Synthesis of 1-(2-Aminovinyl)indoles and 1,3′-Biindoles by Reaction of 2,2-Diaryl-Substituted 2 H-Azirines with α-Imino Rh(II) Carbenoids

Article abstract of DOI:10.1021/acs.joc.8b03205

An effective and operationally simple method for the preparation of 1-(2-(sulfonamido)vinyl)indoles (SAV-indoles) by the Rh(II)-catalyzed reaction of 2,2-diaryl-2H-azirines with 1-sulfonyl-1,2,3-triazoles has been developed. This method enables the stereo

Full text of DOI:10.1021/acs.joc.8b03205

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Featured Article
Synthesis of 1-(2-Aminovinyl)indoles and 1,3'-Biindoles by Reaction
of 2,2-Diaryl-Substituted 2H-Azirines with #-Imino Rh(II) Carbenoids
Adel R. Khaidarov, Nikolai V. Rostovskii, Andrey A. Zolotarev,
Alexander F. Khlebnikov, and Mikhail Sergeevich Novikov
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b03205 • Publication Date (Web): 27 Jan 2019
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Synthesis of 1-(2-Aminovinyl)indoles and 1,3'-Biindoles by Reaction of 2,2-
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Diaryl-Substituted 2H-Azirines with α‑Imino Rh(II) Carbenoids
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Adel R. Khaidarov,1 Nikolai V. Rostovskii,1 Andrey A. Zolotarev,2 Alexander F.
Khlebnikov,1 Mikhail S. Novikov1*
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1
St. Petersburg State University, Institute of Chemistry, 7/9 Universitetskaya nab., St.
Petersburg 199034, Russia
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St. Petersburg State University, Institute of Earth Sciences, 7/9 Universitetskaya nab., St.
Petersburg 199034, Russia
*E-mail: m.novikov@spbu.ru
Graphical abstract
ABSTRACT: An effective and operationally simple method for the preparation of 1-(2-
(sulfonamido)vinyl)indoles (SAV-indoles) by the Rh(II)-catalyzed reaction of 2,2-diaryl-2H-
azirines with 1-sulfonyl-1,2,3-triazoles has been developed. This method enables the
stereoselective synthesis of a variety of 1,2,3-trisubstituted indoles having a Z configuration of
the (1-aryl-2-(sulfonamido)vinyl) substituent. The reaction mechanism, supported by DFT
calculations, involves the formation of 1,4-diazahexa-1,3,5-trienes, which rapidly cyclize to 2,2-
diaryl-1-sulfonyl-1,2-dihydropyrazines. These compounds can be isolated at an early stage of the
reaction, but under prolonged heating they isomerize into 7aH-indolium ylides, followed by a
barrierless 1,5-prototropic shift to SAV-indoles. The developed methodology was also applied to
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the preparation of 1,3'-biindoles from 2,2-diaryl-2H-azirines using 3-diazoindolin-2-imines
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instead of 1-sulfonyl-1,2,3-triazoles.
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INTRODUCTION
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The indole core is a widespread structural unit found in bioactive natural molecules1 and
synthetic drugs.2 For example, some triptans such as Sumatriptan and Naratriptan which are
approved drugs used for the treatment of migraines and cluster headaches, comprise an indole
core and a sulfonamide moiety.3 Sulfonamide functional groups have proved to be important
structural motifs in drug discovery, and introduction of these groups often improves
pharmacological properties.4 In view of the interest for medicinal chemistry, the development of
methods for the synthesis of new indole derivatives, especially those having sulfonamide moiety,
is of great importance. In addition to the sulfonylation of heteroatomic substrates, an alternative
approach to the sulfonamido-substituted compounds makes use of 1-sulfonyl-1,2,3-triazoles 1,5
which allow the incorporation of the (RSO2)NHC=C fragment into a heterocyclic system6 or
insertion of the 2-(R-sulfonamido)vinyl (SAV) moiety into the CH bond of
aromatics/heteroaromatics,7 the CB bond of boronic acids,8 the OH bond of alcohols and
carboxylic acids and the NH bond of primary and secondary amides (Scheme 1, reaction 1).9
The latter reaction was expanded to the insertion into the NH bond of carbazoles to form 1-(2-
sulfonamidovinyl)carbazoles (Scheme 1, reaction 1), which were used as intermediates in the
two step synthesis of indole-carbazole assemblies.10 These reactions proceed via the generation
of rhodium(II) α-iminocarbenoids followed by their formal insertion into the X-H bond (X = O,
N). In a search for effective approaches to new sulfonamide-modified indole derivatives we
attempted to apply this methodology for the preparation of 1-(2-(sulfonamido)vinyl)-substituted
indoles (SAV-indoles) 3. To our surprise 2,3-disubstituted NH-indoles proved to be inactive
toward rhodium(II) carbenoids derived from 1-tosyl-1,2,3-triazole and various rhodium
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carboxylates (Scheme 1, reaction 3). Most likely this is due to steric hindrances created by
substituents in the 2 and 3 position of the indole system to the attack by the carbenoid.
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Scheme 1. Triazoles 1 in the Synthesis of 2-(R-sulfonamido)vinyl-substituted Compounds
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In search for an alternative approach to indoles 3, we found that the use of substrates with
lower steric requirements, 2H-azirines 2, allows the assembly of SAV-indoles to be carried out
in a domino mode after a carbenoid-mediated sulfonamidovinylation of the azirine nitrogen. In
this work, a method for the preparation of SAV-indoles 3 by Rh2(OAc)4-catalyzed reaction of 1-
sulfonyl-1,2,3-triazoles with 2,2-diaryl-2H-azirines and mechanistic details of this domino
process are described. In addition, the developed method was applied to the synthesis of 1,3'-
biindoles using diazoindolimines as a source of rhodium carbenoids.
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RESULTS AND DISCUSSION
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Synthesis of 1-(2-(sulfonamido)vinyl)indoles (SAV-indoles). The idea to drastically change the
scheme of the assemblage of the SAV-indole system was inspired by the previously found
unusual reactivity of 4,4-diphenyl-2-azabutadienes 5 with two electron-withdrawing substituents
at the C=N bond, which can be prepared from azirines 2 and diazo compounds 4 (Scheme 2).11
Compounds 5 were found to easily undergo an unusual pseudopericyclic cyclization to indole
derivatives 6a. We assumed that such a scheme could work in the synthesis of SAV-indoles 3, if
azirines 2 and 1-sulfonyl-1,2,3-triazoles 1 would be used as starting materials (Scheme 2). 1,4-
Diazahexatrienes 7, which are formed in the first stage, could be transformed to the desired
indoles 3 via a 1,5-cyclization and subsequent 1,5-prototropic shift.
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Scheme 2. Rh(II)-Catalyzed Azirine Ring Expansion to Indoles
The feasibility of 1,5-cyclization of azapolyene 7 is the point of challenge in the scheme,
because it is known that а) 2-azadienes having only one electron-withdrawing substituent do not
afford indoles 6b,11 and b) 1-sulfonyl-1,4-diazahexa-1,3,5-trienes are very prone to undergo a
1,6-cyclization to give 1,2-dihydropyrazine derivatives.12 Indeed, the reactions of 2H-azirine 2a
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with triazoles 1a,b in boiling toluene in the presence of Rh2(OAc)4 gave 1,2-dihydropyrazines
8a,b, which were isolated by column chromatography in 71 and 51% yields, respectively
(Scheme 3). 1-Tosyl-1,2,3-triazole 1b reacted with azirine 2b in a similar manner to afford
dihydropyrazine 8c. It was found that the yields of compounds 8ac decrease under longer
heating due to their transformation into another product. A pure sample of 8a when heated under
reflux in toluene for 5 h, was completely consumed, providing, to our delight, the desired
(aminovinyl)indole 3a in 52% yield (Scheme 3). Isomerization of dihydropyrazine 8a was
completely stereoselective, affording exclusively Z stereoisomer of 3a.
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Scheme 3. Formation of 1,2-Dihydropyrazines and (Aminovinyl)indole
Inspired by this result we tried to perform the synthesis of indoles 3 from azirines 2 and
triazoles 1 under Rh(II) catalysis in «one-pot» fashion, without isolation of the intermediate
dihydropyrazines 8.
Optimization of the reaction conditions for the "one-pot" synthesis of indole 3c was carried
using the reaction of azirine 2b with triazole 1b (Table 1). The first step, the preparation of
dihydropyrazine 8c, was carried out until full consumption of the azirine was achieved. This
required the addition of 1.1 equiv. of triazole 1b and heating in toluene under reflux for 30 min.
After this the reaction mixture was refluxed until the dihydropyrazine had been completely
consumed (ca. 1.5 h). The reaction was monitored by TLC (8c: Rf = 0.7, 3c: Rf = 0.4, eluent
benzene–EtOAc, 100 : 1).
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Table 1. Optimization of Conditions for the One-Pot Synthesis of Indole 3c
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entry toluene, mL catalyst
yield of 3c, %a
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Rh2(OAc)4 (3 mol %)
Rh2(OAc)4 (5 mol %)
Rh2(OAc)4 (5 mol %)
Rh2(OAc)4 (5 mol %)
Rh2(Piv)4 (3 mol %)
Rh2(tfa)4 (3 mol %)
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a Isolated yields. b After azirine consumption the reaction mixture (1.5 mL) was
diluted to 5 mL. c 1.3 equiv. of triazole 1b was used.
In all cases where Rh2(OAc)4 was used as the catalyst (entries 1–3), the product was
obtained in good yield (70–73%). It was found that the maximum yield of indole 3c (77%) was
achieved using 5 mol % of Rh2(OAc)4 and conducting the first stage in a concentrated solution,
and the second one in a diluted solution (entry 4). When Rh2(Piv)4 was used as a catalyst, a
noticeable tarring of the reaction mixture with the formation of several side products was
observed. In the presence of Rh2(tfa)4, the triazole did not react with the azirine at all.
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Table 2. Scope of Azirines 2 and Triazoles 1 in the Synthesis of Indoles 3
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Reaction conditions: azirine (0.12 mmol), triazole (1.1–1.6 equiv), Rh2(OAc)4 (5 mol %), reflux
in toluene (1.5 mL) (1st stage); 3.5 mL of toluene was added, reflux in toluene (2nd stage).
A series of one-pot reactions was then carried out, using variously substituted starting
compounds, in order to assess the effect of substituents on the reaction course and the yield of
the target product (Table 2). All reactions were monitored by TLC and in all cases an
intermediate dihydropyrazine was detected. The first stage, the formation of 1,2-
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dihydropyrazine, was complete in all cases within 2030 min. The differences in the overall
reaction times (Table 2) originate from the second stage, i.e. isomerization of 1,2-
dihydropyrazine to indole. The presence of an acceptor substituent on the phenyl ring of the
triazole (R4) led to a marked increase in the time of the second stage (compounds 3g–i). The
opposite situation was observed when an acceptor substituent (p-NO2) was present in the
phenylsulfonyl group of the triazole (compound 3m). The highest yields of indoles were
obtained in the reactions of triazoles bearing an acceptor-substituted phenyl ring at the C4 atom
(R4) (compounds 3g–i). Generally, azirines with a phenyl group at the C3 position gave higher
yields of indoles than azirines with a methyl group at the same position. For example, whereas
the reactions of triazoles 1a and 1b with 3-phenylazirine 2b gave indoles 3c and 3n in 77% and
61% yields respectively, the analogous reactions with the 3-methyl-substituted azirine 2a
afforded indoles 3a,b in only 37% and 52% yields. Note that the conversion of the 3-methyl-
substituted dihydropyrazines into the corresponding indoles was two times slower compared to
the phenyl-substituted analogue. A strong tarring of the reaction mixture was also observed.
Probably this tarring is a reason for the lower yields of indoles 3a,b. Symmetrical substitution in
the phenyl groups at the C2 atom of the azirine led to a slight increase in the yield of the
corresponding indole 3d (59%). Because of the poor solubility of the acetamido-substituted
triazole 1h even in boiling toluene, its reaction was carried out in 1,2-dichloroethane at 110 °C.
Under these conditions indole 3k was synthesized in 58% yield. X-ray diffraction analysis of
indoles 3g and 3i confirmed that the double bond in the eneamide fragment has a Z configuration
(Figures S1, S2).13
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The result of the reaction of triphenylazirine (2b) with triazole 1k bearing a 4-
methoxyphenyl substituent proved to be rather unexpected (Scheme 4). The formation of the 1,2-
dihydropyrazine was not observed by TLC from the very beginning of the reaction. The main
product proved to be 3H-pyrrole 9a (42% yield), whereas indole 3o was isolated in only 9%
yield. Additional experiments have shown that pyrrole 9a does not transform into indole 3o even
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at higher temperatures. This result gave ground to suggest that the triazoles with donor aryl
substituents at the C4 atom are inapplicable for the preparation of indoles 3. However, the
analogous reaction of triazole 1k with methyl-substituted azirine 2a gave the corresponding
indole 3p exclusively (Scheme 4).
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Scheme 4. Reaction of Triazole 1k with Azirines 2a,b
Next, the reactions of triazole 1b with 2H-azirines 2d,e, possessing two various aryl
substituents at the C2 atom, were carried out. These reactions gave mixtures of isomeric indoles
inseparable by column chromatography (Scheme 5). Such a weak donating substituent as a
methyl group on one of the phenyl rings of azirine does not affect regioselectivity of the
cyclization (ratio of indoles 3q and 3q' is ca. 1 : 1). A different result was obtained in the
reaction of triazole 1b with an azirine having a strong donor substituent (R = p-MeO) in the
phenyl ring: cyclization onto the methoxy-substituted phenyl ring was preferable and indoles
3r,r' were obtained in a 4 : 1 ratio with a total yield of 70%.
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Scheme 5. Reactions of Triazoles 1a,b with Unsymmetrical Azirines 2df
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Azirine 2f, bearing a CO2Me group instead of a phenyl substituent at the C2 position, was
also tested in the reaction with triazole 1a (Scheme 5). Under the standard conditions it gave
dihydropyrazine 8s in 85% yield. However, further heating of 8s under reflux in toluene for 20 h
did not lead to any products (only tarring of the reaction mixture was observed). The reaction at
higher temperature (refluxing in o-xylene for 2 h) resulted in complete consumption of
dihydropyrazine 8s. The main product was not SAV-indole, but the aromatic pyrazine 10. We
assume that this result is due to weak ability of dihydropyrazine 8s to undergo ring opening.
Theoretical Calculations. According to the described experimental results, the Rh(II)-
catalyzed reaction of 2,2-diarylazirines 2 with triazoles 1 can afford three types of products:
dihydropyrazines 8, indoles 3 and 3Н-pyrroles 9. The proposed reaction mechanism involves the
formation of the key intermediate, 1,4-diazahexatriene 7, resulting from an attack of the triazole-
derived rhodium carbenoid 11 on the nitrogen of azirine 2, followed by ring opening of the
formed ylide complex 12 (Scheme 6). The formation of end products 8, 3 and 9 proceeds via
three different types of cyclization of diazatriene 7 (routes a, b and c). The 1,6--cyclization of
1,4-diazahexa-1,3,5-triene intermediates into 1,2-dihydropyrazines (route a)12
and 1,5-
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cyclization into pyrrole derivatives (routes c1 or c2)12c–e,14 were earlier postulated in the reactions
of 1-sulfonyl-1,2,3-triazoles with 2,3-disubstituted 2H-azirines. Isomerization of 1,4-diazahexa-
1,3,5-trienes 7 to 7aH-indolium ylide 13 (route b) as a key step on the route to indoles 3 is a new
transformation, which was not previously observed for diazapolyenes. We failed to detect 1,4-
diazahexatrienes 7 by TLC and NMR monitoring of the above described reactions, and so it was
suggested that these species are short-living reactive intermediates. In this connection, quantum-
chemical calculations of cyclization reactions (routes a, b, c) for a series of 1,4-diazahexa-1,3,5-
trienes 7 were indispensable to support the proposed reaction mechanism. We performed DFT
calculations (WB97XD/cc-pvtz, PCM, toluene) for four 1,4-diazahexatrienes 7a,n,t,u in order to
answer two questions: can compounds 3, 8 and 9 be formed according to the general mechanism
depicted in Scheme 6, and what are the structural prerequisites for the formation of a pyrrole-
type byproduct 9?
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Scheme 6. Mechanism for the Formation of Compounds 3, 8, 9
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Three routes of cyclization were considered, namely 1,6-cyclization to 1,2-dihydropyrazines
(TS114), 1,5-cyclization onto the phenyl ring leading to indole (TS214) and 1,5-exo-trig
cyclization to pyrrole derivatives (TS314) for four diazahexatrienes 7a,n,t,u, differently
substituted in positions 3 and 5 (Fig. 1). In all cases, the 1,5-cyclization of diazatriene 7 to 7aH-
indolium ylide (E‡ 21.926.4 kcal/mol, blue lines) is not kinetically favorable when compared
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with both cyclization to the dihydropyrazine (E‡ 17.720.0 kcal/mol, black lines) and 1,5-exo-
trig cyclization to the pyrrole derivative (E‡ 21.423.0 kcal/mol, red lines). It was found that
the prototropic shift in 7aH-indolium ylide 13 (not shown in Fig. 1AD) with the formation of
indole 3 proceeds irreversibly and without an activation barrier in all four cases. The barriers for
the 1,6-cyclization of diazatrienes 7a,n (TS11, TS12) are significantly lower than those for the
other cyclizations, this is in accordance with the experimentally observed rapid formation of
dihydropyrazines from azirines 2 and 4-phenyl-substituted triazoles. 1,2-Dihydropyrazines
8a,n,t,u are more stable than the 1,4-diazahexatrienes by ca. 611 kcal/mol depending on the
substitution pattern. The barriers for ring opening of dihydropyrazines 8a,n,t,u are in the range
of ca. 2630 kcal/mol, which is in good agreement with the rather harsh reaction conditions
experimentally used for the transformation of pyrazine 8a into indole 3a (Scheme 3).
The introduction of an electron-donating p-methoxy-group into the C3-aryl substituent of
the diazatriene (Fig. 1C, 1D) causes a slight increase of the barrier for the indole formation
probably due to resonance destabilization of the anion center at the ylide carbon atom in TS23
and TS24. At the same time, this substituent lowers the energy of the betaine-like transition state
(TS33 TS34) due to the stabilization of the endocyclic cation center. As a result, transition states
,
TS14 and TS34 become close in energy, and in this case 1,5-exo-trig cyclization begins to
compete successfully with 1,6-cyclization.
Changing the phenyl substituent at С5 of the diazatrienes for methyl leads to a decrease in
the barrier for the cyclization to indole by a value of 23 kcal/mol probably due to the enhancing
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stabilization of the cation center at the C2 atom of the indole ring in TS21 and TS23 (Fig. 1A,
1C). The phenyl ring at C2 of the indole system in TS22 and TS24 is arranged at a dihedral angle
of 49 to the plane of the indole and this is not favorable for resonance stabilization of the cation
center.
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The calculations predict that the exo-trig cyclization of diazatrienes 7a,n,t leads to a one-
stage formation of azirinopyrroles 14a,n,t (Fig. 1A1C), which are thermodynamically more
stable than the initial diazatrienes 7a,n,t, but significantly less stable than dihydropyrazines
8a,n,t. The energy barriers for the formation of azirinopyrroles 14a,n,t are higher by 5.3, 4.6 and
3.0 kcal/mol respectively than those for the cyclization to 1,2-dihydropyrazines 8a,n,t. That is
why the reactions, conducted under short-term heating, afford only a dihydropyrazine in the
complete absence of an azirinopyrrole. The energy profile of the exo-trig cyclization for
diazatriene 7u (Fig. 1D) dramatically differs from the previous cases. The presence of p-
methoxyphenyl and phenyl groups in 3 and 5 positions of 7u leads to an effective stabilization of
the endocyclic cation center in TS34 and this results in the appearance of a new intermediate on
the PES, betaine 15u (Fig. 1D). The high degree of conjugation of both the aryl rings with the
azaallyl-cationic system of the pyrroline fragment in transition state TS34 relates to rather small
dihedral angles between the planes of the aryl rings and the pyrroline ring (8.9 for p-MeOC6H4
and 16.1 for Ph). Most likely it is the formation of betaine intermediate 15u, capable of
undergoing intermolecular prototropic shifts to 3H-pyrrole 9, that is the prerequisite for the
formation of 3H-pyrrole 9.
Thus, according to the calculations the formation of indoles 3 under long-term heating is due
to their much higher thermodynamic stability in comparison with 1,2-dihydropyrazines 8 and
azirinopyrroles 14. The formation of the latter compounds is reversible under these conditions.
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C
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Figure 1. Relative energies (in kcal/mol, 383 K, PCM model for toluene) of compounds
3a,n,t,u, 7a,n,t,u, 8a,n,t,u, 14a,n,t, 15u and the transition states TS11−4−TS31−4 computed at the
DFT WB97XD/cc-pvtz level.
Synthesis of 1,3'-biindoles. -(o-Bromophenyl) enamines are known to be good
precursors of indole derivatives in the copper-catalyzed Ullmann reaction.7b,10,15 We decided to
expand this reaction to 1,3'-biindoles, for which only a few examples of synthesis are known.
These include the reaction of 1-hydroxyindoles with large excess of indole in 85% formic acid16
and the Ullmann reaction of 4,5,6-trimethoxyindole with 3-iodo-1-methyl-6-methoxyindole.17 2'-
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Nitro-1,3'-biindole was obtained in 29% yield by the reaction of 2-nitro-1-(phenylsulfonyl)indole
with indole in the presence of NaH.18 In this work, indole 3j, which was synthesized from o-
bromophenyl-substituted triazole 1g (Table 2), was tested in the Ullmann reaction as a new type
of substrate for the preparation of a 1,3'-biindole derivative. Indole 3j was treated with CuI in the
presence of potassium phosphate and DMEDA in toluene at 75 C to give N-tosylated biindole
16 in 82% yield (Scheme 7).
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Scheme 7. Synthesis of Biindole 16 by the Ullmann Reaction
A rather different approach to 1,3'-biindoles is based on the use of indole-based α-
iminocarbenoids 18 in the reaction with 2,2-diarylazirines 2 (Scheme 8). Carbenoids 18, which
can be easily generated from diazo compounds 17 under Rh(II) catalysis, have been successfully
used in recent years for the preparation of various indole-containing compounds.19 Herein we
present a first example of the application of diazoindolin-2-imines to the one-step synthesis of
1,3'-biindole derivatives. Refluxing a solution of azirine 2b, diazo compound 17a and Rh2(OAc)4
(5 mol%) in toluene for 25 min afforded 1,3'-biindole 21a in 76% yield (Scheme 8).
Analogously, biindoles 21b,c were obtained from C5-substituted diazoindolinimines 17b,c in
good yields. Notably, neither intermediate 1,2-dihydropyrazines nor 1,4-diazatrienes 19ac were
detected in these reactions. Nevertheless, there is every reason to believe that the reaction
includes pseudopericyclic 1,5-electrocyclization of intermediate diazatriene 19ac to form ylide
20ac and subsequent prototropic shift. The structure of biindole 21a was confirmed by X-ray
diffraction analysis (Figure S3).13
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Scheme 8. Synthesis of 1,3'-Biindoles from 2H-azirines and Diazoindolin-2-imines
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CONCLUSION
An effective method for the preparation of 1-(2-(sulfonamido)vinyl))indoles by the Rh(II)-
catalyzed reaction of 1-sulfonyl-1,2,3-triazoles with 2,2-diaryl-2H-azirines has been developed.
This method enables the stereoselective synthesis of a variety of 1,2,3-trisubstituted indoles
having Z configuration of the (1-aryl-2-(sulfonamido)vinyl) substituent. According to the DFT
calculations the reaction proceeds via the formation of 1,4-diazahexa-1,3,5-trienes, which rapidly
cyclize to 2,2-diaryl-1-sulfonyl-1,2-dihydropyrazines. The latter were detected experimentally
and isolated in some cases. Under prolonged heating the 1,2-dihydropyrazines open up to 1,4-
diaza-1,3,5-trienes, which undergo 1,5-cyclization to 7aH-indolium ylides, followed by a
barrierless 1,5-prototropic shift to indole derivatives. Along with minor amounts of the indole, a
3H-pyrrole can be formed when the diazatriene intermediate has two electron-donating aryl
groups in positions 3 and 5. The developed methodology was also applied to the preparation of
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1,3'-biindoles from 2,2-diaryl-2H-azirines using 3-diazoindolin-2-imines instead of 1-sulfonyl-
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1,2,3-triazoles.
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EXPERIMENTAL SECTION
General Methods. Melting points were determined on a melting point apparatus and are
1
uncorrected. H (400 MHz) and 13C (100 MHz) NMR spectra were recorded in solvents
indicated below. Chemical shifts (δ) are reported in parts per million downfield from
tetramethylsilane. High-resolution mass spectra were recorded on an HRMS-ESI-QTOF
instrument, electrospray ionization, positive mode. Thin-layer chromatography (TLC) was
conducted on aluminum sheets precoated with SiO2 ALUGRAM SIL G/UV254. Column
chromatography was performed on silica gel 60 M (0.04−0.063 mm). 1,2-Dichloroethane and
dichloromethane were washed with concentrated H2SO4 and water, distilled from P2O5, and
stored over anhydrous K2CO3. Toluene was distilled and stored over sodium metal.
1,2,3-Triazoles 1a–d,k,20 1e,21 1f,12e 1g,9 1h,22 1i,j23 and diazo compounds 17a,c19a are
known compounds, which were prepared by the reported procedures.
Computational Methods. The calculations were performed by using the Gaussian 09 suite
of quantum chemical programs.24 Geometry optimizations and vibrational frequency analysis of
stationary points and transition states were performed at the DFT B3LYP/B3LYP/6-31G(d) level
of theory using the PCM solvation model for toluene. Intrinsic reaction coordinate calculations
confirmed that the optimized transition states connect to their respective reactants and products.
To evaluate the energies for stationary points and transition states, the single point calculations
of optimized structures were carried out at the DFT wB97XD/cc-pvtz level using the PCM
model for toluene.
Synthesis of Azirines 2a,c,d (General Procedure).25 To a solution of the corresponding
1,1-diarylpropan-2-one26 (1 equiv) in EtOH (1.1 M) were added anhydrous NaOAc (1.2 equiv),
1,1-dimethylhydrazine (2 equiv) and 3 drops of glacial acetic acid. The resulting mixture was
refluxed for 36 h, diluted with water and extracted with Et2O. The organic layer was washed
with water, brine and dried over Na2SO4. The solvent was removed in vacuo, and the crude
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hydrazone of 1,1-diarylpropan-2-one obtained was dissolved in MeI (2.4 M). The reaction
mixture was stirred at 40 °C for 4 h. After this, Et2O was added and the precipitated N,N,N-
trimethyl-N’-(1,1-diarylprop-2-ylidene)hydrazonium iodide was filtered off. Hydrazonium
iodide (1 equiv) was dissolved in DMSO (0.4 M) and NaH (1.1 equiv, 60% in oil) was added in
one portion. The reaction mixture was stirred at room temperature for 2 h, then poured onto ice
and extracted with hexane. The organic layer was washed with water and brine, dried over
Na2SO4, and the solvent was removed in vacuo. The residue was purified by column
chromatography on silica gel (eluent: hexane–Et2O, 5:1).
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3-Methyl-2,2-di(4-methylphenyl)-2H-azirine (2c). Light-yellow oil (0.35 g, 24%). H
NMR (CDCl3, δ): 7.16–7.10 (m, 8H), 2.58 (s, 3H), 2.36 (s, 6H). 13C{1H} NМR (CDCl3, δ):
167.7, 139.1, 136.5, 129.0, 127.8, 42.4, 21.1, 12.9. HRMS−ESI [M + Na]+ calcd for
C17H17NNa+, 258.1253; found, 258.1253.
3-Methyl-2-(4-methylphenyl)-2-phenyl-2H-azirine (2d). Light-yellow oil (0.38 g, 32%).
1H NMR (CDCl3, δ): 7.34–7.18 (m, 5H), 7.16–7.08 (m, 4H), 2.58 (s, 3H), 2.35 (s, 3H). C{1H}
13
NМR (CDCl3, δ): 167.6, 142.1, 138.9, 136.7, 129.0, 128.3, 127.9 (2C), 126.9, 42.6, 21.1, 12.9.
HRMS−ESI [M + Na]+ calcd for C16H15NNa+, 244.1097; found, 244.1097.
Synthesis of Azirines 2b,e (General Procedure).27 Hydroxylamine hydrochloride (2 equiv)
and pyridine (4 equiv) were added to a solution of 2-aryl-1,2-diphenylethanone28 (1 equiv) in
EtOH (0.6 M). The resulting mixture was refluxed for 10 h, then poured into water and extracted
with CH2Cl2. The organic layer was washed with water, brine and dried over Na2SO4. The
solvent was removed in vacuo, and the residue was purified by chromatography on silica gel
(eluent: hexane–EtOAc, 6:1). To 0.3 M solution of obtained 2-aryl-1,2-diphenylethanone oxime
(1 equiv) in anhydrous CH2Cl2 DBU (1.1 equiv) and tosyl chloride (1 equiv) were added. The
resulting mixture was stirred at room temperature until the oxime was disappeared (TLC, eluent:
hexane–EtOAc, 5:1). Then a second portion of DBU (1.5 equiv) was added to the reaction
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mixture and stirring was continued for 2 h. The solvent was removed in vacuo and the product
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was purified by flash chromatography on silica gel (eluent: hexane–EtOAc, 20:1).
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2-(4-Methoxyphenyl)-2,3-diphenyl-2H-azirine (2e). Light-yellow solid (0.4 g, 25%). H
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NMR (CDCl3, δ): 8.02–7.96 (m, 2H), 7.63–7.55 (m, 3H), 7.36–7.27 (m, 7H), 6.90–6.85 (m, 2H),
3.82 (s, 3H). 13C{1H} NМR (CDCl3, δ): 167.0, 158.8, 141.9, 133.7, 133.1, 129.7, 129.4,
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129.3, 128.3, 128.0, 127.0, 124.2, 113.8, 55.3, 44.4. HRMS−ESI [M + Na]+ calcd for
C21H17NNaO+, 322.1202; found, 322.1202.
(Z)-N-(3-Diazo-1,5-dimethylindolin-2-ylidene)-4-methylbenzenesulfonamide (17b). This
compound was obtained according to the reported procedure19a in 1.26 g (62% yield). mp 186–
188 °C (EtOAc, dec.). 1H NMR (CDCl3, δ): 7.92–7.88 (m, 2H), 7.33–7.28 (m, 2H), 7.12–6.97
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(m, 3H), 3.46 (s, 3H), 2.44 (s, 3H), 2.43 (s, 3H). C{1H} NМR (CDCl3, δ): 155.2, 142.3, 140.3,
132.9, 132.2, 129.3, 126.7, 126.3, 119.0, 117.3, 109.4, 29.0, 21.4, 21.2. HRMS−ESI [M + H]+
calcd for C17H17N4O2S+, 341.1067; found, 341.1076.
Rh(II)-Catalyzed Reactions of Trisubstituted Azirines with 1-Sulfonyl-1,2,3-triazoles
(General Procedure). Azirine 1a,b (0.12 mmol), triazole 6a,b (1.1–1.6 equiv), Rh2(OAc)4 (5
mol %, calcd on triazole), and anhydrous toluene (1.5 mL) were placed in a 10-mL Schlenk
flask, equipped with a reflux condenser. The mixture was refluxed under an argon atmosphere
until complete disappearance of the azirine (control by TLC, hexane–EtOAc, 5:1). For the
synthesis of 1,2-dihydropyrazines, the solvent was evaporated in vacuo and dihydropyrazine was
purified by column chromatography on silica gel. For the synthesis of aminovinylindoles, the
reaction mixture before evaporation was diluted with anhydrous toluene (3.5 mL), and refluxing
was continued until complete disappearance of 1,2-dihydropyrazine (control by TLC, benzene–
EtOAc, 100:1). Then the solvent was removed in vacuo, and aminovinylindole was purified by
column chromatography on silica gel.
3-Methyl-1-(methylsulfonyl)-2,2,5-triphenyl-1,2-dihydropyrazine (8a). This compound
was obtained from azirine 2a (29 mg, 0.140 mmol) and triazole 1a (34 mg, 0.155 mmol)
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according to the general procedure (3 mol % of Rh2(OAc)4) as a yellow solid (40 mg, 71%). mp
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145 °C (dec.). H NMR (CDCl3, δ): 7.78 (d, J = 7.2 Hz, 2H), 7.73–7.68 (m, 4H), 7.52–7.45 (m,
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4H), 7.45–7.38 (m, 4H), 7.32–7.26 (m, 1H), 7.24 (s, 1H), 2.17 (s, 3H), 1.99 (s, 3H). 13C{1H}
NМR (CDCl3, δ): 159.4, 138.0, 136.5, 129.8, 128.5, 128.4, 128.3, 127.0, 124.2, 124.0, 111.6,
71.7, 41.5, 24.8. HRMS−ESI [M + H]+ calcd for C24H23N2O2S+, 403.1475; found, 403.1479.
3-Methyl-1-(4-methylphenylsulfonyl)-2,2,5-triphenyl-1,2-dihydropyrazine (8b). This
compound was obtained from azirine 2a (26 mg, 0.125 mmol) and triazole 1b (41 mg, 0.137
mmol) according to the general procedure (3 mol % of Rh2(OAc)4) as a colorless foam (30 mg,
51%). 1H NMR (CDCl3, δ): 7.76 (d, J = 8.0 Hz, 2H), 7.62 (s, 1H), 7.53–7.45 (m, 4H), 7.41–7.37
(m, 2H), 7.35–7.25 (m, 7H), 7.07–7.01 (m, 4H), 2.38 (s, 3H), 1.98 (s, 3H). 13C{1H} NМR
(CDCl3, δ): 159.7, 143.2, 138.2, 137.8, 136.6, 129.8, 129.1, 128.5, 128.0, 127.9, 126.9, 126.3,
125.5, 124.1, 112.9, 72.0, 25.3, 21.5. HRMS−ESI [M + H]+ calcd for C30H27N2O2S+, 479.1788;
found, 479.1788.
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1-(4-Methylphenylsulfonyl)-2,2,3,5-tetraphenyl-1,2-dihydropyrazine
(8c).
This
compound was obtained from azirine 2b (30 mg, 0.113 mmol) and triazole 1b (37 mg, 0.124
mmol) according to the general procedure (3 mol % of Rh2(OAc)4) as a yellow foam (34 mg,
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56%). H NMR (CDCl3, δ): 7.77–7.72 (m, 2H), 7.60 (s, 1H), 7.37–7.29 (m, 6H), 7.27–7.20 (m,
5H), 7.17–7.09 (m, 9H), 7.02 (t, J = 7.6 Hz, 2H), 2.38 (s, 3H). 13C{1H} NМR (CDCl3, δ): 158.5,
143.6, 139.0, 138.4, 136.3, 130.6, 129.8, 129.2, 128.6, 128.4 (2C), 128.3, 128.1, 127.6, 127.2
(2C), 126.7, 124.3, 114.3, 72.4, 21.5. HRMS−ESI [M + H]+ calcd for C35H29N2O2S+, 541.1944;
found, 541.1944.
Methyl 1-(methylsulfonyl)-2,3,5-triphenyl-1,2-dihydropyrazine-2-carboxylate (8s). This
compound was obtained from azirine 2f (53 mg, 0.21 mmol) and triazole 1a (72 mg, 0.32 mmol)
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according to the general procedure as a yellow foam (80 mg, 85%). H NMR (CDCl3, δ): 7.78–
7.66 (m, 6H), 7.45–7.29 (m, 9H), 6.96 (s, 1H), 3.58 (s, 3H), 3.08 (s, 3H). 13C{1H} NМR (CDCl3,
δ): 168.8, 152.7, 137.5, 135.6, 135.1, 130.2, 129.20, 129.19, 128.54, 128.49, 128.2, 128.11,
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128.06, 127.6, 124.4, 110.3, 70.0, 53.3, 42.2. HRMS−ESI [M + H]+ calcd for C25H23N2O4S+,
447.1373; found, 447.1373.
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Heating of 1,2-dihydropyrazine 8s in o-xylene under reflux for 2 h gave 2,3,5-
triphenylpyrazine12b in 30% yield.
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(Z)-N-[2-(2-Methyl-3-phenyl-1H-indol-1-yl)-2-phenylvinyl]methanesulfonamide (3a).
This compound was obtained from azirine 2a (26.5 mg, 0.13 mmol) and triazole 1a (31.5 mg,
0.14 mmol) according to the general procedure (total reaction time is 5 h) as a yellow foam (19
mg, 37%). Compound 3a was also obtained (40 mg, 52%) by refluxing solution of 1,2-
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dihydropyrazine 8a (80 mg, 0.19 mmol) in toluene (4 mL) for 5 h. H NMR (CDCl3, δ): 7.80–
7.73 (m, 1H), 7.60–7.46 (m, 4H), 7.39–7.27 (m, 4H), 7.22–7.17 (m, 3H), 7.13–7.09 (m, 1H),
7.05–7.00 (m, 2H), 6.22 (s, 1H), 3.08 (s, 3H), 2.24 (s, 3H). 13C{1H} NМR (CDCl3, δ): 135.5,
135.1, 134.8, 133.2, 129.6, 129.0, 128.6, 128.1, 128.0, 126.3, 123.9, 122.4, 121.7, 121.1, 119.5,
118.9, 116.6, 109.6, 41.9, 11.1. HRMS−ESI [M + H]+ calcd for C24H23N2O2S+, 403.1475; found,
403.1475.
(Z)-4-Methyl-N-[2-(2-methyl-3-phenyl-1H-indol-1-yl)-2-phenylvinyl]benzenesulfonamide
(3b). This compound was obtained from azirine 2a (26.5 mg, 0.13 mmol) and triazole 1b (43
mg, 0.143 mmol) according to the general procedure (total reaction time 3 h) as a yellow foam
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(32 mg, 52%). H NMR (CDCl3, δ): 7.73–7.67 (m, 3H), 7.54–7.45 (m, 4H), 7.37–7.31 (m, 4H),
7.25–7.21 (m, 3H), 7.15–7.10 (m, 1H), 6.96–6.91 (m, 2H), 6.91–6.85 (m, 1H), 6.53 (d, J = 8.1
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Hz, 1H), 6.28 (d, J = 11.7 Hz, 1H), 2.48 (s, 3H), 2.04 (s, 3H). C{1H} NМR (CDCl3, δ): 144.5,
136.7, 135.4, 135.3, 134.8, 133.3, 130.1, 129.6, 129.0, 128.6, 128.0, 127.9, 127.0, 126.2, 124.0,
122.2, 122.0, 121.0, 119.3, 119.2, 116.5, 109.4, 21.6, 10.9. HRMS−ESI [M + Na]+ calcd for
C30H26N2NaO2S+, 501.1607; found, 501.1600.
(Z)-N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-phenylvinyl]-4-methylbenzenesulfonamide
(3c). This compound was obtained from azirine 2b (29 mg, 0.108 mmol) and triazole 1b (35 mg,
0.118 mmol) according to the general procedure (total reaction time 1.5 h) as a yellow foam (45
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mg, 77%). H NMR (CDCl3, δ): 7.84 (d, J = 8.2 Hz, 2H), 7.78 (d, J = 8.0 Hz, 1H), 7.43 (d, J =
8.2 Hz, 2H), 7.31–7.28 (m, 6H), 7.24–7.19 (m, 3H), 7.10–7.06 (m, 2H), 6.96 (t, J = 7.7 Hz, 2H),
6.89–6.82 (m, 2H), 6.80–6.75 (m, 3H), 6.70 (d, J = 8.2 Hz, 1H), 6.34 (dd, J = 7.4, 2.1 Hz, 1H),
2.55 (s, 3H). 13C{1H} NМR (CDCl3, δ): 144.4, 137.1, 136.8, 136.2, 135.6, 134.3, 130.9, 130.12,
130.06, 130.0, 128.4, 128.3, 128.0, 127.9, 127.7, 127.6, 127.0, 126.2, 124.2, 123.3, 121.54,
121.46, 120.2, 120.0, 117.7, 110.2, 21.7. HRMS−ESI [M + H]+ calcd for C35H29N2O2S+,
541.1944; found, 541.1935.
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(Z)-N-[2-(2,6-Dimethyl-3-(4-methylphenyl)-1H-indol-1-yl)-2-phenylvinyl]-4-
methylbenzenesulfonamide (3d). This compound was obtained from azirine 2c (33 mg, 0.140
mmol) and triazole 1b (46 mg, 0.154 mmol) according to the general procedure (total reaction
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time 4.5 h) as a colorless foam (42 mg, 59%). H NMR (CDCl3, δ): 7.75 (d, J = 8.2 Hz, 2H),
7.59 (d, J = 8.1 Hz, 1H), 7.47–7.20 (m, 10H), 7.00–6.94 (m, 3H), 6.43 (s, 1H), 6.38 (d, J = 11.6
13
Hz, 1H), 2.48 (s, 3H), 2.45 (s, 3H), 2.23 (s, 3H), 2.04 (s, 3H). C{1H} NМR (CDCl3, δ): 144.4,
136.8, 135.8, 135.7, 135.3, 132.3, 132.0, 131.9, 130.1, 129.4, 129.2, 128.9, 127.8, 126.8, 125.9,
123.9, 122.5, 121.9, 119.3, 118.9, 116.2, 109.3, 21.6 (2C), 21.2, 10.8. HRMS−ESI [M + Na]+
calcd for C32H30N2NaO2S+, 529.1920; found, 529.1920.
(Z)-N-[2-(4-Chlorophenyl)-2-(2,3-diphenyl-1H-indol-1-yl)vinyl]-4-
methylbenzenesulfonamide (3e). This compound was obtained from azirine 2b (28 mg, 0.104
mmol) and triazole 1c (39 mg, 0.117 mmol) according to the general procedure (total reaction
time 4 h) as a yellow foam (45 mg, 75%). 1H NMR (CDCl3, δ): 7.81 (d, J = 8.0 Hz, 1H), 7.73 (d,
J = 8.2 Hz, 2H), 7.44–7.33 (m, 6H), 7.29–7.10 (m, 4H), 7.09–6.97 (m, 5H), 6.95–6.90 (m, 2H),
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6.70–6.58 (m, 4H), 2.55 (s, 3H). C{1H} NМR (CDCl3, δ): 144.5, 137.0, 136.7, 136.0, 134.2,
134.1, 133.3, 130.7, 130.2, 129.98, 129.96, 128.6, 128.4, 128.10, 128.0, 127.8, 127.0, 126.3,
125.3, 123.4, 122.0, 121.6, 120.2, 119.1, 117.9, 110.0, 21.7. HRMS−ESI [M + Na]+ calcd for
C35H2735ClN2NaO2S+, 597.1374; found, 597.1374.
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methylbenzenesulfonamide (3f). This compound was obtained from azirine 2a (23 mg, 0.111
mmol) and triazole 1c (39 mg, 0.117 mmol) according to the general procedure (total reaction
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time 5 h) as a colorless foam (26 mg, 46%). H NMR (CDCl3, δ): 7.73–7.66 (m, 3H), 7.53–7.45
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(m, 4H), 7.39–7.29 (m, 4H), 7.23–7.19 (m, 2H), 7.15–7.11 (m, 1H), 6.93–6.83 (m, 3H), 6.51 (d,
J = 8.1 Hz, 1H), 6.30 (d, J = 11.7 Hz, 1H), 2.48 (s, 3H), 2.04 (s, 3H). 13C{1H} NМR (CDCl3, δ):
144.6, 136.6, 135.3, 134.6, 133.9, 133.7, 133.0, 130.1, 129.6, 129.2, 128.6, 128.0, 127.0, 126.3,
125.2, 122.37, 122.35, 121.1, 119.3, 118.2, 116.8, 109.3, 21.7, 10.9. HRMS−ESI [M + Na]+
calcd for C30H2535ClN2NaO2S+, 535.1217; found, 535.1219.
(Z)-N-{2-(2,3-Diphenyl-1H-indol-1-yl)-2-[4-(trifluoromethyl)phenyl]vinyl}-4-
methylbenzenesulfonamide (3g). This compound was obtained from azirine 2b (30 mg, 0.113
mmol) and triazole 1d (45 mg, 0.124 mmol) according to the general procedure (total reaction
time 5.5 h) as a colorless solid (60 mg, 89%). mp 110–111 °C. 1H NMR (CDCl3, δ): 7.84 (d, J =
8.0 Hz, 1H), 7.74 (d, J = 8.3 Hz, 2H), 7.43–7.31 (m, 9H), 7.30–7.22 (m, 2H), 7.15–7.11 (m, 1H),
7.04–7.01 (m, 3H), 6.97–6.93 (m, 2H), 6.87 (br s, 1H), 6.83 (d, J = 8.3 Hz, 2H), 6.66 (d, J = 8.2
Hz, 1H), 2.56 (s, 3H). 13C{1H} NМR (CDCl3, δ): 144.6, 139.2, 137.0, 136.6, 136.0, 134.0, 130.6,
130.2, 130.0, 129.9, 129.2 (q, J = 32.5 Hz), 128.4, 128.3, 128.0, 127.9, 127.0, 126.3, 125.4 (q, J
= 3.8 Hz), 124.1, 123.9 (q, J = 272.0 Hz), 123.6, 123.4, 121.7, 120.2, 118.6, 118.0, 110.0, 21.6.
HRMS−ESI [M + Na]+ calcd for C36H27F3N2NaO2S+, 631.1638; found, 631.1631.
(Z)-N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-(4-nitrophenyl)vinyl]-4-
methylbenzenesulfonamide (3h). This compound was obtained from azirine 2b (31 mg, 0.113
mmol) and triazole 1e (43 mg, 0.126 mmol) according to the general procedure (total reaction
time 5 h) as an orange solid (57 mg, 85%). mp 147–149 °C. 1H NMR (CDCl3, δ): 7.91 (d, J = 8.9
Hz, 2H), 7.82 (d, J = 7.9 Hz, 1H), 7.74 (d, J = 8.3 Hz, 2H), 7.43–7.30 (m, 7H), 7.25–7.20 (m,
2H), 7.12–7.06 (m, 1H), 7.03–6.96 (m, 3H), 6.91–6.85 (m, 2H), 6.84–6.78 (m, 3H), 6.59 (d, J =
13
8.1 Hz, 1H), 2.53 (s, 3H). C{1H} NМR (CDCl3, δ): 146.6, 144.9, 142.2, 136.8, 136.5, 135.8,
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133.8, 130.5, 130.3, 129.9 (2C), 128.5, 128.3, 128.12, 128.06, 127.0, 126.5, 125.1, 124.4, 123.9,
123.7, 122.0, 120.4, 118.4, 117.9, 109.8, 21.7. HRMS−ESI [M + Na]+ calcd for
C35H27N3NaO4S+, 608.1614; found, 608.1614.
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(Z)-N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-(2-fluorophenyl)vinyl]-4-
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methylbenzenesulfonamide (3i). This compound was obtained from azirine 2b (31 mg, 0.117
mmol) and triazole 1f (41 mg, 0.128 mmol) according to the general procedure (total reaction
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time 7 h) as a colorless solid (63 mg, 98%). mp 198–200 °C. H NMR (CDCl3, δ): 7.80 (d, J =
7.9 Hz, 1H), 7.75 (d, J = 8.2 Hz, 2H), 7.44 (d, J = 11.5 Hz, 1H), 7.39 (d, J = 8.2 Hz, 2H), 7.37 –
7.19 (m, 6H), 7.11–7.03 (m, 2H), 7.02 – 6.92 (m, 3H), 6.88–6.81 (m, 3H), 6.79–6.72 (m, 2H),
6.63 (d, J = 11.5 Hz, 1H), 6.16 (td, J = 7.9, 1.5 Hz, 1H), 2.52 (s, 3H). 13C{1H} NМR (CDCl3, δ):
158.9 (d, J = 249 Hz), 144.4, 136.9, 136.8, 136.2, 134.2, 130.7, 130.1, 130.0, 129.9, 128.5 (d, J =
8.6 Hz), 128.0, 127.9, 127.7, 127.6 (d, J = 2.6 Hz), 127.1, 126.6 (d, J = 15.2 Hz), 126.2, 124.1
(d, J = 3.4 Hz), 123.5, 123.2 (d, J = 11.1 Hz), 121.6, 120.1, 117.7, 115.7 (d, J = 23.2 Hz), 114.1
(d, J = 4.1 Hz), 110.2, 21.7. HRMS−ESI [M + Na]+ calcd for C35H27FN2NaO2S+, 581.1669;
found, 581.1669.
(Z)-N-[2-(2-Bromophenyl)-2-(2,3-diphenyl-1H-indol-1-yl)vinyl]-4-
methylbenzenesulfonamide (3j). This compound was obtained from azirine 2b (52 mg, 0.193
mmol) and triazole 1g (109 mg, 0.289 mmol) according to the general procedure (total reaction
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time 3 h) as a colorless foam (90 mg, 75%). H NMR (CDCl3, δ): 7.87 (d, J = 8.2 Hz, 2H), 7.80
(d, J = 7.9 Hz, 1H), 7.45 (d, J = 8.2 Hz, 2H), 7.35–7.20 (m, 8H), 7.14–7.07 (m, 2H), 6.98 (t, J =
13
7.6 Hz, 2H), 6.93–6.72 (m, 6H), 6.37 (dd, J = 7.4, 1.9 Hz, 1H), 2.57 (s, 3H). C{1H} NМR
(CDCl3, δ): 144.5, 137.1, 136.9, 136.1, 135.6, 134.1, 133.6, 131.1, 130.1, 130.0, 129.9, 129.8,
128.5, 128.2, 128.1, 127.9, 127.7, 127.3, 127.0, 126.2, 125.1, 123.4, 121.5, 121.0, 120.2, 118.0,
117.7, 110.8, 21.7. HRMS−ESI [M + Na]+ calcd for C35H27BrN2NaO2S+, 641.0869; found,
641.0872.
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(Z)-N-(4-{N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-
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phenylvinyl]sulfamoyl}phenyl)acetamide (3k). This compound was obtained from azirine 2b
(28.5 mg, 0.106 mmol) and triazole 1h (43.5 mg, 0.127 mmol) according to the general
procedure (total reaction time 2 h, DCE as a solvent, 110 °C, in sealed tube; eluent for
chromatography benzene–acetone, 4:1) as a colorless solid (36 mg, 58%). mp 229–230 °C (dec.).
1H NMR (CDCl3, δ): 7.80 (d, J = 7.9 Hz, 1H), 7.73 (d, J = 8.8 Hz, 2H), 7.64 (d, J = 8.8 Hz, 2H),
7.54 (s, 1H), 7.36–7.27 (m, 4H), 7.25–7.17 (m, 3H), 7.14–7.06 (m, 5H), 7.05–6.93 (m, 5H),
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6.76–6.70 (m, 3H), 2.15 (s, 3H). C{1H} NМR (CDCl3, δ): 168.8, 142.4, 137.2, 136.3, 135.6,
134.4, 134.3, 130.9, 130.0, 129.9, 128.4, 128.33, 128.31, 128.0, 127.9, 127.8, 127.6, 126.2,
124.1, 123.3, 121.6, 121.5, 120.2, 120.0, 119.5, 117.6, 110.3, 24.6. HRMS−ESI [M + Na]+ calcd
for C36H29N3NaO3S+, 606.1822; found, 606.1844.
(Z)-N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-phenylvinyl]-2,4,6-
trimethylbenzenesulfonamide (3l). This compound was obtained from azirine 2b (31 mg, 0.115
mmol) and triazole 1i (41 mg, 0.127 mmol) according to the general procedure (total reaction
time 1 h) as a colorless foam (27 mg, 41%). 1H NMR (CDCl3, δ): 7.82 (d, J = 7.9 Hz, 1H), 7.40–
7.29 (m, 4H), 7.28–7.20 (m, 2H), 7.16–6.94 (m, 12H), 6.81 (d, J = 8.2 Hz, 1H), 6.78–6.74 (m,
2H), 6.59 (d, J = 11.6 Hz, 1H), 2.45 (s, 6H), 2.35 (s, 3H). 13C{1H} NМR (CDCl3, δ): 143.0,
139.0, 137.2, 136.5, 135.7, 134.4, 134.1, 132.4, 130.8, 130.1, 130.0, 128.5, 128.4, 127.92,
127.89, 127.8, 127.4, 126.2, 124.0, 123.3, 121.7, 121.5, 120.0, 119.7, 117.5, 110.3, 23.1, 21.0.
HRMS−ESI [M + Na]+ calcd for C37H32N2NaO2S+, 591.2077; found, 591.2077.
(Z)-N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-phenylvinyl]-4-nitrobenzenesulfonamide (3m).
This compound was obtained from azirine 2b (32.5 mg, 0.121 mmol) and triazole 1j (44 mg,
0.133 mmol) according to the general procedure (total reaction time 1 h) as a yellow solid (48
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mg, 70%). mp 106–107 °C. H NMR (CDCl3, δ): 8.32 (d, J = 8.8 Hz, 2H), 7.88 (d, J = 8.8 Hz,
2H), 7.79 (d, J = 8.0 Hz, 1H), 7.38–7.28 (m, 4H), 7.24–7.06 (m, 7H), 7.02–6.91 (m, 5H), 6.89–
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6.79 (m, 2H), 6.64 (d, J = 8.2 Hz, 1H), 6.56 (d, J = 11.4 Hz, 1H). C{1H} NМR (CDCl3, δ):
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150.3, 145.0, 136.7, 136.2, 135.2, 134.1, 130.6, 130.0, 129.9, 128.7, 128.4, 128.13, 128.09 (2C),
128.0, 127.9, 126.4, 124.6, 124.3, 123.3, 121.6, 121.6, 120.3, 120.2, 118.0, 110.1. HRMS−ESI
[M + Na]+ calcd for C34H25N3NaO4S+, 594.1458; found, 594.1458.
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(Z)-N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-phenylvinyl]methanesulfonamide (3n). This
compound was obtained from azirine 2b (28.5 mg, 0.106 mmol) and triazole 1a (29.5 mg, 0.132
mmol) according to the general procedure (total reaction time 3 h) as a yellow foam (30 mg,
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61%). H NMR (CDCl3, δ): 7.84–7.81 (m, 1H), 7.43–7.31 (m, 4H), 7.25–7.15 (m, 11H), 7.13–
7.07 (m, 2H), 7.07–7.02 (m, 2H), 6.22 (d, J = 11.4 Hz, 1H), 2.63 (s, 3H). 13C{1H} NМR
(DMSO-d6, δ): 137.8, 136.4, 136.3, 134.6, 131.4, 130.1, 129.6, 128.29, 128.26, 127.70, 127.65,
127.3, 126.6, 125.8, 124.2, 123.1, 122.5, 120.8, 119.0, 116.0, 115.9, 110.8, 41.4. HRMS−ESI [M
+ H]+ calcd for C29H25N2O2S+, 465.1631; found, 465.1631.
(Z)-N-[2-(2,3-Diphenyl-1H-indol-1-yl)-2-(4-methoxyphenyl)vinyl]-4-
methylbenzenesulfonamide (3o) and N-[5-(4-methoxyphenyl)-2,3,3-triphenyl-3H-pyrrol-4-
yl]-4-methylbenzenesulfonamide (9a). These compounds were obtained from azirine 2b (30
mg, 0.110 mmol) and triazole 1k (40 mg, 0.121 mmol) according to the general procedure (total
reaction time 1 h).
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Compound 3o: colorless foam (6 mg, 9%). H NMR (CDCl3, δ): 7.78 (d, J = 8.0 Hz, 1H),
7.69 (d, J = 8.2 Hz, 2H), 7.38–7.27 (m, 6H), 7.25–7.15 (m, 2H), 7.12–6.89 (m, 7H), 6.68–6.57
(m, 5H), 6.46 (d, J = 11.5 Hz, 1H), 3.68 (s, 3H), 2.51 (s, 3H). 13C{1H} NМR (CDCl3, δ): 159.2,
144.3, 137.1, 136.8, 136.2, 134.3, 130.9, 130.1, 130.0 (2C), 128.3, 128.2, 128.0, 127.9 (2C),
127.7, 127.0, 126.2, 125.5, 123.2, 121.4, 120.2, 120.0, 117.6, 113.9, 110.2, 55.2, 21.7.
HRMS−ESI [M + Na]+ calcd for C36H30N2NaO3S+, 593.1869; found, 593.1898.
Compound 9a: colorless solid (27 mg, 42%). mp 179–181 °C. 1H NMR (CDCl3, δ): 8.01 (d,
J = 8.9 Hz, 2H), 7.81 (d, J = 7.3 Hz, 2H), 7.31–7.18 (m, 15H), 7.05 (d, J = 8.1 Hz, 2H), 6.90 (d,
J = 8.9 Hz, 2H), 5.60 (s, 1H), 3.87 (s, 3H), 2.40 (s, 3H). 13C{1H} NМR (CDCl3, δ): 180.6, 160.0,
148.2, 142.9, 138.4, 135.9, 133.8, 132.5, 130.4, 130.0, 129.2, 129.00, 128.95, 128.8, 128.0,
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127.7, 127.0, 125.5, 113.7, 74.6, 55.3, 21.5. HRMS−ESI [M + Na]+ calcd for C36H30N2NaO3S+,
593.1869; found, 593.1869.
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(Z)-N-[2-(4-Methoxyphenyl)-2-(2-methyl-3-phenyl-1H-indol-1-yl)vinyl]-4-
methylbenzenesulfonamide (3p). This compound was obtained from azirine 2a (40 mg, 0.19
mmol) and triazole 1k (83 mg, 0.29 mmol) according to the general procedure (total reaction
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time 30 min) as a yellow foam (29 mg, 30%). H NMR (CDCl3, δ): 7.73–7.66 (m, 3H), 7.54–
7.44 (m, 4H), 7.37–7.30 (m, 3H), 7.19 (d, J = 11.4 Hz, 1H), 7.11 (t, J = 7.2 Hz, 1H), 6.91–6.83
(m, 3H), 6.79–6.75 (m, 2H), 6.53 (d, J = 8.1 Hz, 1H), 6.20 (d, J = 11.4 Hz, 1H), 3.75 (s, 3H),
2.48 (s, 3H), 2.04 (s, 3H). C{1H} NМR (CDCl3, δ): 159.5, 144.4, 136.7, 135.4, 134.9, 133.3,
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130.0, 129.6, 128.5, 127.9, 127.8, 127.0, 126.2, 125.4, 122.2, 120.9, 120.2, 119.4, 119.1, 116.4,
114.4, 109.5, 55.3, 21.6, 10.9. HRMS−ESI [M + H]+ calcd for C31H29N2O3S+, 509.1893; found,
509.1875.
(Z)-N-[2-(2,6-Dimethyl-3-phenyl-1H-indol-1-yl)-2-phenylvinyl]-4-
methylbenzenesulfonamide (3q) and (Z)-N-{2-[2-methyl-3-(4-methylphenyl)-1H-indol-1-yl]-
2-phenylvinyl}-4-methylbenzenesulfonamide (3q'). These compounds were obtained from
azirine 2d (24 mg, 0.107 mmol) and triazole 1b (35 mg, 0.117 mmol) according to the general
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procedure (total reaction time 1 h) as a yellow foam (23 mg, 43%, ca. 1:1 ratio). H NMR
(CDCl3, δ): 7.76–7.70 (m, 5H), 7.63–7.59 (m, 2H), 7.55–7.22 (m, 5H), 7.19–7.11 (m, 2H), 7.00–
6.94 (m, 5H), 6.90 (t, J = 7.6 Hz, 1H), 6.55 (d, J = 8.1 Hz, 1H), 6.44 (s, 1H), 6.35 (d, J = 11.7
Hz, 1H), 6.32 (d, J = 11.9 Hz, 1H), 2.50 (s, 3H), 2.48 (s, 3H), 2.46 (s, 3H), 2.23 (s, 3H), 2.05 (s,
6H). 13C{1H} NМR (CDCl3, δ): 144.5, 144.4, 136.8, 136.7, 135.84, 135.82, 135.4, 135.31,
135.29, 135.0, 133.0, 132.6, 132.0, 131.8, 130.1, 129.5, 129.4, 129.3, 128.97, 128.96, 128.5,
127.88, 127.83, 126.97, 126.85, 126.1, 125.8, 124.0, 123.9, 122.6, 122.1, 121.91, 121.86, 120.8,
119.22, 119.19, 118.9, 116.4, 116.3, 109.37, 109.36, 21.6, 21.2, 10.86, 10.84. HRMS−ESI [M +
Na]+ calcd for C31H28N2NaO2S+, 515.1764; found, 515.1798.
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Page 28 of 36
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(Z)-N-[2-(6-Methoxy-2,3-diphenyl-1H-indol-1-yl)-2-phenylvinyl]-4-
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methylbenzenesulfonamide (3r) and (Z)-N-{2-[3-(4-methoxyphenyl)-2-phenyl-1H-indol-1-
yl]-2-phenylvinyl}-4-methylbenzenesulfonamide (3r'). These compounds were obtained from
azirine 2e (33 mg, 0.111 mmol) and triazole 1b (34.5 mg, 0.115 mmol) according to the general
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procedure (total reaction time 1 h) as a yellow foam (44 mg, 70%, ca. 4:1 ratio). H NMR
(CDCl3, δ): 7.80–7.69 (m, 3H), 7.39–6.88 (m, 15H), 6.83–6.79 (m, 1.6H), 6.77–6.72 (m, 0.4H),
6.70–6.61 (m, 1H), 6.36 (d, J = 2.1 Hz, 0.8H), 3.84 (s, 0.6H), 3.66 (s, 2.4H), 2.54 (s, 0.6H), 2.51
(s, 2.4H). C{1H} NМR (CDCl3, δ, from 140.0 to 120.0 ppm only signals of major isomer are
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listed): 158.1, 157.4, 144.36, 144.33, 137.3, 136.9, 135.9, 135.6, 134.5, 131.04, 131.02, 130.1,
130.0, 129.9, 128.5, 128.4, 127.8, 127.54, 127.45, 127.0, 126.8, 126.2, 124.1, 122.2, 121.6,
120.8, 120.0, 117.6, 117.4, 113.9, 113.6, 111.1, 110.2, 94.00, 55.5, 55.2, 21.66, 21.63.
HRMS−ESI [M + Na]+ calcd for C36H30N2NaO3S+, 593.1869; found, 593.1887.
1'-(4-Methylphenylsulfonyl)-2,3-diphenyl-1'H-1,3'-biindole (16). CuI (1.5 mg, 0.007
mmol), N,N'-dimethylethylene-1,2-diamine (2 µl, 0.013 mmol) and K3PO4 (55 mg, 0.26 mmol)
were added to a solution of aminovinylindole 3j (80 mg, 0.13 mmol) in anhydrous toluene (2
mL) and the reaction mixture was stirred at 75 °C for 3 h. The solvent was evaporated in vacuo
and the crude product was purified by silica gel column chromatography (eluent: CH2Cl2–
EtOAc–hexane, 10:1:90). Compound 16 was obtained as a light-yellow foam (57 mg, 82%). 1H
NMR (CDCl3, δ): 8.00 (d, J = 8.4 Hz, 1H), 7.84–7.78 (m, 1H), 7.54 (d, J = 8.3 Hz, 2H), 7.41–
7.29 (m, 7H), 7.25–7.13 (m, 7H), 7.11–6.99 (m, 5H), 2.41 (s, 3H). C{1H} NМR (CDCl3, δ):
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145.1, 138.3, 137.5, 134.9, 134.6, 133.9, 131.4, 130.7, 130.1, 130.0, 128.3, 128.0, 127.9, 127.8,
127.5, 126.9, 126.1, 125.5, 123.7, 123.6, 123.0, 121.3, 121.2, 119.8, 119.7, 117.2, 113.9, 111.1,
21.7. HRMS−ESI [M + H]+ calcd for C35H27N2O2S+, 539.1788; found, 539.1795.
N-(1'-Methyl-2,3-diphenyl-1'H-[1,3'-biindol]-2'-yl)-4-methylbenzenesulfonamide (21a).
This compound was obtained from azirine 2b (30 mg, 0.11 mmol) and diazoindolinimine 17a
(77 mg, 0.24 mmol) according to the general procedure (total reaction time 30 min) as a
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colorless solid (48 mg, 76%). mp 216–218 °C. 1H NMR (CDCl3, δ): 7.66 (d, J = 7.4 Hz, 1H),
7.51 (d, J = 8.3 Hz, 1H), 7.47–7.37 (m, 4H), 7.34–7.27 (m, 4H), 7.26–7.10 (m, 7H), 7.00 (d, J =
7.2 Hz, 2H), 6.93 (d, J = 7.8 Hz, 1H), 6.67 (d, J = 8.1 Hz, 2H), 5.18 (s, 1H), 3.80 (s, 3H), 2.19 (s,
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3H). C{1H} NМR (CDCl3, δ): 143.2, 137.3, 135.3, 135.0, 134.6, 133.7, 131.5, 129.9, 129.8,
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128.92, 128.86, 128.4, 128.3, 127.4, 126.1, 125.9, 124.7, 123.5, 122.4, 122.2, 120.8, 120.5,
119.7, 119.1, 116.1, 112.0, 110.4, 109.7, 29.7, 21.8. HRMS−ESI [M + Na]+ calcd for
C36H29N3NaO2S+, 590.1873; found, 590.1874.
N-(1',5'-Dimethyl-2,3-diphenyl-1'H-[1,3'-biindol]-2'-yl)-4-methylbenzenesulfonamide
(21b). This compound was obtained from azirine 2b (35 mg, 0.13 mmol) and diazoindolinimine
17b (88 mg, 0.26 mmol) according to the general procedure (total reaction time 30 min) as a
yellow solid (54 mg, 71%). mp 203–206 °C. 1H NMR (CDCl3, δ): 7.60 (d, J = 7.0 Hz, 1H), 7.38–
7.32 (m, 3H), 7.29–7.06 (m, 12H), 6.97–6.93 (m, 2H), 6.89 (d, J = 7.6 Hz, 1H), 6.62 (d, J = 8.1
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Hz, 2H), 5.10 (s, 1H), 3.72 (s, 3H), 2.41 (s, 3H), 2.15 (s, 3H). C{1H} NМR (CDCl3, δ): 143.2,
137.4, 135.4, 135.1, 134.7, 132.2, 131.5, 130.02, 129.99, 129.8, 129.0, 128.9, 128.4, 128.3,
127.4, 126.1, 125.9, 125.3, 124.6, 122.4 (2С), 120.7, 119.1 (2С), 116.1, 112.1, 110.2, 109.2,
29.7, 21.8, 21.5. HRMS−ESI [M + Na]+ calcd for C37H31N3NaO2S+, 604.2029; found, 604.2056.
N-(5'-Methoxy-1',2-dimethyl-3-phenyl-1'H-[1,3'-biindol]-2'-yl)-4-
methylbenzenesulfonamide (21c). This compound was obtained from azirine 2a (33 mg, 0.15
mmol) and diazoindolinimine 17c (113 mg, 0.32 mmol) according to the general procedure (total
reaction time 30 min) as a yellow foam (50 mg, 59%). 1H NMR (CDCl3, δ): 7.75 (d, J = 7.4 Hz,
1H), 7.55–7.48 (m, 4H), 7.39–7.31 (m, 2H), 7.18–7.08 (m, 4H), 7.00 (dd, J = 9.0, 2.4 Hz, 1H),
6.79 (d, J = 8.0 Hz, 2H), 6.76 (d, J = 7.7 Hz, 1H), 6.59 (d, J = 2.4 Hz, 1H), 6.40 (br s, 1H), 3.97
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(s, 3H), 3.70 (s, 3H), 1.96 (s, 3H), 1.85 (s, 3H). C{1H} NМR (CDCl3, δ): 155.0, 143.8, 136.7,
135.6, 135.3, 134.2, 129.4, 129.3, 129.2, 128.5, 127.3, 126.3, 125.77, 125.75, 123.1, 122.2,
120.5, 119.2, 114.7, 114.4, 111.4, 109.1, 108.6, 100.0, 55.9, 30.4, 21.2, 11.5. HRMS−ESI [M +
H]+ calcd for C32H30N3O3S+, 536.2002; found, 536.1986.
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