Br?nsted Acid Catalyzed Friedel–Crafts-Type Coupling and Dedinitrogenation Reactions of Vinyldiazo Compounds

Article abstract of DOI:10.1002/anie.202004328

The direct Friedel–Crafts-type coupling and dedinitrogenation reactions of vinyldiazo compounds with aromatic compounds using a metal-free strategy are described. This Br?nsted acid catalyzed method is efficient for the formation of α-diazo β-carbocations (vinyldiazonium ions), vinyl carbocations, and allylic or homoallylic carbocation species via vinyldiazo compounds. By choosing suitable nucleophilic reagents to selectively capture these intermediates, both trisubstituted α,β-unsaturated esters, β-indole-substituted diazo esters, and dienes are obtained with good to high yields and selectivity. Experimental insights implicate a reaction mechanism involving the selective protonation of vinyldiazo compounds and the subsequent release of dinitrogen to form vinyl cations that undergo intramolecular 1,3- and 1,4- hydride transfer processes as well as fragmentation.

Full text of DOI:10.1002/anie.202004328

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Accepted Article
Title: Brønsted Acid Catalyzed Friedel-Crafts-type Coupling and
Dedinitrogenation Reactions of Vinyldiazo Compounds
Authors: Michael P. Doyle, Haifeng Zheng, Kuiyong Dong, Daniel
Wherritt, and Hadi Arman
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Brønsted Acid Catalyzed Friedel-Crafts-type Coupling and
Dedinitrogenation Reactions of Vinyldiazo Compounds
Haifeng Zheng, Kuiyong Dong, Daniel Wherritt, Hadi Arman, Michael P. Doyle*
Abstract:
The
direct
Friedel-Crafts-type
coupling
and
and nine products.12 Inspired by these reports, we postulated that
a suitable Brønsted acid could undergo proton addition to a
vinyldiazo compound to produce a vinyldiazonium ion, which is
itself susceptible to nucleophilic trapping, that upon releasing
dinitrogen delivers the corresponding weakly coordinating counter
ion-stablized vinyl carbocation for subsequent transformations.
We have discovered that bis(trifluoromethanesulfonyl)imide
(HNTf2) serves as a uniquely efficient Brønsted acid that
selectively protonates the vinylogous position of vinyldiazo
compounds forming a vinyldiazonium ion. Further transformation
into vinyl and allylic or homoallylic carbocation intermediates
occurs via sequetial loss of dinitrogen and hydride transfer,
dedinitrogenation reactions of vinyldiazo compounds with aromatic
compounds using a metal-free strategy are described. This acid-
catalyzed methodology is efficient for the formation of α-diazo β-
carbocations (vinyldiazonium ions), vinyl carbocations, and allylic or
homoallylic carbocation species via vinyldiazo compounds. By
choosing suitable nucleophilic reagents to selectively capture these
intermediates, both trisubstituted α,β-unsaturated esters, β-indole-
substituted diazo esters, and dienes are obtained in good to high
yields and selectivities. Experimental insights implicate a reaction
mechanism involving the selective protonation of vinyldiazo
compounds and the subsequent release of dinitrogen to form vinyl
cations that undergo intramolecular 1,3- and 1,4- hydride transfer
processes as well as fragmentation.
realizing
catalytic
Friedel-Crafts-type
coupling
and
dedinitrogenation transformations. The strong acidity of triflimide,
as well as the low nucleophilicity and weak coordination of its
counter anion Tf2N−, allows this superacid to serve as an
exceptional catalyst in a wide range of organic reactions,[16] but
none have been reported with diazo compounds. In this metal free
strategy, both α,β-unsaturated esters, β-indole substituted diazo
esters, and dienes are obtained in good yields and selectivities
(Scheme 1c).
Vinyldiazo compounds are prominent building blocks for
organic synthesis.[1] Their dipolar nature makes them susceptible
to electrophilic addition, but when transformed to their carbenic
state, especially as metallocarbenes, the vinylcarbenes are
electrophiles (Scheme 1a, right),[2] and their role as electrophiles
has revealed a diversity of cycloaddition reactions, accessing
carbocyclic
and
heterocyclic
compounds
via
[3+n]-
transformations with rhodium(II),[3] copper(I),[4] and gold(I)[5]
catalysts. In contrast, vinyldiazo compounds are also effective
nucleophiles that undergo cycloaddition reactions with
electrophiles to produce increasingly complex structures,
dependent on the nature of the electrophiles,[6] and they have the
potential to offer complimentary processes to those of metal
carbenes. However, synthetically effective cationic addition
reactions with vinyldiazo compounds have not been explored
(Scheme 1a, left).
Although viable catalytic methods involving protonation of
diazo compounds to afford diazonium ions are well established,[7]
this strategy has not been applied to easily accessible and stable
vinyldiazo compounds. Vinyl carbocations[8] formed by loss of
dinitrogen are intriguing reactive intermediates that have gained
increasing attention in recent years,[9] and the carbene-like
reactivity of cyclic vinyl cations has been uncovered,[10-15]
revealing ring-expansion/contraction,12 inter- and intra-molecular
C-H insertion,[13,14] as well as fragmentation reactions (Scheme
1b).[15a] In the only previous example of an acyclic system that
generated
a
vinyldinyldiazonium ion, 1-(ethoxycarbonyl-
diazomethyl)-2-phenylisopropyl alcohol was treated with 150
mol% of BF3Et2O under various conditions to form between five
Scheme 1. Background and this work.
[a]
Dr. H. F. Zheng, K. Y. Dong, Dr. D. Wherritt, Dr. H. Arman, Prof. Dr.
M. P. Doyle
Phenylvinyldiazoacetate 1a and benzene 2a were selected
as model substrates to evaluate the title reaction. Commercially
available Brønsted acids, such as CH3COOH and H2SO4 were
initially employed as catalysts, but no cross-coupled products
were obtained (Table 1, entries 1 and 2). However, when
Department of Chemistry, The University of Texas at San Antonio
One UTSA Circle, San Antonio, TX 78249 (USA)
E-mail: michael.doyle@utsa.edu
Supporting information for this article is given via a link at the end of
the document.
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CF3COOH or TfOH were used to effect this transformation, 3-
phenyl vinyl diazoacetate 1a was slowly consumed, and,
surprisingly, α,β-unsaturated ester 3a was isolated (Table 1,
entries 3 and 4 ), albeit in low yield. There was no trace of product
(ethyl 2,3-diphenyl-2-butenoate) anticipated from direct reaction
with the vinyl cation. Futher optimization with different acids
demonstrated that superacid HNTf2, with the low nucleophilicity
and coordinating ability of its conjugate base (Tf2N−),[16] was the
most efficient catalyst; product 3a was obtained in 81% yield with
8:1 Z/E-selecticity (Table 1, entry 5). The Z/E stereoisomers could
be separated chromatographically, and Z-3a was obtained in 72%
isolated yield. Attempts to optimize the yield of 3a by decreasing
the temperature were unsuccessful (Table 1, entry 6) and
reducing the catalyst loading (Table 1, entry 7), while prolonging
the reaction time, did not provide full consumption of the 1a.
Table 1. Optimization of reaction conditions for coupling of 1a and 2a.[a]
the vinyldiazonium ion prior to its release of dinitrogen to form the
vinyl cation. The scope of this Friedel-Crafts coupling reaction
with indoles 4 (Scheme 3, top) showed that the 3-aryl substituent
of vinyldiazo compounds
1 bearing an electron-donating
substituent provided a higher yield than that with an electron-
withdrawing group (EWG) (5b versus 5c). Furthermore,
substituents at different positions of the phenyl ring (1e and 1f)
and the ester substituent 1g had a little influence on the reaction
(5d-5f). The β-alkyl substituted vinyldiazo compounds (R = Me,
Et, n-Pr; 1h-1j) showed higher reactivities than β-aryl substituted
substrates in this coupling reaction, and the catalyst loading could
be reduced to 2.5 mol% (5n-5p).
Scheme 2. Scope of the HNTf2-promoted Friedel-Crafts-type coupling of arenes
and vinyl diazo compounds.[a]
Entry[a]
1
2
3
4
5
HX (30 mol %)
CH3COOH
H2SO4
CF3COOH
TfOH
HNTf2
HNTf2
HNTf2
Conditions
rt, 12 h
rt, 12 h
rt, 12 h
rt, 12 h
rt, 2 h
Z/E[b]
-
-
4:1
4:1
8:1
8:1
8:1
Yield of Z-3a (%)[c]
-
-
20
23
72
42
56
6
0 oC, 12 h
rt, 12 h
7[d]
[a] Reactions were performed by adding 1a (0.2 mmol) to HX (30 mol%) in
benzene/CH2Cl2 solvent (v:v = 1:1, 2 mL). [b] Z/E ratio was determined by 1H
NMR analysis of the reaction mixture. [c] Yields of isolated Z-3a product. [d] 20
mol% HNTf2 catalyst loading.
With optimized conditions in hand, we examined the scope of
Friedel-Crafts-type coupling reactions of β-aryl substituted
vinyldiazo esters 1 with arenes 2 (Scheme 2). Both moderately
electron-withdrawing and electron-donating substituents on the
para-position of the phenyl ring of 1 were compatable with the
formation of α,β-unsaturated esters Z-3b-Z-3d in good yields and
selectivities. Furthermore, substituents at different positions of the
phenyl ring had little effect on the reaction (3e and 3f). Benzyl
ester 1g also underwent Friedel-Crafts coupling with benzene 2a
in good yield and selectivity without debenzylation. However,
analogous β-alkyl substituted vinyldiazo compounds did not
produce any of the desired coupling products (for details, see
Supporting Information), possibly due to the instability of these
vinyl carbocation intermediates. The substrate scope of arenes 2
for this Friedel-Crafts reaction was also explored (Scheme 2).
Symmetric mesitylene 2b and p-xylene 2c underwent this
reaction, and the corresponding products 3h and 3i were obtained
in good yields. Arenes 2d-2f were suitable substrates (3j-3m,
35%-61% yields, 5:1-8:1 Z/E selectivities), but their
regioselectivities were not remarkable (1:1-3:1).
Based on the successful coupling with arenes and vinyldiazo
compounds, we investigated their use in this metal-free strategy
with the more nucleophilic indoles. In a reaction performed at
room temperature with catalytic HNTf2 the β-indole substituted
diazo ester 5a was isolated in 68% yield, consistent with
nucleophilic trapping of a vinlyldiazonium ion. The absence of
these similar diazo compounds in reactions with arenes like
anisole with its strong electron-donating substituent suggests that
there is a threshold in nucleophilicity for substrates that can trap
[a] Reactions were performed by adding 1 (0.3 mmol) to HNTf2 (30 mol%) in
arene/CH2Cl2 solvent (v:v = 1:1, 3 mL), unless otherwise noted: Z/E ratio was
detected by crude 1H NMR spectroscopy; Yield was for the isolated Z product.
Both
electron-withdrawing
and
electron-donating
substituents on the indole ring produced the corresponding
products (5g-5k, 44%-70% yield) in good yields, the lowest yield
being due to decomposition of 5-methoxy-substituted indole 4c
with HNTf2. N-Benzyl substituted indole 4g was a suitable
substrate (5l, 66% yield), but the N-H substituted indole did not
form the coupling product (for details, see Supporting Information).
Furthermore, 1,2-dimethylindole 4m and pyrrole 4i underwent this
transformation smoothly. However, attempts with other
heterocyclic compounds, including furan, benzofuran and phenol,
were not successful.
The diazo esters formed from indoles and pyrroles by this
process have a quaternary carbon adjacent to the diazo carbon
in which all of the attachments are carbon. These compounds are
susceptible to 1,2-migration in transition metal catalyzed
processes,[1a] that opens a pathway to tetrasubstituted alkenes. [17]
The [Cu(CH3CN)4][BF4] catalyzed indole migration of 5n and 5q
to tetra-substituted alkenes 6n and 6q occur in excellent yields
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(Scheme 3, bottom). The structure of 6n was demonstrated by X-
ray diffraction of its derivative 7n (Scheme 3, bottom).[18]
Scheme 3. Scope of the HNTf2-promoted Friedel-Crafts-type coupling of
indoles and vinyl diazo compounds.[a]
Scheme 4. 1,3-Hydride transfer determined from labeling experiment.
Based on the experimental results for these reactions, we
propose in Figure 1 the probable mechanism of HNTf2 catalyzed
Friedel-Crafts-type coupling reactions of vinyldiazo compounds.
The reaction is initiated by protonation of vinyldiazo compounds 1
with HNTf2 to give the corresponding vinyldiazonium ion
intermediate int-I, which is captured by nucleophilic indoles and
pyrrole affording substituted diazo esters 5. In the absence of a
nucleophile suitable to trap the vinylydiazonium ion, β-aryl
substituted int-I releases dinitrogen either stepwise through the
vinyl carbocation (int-II) or synchroneously to form the allylic
carbocation int-III by 1,3-hydride transfer, which undergoes the
Friedel-Crafts alkylation of arenes.
Figure 1. Proposed mechanism for Friedel-Crafts-type coupling.
A different outcome occurred when γ-methyl substituted
vinyldiazo compound 8a was subjected to HNTf2 catalysis in the
absence of a nucleophile. From prior results with vinyl cations we
[a] Reactions were performed by adding HNTf2 (30 mol%) to 1 (0.3 mmol) and
4 (0.2 mmol) in CH2Cl2 solvent (4 mL) at 0 oC, unless otherwise noted: Isolated
yield after chromatography. [b] 2.5 mol% catalyst loading.
[13]
expected that an intramolecular carbene-like C-H insertion
might occur, possibly affording a cyclobutene derivative, but diene
9a was isolated in 84% yield with excellent Z-selectivity (Scheme
5). The same product was formed exclusively when the reaction
of 8a with Tf2NH was performed in benzene; no Friedel-Crafts
alkylation product was detected. These results suggested a
reaction process involving either or both allylic and homoallylic
carbocation intermediates. In addition, the substrate scope shows
that both moderately electron-withdrawing and electron-donating
substituents on the 4-position of phenyl ring of vinyldiazo
compound favor production of the corresponding dienes (9b-9f)
in good yields with excellent selectivities (Scheme 5). However,
β-alkyl (8g) and β-hydrogen (8h and 8i) substituted vinyldiazo
compounds were not suitable reactants for this transformation,
affording complex product mixtures; and treatment of
triisopropylsilyl (TIPS) protected enoldiazoacetate (8j) and
enoldiazoacetamide (8k) with HNTf2 only gave the desilyated
diazoketo compounds (for details, see Supporting Information).
To assess hydride transfer in the formation of dienes 9 from
vinydiazoesters 8 deuterium-labeled 8a-d1 and 8a-d3 were
prepared and subjected to treatment with Tf2NH. Compound 9a-
To better understand the mechanism of the Friedel-Crafts-
type coupling reactions we performed duterium-labeling studies
to follow the hydride-transfer reaction. Deuterium labeled
substrate 1a-d2 was prepared and treated with Tf2NH under the
standard reaction conditions (Scheme 4). Products 3a-2,4-d2 and
3a-4,4-d2, formed from 1a-d2 in a ratio of 3:7 (Scheme 5a), result
from selective protonation the vinylogous position of the
vinyldiazo compound by Tf2NH and subsequent 1,3-H/D transfer.
Since the methyl group formed by proton addition from Tf2NH
possesses two deuterium and one proton, the 3a-4,4-d2/3a-2,4-
d2 product ratio provides an estimate of the product isotope effect
(4.7).
d1 was the sole diene product formed from 8a-d1 and its
,
deuterium resided only at the γ-position, suggesting that 1,3-
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Scheme 6. 1,4-Hydride transfer and fragmentation determined from labelling
experiment.
hydride transfer is not involved in the formation of this product
(Scheme 6a). Treatment of 8a-d3 under the standard reaction
Scheme 5. Scope of the HNTf2-promoted dedinitrogenation of γ-methyl
substituted vinyldiazo compounds.[a]
The vinyl cation pathway to diene and cleavage products is
less certain than is that for Friedel-Crafts-type reactions.
Deuterium isotope studies point to 1,4-hydride transfer as being
the dominant route, but 1,3-hydride transfer or 1,4-hydride
transfer to the homoallylic cation (int-V) with subsequent 1,2-
hydride transfer to the allyl cation (int-VI) cannot be ruled out
(Figure 2). Trapping of int-VI by a phenol demonstrates that this
cationic intermediate is formed, even though the deuterium-
labeling experiment suggests that this intermediate is not formed
by direct 1,3-hydride transfer. The C-C bond cleavage reaction of
the vinyl cation that forms ethyl propiolate (10) may or may not
invole formation of an ethyl cation intermediate. Attempts to trap
this cation or its triflimide[9b] were unsuccessful.
[a] Reactions were performed by adding HNTf2 (20 mol%) to 1 (0.3 mmol) in
CH2Cl2 solvent (3 mL), unless otherwise noted; Isolated yield after
chromatography. [b] 10 mol% catalyst loading. [c] Cleavage product p-
MeC6H4CCCO2Et was obtained in 7% yield.
conditions formed 9a-d3, confirming 1,4-deuterium transfer, but
also formed 9a-d2, which in view of the outcome of reaction with
8a-d1 is not consistent with 1,3-hydride transfer. Relative to the
reaction with the undeuterated 8a, that with 8a-d3 underwent
diene formation in much lower yield (33% vs, 84%), but a C-C
bond cleavage product, ethyl 3-phenylpropiolate (10) was also
isolated (Scheme 6b) in a yield comparable to those of 9a-d3 and
9a-d2. Fragmentation products resulting in alkyne products from
vinyl cation intermediates have been well documented,[19] but this
is the first reported example that formally releases an alkyl
cation.[20] In efforts to trap chemical intermediates, a variety of
nucleophiles were added to the reaction mixture prior to treatment
with Tf2NH; as previously mentioned, no Friedel-Crafts product
was formed in the reaction conducted in benzene, but in the
presence of p-phenylphenol diene 9a, alkyne cleavage product
10, and the phenolic trapping product 11 were formed (Scheme
6c). Compound 11 is consistent with 1,3-hydride transfer or 1,2-
hydride transfer following initial 1,4-hydride transfer from the vinyl
cation. The ethyl ether of p-phenylphenol was detected by LC-MS,
but only in a trace amount.
Figure 2. Proposed mechanism for dedinitrogenation reaction.
In summary, we have realized Friedel-Crafts-type coupling
and dedinitrogenation reactions of vinyldiazo compounds via
Brønsted acid catalysis. Vinyldiazo compounds are the
precursors of α-diazo β-carbocations (vinyldiazonium ions) that,
upon extrusion of dinitrogen, form highly reactive acyclic vinyl
cations. These reactive intermediates were not trapped by
nucleophiles and, instead, rearranged to allylic or homoallylic
carbocationic species. With indoles as nucleophiles,
vinyldiazonium ion intermediates are captured, delivering β-indole
substituted diazo esters having an adjacent quaternary center in
good yields. Loss of dinitrogen to the putative vinyl cation then
enabled 1,3-hydride transfer to the more stable allyl cation that
underwent Friedel-Crafts reaction with arenes to form α,β-
unsaturated esters in good to high yields and selectivities. γ-
Methyl-substituted vinyldiazo compounds also formed vinyl
cations that underwent hydride transfer to reform the HNTf2
catalyst without being trapped by an arene. These results
demonstrate the intriguing reactivity of vinyldiazo compounds in
Brønsted acid catalysis and also provide
a fascinating
methodology for the selective synthesis of trisubstituted α,β-
unsaturated esters, β-indole substituted diazo esters, and dienes.
Further studies are ongoing to explore the full scope of cation
addition to the vinylogous position of vinyldiazo compounds that
form vinyldiazonium ions.
Acknowledgements
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Can. J. Chem. 1996, 74, 1369; d) D. J. Miller, C. J. Moody, C. N. Morfitt,
Aust. J. Chem. 1999, 52, 97; e) Y. Zhang, J. B. Wang, Chem. Commun.
2009, 5350; f) J. N. Johnston, H. Muchalski, T. L. Troyer, Angew. Chem.,
Int. Ed. 2010, 49, 2290; Angew. Chem. 2010, 122, 2340; g) C. W. Zhai,
D. Xing, C. C. Jing, J. Zhou, C. J. Wang, D. W. Wang, W. H. Hu, Org.
Lett. 2014, 16, 2934.
We are grateful to the National Science Foundation
(CHE−1763168) for their funding of this research. The NMR
spectrometer used in this research was supported by a grant from
the National Science Foundation (CHE−1625963) and funding for
the X-ray diffractometer was supported by CHE-1920057.
[8]
[9]
a) P. J. Stang, M. H. Rappoport, M. Hannack, and L. B. Subramanian,
Vinyl Cations, Academic Press, New York, 1979. b) T.Okuyama, Acc.
Chem. Res. 2002, 35, 12.
Keywords: trifluoromethanesulfonimide • vinyldiazo
compounds• Friedel-Crafts coupling • dedinitrogenation • vinyl
cation
a) M. Niggeman, S. Gao, Angew. Chem. Int. Ed. 2018, 57, 16942, Angew.
Chem. 2018, 130, 17186; b) S. Schroeder, C. Strauch, N. Gaelings, M.
Niggemann, Angew. Chem. Int. Ed. 2019, 58, 5119, Angew. Chem. 2019,
131, 5173. c) T. Okuyama, M. Fujita in “Recent Developments in
Carbocation and Onium Ion Chemistry”, K. L. Laali, Ed. ACS Symposium
Series, Vol. 965, Ch. 4, 2007.
[1]
a) M. P. Doyle, M. A. McKervey, T. Ye, Modern Catalytic Methods for
Organic Synthesis with Diazo Compounds: From Cyclopropanes to
Ylides, Wiley, New York, 1998; b) H. M. L. Davis, Y. J. Lian, Acc. Chem.
Res. 2012, 45, 923; c) A. Ford, H. Miel, A. Ring, C. N. Slattery, A. R.
Maguire, M. A. McKervey, Chem. Rev. 2015, 115, 9981; d) N. R.
Candeias, R. Paterna, P. M. P. Gois, Chem. Rev. 2016, 116, 2937; e) M.
Marinozzi, F. Pertusati, M. Serpi, Chem. Rev. 2016, 116, 13991; f) L. Liu,
J. Zhang, Chem. Soc. Rev. 2016, 45, 506.
[10] U. Biermann, R. Koch, J. O. Metzger, Angew. Chem. Int. Ed. 2006, 45,
3076; Angew. Chem. 2006, 118, 3146.
[11] F. Zhang, S. Das, A. J. Walkinshaw, A. Casitas, M. Taylor, M. G. Suero,
M. J. Gaunt, J. Am. Chem. Soc. 2014, 136, 8851.
[12] R. Pellicciari, B. Natalini, B. M. Sadeghpour, M. Marinozzi, J. P. Snyder,
B. L. Williamson, J. T. Kuethe, A. Padwa, J. Am. Chem. Soc. 1996, 118,
1.
[2]
[3]
a) R. A. Moss, M. P. Doyle, Contemporary Carbene Chemistry, Wiley,
New York, 2013, pp 404-451; b) Q. Q. Chen, Y. M. Deng, M. Lankelma,
M. P. Doyle, Chem. Soc. Rev. 2017, 46, 5425.
[13] S. E. Cleary, M. J. Hensinger, M. Brewer, Chem. Sci. 2017, 8, 6810.
[14] a) B. Shao, A. L. Bagdasarian, S. Popov, H. M. Nelson, Science 2017,
355, 1403; b) S. Popov, B. Shao, A. L. Bagdasarian, T. R. Benton, L. Zou,
Z. Yang, K. N. Houk, H. M. Nelson, Science 2018, 361, 381; c) B.
Wigman, S. Popov, A. L. Bagdasarian, B. Shao, T. R. Benton, C. G.
Williama, S. P. Fisher, V. Lavallo, K. N. Houk, H. M. Nelson, J. Am. Chem.
Soc. 2019, 141, 9140.
a) X. C. Wang, Q. M. Abrahams, P. Y. Zavalij, M. P. Doyle, Angew. Chem.
Int. Ed. 2012, 51, 5907; Angew. Chem. 2012, 124, 6009; b) X. C. Xu, P.
Y. Zavalij, M. P. Doyle, J. Am. Chem. Soc. 2013, 135, 12439; c) C. M.
Qin, H. M. L. Davies, J. Am. Chem. Soc. 2013, 135, 14516.
a) J. Barluenga, L. Riesgo, L. A. López, E. Rubio, M. Tomάs, Angew.
Chem. Int. Ed. 2009, 48, 7569; Angew. Chem. 2012, 121, 7705; b) E.
López, L. A. López, Angew. Chem. Int. Ed. 2017, 56, 5121; Angew.
Chem. 2017, 129, 5203.
[4]
[15] a) C. Draghici, M. Brewer, J. Am. Chem. Soc. 2008, 130, 3766; b) S. E.
Cleary, X. Li, L. C. Yang, K. N. Houk, X. Hong, M. Brewer, J. Am. Chem.
Soc. 2019, 141, 3558.
[5]
[6]
a) V. V. Pagar, A. M. Jadhav, R. S. Liu, J. Am. Chem. Soc. 2011, 133,
20728; b) V. V. Pagar, R. S. Liu, Angew. Chem. Int. Ed. 2015, 54, 4923;
Angew. Chem. 2015, 127, 5005.
[16] W. X. Zhao, J. W. Sun, Chem. Rev. 2018, 118, 10349.
[17] A. B. Flynn, W. W. Ogilvie, Chem. Rev. 2007, 107, 4698.
[18] CCDC 1984611 (8n).
a) M. P. Doyle; M. Yan; W. Hu; L. S. Gronenberg J. Am. Chem. Soc.
2003, 125, 4692. b) F. J. Sarabia, Q. K. Li, E. M. Ferreira, Angew. Chem.
Int. Ed. 2018, 57, 11015; Angew. Chem. 2018, 130, 11181. c) A. S. K.
Raj, R. S. Liu, Angew. Chem. Int. Ed. 2019, 58, 10980; Angew. Chem.
2019, 131, 11096.
[19] J. Yang, T. T. Hoang, G. B. Dudley, Org. Chem. Front. 2019, 6, 2560.
[20] Reassessment of results presented in Scheme 5 showed that the alkyne
cleavage product was present in most reaction mixtures, albeit in small
amounts, but in 7% yield from reaction with 9b.
[7]
a) A. B. Smith III, R. K. Dieter, Tetrahedron 1981, 37, 2407; b) L. I. Smith,
Chem. Rev. 1938, 23, 193. c) E. A. Jefferson, A. J. Kresge, S. W. Paine,
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10.1002/anie.202004328
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
H. F. Zheng, K. Y. Dong, D. Wherritt, H.
Arman, M. P. Doyle
Page No. – Page No.
Brønsted Acid Catalyzed Friedel-
Crafts-type Coupling and
Dedinitrogenation Reactions of
Vinyldiazo Compounds
Brønsted acid catalysis provides direct Friedel-Crafts-type coupling and
dedinitrogenation reactions of vinyldiazo compounds. In this acid-catalyzed
methodology, vinyldiazo compounds serve as the precursor of vinyldiazonium ions,
vinyl, and high reactive allylic and homoallylic carbocation species. By choosing
suitable nucleophilic reagents to capture these intermediates, both trisubstituted α,β-
unsaturated esters, β-indole substituted diazo esters and dienes are obtained in good
yields and selectivities.
This article is protected by copyright. All rights reserved.