Cyclic Diaryl λ3-Bromanes as Original Aryne Precursors

Article abstract of DOI:10.1002/anie.202103625

Despite the widespread application of hypervalent iodines, the corresponding λ³-bromanes are less explored. Herein we report a general, safe, and high-yielding strategy to access cyclic diaryl λ³-bromanes. These unique compounds feature reactivity that is appealing and complementary to that of λ³-iodanes, generating arynes under mild reaction conditions and in the presence of a weak base. Accordingly, formal meta-selective transition-metal-free C–O and C–N couplings may be achieved. Mechanistic studies unambiguously support the aryne generation mechanism.

Full text of DOI:10.1002/anie.202103625

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Accepted Article
Title: Cyclic Diaryl l3-Bromanes as Original Aryne Precursors
Authors: Matteo Lanzi, Quentin Dherbassy, and Joanna Wencel-
Delord
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l3
Cyclic Diaryl -Bromanes as Original Aryne Precursors.
Dr. Matteo Lanzi,[a] Dr. Quentin Dherbassy,[a] Dr. Joanna Wencel-Delord*[a]
[a]
Dr. Matteo Lanzi, Dr. Quentin Dherbassy, Dr. Joanna Wencel-Delord
Laboratoire d’Innovation Moléculaire et Applications (UMR CNRS 7042)
Université de Strasbourg/Université de Haute Alsace, ECPM
25 rue Becquerel, 67087, Strasbourg, France
E-mail: wenceldelord@unistra.fr
Supporting information for this article is given via a link at the end of the document.
Abstract: Despite the widespread application of hypervalent iodines,
the corresponding l3-bromanes are less explored. Herein we report a
general, safe, and high-yielding strategy to access cyclic diaryl l3-
bromanes. These unique compounds feature appealing and
complementary reactivity to l3-iodanes, generating arynes under mild
reaction conditions and in a presence of a weak base. Accordingly,
formal meta-selective transition metal-free C-O and C-N couplings
may be achieved. The mechanistic studies unambiguously support
the aryne generation mechanism.
bromanes. Furthermore, these bromanes feature an original
reactivity, undergoing metal-free C-O and C-N couplings. At room
temperature and in the presence of a weak base, these diaryl λ3-
bromanes act as aryne-synthons, providing reactivity not
attainable with the corresponding diaryl λ3-iodanes,15 thus
illustrating disparity between these hypervalent compounds. This
reactivity, implying formal C-H functionalization, occurring under
mild reaction conditions and obviating need of fluorinating agents,
is arguably amongst the most appealing and general routes
furnishing arynes.16
The chemistry of hypervalent compounds occupies a central role
in modern organic synthesis.1 In particular, the iodine atom has
become the most established and widely applied within the λ3-
and λ5- hypervalent molecules, serving as oxidants, electrophiles,
catalysts, or radical initiators.2 Among others, the commercially
available diaryliodonium salts3 and diacetoxy-iodobenzene4 are
key modern tools in arylation and oxidation reactions.
Scheme 1. Hypervalent iodines and bromines reactivities
In marked contrast, the chemistry of hypervalent bromine
compounds has attracted considerably less attention,5 although
their greater electronegativity and higher ionization potential6
might confer increased and/or complementary reactivity (Scheme
7
1). Accordingly, superior nucleofugality of λ3-bromanes was
8
witnessed in the arylation
reactions while sulfonylimino-λ3-
bromanes turned out to be potent aminating agents, mediating
transition metal-free C(sp3)-H activation of simple alkanes. 9 Very
recently, cyclic hypervalent λ3-bromide has been also engaged as
10
Lewis-acid organo-catalyst for Michael reactions. Despite the
unique intrinsic properties of l3-bromanes, the lack of efficient
protocols to prepare them has limited the development of this
research field. While thermal decomposition of diazonium salts in
presence of aryl bromide furnished λ3-bromane as early as
1952,11 harsh reaction conditions and low yields hampered further
progress. More recently, a strategy based on ligand-exchange
12
reactions using BrF3
as the key Br(III)-precursor has been
designed but the extreme corrosivity and toxicity of this gaseous
and poorly available reagent render this pathway unsuitable for
general applications.
Expanding our interest in hypervalent compounds,13 and
considering the potential of biaryl λ3-iodanes14 as prominent
substrates in transition metal-catalyzed cross coupling reactions,
we have embarked on the exploration of the synthesis and
chemical behavior of rare yet fascinating cyclic biaryl λ3-bromanes.
We hypothesized that their increased reactivity might render them
appealing in transition metal-free transformations, thus paving the
way towards complementary reactivity to the λ3-iodane congeners.
Here, we report the efficient, versatile and safe synthesis,
isolation, and characterization of a large panel of cyclic diaryl λ3-
While the rare literature known protocols to access diaryl λ3-
bromanes are low-yielding, require several steps and harsh
reaction conditions,10,11 we surmised that 2a might be afforded
1
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10.1002/anie.202103625
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COMMUNICATION
efficiently from 1a via a single oxidation step while using finely
selected oxidant and Brønsted acid (Figure 2). Rewardingly,
while reacting, under mild conditions, 1a with tBuONO and
MeSO3H, the desired compound 2a-OMs was isolated in 93%
yield. In marked contrast to the literature, the use of organic
oxidant and solvent, together with only a small excess of the acid,
turned out to be essential for the high-yielding reaction outcome.
First, compatibility of this reaction with various acids was
confirmed, thus delivering 2a with different counter anions in
excellent to moderate yields (93% to 29%). Subsequently, the
reaction was extended towards an array of differently substituted
1,1’-bromo(amino)biphenyl 1b-p, providing a collection of cyclic
diaryl l3-bromanes. Electron-donating groups, such as methyl (2b,
2i, 2k) and methoxy (2f), were well tolerated at different positions
affording the products in excellent to quantitative yields (71 –
96%). Halogen-substituted starting materials were efficiently
converted into the corresponding bromanes (2d, 2e, 2g, 2j, and
2l) in high yields (64 – 72%). The presence of electron-
withdrawing group such as methyl ester (2c, 86%) did not alter
the reaction outcome while the CF3 group (2h, 46%) significantly
reduced the yield. The reaction protocol is also amenable to
assemble dissymmetric cyclic diaryl l3-bromanes (2m, 2n, 2o and
2p).
The gram-scale synthesis furnished 2a-OMs in 74% yield via
simple precipitation from diethyl ether.
17
Moreover, air and
moisture stability of 2a-OMs was further confirmed, as the storage
of this compound over several months in the refrigerator altered
neither its purity nor its reactivity. The X-ray analysis of 2a-OMs
reveals a tricyclic planar structure with a dihedral angle of -
1.04(4)°.
Figure 1. X-ray structure of 2a-OMs
To compare the reactivity of this new class of hypervalent
compounds with their iodinated congeners and drawing
inspiration from Gu and Zhao works on metal-catalyzed
19
functionalization of hypervalent l3-iodanes,
2a-OMs was
reacted with a carboxylic acid 3A, in a presence of Cu-catalyst
and Cs2CO3 base (Table 1). The C-O bond formation occurred
smoothly, but instead of the expected, as in the case of l3-iodanes,
ortho-substituted product 4aA, meta-functionalization took place
selectively, furnishing 5aA in 96% yield. This observation clearly
shows a divergent reactivity between the l3-iodanes and l3-
bromanes compounds.
The carbon-bromine bonds (C1-Br1 and C12-Br1) are slightly
longer, (1.928(2) Å and 1.932(2) Å respectively) with respect to
the bromobenzene (1.850 Å) consistently with a weak and
therefore more reactive bond. Moreover, the angle between C1-
Br1-C12 is 86.93(9)° reflects a T-shape structure typical for three-
centered–four-electron (3c-4e) bonding.10,16,18
Table 1. Selected optimization reactions.
The generality of this protocol delivering diaryl l3-bromanes was
further surveyed (Figure 2).
O
O
R
3A (1 equiv)
Cs2CO3 (3 equiv)
O
O
R
Br
Br
CH2Cl2, 16 h, r.t.
R = 3-F C6H4
Figure 2. Scope of Cyclic Diaryl l3-bromanes
Br+
MsO-
2a-OMs
4aA
5aA
NH2
tBuONO (2 equiv)
HX (2 equiv)
Ar1
Br+
2a-p
Ar1
Br
Deviation from the standard conditions[a]
Yield of 5aA[b]
Ar2
Ar2
0 °C, 1 h then 65 °C, 1 h
CH3CN (0.1M)
X-
10 mol% Cu(OTf)2
None/with Cs2CO3 99.994% Pure
No Cs2CO3
96%
1a-p
95%
R
-
-
Br+
X-
Br+
I-OTf or I-OMs instead of 2a-OMs
MsO-
2a-OMs, X = MsO-, 93%
2a-OTs, X = TsO-, 93%
2a-OTf, X = TfO-, 59%
2a-Cl, X = Cl-, 49%
2b, R = Me, 84%
2c, R = COOMe, 86%
2d, R = Cl, 68%
[a] Conditions: 0.1 mmol of hypervalent reagents (2a-OMs, I-OTf, I-OMs), 0.083
mmol of 3A and 0.3 mmol of Cs2CO3 in 1 mL of CH2Cl2 at r.t. for 16 h. [b] Isolated
yields.
X-ray structure of 2b
CCDC 2063899
2a-BF4, X = BF4-, 71%
2a-PF6, X = PF6-, 70%
2e, R = Br, 72%
2a-CF3CO2, X = CF3CO2-, 29%
To validate our hypothesis that 2a might be an amenable
substrate for metal-free transformations, coupling of 2a-OMs and
3A was performed in absence of the Cu-catalyst and at room
temperature, delivering 5aA in almost quantitative yield. The use
of Cs2CO3 is essential to trigger the reaction, while high purity
base (99.994%) confirmed the metal-free conditions. Remarkably,
hypervalent iodines I-OTf and I-OMs are totally unreactive under
such metal-free protocol.15 Following these preliminary results,
the generality of this transformation was explored (Figure 3). The
mildness of the reaction conditions warrants its compatibility with
a diversity of carboxylic acid coupling partners, including 3-
halogenated benzoic acids, delivering 5aA and 5aB in high yields
(95%). The strong electron-withdrawing CF3 group slightly
R
R
Br+
MsO-
Br+
MsO-
2f, R = OMe, 85%
2g, R = Cl, 64%
2h, R = CF3, 46%
2i, R = Me, 71%
2j, R = Cl, 72%
X-ray structure of 2g
CCDC 2063900
R
R’
Cl
MeO
Br+
Br+
Br+
MsO-
MsO-
MsO-
R
Me
2k, R = R’ = Me, 96%
2l, R = R’ = Cl, 65%
2m, R = Me, R’ = Cl, 61%
2p, 61%
2n, R = Cl, 73%
2o, R = COOMe, 82%
2
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10.1002/anie.202103625
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impacted the yield of 5aC (78%) while halogenated and
perfluorinated benzoic acids performed well furnishing 5aD-E.
Sterically hindered substrates were also found amenable
is also suitable for the synthesis of trisubstituted anilines and
alkyl-anilines. Notably, the increased steric hindrance of the
coupling partners allows superior regiocontrol. The 2,4,6-
providing 5aG, 5aH and 5aI in good yields (up to 94%). In addition, trimethyl-N-methyl aniline 6I afforded 8aI as a single regioisomer
the simple acetic acid 3J successfully delivered 5aJ in almost
quantitative yield (95%). Our protocol also allows functionalization
of complex substrates including trans-b-ionylidene acetic acid 3K
and menthyloxy acetic acid 3L furnishing decorated products 5aK
and 5aL.
in 82% yield, while tert-butylamine 6J and adamantylamine 6K
furnished selectively 8aJ and 8aK in 85% and 47% yields.
The unexpected meta-selectivity observed for these C-O and C-
N couplings, combined with their metal-free character, clearly
suggests a reaction pathway implying aryne intermediates.
Encouraged by the potential of the cyclic diaryl l3-bromanes in
metal-free C-O couplings, we then focused on extending this
reactivity towards amination reaction (Figure 4). Rewardingly, 2a-
OMs reacted smoothly with sterically hindered mesitylaniline 6A,
delivering the expected products 8aA and 7aA in excellent total
yield (89%). The use of amines as nucleophiles seems to be less
Figure 4. Scope of C-N bond formation
R’
R
6A-K (1.5 equiv)
N
NH
’R
R
R'
N
Cs2CO3 ( 3 equiv)
CH2Cl2,16 h, r.t.
Br
Br
Br+
MsO
R
selective; although the meta-product is still favored,
a
considerable amount of ortho-functionalization was also formed.
20 However, both regioisomers were isolated separately, providing
pure 8a and 7a in respectively 69 and 20% yield.
2a-OMs
7aA-aH
8aA-aK
iPr
Me
H
N
H
N
Br
Br
Me
iPr
Me
Figure 3. Scope of C-O bond formation
89%
X-ray structure of 8aA
CCDC 2063901
68%
(8aA, 69% + 7aA, 20%)
(8aB, 49% + 7aB, 19%)
O
O
R
3A-L (1 equiv)
R = 2-Me, 76%
(8aC, 64% + 7aC, 12%)
R = 2-Me, 5-Me, 87%
(8aD, 49% + 7aD, 38%)
R = 2-Me, 3-Cl, 99%
(8aE, 59% + 7aE, 40%)
R = 2-Cl, 6-Me, 71%
(8aF, 59% + 7aF, 12%)
R = 2-Br, 4-F, 75%c
(8aG, 48% + 7aG, 27%)
OH
R
O
Cs2CO3 ( 3 equiv)
CH2Cl2,16 h, r.t.
Br
H
N
H
N
Br+
MsO
R
Br
Br
2a-OMs
5aA-J
F
Cl
O
F5
O
O
O
75%
R
(8aH, 52% + 7aH, 23%)
R
O
O
Me
Me
N
H
H
N
Br
Br
Br
Me
N
Me
Me
Me
Br
Br
Br
Me
5aA, R = F, 95%
5aB, R = Cl, 95%
5aC, R = CF3, 78%
5aD, R = 3-Cl, 86%
5aE, R = 4-Br, 82%
5aF, 88%
Me
O
R
8aK, 47%
8aI, 82%
X-Ray strucure
CCDC 2063902
8aJ, 85%
Me
O
Me
O
O
O
O
Br
Me
Br
Br
In accordance with multiple experimental21 and DFT22 models,
steric and electronic effects induce the meta- nucleophilic attack
with respect to the more sterically congested and less stabilized
ortho- functionalization. This selectivity trend is clearly reflected in
our coupling reactions, with the generation of the major meta-
substituted compounds. Accordingly, interesting reactivity
patterns might be expected while exploring the reactivity of the
dissymmetrical cyclic diaryl l3-bromanes (Figure 5). Not
surprisingly, the substrate 2i undergoes highly selective
functionalization on one aromatic unit, delivering the meta-
substituted products 5iA and 8iI in good to moderate yields (67%
and 41% respectively). In clear contrast, the presence of chloro-
substituents at 4-position of the symmetric substrates 2l
completely alters the selectivity pattern and the ortho-
functionalized products 4lA and 7lA are afforded in high yields
(68%). Herein, the electronic withdrawing inductive effect of the
Cl-substituent outweighs the steric hindrance. The presence of
Cl-atom on the aromatic ring of 2d improved its reactivity, the
aryne formation occurs selectively on the Cl-substituted aromatic
ring thus delivering a single product 4da and 7dA out of four
possible regioisomers. Finally, the reaction between 2n and
glacial acetic acid 3J provided quantitatively 4nJ.
5aG, 75%
5aH, R = 2-OMe, 85%
5aI, R = 2,5-Me, 94%
5aJ, 95%
Me
Me
Me
Me
O
O
O
O
Me
Me
O
Br
Me
Br
5aK, 50%
5aL, 54%
In analogy to the previous coupling, no reaction was observed
while using l3-iodanes. Cs2CO3 and DCM remained the optimal
base and solvent. Although C-N bond couplings are generally
sensitive to steric hindrance, under this mild protocol encumbered
anilines such as 2,4,6-trimethylaniline 6A and 2,6-
diisopropylaniline 6B were found suitable, supplying the desired
products (8aA + 7aA and 8aB + 7aB) in good yields (89%, 69%
respectively). Moreover, o-toluidine derivatives as 6C and 6D
reacted smoothly and the presence of Cl-substituents (6E, 6F)
does not influence the efficiency of the reaction. The fluoro-
substituted anilines were successfully converted to the desired
products providing densely decorated anilines. This C-N coupling
3
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10.1002/anie.202103625
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COMMUNICATION
Figure 5. Selectivity with substituted Cyclic Diaryl l3-Bromanes
1.63 for -Br(Ph)BF4) account for the b-elimination in a presence
of a weak base. 23
Figure 6. Mechanistic Investigations
Ar2
3A
Nu
Ar2
or
Cs2CO3 (3 equiv)
Br
Ar1
3J
or
Br+
MsO
(a)
CH2Cl2, 16 h, r.t.
Ar1
6A
3A
or
5aA
or
2h-m
4/5 or 7/8
1 equiv of TEMPO
Cs2CO3 (3 equiv)
Br+
MsO-
Cl
CH2Cl2, 16 h, r.t.
F
Cl
6A
8aA
2a-OMs
O
O
O
O
Conditions
with 3A
Yields of
5aA
Conditions
with 6A
Yields of
8aA
Br
O
O
Me
Br
Me
Br
Me
Standard
Standard
78%
78%
63%
62%
F
with TEMPO
with TEMPO
R
(b)
4nJ, 99%
4lA, R = Cl, 68%
4dA, R = H 99%
5iA, 67%
O
CD3
O
D<10%
Cl
Cs2CO3 (3 equiv)
Me
N
Br
Me
Me
Me
H
CD3COOD
Cl
+
Br+
CH2Cl2, 16 h, r.t.
N
MsO-
Me
[D]4-3J
Me
Me
Me
Br
5iJ, 79%
D98%
Br
Me
2i
Me
Me
Me
N
H
Br
(c)
Me
D
D98%
D
D
D
CH3COOH
Cl
O
8iI, 41%
(< 10% of 7iI)
CD3
7dA, 67%
68%
3J
or
D98%
Br
Cs2CO3 (3 equiv)
CH2Cl2, 16 h, r.t.
O
D
(8lA:7lA, 25:75)
+
Br+
MsO-
CD3COOD
Me
Me
with 3J; [D]4-5iJ, 95%, 40% D
with [D]4-3J, [D]4-5iJ, 90%, 80% D
To complete this study, experimental mechanistic investigations
were undertaken. The radical-type mechanistic scenario was
ruled out as the addition of one equivalent of a radical scavenger,
namely TEMPO, did not alter the reaction outcome either in
presence of aniline 6A or carboxylic acid 3A (Figure 6a).
[D]4-3J
[D]4-2i
D
(d)
O
D98%
CD3
D
D
D98%
O
CD3
O
D<10%
D
Subsequently, studies involving deuterated substrates have been
conducted. The reaction between the l3-bromane 2i and the [D]4-
3J provided the meta- functionalized product 5iJ in good yield with
a low deuterium incorporation at the ortho- position (Figure 6b).
Even such a small D-incorporation supports the generation of a
carbanion intermediate during the reaction, which is either
protonated or trapped by deuterated carboxylic acid. The
reactivity of the partially deuterated [D]4-2i was surveyed and the
product [D]4-5iJ was obtained by the reaction with 3J and [D]4-3J
(Figure 6c). The formation of aryne and subsequent reaction with
the carboxylic acid provided significant deuterium incorporation at
the ortho-position (up to 80%). The reaction with 3J indicates that
this deuteration arises from the D-transfer between the substrate
[D]4-2i and the product [D]4-5iJ, while not surprising even higher
deuteration ratio was observed while omitting any proton source
in the reaction mixture (reaction with [D]4-3J). This observation
suggests a possible “autocatalytic aryne generation” (Scheme 2).
Moreover, when [D]4-2a, the substrate bearing two reactive sites,
potential to undergo aryne formation either via C-H or C-D
cleavage, was reacted with CD3CO2D, two compounds [D]4-5aJa
and [D]4-5aJb (corresponding to the functionalization of the
Br
as above
D98%
Br
O
D98%
Br+
D<10%
MsO-
D98%
D98%
[D]4-2a
D98%
[D]4-5aJa
7:3
76%
[D]4-5aJb
Notably, strong lithium bases are usually required to generate
arynes via deprotonative C-H approach from the
monofunctionalized precursors24 and the nucleofugality of l3-
iodanes seems inadequate as no reaction was observed while
using these more common hypervalent compounds. The
subsequent meta- selective nucleophilic attack onto the benzyne
intermediate A forms the new C-O bond and generates the
carbanion intermediate B. Considering the strong reactivity of B
and based on the deuteration experiments (Figure 6c), the
autocatalytic process may be expected, implying the attack of B
on the new molecule of the hypervalent bromine resulting in the
protonation of B and concomitant generation of the aryne
intermediate A. However, a partial protonation of B either from the
carboxylic acid and/or from the hydrogen carbonate conjugate
Brønsted acid cannot be excluded.
protonated or deuterated aromatic unit) were afforded (Figure 6d). In conclusion, we report herein the first simple, versatile, safe and
The products ratio of 7:3 suggest favored functionalization of the
H4-aromatic unit and therefore this aryne generation features KIE
of 2.3.
Based on these investigations, a plausible mechanism for the C-
O coupling is proposed (Scheme 2). Initially, base-mediated
deprotonation of 2 furnishes the first benzyne intermediate A.
Remarkably, the unusual nucleofugality and the strong electron-
withdrawing ability of trivalent bromide (Hammet constant σI =
scalable protocol for the synthesis of cyclic diaryl l3-bromanes.
The study of the reactivity of these bromanes highlights their
unique behavior and thus a set of mild reaction conditions for the
generation of benzyne was established. A carbonate-mediated
arylation of carboxylic acids and anilines was achieved delivering
a family of decorated bromo-biaryl compounds. This study
constitutes a key step toward the development of the chemistry of
hypervalent bromines.
4
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10.1002/anie.202103625
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COMMUNICATION
Scheme 2. A plausible reaction mechanism for the C-O bond formation
[8]
[9]
(a) Grushin, V. V.; Kantor, M. M.; Tolstaya, T. P.; Shcherbina, T. M., Russ
Chem Bull 1984, 33, 2130–2135. (b) Lubinkowski, J. J.; McEwen, W. E.,
Tetrahedron Letters 1972, 13, 4817–4820.
(a) Ochiai, M.; Miyamoto, K.; Kaneaki, T.; Hayashi, S.; Nakanishi, W.
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Md. M.; Ochiai, M., Org. Biomol. Chem. 2015, 13, 2129–2133.
O
H
H
Br
R
O
[10] Y. Yoshida, S. Ishikawa, T. Mino, M. Sakamoto, Chem. Commun. 2021,
57, 2519–2522.
2
3
2-
CO3
Aryne generation under
mild conditions
2-
CO3
[11] Sandin, R. B.; Hay, A. S., J. Am. Chem. Soc. 1952, 74, 274–275.
[12] (a) Nesmeyanov, A. N.; Vanchikov, A. N.; Lisichkina, I. N.; Lazarev, V.
V.; Tolstaya, T. P., Dokl. Akad. Nauk SSSR, 1980, 255, 1136 – 1140. (b)
Nesmeyanov, A. N.; Vanchikov, A. N.; Lisichkina, I. N.; Grushin, V. V.;
Tolstaya, T. P., Dokl. Akad. Nauk SSSR, 1980, 255, 1386 – 1389. (c)
Nesmeyanov, A. N.; Vanchikov, A. N.; Lisichkina, I. N.; Khruscheva, N.
S.; Tolstaya, T. P., Dokl. Akad. Nauk SSSR, 1980, 254, 652 – 656.
[13] (a) Frey, J.; Malekafzali, A.; Delso, I.; Choppin, S.; Colobert, F.; Wencel-
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J.; Jerhaoui, S.; Choppin, S.; Wencel-Delord, J.; Colobert, F., ACS Catal.
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Br
O
Br
-
HCO3
O
R
O
H
R
O
A
5
2-
CO3
Possible
Autocatalytic
process
Selective
functionalization
-
HCO3
Br
O
H
O
R
[14] (a) Grushin, V. V., Chem. Soc. Rev. 2000, 29 (5), 315–324. (b)
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Acknowledgements
We thank the CNRS (Centre National de la Recherche
Scientifique), the “Ministere de l’Education Nationale et de la
Recherche“) France for financial support. M.L. is very grateful to
CNRS (Centre National de la Recherche Scientifique) for the
postodoctoral felowship (CNRS Emergence@INC), Q.D.
acknowledges the “Ministere de l’Education Nationale et de la
Recherche“, France for a doctoral grant. We are also very grateful
to Dr. Lydia Karmazin, Dr. Corinne Bailly and Dr. Nathalie Gruber
for single crystal X-ray diffraction analysis.
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10.1002/anie.202103625
Angewandte Chemie International Edition
COMMUNICATION
Diaryl ꢀ3-bromanes are rare and unexplored hypervalent compounds. Efficient and mild protocol affords now a large panel of these
hypervalent compounds, featuring complimentary reactivity to the corresponding diaryl ꢀ3-iodanes. Due to their high reactivity, metal-
free meta-selective C-O and C-N coupling occurs through the in situ aryne generation.
6
This article is protected by copyright. All rights reserved.