidines bear-
ing a quaternary carbon center were obtained in modest to
excellent yields by a formal [4+1] cycloaddition for all cases.
About the substituted phenyl diazoacetates, the phenyl ring
bearing electron-rich groups gave higher yields than those
bearing electron-poor ones (3b, 3d, 3 f versus 3c, 3e). The
thiophene diazoacetate 2h was tolerated and afforded the
corresponding product 3h in 65% yield. The use of the methyl
diazoacetate 2j gave 3j in 46% yield, and even the simple
diazoacetate 2i worked well to furnish 3i in 52% yield. It is
noteworthy that when the vinyl diazoacetates were used, the
catalytic system still worked well to provide the desired five-
membered imidazolidines (3k–m) in modest yields. Also, the
reaction of 1a with cyclic diazo compounds furnished the
spiro-imidazolidines 3n and 3o in 82 and 81% yield,
respectively. The diazo esters (2p and 2q) with two acceptor
groups were also examined and the corresponding products
were obtained in 72 and 38% yield, respectively. Moreover,
the different aryl substituted 1,3,5-triazines were also exam-
ined, thus providing the corresponding products in moderate
[
a] Reactions were carried out with 1 (0.25 mmol), 2 (0.3 mmol), and
tBuXPhosAuCl (5 mol%) in THF (5 mL) at 608C for 12 h. [b] Yields of
isolated products.
yields (3r–t). The structure of the products was determined by
NMR analysis and additionally confirmed by X-ray analysis
of 3g.
It is well known that the metallo-vinylcarbene and
metallo-enolcarbene species have electrophilic character at
both of the carbenic and vinylogous positions. Generally the
nucleophilic addition occurs preferentially at the vinylogous
position (Scheme 2).
that the activity of the vinylogous position for vinyl gold
[14]
[
15]
Indeed, literature reports revealed
[
6b,9f,g]
carbenes was dominant for most cases.
However, we
found that the carbenic reactivity was preferred in this case
(3k–m of Table 1). Moreover, for the enol diazoacetates, the
electron-donating oxygen atom of the silyl ether group would
2
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
diphenylsilyl) protected enol diazoacetates were tolerated
and gave the corresponding polysubstituted heterocycles in
moderate to high yields. To further determine the structure of
the products, the reaction between the enol diazoacetate 4d
and 1a was performed and finally the single-crystal X-ray
[14]
analysis of 5d was obtained.
The substrate scope with
respect to the diazo compounds was also investigated, and we
found that the enol diazoacetates having substituents at the
terminal alkene position furnished the corresponding prod-
ucts in moderate yields (5 f–h). Moreover, the enol diazo-
acetamide 4i also reacted well and gave 5i in 57% yield. Next,
two different hexahydro-1,3,5-triazines were examined and
also gave the corresponding products 5j and 5k in moderate
yields.
Scheme 2. Known reaction pathway and novel reaction modes (our
work).
enhance the electrophilic character at the vinylogous posi-
To gain insight into the reaction mechanism, deuterium-
labeling experiments were conducted (Scheme 3). First, the
[
1c]
tion,
and probably resulted in reaction modes different
from those of linear vinyl diazoacetates. To our knowledge, no
reports for the gold metallo-enolcarbene reaction have been
described before.
Next, to further evaluate the generality of this catalytic
system, various enol diazo compounds (4) were employed
(
Table 3). Indeed, in contrast to the vinyldiazoacetates which
gave the five-membered heterocycles as the sole products, the
reaction of 1a and the enol diazoacetates 4 proceeded
smoothly through a formal [4+3] annulation to provide
seven-membered heterocycles (5) with the CÀN bond form-
ing at the vinylogous position. All of the TBS (tert-butyldi-
methylsilyl), TIPS (triisopropylsilyl), and TBDPS (tert-butyl-
[
a,b]
Table 3: Gold-catalyzed formal [4+3] cycloadditions.
Scheme 3. Deuterium-labeling experiments. THF=tetrahydrofuran.
reaction of [D]-1a and 2a afforded the fully deuterated
product [D]-3a (Scheme 3a). Moreover, [D]-5 f was obtained
in moderate yield, and indicated that the CÀN bond
formation occurred at the vinylogous position of the enol
diazoacetates (Scheme 3b). Furthermore, upon treatment of
1
equivalent of 1a and [D]-1a with 1.2 equivalents of 2a, 3a
and [D]-3a were obtained almost in a 1:1 ratio. It is important
to note that the cross-cyclization products were not observed
(Scheme 3c).
To further understand the reaction process, the reaction of
1
3
a and 1b with 2a was performed (Scheme 4). However, only
a and 3r were cleanly isolated in 77 and 71% yield,
respectively. No cross-cyclization products were observed.
Since the cross-cycloaddition adducts were not detected
(Schemes 3c and 4), the possible route by the formation the
formaldimine A and subsequent cycloaddition with the metal-
[
16]
carbene B should be excluded (Scheme 5a). Then a general
mechanism for the formal [4+1] cycloaddition was proposed
[
a] Reactions were carried out with 1 (0.25 mmol), 2 (0.3 mmol), and
(
Scheme 5b). First, the reaction of the triazine 1 with B
tBuXPhosAuCl (5 mol%) in THF (5 mL) at 608C for 12 h. [b] Yields of
isolated products. [c] X-ray structure of 5d. Thermal ellipsoids shown
[
17]
[
14]
provides the intermediate C by ylide formation.
The
at 30% probability.
intramolecular electrophilic trapping associated with rear-
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
[
[
1] For selected leading reviews, see: a) H. M. L. Davies, S. J.
Hedley, Chem. Soc. Rev. 2007, 36, 1109; b) X. Zhao, Y. Zhang,
J. Wang, Chem. Commun. 2012, 48, 10162; c) X. Xu, M. P. Doyle,
Acc. Chem. Res. 2014, 47, 1396; d) A. Ford, H. Miel, A. Ring,
C. N. Slattery, A. R. Maguire, M. A. McKervey, Chem. Rev.
Scheme 4. Control experiments.
2
015, 115, 9981.
2] a) X. Wang, X. Xu, P. Y. Zavalij, M. P. Doyle, J. Am. Chem. Soc.
011, 133, 16402; b) X. Xu, Y. Qian, P. Y. Zavalij, M. P. Doyle, J.
2
Am. Chem. Soc. 2013, 135, 1244; c) X. Xu, P. Y. Zavalij, M. P.
Doyle, Angew. Chem. Int. Ed. 2013, 52, 12664; Angew. Chem.
2013, 125, 12896; d) Q.-Q. Cheng, J. Yedoyan, H. Arman, M. P.
Doyle, J. Am. Chem. Soc. 2016, 138, 44; e) Q.-Q. Cheng, J.
Yedoyan, H. Arman, M. P. Doyle, Angew. Chem. Int. Ed. 2016,
55, 5573; Angew. Chem. 2016, 128, 5663.
[
[
3] a) A. G. Smith, H. M. Davies, J. Am. Chem. Soc. 2012, 134,
18241; b) J. E. Spangler, H. M. L. Davies, J. Am. Chem. Soc.
2013, 135, 6802; c) P. E. Guzmꢁn, Y. Lian, H. M. L. Davies,
Angew. Chem. Int. Ed. 2014, 53, 13083; Angew. Chem. 2014, 126,
3299.
1
4] For selected examples, see: a) T. Achard, C. Tortoreto, A. I.
Pablador-Bahamonde, L. Guꢂnꢂe, T. Bꢃrgi, J. Lacour, Angew.
Chem. Int. Ed. 2014, 53, 6140; Angew. Chem. 2014, 126, 6254;
b) F. Ye, S. Qu, L. Zhou, C. Peng, C. Wang, J. Cheng, M. L.
Hossain, Y. Liu, Y. Zhang, Z.-X. Wang, J. Wang, J. Am. Chem.
Soc. 2015, 137, 4435; c) S. M. Nicolle, W. Lewis, C. J. Hayes, C. J.
Moody, Angew. Chem. Int. Ed. 2015, 54, 8485; Angew. Chem.
Scheme 5. Proposed mechanisms.
2015, 127, 8605; d) P. Q. Le, J. A. May, J. Am. Chem. Soc. 2015,
1
37, 12219; e) C. Jing, D. Xing, L. Gao, J. Li, W. Hu, Chem. Eur.
rangement, and subsequent reductive elimination affords the
cycloaddition product 3. For the formal [4+3] cycloaddition,
the generation of a gold enolcarbene species is the key step.
Then the nucleophilic addition of 1 at the vinylogous position
of enolcarbene affords the intermediate D, which undergoes
intramolecular cycloaddition and reductive elimination to
provide the final product 5 and regenerates the gold catalysts
J. 2015, 21, 19202; f) S. K. Alamsetti, M. Spanka, C. Schneider,
Angew. Chem. Int. Ed. 2016, 55, 2392; Angew. Chem. 2016, 128,
2438; g) S. M. Nicolle, W. Lewis, C. J. Hayes, C. J. Moody,
Angew. Chem. Int. Ed. 2016, 55, 3749; Angew. Chem. 2016, 128,
3
5
Chem. Int. Ed. 2015, 54, 12962; Angew. Chem. 2015, 127, 13154;
j) R. A. Panish, S. R. Chintala, J. M. Fox, Angew. Chem. Int. Ed.
2
Gonzꢁlez, L. A. Lꢄpez, Adv. Synth. Catal. 2016, 358, 1428; l) J.
Kalepu, S. Katukojvala, Angew. Chem. Int. Ed. 2016, 55, 7831;
Angew. Chem. 2016, 128, 7962.
813; h) T. Shi, X. Guo, S. Teng, W. Hu, Chem. Commun. 2015,
1, 15204; i) K. Liu, C. Zhu, J. Min, S. Peng, G. Xu, J. Sun, Angew.
(
Scheme 5c).
016, 55, 4983; Angew. Chem. 2016, 128, 5067; k) E. Lꢄpez, J.
In summary, we have developed unprecedented gold-
catalyzed formal [4+1]/[4+3] cycloaddition reactions of diazo
esters with hexahydro-1,3,5-triazines, thus affording five- and
seven-membered N-containing heterocycles in moderate to
high yields under mild reaction conditions with a broad
substrate scope. This protocol features the first example of
gold-catalyzed [4+1]/[4+3] cycloadditions using different
diazo substrates, especially for the enol diazo compounds.
Notably, mechanistic investigations offered strong evidence
for the triazines reacting directly with the metal carbene.
[
5] a) V. V. Pagar, A. P. Jadhav, R.-S. Liu, J. Am. Chem. Soc. 2011,
1
33, 20728; b) A. M. Jadhav, V. V. Pagar, R.-S. Liu, Angew.
Chem. Int. Ed. 2012, 51, 11809; Angew. Chem. 2012, 124, 11979;
c) S. K. Pawar, C.-D. Wang, S. Bhunia, A. M. Jadhav, R.-S. Liu,
Angew. Chem. Int. Ed. 2013, 52, 7559; Angew. Chem. 2013, 125,
7707; d) V. V. Pagar, R.-S. Liu, Angew. Chem. Int. Ed. 2015, 54,
4923; Angew. Chem. 2015, 127, 5005; e) R. R. Singh, R.-S. Liu,
Adv. Synth. Catal. 2016, 358, 1421.
[
6] a) J. F. Briones, H. M. L. Davies, J. Am. Chem. Soc. 2012, 134,
11916; b) J. F. Briones, H. M. L. Davies, J. Am. Chem. Soc. 2013,
135, 13314.
Acknowledgments
[
7] a) Z.-Y. Cao, X. Wang, C. Tan, X. Zhao, J. Zhou, K. Ding, J. Am.
Chem. Soc. 2013, 135, 8197; b) J. Wang, X. Yao, T. Wang, J. Han,
J. Zhang, X. Zhang, P. Wang, Z. Zhang, Org. Lett. 2015, 17, 5124;
c) Z. Yu, H. Qiu, L. Liu, J. Zhang, Chem. Commun. 2016, 52,
We thank the National Natural Science Foundation of China
(
(
21572024), Natural Science Foundation of Jiangsu Province
BK20151184), and Jiangsu Key Laboratory of Advanced
2257.
[
8] For reviews, see: a) F. Wei, C. Song, Y. Ma, L. Zhou, C.-H. Tung,
Z. Xu, Sci. Bull. 2015, 60, 1479; b) L. Liu, J. Zhang, Chem. Soc.
Rev. 2016, 45, 506; c) M. R. Fructos, M. M. Dꢅaz-Requejo, P. J.
Pꢂrez, Chem. Commun. 2016, 52, 7326.
Catalytic Materials & Technology (BM2012110) for their
financial support.
Keywords: cycloaddition · diazo compounds · gold ·
heterocycles · reaction mechanisms
[
9] For selected representative examples, see: a) M. R. Fructos,
T. R. Belderrain, P. de Frꢂmont, N. M. Scott, S. P. Nolan, M. M.
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
Dꢅaz-Requejo, P. J. Pꢂrez, Angew. Chem. Int. Ed. 2005, 44, 5284;
Asian J. 2014, 9, 3066; j) R. Dorel, A. M. Echavarren, Chem.
Angew. Chem. 2005, 117, 5418; b) I. Rivilla, B. Gꢄmez-Emeterio,
M. R. Fructos, M. M. Dꢅaz-Requejo, P. J. Pꢂrez, Organometallics
Rev. 2015, 115, 9028.
[11] a) S. Oda, B. Sam, M. J. Krische, Angew. Chem. Int. Ed. 2015, 54,
8525; Angew. Chem. 2015, 127, 8645; b) S. Oda, J. Franke, M. J.
Krishce, Chem. Sci. 2016, 7, 136.
[12] G. Qin, L. Li, J. Li, H. Huang, J. Am. Chem. Soc. 2015, 137,
12490.
[13] a) D. Zhang, G. Xu, D. Ding, C. Zhu, J. Li, J. Sun, Angew. Chem.
Int. Ed. 2014, 53, 11070; Angew. Chem. 2014, 126, 11250; b) G.
Xu, C. Zhu, W. Gu, J. Li, J. Sun, Angew. Chem. Int. Ed. 2015, 54,
883; Angew. Chem. 2015, 127, 897; c) C. Zhu, G. Xu, K. Liu, L.
Qiu, S. Peng, J. Sun, Chem. Commun. 2015, 51, 12768; d) C. Zhu,
L. Qiu, G. Xu, J. Li, J. Sun, Chem. Eur. J. 2015, 21, 12871.
[14] CCDC 1486814 (3g) and 1486792 (5d) contain the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre.
2011, 30, 2855; c) A. Prieto, M. R. Fructos, M. M. Dꢅaz-Requejo,
P. J. Pꢂrez, P. Pꢂrez-Galꢁn, N. Delpont, A. M. Echavarren,
Tetrahedron 2009, 65, 1790; d) I. Rivilla, W. M. C. Sameera, E.
ꢆlvarez, M. M. Dꢅaz-Requejo, F. Maseras, P. J. Pꢂrez, Dalton
Trans. 2013, 42, 4132; e) J. Barluenga, G. Lonzi, M. Tomꢁs, L. A.
Lꢄpez, Chem. Eur. J. 2013, 19, 1573; f) G. Lonzi, L. A. Lꢄpez,
Adv. Synth. Catal. 2013, 355, 1948; g) E. Lꢄpez, G. Lonzi, L. A.
Lꢄpez, Organometallics 2014, 33, 5924; h) Z. Yu, B. Ma, M.
Chen, H.-H. Wu, L. Liu, J. Zhang, J. Am. Chem. Soc. 2014, 136,
6
904; i) Y. Xi, Y. Su, Z. Yu, B. Dong, E. J. McClain, X. Shi,
Angew. Chem. Int. Ed. 2014, 53, 9817; Angew. Chem. 2014, 126,
975; j) Y; Liu, Z. Yu, J. Z. Zhang, L. Liu, F. Xia, J. Zhang,
9
Chem. Sci. 2016, 7, 1988.
[
10] For selected reviews, see: a) A. S. K. Hashmi, G. J. Hutchings,
Angew. Chem. Int. Ed. 2006, 45, 7896; Angew. Chem. 2006, 118,
[15] H. M. L. Davies, Y. Lian, Acc. Chem. Res. 2012, 45, 923.
[16] H.-J. Ha, C.-J. Choi, Y.-G. Ahn, H. Yun, Y. Dong, W. K. Lee, J.
Org. Chem. 2000, 65, 8384.
8064; b) A. Fꢃrstner, P. W. Davies, Angew. Chem. Int. Ed. 2007,
46, 3410; Angew. Chem. 2007, 119, 3478; c) A. S. K. Hashmi,
Chem. Rev. 2007, 107, 3180; d) E. Jimꢂnez-NfflÇez, A. M.
Echavarren, Chem. Rev. 2008, 108, 3326; e) D. J. Gorin, B. D.
Sherry, F. D. Toste, Chem. Rev. 2008, 108, 3351; f) N. Krause, C.
Winter, Chem. Rev. 2011, 111, 1994; g) A. Corma, A. Leyva-
Pꢂrez, M. J. Sabater, Chem. Rev. 2011, 111, 1657; h) A. S. K.
Hashmi, M. Rudolph, Chem. Soc. Rev. 2012, 41, 2448; i) M. E.
Muratore, A. Homs, C. Obradors, A. M. Echavarren, Chem.
[17] For a leading account on trapping ylides with electrophiles, see:
X. Guo, W. Hu, Acc. Chem. Res. 2013, 46, 2427.
Received: June 24, 2016
Published online: && &&, &&&&
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Heterocycles
C. Zhu, G. Xu, J. Sun*
&&&& — &&&&
Gold-Catalyzed Formal [4+1]/[4+3]
Cycloadditions of Diazo Esters with
Triazines
Golden performance: The title reaction
has been accomplished, thus providing
five- and seven-membered heterocycles in
moderate to high yields under mild
ture the use of a gold complex to
accomplish the diverse annulations and
serve as an example of the involvement of
a gold metallo-enolcarbene in a cycload-
dition. Si=silyl protecting group.
reaction conditions. These reactions fea-
6
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!