Cyclopropenation of internal alkynylsilanes and diazoacetates catalyzed by copper(i) N-heterocyclic carbene complexes

Article abstract of DOI:10.1039/c5ob02259b

Copper(i) N-heterocyclic carbene (CuNHC) complexes are more catalytically active than traditional transition metal salts for the cyclopropenation of internal alkynylsilanes and diazoacetate compounds. A series of 1,2,3-trisubstituted and 1,2,3,3-tetrasubstituted cyclopropenylsilane compounds were isolated in good overall yields. An interesting regioselective and chemodivergent reaction pathway was also observed to furnish a tetra-substituted furan for an electron-rich donor/acceptor diazoacetate. Finally, a practical synthesis of a cyclopropenyl-containing starting material that is useful for bioorthogonal chemistry is also described.

Full text of DOI:10.1039/c5ob02259b

Organic &
Biomolecular Chemistry
View Article Online
View Journal
PAPER
Cyclopropenation of internal alkynylsilanes
and diazoacetates catalyzed by copper(I)
Cite this: DOI: 10.1039/c5ob02259b
N-heterocyclic carbene complexes†
Thomas J. Thomas, Benjamin A. Merritt, Betsegaw E. Lemma, Adina M. McKoy,
Tri Nguyen, Andrew K. Swenson, Jeffrey L. Mills and Michael G. Coleman*
Copper(I) N-heterocyclic carbene (CuNHC) complexes are more catalytically active than traditional tran-
sition metal salts for the cyclopropenation of internal alkynylsilanes and diazoacetate compounds.
A series of 1,2,3-trisubstituted and 1,2,3,3-tetrasubstituted cyclopropenylsilane compounds were isolated
in good overall yields. An interesting regioselective and chemodivergent reaction pathway was also
observed to furnish a tetra-substituted furan for an electron-rich donor/acceptor diazoacetate. Finally, a
practical synthesis of a cyclopropenyl-containing starting material that is useful for bioorthogonal
chemistry is also described.
Received 2nd November 2015,
Accepted 21st December 2015
DOI: 10.1039/c5ob02259b
www.rsc.org/obc
cycloisomerizations,18 Pauson-Khand transformations,12a,19
gold-catalyzed isomerizations,20 and rearrangements into
Introduction
Cyclopropene compounds are a valuable class of highly complex Vaska-type iridium complexes.13a Furthermore, 1-silyl-
strained (54.5 kcal mol−1)1 three-membered carbocyclic mole- cyclopropene compounds are also valuable starting materials
cules which possess a uniquely reactive π bond. Many useful for the synthesis of a new class of bioorthogonal chemical
synthetic activation modes are known for their conversion into reporters that are used in cellular metabolic labeling
a diverse array of complex cyclic and acyclic molecular build- experiments.21
ing blocks.2 To the contrary, the synthesis of cyclopropene
There are two methods that are used for the synthesis of
compounds has received less attention. One promising 1- and 2-silylcyclopropenes.22 In the first method, cyclopro-
approach is the transition metal-catalyzed cyclopropenation of pene starting materials are treated to strongly basic/nucleo-
alkynes and diazoacetates, which has several distinct synthetic philic reaction conditions that are incompatible with
advantages over traditional 1,2-elimination strategies.3 base-sensitive functional groups and are more susceptible to
However, only a few transition metal catalysts (e.g. Rh(II),4 Cu destructive ring-opening reactions.22a To circumvent this, an
(I),5 Co(II),6 and Ir(II)7) are reported for the cyclopropenation of inverse-addition protocol,22b carboxylate dianion approach,22c
terminal alkynes and diazoacetates; while, an entirely different and
a more mild, Cu(I)-catalyzed silylation have been
set of catalysts (e.g. Cu(I),8 Ag(I),9 and chiral Ag(I)/Au(I),10) are reported.22d Still, the transition metal-catalyzed [2 + 1] cyclo-
reportedly known to be most effective for the cyclopropenation addition of alkynylsilanes and diazoacetates is the most
of internal alkynes with the exception of the copper(I)-homo- direct and general approach for the synthesis of 1-silylcyclopro-
scorpionate catalysts.11 And yet, to a much lesser extent, a penes, but these strategies are often fraught with consistently
series of miscellaneous reactions have been reported for the low yields (< 41%) and use an excess of alkynylsilane (2.5–10
cyclopropenation of internal alkynylsilanes with rather ineffec- fold) (Scheme 1). Recently, we reported
a CuI-catalyzed
tive catalysts (e.g Rh(II)-,4b,12 Cu(0)-,13 Cu(I)-,14 and Cu(II)-8,15). cyclopropenation of 1-TMS-2-(4-methoxyphenyl)acetylene
1
This is despite the fact that 1-silylcyclopropenes are useful (1.00 mmol) in the presence of a donor–acceptor diazoacetate
starting materials for platinum-catalyzed rearrangements,16 2a (3.00 mmol) that afforded the corresponding 1,2,3,3-tetra-
Sila Morita–Baylis–Hillman reactions,17 indium-catalyzed substituted cyclopropenylsilane 3a in modest yield
(Scheme 2).23 Given that this new finding gave slightly higher
yields than all other previous examples, in addition to the
School of Chemistry and Materials Science, Rochester Institute of Technology,
commercial availability of highly active copper(I) N-heterocyclic
Rochester, NY 14623, USA. E-mail: mgcsch@rit.edu
†Electronic supplementary information (ESI) available. CCDC 1434815. For ESI
carbene complexes for catalytic carbene transfer reactions,24
we set out to examine their overall effectiveness for this
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
transformation.
c5ob02259b
This journal is © The Royal Society of Chemistry 2015
Org. Biomol. Chem.

View Article Online
Paper
Organic & Biomolecular Chemistry
Scheme 1 Collection of metal-catalyzed cyclopropenation of internal alkynylsilanes and diazoacetates.
Scheme 2 Cu(I)-catalyzed synthesis of a tetra-substituted cyclopropene.
i
entry 7). PrCuCl is a N-heterocyclic carbene (NHC) copper (I)
choride salt that is useful for the cyclopropanation and aziridi-
Results and discussion
The study began by measuring the catalytic activities of nation reactions of olefins.24 Other Cu(I)–NHC salts were
various Cu(I)- and Rh(II)- salts for the cyclopropenation of screened, but no significant improvement in the isolated yield
1-phenyl-2-trimethylsilylacetylene
towards the synthesis of 1,2,3,3-tetrasubstituted cyclopropenyl- benchmark catalyst for carbene transfer reactions, afforded
silane 5a (Table 1). cyclopropene 5a in significantly lower isolated yield (24%,
4
and diazoacetate 2a was observed (Table 1, entries 9–11). Dirhodium(II) acetate, a
Although no product was observed at room temperature Table 1, entry 12). Finally, the thermally–induced cycloprope-
(Table 1, entries 1–2, 8), higher reaction temperatures (110 °C) nation of 4 and 2a afforded 5a in comparable yield (24%).
i
resulted in modest isolated yields of the cyclopropenylsilane
With the optimized PrCuCl-catalyzed reaction conditions
product 5a (Table 1, entries 3–6) with cuprous salts. Compara- in hand, we investigated the role of the silyl group’s steric size
tively, trifluorotoluene proved to be a more inert solvent on the reactivity of the cyclopropenation reaction (Table 2).
than toluene and we did not observe any appreciable amount
of cyclopropanation byproducts (Table 1, entry 4). (1,3-Bis-(dii- corresponding cyclopropene 11a in good yield (81%), while
sopropyl-phenyl)imidazole-2-ylidene) copper(I) chloride, phenyl tripropylsilylacetylene 7 afforded cyclopropene 12a in
(iPrCuCl), afforded 5a in high isolated yield (84%, Table 1, poor yield (8%). Increasing the steric bulk of the silane group
1-TBS-2-phenylacetylene 6 was easily converted to the
Org. Biomol. Chem.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Organic & Biomolecular Chemistry
Paper
Table 1 Optimization of reaction conditions
Table 3 Cyclopropenation of electronically and structurally diverse
alkynylsilanes
Entry Catalyst
Solvent Temperature (°C) Isolated yield (%)
1
2
3
Cul
Cul
Cul
Cul
CH2Cl2
CH3Ph
CH3Ph
CF3Ph
CF3Ph
CF3Ph
CF3Ph
CF3Ph
CF3Ph
CF3Ph
23
23
—
—
26
34
8
15
84
—
74
65
64
24
24
110
110
110
110
110
23
110
110
110
110
110
4
5a
6
Cul
CuTC
iPrCuCl
iPrCuCl
MesCuCl
iPrCuBF4
7
8
9
10
11
12
13
(iPr)2CuBF4 CF3Ph
Rh2(OAc)4
None
CF3Ph
CF3Ph
Reaction conditions: A solution of 4 and catalyst in CF3Ph (2 mL) was
added a solution of 2a in CF3Ph (20 mL) at 1.00 mL min−1 at 110 °C.
The reaction was concentrated and purified by chromatography.
Electron-deficient para-halophenyl(trimethylsilyl)acetylenes
furnished the corresponding cyclopropenes 14a–17a in moder-
ate overall yields, while 2-(4-iodophenyl)cyclopropene 17a was
isolated in low yield (3.8%). In a straightforward manner, tri-
fluorotolyl, 1-naphthyl, and meta-methoxyphenyl alkynylsi-
lanes furnished cyclopropenyl esters 18a–20a in useful overall
yields (>49%, Table 3). Interestingly, both 2- and 3-thiophene
substituted alkynylsilanes were converted into cyclopropenes
21a and 22a in modest isolated yields. 2-Alkyl-1-trimethyl-
Table 2 Silane
cyclopropenation
steric
effects
on
the
iPrCuCl-catalyzed
Entry
Alkyne
R
Product
Isolated yield (%)
t
1
2
3
4
5
6
7
8
9
10
(CH3)2 BUSi
(nPr)3Si
11a
12a
81
8
—
—
—
(iPr)3tSi
(Ph)2 BuSi
(Ph)3Si
any further had a detrimental effect on the reactivity and
alkynylsilanes 8–10 were recovered without significant
decomposition. This feature may be especially useful when
one or more acetylenic sites are reactive.19
With the optimum reaction conditions in hand, we sur-
veyed various aliphatic and aromatic alkynylsilanes to measure
i
the activity of PrCuCl-catalyzed cyclopropenation in the pres-
ence of 2a (Table 3). The relatively electron-rich and sterically-
hindered ortho-tolyl(trimethylsilyl)acetylene was converted into
the corresponding cyclopropene 13a in good yield (71%).
Fig. 1 OTREP diagram of 15a.
This journal is © The Royal Society of Chemistry 2015
Org. Biomol. Chem.

View Article Online
Paper
Organic & Biomolecular Chemistry
Fig. 2 Three classes of diazoacetate compounds used in carbene transfer reactions With this in mind, we tested the reactivity and selectivity of
various diazoacetate compounds for the iPrCuCl-catalyzed cyclopropenation of internal alkynylsilane compounds (Table 4).
silylacetylenes were smoothly converted into 23a and 24a in
Several decades of transition metal carbenoid research
good isolated yields (61% and 64%, respectively, Table 3). suggests that the selectivity for carbene transfer reactions is
Unfortunately, both bistrimethylsilylacetylene and ethyl 3-(tri- largely dependent on the electronic nature of the diazo-
methylsilyl)propiolate were unreactive presumably due to their acetate.25 As a result, three classes of diazoacetate compounds
relatively higher electron deficient nature (Table 3). Compound have been classified based primarily on their differing reactiv-
15a, serving as a representative example of the 1,2,3,3-tetrasub- ity and/or selectivity observed for carbene transfer reactions
stituted cyclopropenes synthesized in this study, was recrystal- (Fig. 2).
i
lized from refluxing hexane to yield suitable crystals for X-ray
crystallography (Fig. 1).
Both the CuI- and PrCuCl-catalyzed cyclopropenation of
alkynylsilane 4 in the presence of acceptor-substituted diazo-
Table 4 Survey of the reactivity of various diazoacetate compounds
Entry
Diazoacetate
R1
R2
Product
Isolated yield (%)
1a
2
25b
25b
26c
H
H
CH2CH3
CH2CH3
CH3
32b
32b
—
41
77
n.d.
3b
CO2CH3
4
27d
CH3
33d
63
54
5
28e
CH3
34e
6
29f
CH3
35f
69
7
30g
31h
CH3
CH3
36g
37h
61
69
8c
a 5 mol% Cul. b n.d. = not determined. c Tetra-substituted furan 38h was also isolated.
Org. Biomol. Chem.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Organic & Biomolecular Chemistry
Paper
alkynylsilanes and diazoacetate towards the synthesis of poly-
substituted 1-silylcyclopropene compounds in good overall
yields. In particular, diazoacetate compounds displayed a wide
range of reactivity ranging from unreactive to facilitating an
unexpected regioselective tetra-substituted furan product by
i
means of a chemodivergent pathway. Finally, the PrCuCl-cata-
Scheme 3 Synthesis of a bioorthogonal chemical reporter precursor.
lyzed cyclopropenation of 1-TMS-2-propyne and ethyl diazoace-
tate is a highly effective method for the synthesis of a
bioorthogonal chemical reporter that is useful for imaging cel-
lular processes.
acetate 25b cleanly furnished cyclopropene 32b in substantially
higher overall isolated yields than previous reports (Table 4,
entries 1 and 2).12c,13 The acceptor-acceptor substituted diazo-
malonate compound 26c was completely unreactive in the pres-
ence of alkynylsilane 4 (Table 4, entry 3). Electron-deficient
donor–acceptor diazoacetates 27d and 28e afforded cyclopro-
pene compounds 33d and 34e in satisfactory isolated yields
(63% and 54%, respectively) (Table 4, entries 4 and 5). Cyclopro-
penes 35f and 36g were also isolated in good yields from
donor–acceptor diazoacetates 29f and 30g (69% and 61%,
respectively) (Table 4, entries 6 and 7). Interestingly, electron-
rich donor–acceptor diazoacetate 31h afforded tetra-substituted
cyclopropene 37h and a tetra-substituted furan 38h as a separ-
able mixture by flash chromatography in good overall yields
(Table 4, entry 9). To the best of our knowledge, this is the first
example of a donor–acceptor diazoacetate compound under-
Acknowledgements
This work was supported in part by the Rochester Institute of
Technology (RIT) FEAD grant and the RIT Office of the Vice
President of Research. B. A. M thanks the RIT Honor’s
program for summer financial support. T. N. thanks RIT SCMS
for the Daniel J. Pasto Undergraduate Cooperative Fellowship
award. Thank you to Dr William W. Brennessel and the X-ray
Crystallographic Facility in the Department of Chemistry at the
University of Rochester for structural analysis. Special thanks
to Dr Sandip Sur and the Nuclear Magnetic Resonance Spectro-
meter Facility in the Department of Chemistry at the University
of Rochester for NMR spectral analysis.
going
a
formal [3
+
2] cycloaddition to form
a tetra-
substituted furan.
A
two-dimensional [1H, 1H]-NOESY
spectrum was recorded to corroborate the structure of 38h. NOE
crosspeaks were observed between the TMS group and both the
(i) phenyl group and (ii) para-methoxy-substituted phenyl group
(see ESI†). It is plausible that the β-silicon hyperconjugation in
close proximity to the site of C–O bond formation is responsible
for the high regioselectivity observed.
References
1 P. v. R. Schleyer, J. E. Williams and K. R. Blanchard, J. Am.
Chem. Soc., 1970, 92, 2377.
2 (a) C. Song, J. Wang and Z. Xu, Org. Biomol. Chem., 2014,
12, 5802; (b) L. H. Phun, J. Aponte-Guzman and S. France,
Synlett, 2012, 2723; (c) M. Rubin and P. G. Ryabchuk, Chem.
Heterocycl. Compd., 2012, 48, 126; (d) Z.-B. Zhu, Y. Wei and
M. Shi, Chem. Soc. Rev., 2011, 40, 5534; (e) F. Miege,
C. Meyer and J. Cossy, Beilstein J. Org. Chem., 2011, 7, 717;
(f) M. Rubin, M. Rubina and V. Gevorgyan, Chem. Rev.,
2007, 107, 3117; (g) M. Rubin, M. Rubina and
V. Gevorgyan, Synthesis, 2006, 1221.
3 (a) A. R. A. Dulayymi, J. R. A. Dulayymi, M. S. Baird and
G. Koza, Russ. J. Org. Chem., 1997, 33, 798;
(b) K. B. Baucom and G. B. Butler, J. Org. Chem., 1972, 37,
1730; (c) M. S. Baird, H. H. Hussain and W. Nethercott,
J. Chem. Soc., Perkin Trans. 1, 1986, 1845; (d) W. M. Sherrill,
R. Kim and M. Rubin, Synthesis, 2009, 1477.
The real-time labelling of a biomolecule which contains a
reactive non-natural functional group with a molecular imaging
agent – often referred to as bioorthogonal chemistry – is among
the most essential tools used for imaging cellular processes
under physiological conditions.26 In recent years, cyclopropenyl-
containing compounds have emerged as an important class of
bioorthogonal moieties that are effectively incorporated in bio-
molecules and subsequently labeled via an inverse-demand
Diels–Alder cycloaddition reaction with a tetrazine fluorescent
tag.21 We applied our methodology towards the synthesis of a
frequently utilized cyclopropene starting material 39b and
observed the highest isolated yield (71%) reported to date from
1-TMS-propyne and ethyl diazoacetate (Scheme 3). In compari-
son to other previously reported transition metal-catalyzed pro-
cesses (Scheme 1, eqn (3)),15b–d,19 this strategy is a more
sustainable alternative for the synthesis 1-silylcyclopropenyl-
containing bioorthogonal ligands.
4 (a) N. Petiniot, A. J. Anciaux, A. F. Noels, A. J. Hubert and
P.
Teyssie,
Tetrahedron
Lett.,
1978,
1239;
(b) M. N. Protopopova, M. P. Doyle, P. Mueller and D. Ene,
J. Am. Chem. Soc., 1992, 114, 2755; (c) M. P. Doyle,
M. Protopopova, P. Muller, D. Ene and E. A. Shapiro, J. Am.
Chem. Soc., 1994, 116, 8492; (d) P. Muller and H. Imogai,
Tetrahedron: Asymmetry, 1998, 9, 4419; (e) H. M. L. Davies
and G. H. Lee, Org. Lett., 2004, 6, 1233; (f) L.-a. Liao,
F. Zhang, N. Yan, J. A. Golen and J. M. Fox, Tetrahedron,
2004, 60, 1803; (g) Y. Lou, M. Horikawa, R. A. Kloster,
Conclusions
Cu(I)–NHC salts are efficient catalysts for the direct transition
metal-catalyzed cyclopropenation of a wide range of internal
This journal is © The Royal Society of Chemistry 2015
Org. Biomol. Chem.

View Article Online
Paper
Organic & Biomolecular Chemistry
N. A. Hawryluk and E. J. Corey, J. Am. Chem. Soc., 2004, 126,
1316; (d) E. A. Shapiro, G. V. Lun’kova, A. O. Nefedov,
I. E. Dolgii and O. M. Nefedov, Izv. Akad. Nauk. SSSR, Ser.
Khim., 1981, 2535; (e) T. N. Wheeler and J. Ray, J. Org.
Chem., 1987, 52, 4875.
8916; (h) M. Rubin and V. Gevorgyan, Synthesis, 2004, 796;
(i) D. T. Nowlan III and D. A. Singleton, J. Am. Chem. Soc.,
2005, 127, 6190; ( j) Y. Lou, T. P. Remarchuk and E. J. Corey,
J. Am. Chem. Soc., 2005, 127, 14223; (k) S. Chuprakov and 16 J. Li, C. Sun, S. Demerzhan and D. Lee, J. Am. Chem. Soc.,
V. Gevorgyan, Org. Lett., 2007, 9, 4463; (l) J. F. Briones, 2011, 133, 12964.
J. Hansen, K. I. Hardcastle, J. Autschbach and 17 S. Chuprakov, D. A. Malyshev, A. Trofimov and
H. M. L. Davies, J. Am. Chem. Soc., 2010, 132, 17211; V. Gevorgyan, J. Am. Chem. Soc., 2007, 129, 14868.
(m) J. F. Briones, J. Hansen, K. I. Hardcastle, J. Autschbach 18 L. H. Phun, J. Aponte-Guzman and S. France, Angew.
and H. M. L. Davies, J. Am. Chem. Soc., 2010, 132, 17211; Chem., Int. Ed., 2012, 51, 3198.
(n) A. DeAngelis, O. Dmitrenko and J. M. Fox, J. Am. Chem. 19 M. K. Pallerla and J. M. Fox, Org. Lett., 2007, 9,
Soc., 2012, 134, 11035. 5625.
5 (a) P. J. Perez, M. Brookhart and J. L. Templeton, Organo- 20 J. T. Bauer, M. S. Hadfield and A.-L. Lee, Chem. Commun.,
metallics, 1993, 12, 261; (b) D.-J. Cho, S.-J. Jeon, H.-S. Kim, 2008, 6405.
C.-S. Cho, S.-C. Shim and T.-J. Kim, Tetrahedron: Asymmetry, 21 (a) D. M. Patterson and J. A. Prescher, Curr. Opin. Chem.
1999, 10, 3833; (c) M. Mar Diaz-Requejo and P. J. Perez,
J. Organomet. Chem., 2001, 617–618, 110; (d) H. Martinez-
Garcia, D. Morales, J. Perez, M. Puerto and D. Miguel,
Inorg. Chem., 2010, 49, 6974; (e) C. Martin, M. Sierra,
E. Alvarez, T. R. Belderrain and P. J. Perez, Dalton Trans.,
2012, 41, 5319.
6 (a) X. Cui, X. Xu, H. Lu, S. Zhu, L. Wojtas and X. P. Zhang,
J. Am. Chem. Soc., 2011, 133, 3304; (b) X. Cui, X. Xu,
L. Wojtas, M. M. Kim and X. P. Zhang, J. Am. Chem. Soc.,
2012, 134, 19981.
7 M. Uehara, H. Suematsu, Y. Yasutomi and T. Katsuki, J. Am.
Chem. Soc., 2011, 133, 170.
8 N. P. a. E. A. S. Marina, Russ. Chem. Rev., 1989, 58, 667.
9 J. F. Briones and H. M. L. Davies, Org. Lett., 2011, 13, 3984.
10 J. F. Briones and H. M. L. Davies, J. Am. Chem. Soc., 2012,
134, 11916.
11 M. M. Diaz-Requejo, M. A. Mairena, T. R. Belderrain,
M. C. Nicasio, S. Trofimenko and P. J. Perez, Chem.
Commun., 2001, 1804.
12 (a) M. K. Pallerla and J. M. Fox, Org. Lett., 2005, 7, 3593;
(b) D. W. Kohn and P. Chen, J. Am. Chem. Soc., 1993, 115,
2844; (c) P. Mueller and C. Graenicher, Helv. Chim. Acta,
1993, 76, 521.
Biol., 2015, 28, 141; (b) D. M. Patterson, L. A. Nazarova and
J. A. Prescher, ACS Chem. Biol., 2014, 9, 592;
(c) D. M. Patterson, K. A. Jones and J. A. Prescher, Mol.
BioSyst., 2014, 10, 1693; (d) D. N. Kamber, L. A. Nazarova,
Y. Liang, S. A. Lopez, D. M. Patterson, H.-W. Shih,
K. N. Houk and J. A. Prescher, J. Am. Chem. Soc., 2013, 135,
13680; (e) D. M. Patterson, L. A. Nazarova, B. Xie,
D. N. Kamber and J. A. Prescher, J. Am. Chem. Soc., 2012,
134, 18638.
22 (a) I. Zrinski and M. Eckert-Maksic, Synth. Commun., 2003,
33, 4071; (b) I. Zrinski, G. Gadanji and M. Eckert-Maksic,
New J. Chem., 2003, 27, 1270; (c) L.-a. Liao, N. Yan and
J. M. Fox, Org. Lett., 2004, 6, 4937; (d) E. A. F. Fordyce,
Y. Wang, T. Luebbers and H. W. Lam, Chem. Commun.,
2008, 1124.
23 A. K. Swenson, K. E. Higgins, M. G. Brewer,
W. W. Brennessel and M. G. Coleman, Org. Biomol. Chem.,
2012, 10, 7483.
24 (a) B. M. Trost and G. Dong, J. Am. Chem. Soc., 2006, 128,
6054; (b) R. E. Gawley and S. Narayan, Chem. Commun.,
2005, 5109; (c) M. R. Fructos, T. R. Belderrain,
M. C. Nicasio, S. P. Nolan, H. Kaur, M. M. Diaz-Requejo
and P. J. Perez, J. Am. Chem. Soc., 2004, 126, 10846.
13 (a) H.-P. Wu, D. H. Ess, S. Lanza, T. J. R. Weakley, 25 (a) M. P. Doyle, Chem. Rev., 1986, 86, 919; (b) M. P. Doyle,
K. N. Houk, K. K. Baldridge and M. M. Haley, Organometal-
lics, 2007, 26, 3957; (b) H. Neunhoeffer, R. Bopp and
W. Diehl, Liebigs Ann. Chem., 1993, 367.
M. A. McKervey and T. Ye, Modern Catalytic Methods for
Organic Synthesis with Diazo Compounds: From Cyclo-
propanes to Ylides, 1998, 652 pp.
14 G. Maier, M. Hoppe, H. P. Reisenauer and C. Krueger, 26 (a) C. P. Ramil and Q. Lin, Chem. Commun., 2013, 49,
Angew. Chem., Int. Ed. Engl., 1982, 94, 445.
11007; (b) M. F. Debets, J. C. M. van Hest and F. P. J.
T. Rutjes, Org. Biomol. Chem., 2013, 11, 6439; (c) K. Lang
and J. W. Chin, ACS Chem. Biol., 2014, 9, 16; (d) K. Lang
and J. W. Chin, Chem. Rev., 2014, 114, 4764; (e) P. Shieh
and C. R. Bertozzi, Org. Biomol. Chem., 2014, 12, 9307;
(f) M. Zheng, L. Zheng, P. Zhang, J. Li and Y. Zhang,
Molecules, 2015, 20, 3190.
15 (a) E. A. Shapiro, A. V. Kalinin, D. N. Platonov and
O. M. Nefedov, Izv. Akad. Nauk. Ser. Khim., 1993, 1248;
(b) E. A. Shapiro, G. V. Lun’kova, I. E. Dolgii and
O. M. Nefedov, Izv. Akad. Nauk. SSSR, Ser. Khim., 1984,
2529; (c) E. A. Shapiro, G. V. Lun’kova, I. E. Dolgii and
O. M. Nefedov, Izv. Akad. Nauk SSSR, Ser. Khim., 1981,
Org. Biomol. Chem.
This journal is © The Royal Society of Chemistry 2015