Cp*CoIII-Catalyzed C(7)–H Bond Annulation of Indolines with Alkynes

Rajib Mandal, Bholanath Garai, and Basker Sundararaju*

Article

III

Cp*Co -Catalyzed C(7)−H Bond Annulation of Indolines with

Alkynes

Cite This: J. Org. Chem. 2021, 86, 9407 −9417

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sı Supporting Information

ABSTRACT: An eﬃcient protocol for the synthesis of biologicall_I_Iy_I

essential pyrroloquinolinones has been developed under Cp*Co

catalysis, which involves a cascade reaction of C(7)−H

alkenylation with alkynes followed by nucleophilic addition. A

wide variety of internal alkynes including enyne, diyne, and

ynamide and more challenging terminal alkynes were successfully

employed for the annulation in good to excellent yield with high

regioselectivity.

INTRODUCTION

■

Over the past few decades, directing-group-assisted catalytic

C−H bond functionalizations have been paramount in the ﬁeld

of synthetic organic chemistry to construct new carbon−

carbon and carbon−heteroatom bonds. The scarcity of

abundance and extensive use of precious transition metals such

as [Ir], [Rh], [Ru], etc. in catalytic C−H bond functionaliza-

tion call for the synthetic community to look for an economical

and sustainable alternative. In the past few years, catalysts

based on earth-abundant 3d metals have been explored

extensively for the aforementioned processes. Among them,

the Cp*Co catalytic system has demonstrated its signiﬁcance

Figure 1. Representative Examples of Bio-Relevant Molecules

Containing the Pyrroloquinolinone Core Unit.

III

complementary to the other group 9 congeners such as [Rh]

and [Ir] because of its unique and versatile reactivity, as

from limited scope, as only internal alkynes are amenable to

annulation and no reactivity has been observed with terminal

pioneered by Matsunaga and Kanai and later by many other

groups. However, the overdependence on strongly coordinat-

alkynes. Inspired by the unique nucleophilic activity of

organocobalt species over organorhodium species reported by

ing directing groups such as pyridyl, pyrimidyl, and pyrazoyl is

a major problem in cobalt-catalyzed C−H functionalizations.

b,e

Matsunaga and Kanai,

we envisaged annulating the C(7)−

Hence, it is important to develop novel C−H functionalization

protocols using a Cp*Co catalyst with weakly coordinating

III

H bond of indoline with various alkynes. It is expected that the

cobalt catalyst may undergo six-membered cyclometalation at

directing groups. However, only handful of examples have been

explored using directing groups such as amides, ketones, and

3,14

the C(7) position

of indoline assisted by a carbamoyl

III

directing group. The alkyne further inserts into the

organocobalt species to produce an alkenyl−cobalt intermedi-

ate that subsequently facilitates the nucleophilic attack of

carboxylic acids with Cp*Co catalysts, probably because of

the less favored formation of the key metallacyclic

intermediate.

Indole and its derivatives are omnipresent in various natural

[

Co]−C to the less electrophilic carbamoyl group, leading to

the annulation product with the liberation of a secondary

products and bioactive molecules. More speciﬁcally, hetero-

cycles such as the pyrroloquinolinone unit constitute the core

structure of various natural products and medicinally

important molecules toward asthma, obesity, and epilepsy

Received: March 26, 2021

Published: July 2, 2021

and inhibit antiacetylcholinesterase activity (Figure 1). In

this context, precious 4d and 5d transition metals have been

utilized for their synthesis via the coupling of N-carbamoyl-

protected indoline with alkyne. However, these protocols suﬀer

2021 American Chemical Society

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Article

amine. In a continuation of our earlier work on weakly

(entry 6) and provided the expected product 3aa in 72% yield.

Although the role of the zinc triﬂate is not clear at this point,

we believe that it may likely play a role in the cyclization. A

change of solvent from 2,2,2-triﬂuoroethanol (TFE) to 1,2-

dichloroethane (DCE) did not improve the reactivity (entry

7); however, a satisfactory yield of 3aa was obtained when

III

coordinating directing-group-assisted Cp*Co -catalyzed C−H

bond functionalizations, we sought to access such bio-

logically important skeletons via coupling with a diverse range

of alkynes, including terminal alkynes, diynes, enynes,

ynamides, etc.

AgOTf was used in place of AgSbF (entries 6 and 8).

To our surprise, the chloride and iodide dimers of Cp*Co

III

RESULTS AND DISCUSSION

■

We began our studies with 0.2 mmol of N,N-dimethylindoline-

both failed to provide a satisfactory yield of 3aa (Table 1,

entries 9 and 10). Finally, the product 3aa was isolated in an

excellent yield of 95% when the reaction was performed using

a 0.1 M concentration (entry 11). A further lowering of

temperature or catalyst loading did not show promising results

(entries 13 and 14). Control experiments revealed that both

silver salt and additive are crucial to deliver the product 3aa in

high yield (entries 15 and 16). A blank experiment revealed

that the catalyst is essential to obtain the annulated product

-carboxamide (1a) as the limiting reagent and 1,2-

diphenylethyne (2a) as the coupling partner in the presence

of Cp*Co(CO)I (10 mol %), AgSbF (20 mol %), and

sodium acetate (30 mol %) in TFE (0.2 M) at 110 °C (Table

). To our delight, the desired annulated product 3aa was

Table 1. Results of Optimization

aa (entry 17). We further examined various indoline

derivatives protected with diﬀerent weakly coordinating

directing groups such as indolin-1-yl(morpholino)methanone

(

1j), N,N-diisopropylindoline-1-carboxamide (1k), and ethyl

indoline-1-carboxylate (1l). The sterically hindered carbamoyl

groups were less suitable in delivering the desired product,

whereas the ester failed to provide the desired product.

With the optimized conditions in hand, the scope of the

annulation reactions was explored. As shown in Scheme 1, a

wide variety of internal symmetrical alkynes containing

electron-donating and electron-withdrawing substituents annu-

lated smoothly with N,N-dimethylindoline-1-carboxamide (1a)

to provide the corresponding pyrroindolinone derivatives in

additive

(mol %)

yield

entry

[Co] (mol %)

[Ag] (mol %)

(%)

2−91% yields (3ab−ah) (Scheme 1a). The scalability of the

Cp*Co(CO)I (10) AgSbF (20) NaOAc (30)

reaction was further checked on a 1.0 mmol scale, and to our

delight an excellent yield of 92% was obtained (3aa).

Symmetrical bis-aliphatic alkynes (2e−h) underwent

annulation smoothly with excellent yields, whereas moderate

yields were obtained under the optimized conditions reported

previously. A further examination revealed that a variety of

unsymmetrical alkynes also aﬀorded the expected products

(3ai−at) in moderate to good yields (39−78%) with high

regioisomeric ratios (Scheme 1b). The regioselectivity was

Cp*Co(CO)I (10) AgSbF (20) NaOPiv (30)

Cp*Co(CO)I (10) AgSbF (20) AgOPiv (30)

Cp*Co(CO)I (10) AgSbF (20) PivOH (30)

Cp*Co(CO)I (10) AgSbF (20) AdCO H (30)

Cp*Co(CO)I (10) AgSbF (20) Zn(OTf) (30)

Cp*Co(CO)I (10) AgOTf (20)

Zn(OTf) (30)

[Cp*CoI ] (5)

AgOTf (20)

[Cp*CoCl ] (5)

further conﬁrmed by determining the X-ray structure of 3aj.

Cp*Co(CO)I (10) AgOTf (20)

Aryl/aliphatic alkynes having phenyl, naphthyl, and aliphatic

variants with diﬀerent chain lengths were amenable under the

reaction conditions. Interestingly, alkynes such as (3-

Cp*Co(CO)I (10) AgOTf (20)

Cp*Co(CO)I (5)

AgOTf (10)

(

benzyloxy)prop-1-yn-1-yl)benzene (2o), 3-phenylprop-2-yn-

-ol (2p), and 4-methyl-N-(3-phenylprop-2-yn-1-yl)-

Cp*Co(CO)I (10) AgOTf (10)

Cp*Co(CO)I (10)

Zn(OTf) (30)

benzenesulfonamide (2q) provided the corresponding prod-

ucts in moderate to good yields (3ao−aq). In addition to

alkynes, the methodology was also quite eﬀective with a diyne

AgOTf (10)

All of the reactions were carried out under an argon atmosphere,

unless otherwise stated, using 0.2/0.24/0.02/0.04/0.06 mmol of 1a/

a/[Co]/[Ag]/additive at 110 °C in TFE (0.2 M). Abbreviations:

TFE, 2,2,2-triﬂuoroethanol; DCE, 1,2-dichloroethane; ND, not

(

2r), an enyne (2s), and an ynamide (2t), aﬀording the

regioselective annulated products (3ar−3at) with acceptable

yields (39−46%) using 30 mol % of NaOPiv as an additive

determined. Isolated yield. DCE (0.2 M) was used as the solvent.

instead of Zn(OTf) . Subsequently, the scope of the indolines

Reaction performed in TFE (0.1 M). Reaction performed in TFE

was examined under the optimized reaction conditions

(0.4 M). Reaction performed at 90 °C.

(

Scheme 1c). Indolines containing electron-donating as well

as electron-withdrawing substituents present on the phenyl

ring underwent annulation smoothly to produce the cyclized

products (3ba−ga) in good to excellent yields (81−94%).

Useful functional groups such as −OMe, −Cl, and −Br were

kept intact after annulation, which can be used as additional

handles for further transformations. Both 2-methyl N-

carbamoyl indoline (2h) and 3-methyl N-carbamoyl indoline

(2i) underwent cyclization with diphenylacetylene to provide

isolated in 42% yield after 24 h (Table 1, entry 1). In order to

improve the eﬃciency of the reaction, we optimized various

reaction parameters, including additives (entries 2−6), solvents

(

entries 6 and 7), silver salts (entries 6 and 8), cobalt catalyst

precursors (entries 9 and 10), solvent concentration (entries

1 and 12), and reaction temperature (entry 13). Among the

various additives screened, zinc triﬂate was found to be optimal

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Scheme 1. Substrate Scope^a^,^b

Scheme 2. Scope with Terminal Alkynes

All of the reactions were carried out under an argon atmosphere

using 0.6/0.2/0.02/0.04/0.06 mmol of 1a/4/[Co]/[Ag]/PivOH at

110 °C in TFE (0.1 M) for 36 h.

C−H bond functionalizations provided only trace amounts of

products under our optimized conditions. We further tested

phenylacetylene toward annulation with the previously

reported reaction conditions with [Ru] and [Rh] metal

precursors, and similar results were encountered with no

desired product. To understand the stereoelectronic eﬀect

involved in the reaction, several phenylacetylenes having

electron-donating and electron-withdrawing substituents were

tested under the optimized reaction conditions (Scheme 2).

All of the alkynes irrespective of their substituents present at

either meta or para positions reacted smoothly to provide the

annulated products (5ab−ag) as single regioisomers with

moderate to good yields (59−69%). The product regiochem-

istry of 5ae was further established by an X-ray crystal structure

All of the reactions, unless stated otherwise, were carried out under

determination. Functional groups such as −F, −Br, and

an argon atmosphere using 0.2/0.24/0.02/0.04/0.06 mmol of 1/2/

−

NHTs were tolerated and hence could serve as additional

[

Co]/[Ag]/additive at 110 °C in TFE (0.1 M) for 24 h. Isolated

handles for postsynthetic derivatizations. Delightfully, 2-

ethynylnaphthalene (2h) underwent the desired annulation

smoothly, whereas electron-rich aliphatic terminal alkynes (4i)

failed to provide the desired product under the optimized

conditions.

yield of single regioisomer. Reaction time 48 h. 3-Phenylprop-2-yn-

-yl acetate was used as the alkyne. 30 mol % of NaOPiv was used in

place of Zn(OTf) , and the reaction was carried out for 36 h.

the expected annulated products (3ha,ia) in good yields (56−

To further illustrate the synthetic utility of this protocol, 5-

phenyl-1,2-dihydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one (5aa)

was subjected to oxidation and reduction separately (Scheme

3). The reduction of 5aa using [Pd] catalyst and molecular

hydrogen as the sole reductant gave 5-phenyl-5,6-dihydro-1H-

pyrrolo[3,2,1-ij]quinolin-4(2H)-one (6) in 69% yield (Scheme

3a). On the other hand, DDQ oxidation provided the

3%).

We next examined the scope of annulation using more

challenging terminal alkynes (Scheme 2). In comparison to

internal alkynes, terminal alkynes have been considered as

nontrivial coupling partners in transition-metal-catalyzed C−H

bond functionalizations due to competent self-dimerization or

-trimerization. Under the conditions optimized for internal

alkynes, phenylacetylene 4a failed to deliver the annulated

product 5aa. A brief screening of additives and reaction

stoichiometry revealed that 50 mol % of pivalic acid (PivOH)

is suﬃcient to acquire 5-phenyl-1,2-dihydro-4H-pyrrolo[3,2,1-

ij]quinolin-4-one (5aa) in 69% yield as a single regioisomeric

product. On the other hand, widely explored metal precursors

such as [Cp*RhCl ] , Ru(p-cymene) Cl , and [Cp*IrCl ] for

Scheme 3. Applications of 5aa

2 2

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synthetically important 5-phenyl-4H-pyrrolo[3,2,1-ij]quinolin-

Scheme 5. Plausible Mechanism

-one (7) in 62% yield (Scheme 3b).

To get an insight into the reaction mechanism, preliminary

control experiments were carried out as shown in Scheme 4. At

Scheme 4. Mechanistic Studies

metalation step is reversible. The isolation of reaction

intermediates and further mechanistic investigations are

currently ongoing in our laboratory.

ﬁrst, intermolecular competitive experiments with equimolar

amounts of alkyne implied the faster formation of product 3ae

with the aliphatic alkyne 2e in comparison with the aromatic

alkyne 2a (3aa:3ae = 1:1.23) (Scheme 4a). This is probably

due to facile insertion into the M−C bond with the electron-

rich alkyne 2e over the electron-deﬁcient partner 2a. Other

intermolecular competitive experiments with equimolar

amount of N-carbamoyl indoline 1b,e were carried out, and

it was found that both substrates react with 1,2-diphenylace-

tylene (2a) with similar eﬃciency (3ba:3ea = 1:1) (Scheme

EXPERIMENTAL SECTION

General Information. Unless otherwise mentioned, all reactions

were carried out under an argon atmosphere. 1,2-Dichloroethane

■

(

1,2-DCE) was dried using calcium hydride according to the the

established protocol. Reagent-grade 2,2,2-triﬂuoroethanol (TFE) and

,4-dioxane and HPLC-grade ethyl acetate (EtOAc) were used as

such from the commercial sources. H and C NMR were recorded

on JEOL 400 and 500 MHz spectrometers using CDCl and DMSO-

d₆as solvents. Chemical shifts (δ) are given in ppm relative to TMS

and coupling constants (J) in Hz. The solvent signals used as

references and the chemical shifts were converted to the TMS scale

(CDCl , δ 77.0 ppm, δ_H7.26 ppm; DMSO-d , δ 39.52 ppm, δ_H

b). Deuterium incorporation at the C(7) and C(5) positions

observed to be 89% and 88%, respectively, in H/D scrambling

experiments suggested that the cyclometalation step is

reversible in nature and that the C−H bond cleavage follows

an electrophilic activation pathway (Scheme 4c).

2.50 ppm). All of the reactions were monitored by analytical thin-

layer chromatography (TLC) using commercial aluminum sheets

precoated with silica gel. Column chromatography was conducted on

silica gel (Merck, 200−400 mesh). HRMS measurements were

recorded on a quadrupole time-of-ﬂight mass spectrometer. Unless

otherwise mentioned, all other chemicals were received and used as

such from the commercial sources. Alkynes, enynes, diynes, and

On the basis of the preliminary experiments and previous

,9,14

literature,

a plausible mechanism is proposed in Scheme 5.

The reaction mechanism is initiated by the formation of the in

situ generated cationic [Co] complex A. Substrate binding to

the metal via weak coordination followed by cyclometalation

leads to intermediate B. Subsequent coordination of the alkyne

to B, followed by insertion of the alkyne into the [Co]−C

bond, provides the intermediate D. Nucleophilic addition of

the alkenyl−Co(III) bond to an electrophilic carbamoyl group

leads to intermediate E, which ﬁnally undergoes protodeme-

talation to give the desired [4 + 2] annulated product 3/5 with

concomitant release of a secondary amine and the active

catalyst A back into the catalytic cycle.

ynamides were prepared according to the literature procedure.

General Procedure for the Synthesis of N-Acyl or N-

Carbamoyl Indolines 1a−l. To a stirred solution of the indoline

derivative (10 mmol, 1.0 equiv) prepared by the literature procedure

and triethylamine (30 mmol, 3.0 equiv) in DCM (30 mL) was added

dropwise a solution of N-acyl or N-carbamoyl chloride (1.5 equiv) in

DCM (10 mL) at 0 °C. The reaction mixture was further stirred at

room temperature for 6−8 h. The reaction mixture was quenched

with water and portioned between DCM and water layers. The

organic layer was further dried with Na SO and puriﬁed by silica gel

chromatography using n-hexanes/EtOAc to give the corresponding

products 1a−l. Characterization data of these compounds matched

CONCLUSION

In summary, we have developed an eﬃcient Cp*Co -

■

III

well those of previous reports.

General Procedure A of Catalytic Couplings of N-

Carbamoyl Indoline 1 with Internal Alkynes 2a−q. An oven-

dried Schlenk tube equipped with a magnetic stir bar was charged

catalyzed regioselective protocol for the synthesis of bio-

logically important pyrroloquinolinones. A diverse range of

alkynes, including internal alkynes, terminal alkynes, diyne,

ynamide, and enyne, were amenable in delivering the

pyrroloquinolinone derivatives in good to excellent yields.

Preliminary experiments revealed that the electrophilic cyclo-

with Cp*Co(CO)I (9.5 mg, 0.02 mmol, 10 mol %) and AgOTf (10.3

mg, 0.04 mmol, 20 mol %) under an argon atmosphere. A small

amount of 1,2-TFE (0.5 mL) was placed in the Schlenk tube, and the

mixture was stirred for 1−2 min. N-Carbamoyl indoline 1 (0.2 mmol,

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Article

.0 equiv) and alkyne 2 (0.24 mmol, 1.2 equiv) followed by Zn(OTf)₂

4.53 (t, J = 8.1 Hz, 2H), 3.47 (t, J = 8.1 Hz, 2H), 2.32 (s, 3H), 2.26 (s,

(

21.8 mg; 0.06 mmol, 30 mol %) and 1.5 mL of TFE were

3H). C{ H} NMR (101 MHz, CDCl ): δ 160.6, 146.9, 141.6, 137.2,

successively placed in the Schlenk tube. The closed tube was placed in

a preheated oil bath at 110 °C, and the contents were stirred for 24 h.

After completion of the reaction, the reaction mixture was then cooled

to room temperature. The crude mixture was puriﬁed by ﬂash column

chromatography (ethyl acetate/hexane) on silica gel, aﬀording 3 as

the desired product.

General Procedure B of Catalytic Couplings of N-Carbamoyl

Indoline 2a with Alkynes 2r−t. An oven-dried Schlenk tube

equipped with a magnetic stir bar was charged with Cp*Co(CO)I

(

9.5 mg, 0.02 mmol, 10 mol %) and AgOTf (10.3 mg, 0.04 mmol, 20

mol %) under argon atmosphere. A small amount of 1,2-TFE (0.5

mL) was placed in the Schlenk tube, and the mixture was stirred for

−2 min. N-Carbamoyl indoline 1 (0.2 mmol, 1.0 equiv) and alkynes

r−t (0.24 mmol, 1.2 equiv) followed by NaOPiv (7.4 mg; 0.06

mmol, 30 mol %) and 1.5 mL of TFE were successively placed in the

Schlenk tube. The closed tube was placed in a preheated oil bath at

10 °C, and the contents were stirred for 36 h. After completion of

the reaction, the reaction mixture was then cooled to room

temperature. The crude mixture was puriﬁed by ﬂash column

chromatography (ethyl acetate/hexane) on silica gel, aﬀording 3 as

the desired product.

General Procedure C of Catalytic Couplings of N-

Carbamoyl Indoline 1a with Terminal Alkynes 4. An oven-

dried Schlenk tube equipped with a magnetic stir bar was charged

6-m-Tolyl-5-p-tolyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3ad).

Compound 3ad was prepared according to the general procedure A

and then was puriﬁed by ﬂash column chromatography (EtOAc/

hexane 20/80) o aﬀord 57.6 mg of 3ad in 82% yield as a colorless

12c

solid. The NMR data of 3ad are in accordance with the literature.

H NMR (400 MHz, CDCl ): δ 7.34 (dd, J = 6.7, 1.1 Hz, 1H), 7.16−

7.12 (m, 2H), 7.08−7.02 (m, 3H), 6.98 (br s, 1H), 6.93−6.87 (m,

4H), 4.54 (t, J = 8.2 Hz, 2H), 3.48 (t, J = 8.1 Hz, 2H), 2.26 (s, 3H),

2.22 (s, 3H). C{ H} NMR (101 MHz, CDCl ): δ 160.6, 147.1,

with Cp*Co(CO)I (9.5 mg, 0.02 mmol, 10 mol %) and AgOTf (10.3

mg, 0.04 mmol, 20 mol %) under an argon atmosphere. 1,2-TFE (1.0

mL) was placed in the Schlenk tube, and the contents were stirred for

141.7, 135.5, 136.8, 136.0, 135.5, 133.5, 131.6, 130.51, 130.47, 128.3,

128.0, 127.9, 127.8, 127.4, 126.9, 124.7, 123.9, 123.0, 118.8, 47.4,

−2 min. N-Carbamoyl indoline 1a (38.0 mg, 0.2 mmol, 1.0 equiv)

and PivOH (10.2 mg; 0.1 mmol, 50 mol %) followed by alkyne 4

0.24 mmol, 1.2 equiv) and 1.0 mL of TFE were successively placed

−

27.3, 21.4 (overlapped). IR (neat): 2922, 2852, 1646, 1600, 738 cm .

Mp: 149−152 °C.

(

in the Schlenk tube. The closed tube was placed in a preheated oil

bath at 110 °C, and the contents were stirred for 36 h. After

completion of the reaction, the reaction mixture was then cooled to

room temperature. The crude mixture was puriﬁed by ﬂash column

chromatography (ethyl acetate/hexane) on silica gel, aﬀording 5 as

the desired product.

5,6-Dipentyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3ae). Com-

pound 3ae was prepared according to the general procedure A and

then was puriﬁed by ﬂash column chromatography (EtOAc/hexane

20/80) to aﬀord 56.7 mg of 3ae in 91% yield as a colorless solid. H

NMR (400 MHz, CDCl ): δ 7.42 (d, J = 8.2 Hz, 1H), 7.25 (d, J = 5.7

Hz, 1H), 7.12 (t, J = 7.6 Hz, 1H), 4.41 (t, J = 8.1 Hz, 2H), 3.37 (t, J =

8.0 Hz, 2H), 2.82 (t, J = 8.2 Hz, 2H), 2.70 (t, J = 7.9 Hz, 2H), 1.64−

Synthesis of 5,6-Diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-

(2H)-one (3aa) on a 1.0 mmol Scale. An oven-dried Schlenk

.52 (m, 4H), 1.48−1.34 (m, 8H), 0.94−0.88 (m, 6H). C{ H}

tube equipped with a magnetic stir bar was charged with

NMR (101 MHz, CDCl ): δ 162.2, 145.1, 141.0, 133.0, 130.8, 123.7,

Cp*Co(CO)I (47.5 mg, 0.1 mmol, 10 mol %) and AgOTf (51.4

122.8, 121.1, 118.4, 46.9, 32.42, 32.40, 29.8, 29.3, 28.8, 27.4, 27.2,

mg, 0.02 mmol, 20 mol %) under an argon atmosphere. A 2.0 mL

portion of 1,2-TFE was placed in the Schlenk tube, and the contents

were stirred for 2−3 min. N-Carbamoyl indoline 1a (192.2 mg, 1.0

mmol, 1.0 equiv) and alkyne 2a (213.8 mg, 1.2 mmol, 1.2 equiv)

2.7, 22.6, 14.2, 14.1. HRMS: calcd for C H NNaO is [M + Na] :

34.2147; found: 334.2139. IR (2871, 2919, 2850, 1635, 1609, 771

−

cm . Mp: 128−131 °C.

,6-Dipropyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3af). Com-

followed by Zn(OTf) (109.1 mg; 0.3 mmol, 30 mol %) and 8.0 mL

pound 3af was prepared according to the general procedure A and

then was puriﬁed by ﬂash column chromatography (EtOAc/hexane

of TFE were successively placed in the Schlenk tube. The closed tube

was placed in a preheated oil bath at 110 °C, and the contents were

stirred for 36 h. After completion of the reaction, the reaction mixture

was then coolrf to room temperature. The crude mixture was puriﬁed

by ﬂash column chromatography (ethyl acetate/hexane) on silica gel,

aﬀording 3aa in 92% (297.5 mg) yield.

0/80) to aﬀord 45.4 mg of 3af in 89% yield as a colorless solid. The

12c

NMR data of 3af are in accordance with the literature.

H NMR

(400 MHz, CDCl ): δ 7.42 (d, J = 8.0 Hz, 1H), 7.25 (d, J = 7.4 Hz,

1H), 7.12 (t, J = 7.6 Hz, 1H), 4.41 (t, J = 8.1 Hz, 2H), 3.37 (t, J = 8.2

Hz, 2H), 2.84−2.80 (m, 2H), 2.71−2.67 (m, 2H), 1.68−1.52 (m,

,6-Diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3aa). Com-

4H), 1.07 (t, J = 7.4 Hz, 3H), 1.02 (t, J = 7.3 Hz, 3H). C{ H} NMR

pound 3aa was prepared according to general procedure A and was

puriﬁed by ﬂash column chromatography (EtOAc/hexane 20/80),

aﬀording 61.4 mg of 3aa in 95% yield as a white solid. The NMR data

(101 MHz, CDCl ): δ 161.1, 145.0, 140.9, 132.9, 130.7, 123.7, 122.8,

121.1, 118.3, 46.9, 30.7, 29.5, 27.2, 23.4, 22.8, 14.7, 14.6. IR (neat):

−1

2926, 2864, 1634, 1602, 1462, 740 cm . Mp: 117−119 °C.

5,6-Bis(benzyloxymethyl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

(3ag). Compound 3ag was prepared according to the general

procedure A and then was puriﬁed by ﬂash column chromatography

12b

of 3aa are in accordance with the literature.

H NMR (400 MHz,

CDCl ): δ 7.31 (d, J = 6.5 Hz, 1H), 7.26−7.21 (m, 3H), 7.16−7.08

(

m, 8H), 7.05−7.01 (m, 1H), 4.50 (t, J = 8.1 Hz, 2H), 3.42 (t, J = 8.1

13 1

Hz, 2H). C{ H} NMR (101 MHz, CDCl ): δ 160.2, 146.9, 141.6,

(EtOAc/hexane 20/80) to aﬀord 59.2 mg of 3ag in 72% yield as a

35.9, 135.5, 133.2, 130.9, 130.4, 129.7, 127.9, 127.5, 127.4, 126.8,

24.8, 123.6, 123.0, 118.4, 47.3, 27.1. IR (neat): 3043, 2921, 2856,

white solid. H NMR (400 MHz, CDCl ): δ 7.69 (d, J = 8.0 Hz, 1H),

7.37−7.27 (m, 11H), 7.15 (t, J = 7.7 Hz, 1H), 4.86 (s, 2H), 4.73 (s,

−

638, 1612, 1309, 774, 712 cm . Mp: 166−170 °C.

2H), 4.58 (s, 2H), 4.54 (s, 2H), 4.43 (t, J = 8.1 Hz, 2H), 3.39 (t, J =

,6-Di-p-tolyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3ab).

8.0 Hz, 2H). C{ H} NMR (101 MHz, CDCl ): δ 160.6, 144.6,

141.9, 138.4, 137.9, 130.6, 130.1, 128.5, 128.4, 128.1, 128.0, 127.9,

127.7, 125.2, 123.3, 122.7, 117.7, 73.0, 72.8, 65.4, 63.0, 47.2, 27.1.

HRMS: calcd for C H NO [M + H] , 434.1913; found, 412.1907.

−1

IR (neat): 3043, 2925, 1630, 1611, 1599, 745 cm . Mp: 122−125

°C.

411

J. Org. Chem. 2021, 86, 9407−9417

The Journal of Organic Chemistry

Article

,6-Bis(hydroxymethyl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

3ah). Compound 3ah was prepared according to the general

procedure A and then was puriﬁed by ﬂash column chromatography

EtOAc/hexane 60/40) to aﬀord 27.3 mg of 3ah in 59% yield as a

J = 7.7 Hz, 1H), 7.52−7.47 (m, 2H), 7.42 (dd, J = 8.4, 1.7 Hz, 1H),

7.37 (d, J = 7.3 Hz, 1H), 7.21 (t, J = 7.6 Hz, 1H), 4.48 (t, J = 8.1 Hz,

2H), 3.46 (t, J = 8.1 Hz, 2H), 2.74−2.72 (m, 2H), 1.17 (t, J = 7.6 Hz,

(

3H). C{ H} NMR (101 MHz, CDCl ): δ 160.7, 148.7, 141.9, 134.1,

brown solid. The reaction was continued for 48 h. H NMR (500

MHz, DMSO-d ): δ 7.71 (d, J = 8.1 Hz, 1H), 7.37 (d, J = 7.1 Hz,

H), 7.16 (t, J = 7.6 Hz, 1H), 5.27 (br s, 1H), 4.85 (br s, 1H), 4.79 (s,

H), 4.59 (s, 2H), 4.28 (t, J = 7.9 Hz, 2H), 3.37 (t, 7.7 Hz, 2H).

C{1H} NMR (126 MHz, DMSO-d ): δ 160.0, 145.7, 141.3, 131.2,

30.8, 124.8, 122.8, 122.3, 117.1, 56.4, 54.5, 47.0, 26.6. HRMS: calcd

for C H NO [M + H] , 232.0974; found, 232.0974.

133.5, 133.3, 132.9, 131.1, 128.7, 128.23, 128.21, 128.0, 127.8, 126.03,

126.00, 124.8, 123.1, 121.8, 117.7, 47.2, 27.3, 23.0, 14.7. HRMS: calcd

for C H NO [M + H] , 326.1545; found, 326.1539. IR (neat):

−

2924, 1636, 1595, 798, 758 cm . Mp: 117−119 °C.

6-Ethyl-5-(naphthalen-2-yl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-

one (3an). Compound 3an was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

(EtOAc/hexane 15/85) to aﬀord 32.0 mg of 3an in a 42% yield of the

-Methyl-5-phenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3ai).

Compound 3ai was prepared according to the general procedure A

and was puriﬁed by ﬂash column chromatography (EtOAc/hexane

major regioisomer as a white solid. The crude H NMR analysis

shows the formation of regioisomeric products with a ratio of 10:1. H

5/85) to aﬀord 39.7 mg of 3ai in a 76% yield of the major

NMR (400 MHz, CDCl ): δ 7.93−7.83 (m, 3H), 7.75 (s, 1H), 7.55−

regioisomer as a white solid. The crude H NMR analysis shows the

formation of regioisomeric products with a ratio of 14:1. The NMR

data of 3ai are in accordance with the literature.

7.47 (m, 3H), 7.40 (dd, J = 8.4, 1.7 Hz, 1H), 7.36 (dd, J = 7.3, 0.8 Hz,

1H), 7.22−7.18 (m, 1H), 4.48 (t, J = 8.6 Hz, 2H), 3.45 (t, J = 8.1 Hz,

2H), 2.71−2.69 (m, 2H), 1.61−1.54 (m, 2H), 1.26−1.11 (m, 6H),

12b

H NMR (400

MHz, CDCl ): δ 7.51 (d, J = 8.7 Hz, 1H), 7.45−7.42 (m, 2H), 7.38−

0.75 (t, J = 7.0 Hz, 3H). C{ H} NMR (101 MHz, CDCl ): δ 160.6,

.34 (m, 2H), 7.29−7.26 (m, 2H), 7.19 (t, J = 7.6 Hz, 1H), 4.46 (t, J

147.4, 141.7, 134.0, 133.35, 133.33, 132.7, 130.9, 128.8, 128.2, 128.0,

127.72, 127.66, 125.84, 125.80, 124.6, 122.9, 121.7, 117.9, 47.0, 31.3,

8.3 Hz, 2H), 3.44 (t, J = 8.1 Hz, 2H), 2.31 (s, 3H). C{ H} NMR

(

101 MHz, CDCl ): δ 160.3, 142.2, 141.2, 136.3, 133.6, 130.6, 130.2,

30.3, 29.6, 29.4, 27.1, 22.4, 13.9. HRMS: calcd for C H NNaO [M

27 27

28.1, 127.4, 124.6, 122.9, 121.6, 118.8, 47.0, 27.1, 16.1. IR (neat):

+ Na] , 404.1990; found, 404.1976. IR (neat): 3029, 2856, 1640,

−

−1

922, 2852, 1646, 1600, 738 cm . Mp: 149−152 °C.

1603, 1066, 737 cm . Mp: 122−124 °C.

-Ethyl-5-phenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3aj).

6-(Benzyloxymethyl)-5-phenyl-1H-pyrrolo[3,2,1-ij]quinolin-

4(2H)-one (3ao). Compound 3ao was prepared according to the

general procedure A and was puriﬁed by ﬂash column chromatog-

Compound 3aj was prepared according to the general procedure A

and was puriﬁed by ﬂash column chromatography (EtOAc/hexane

5/85) to aﬀord 40.7 mg of 3aj in a 74% yield of the major

raphy (EtOAc:/hexane 30/70) to aﬀord 57.3 mg of 3ao in 78% yield

regioisomer as a white solid. The crude H NMR analysis shows the

formation of regioisomeric products with a ratio of 12:1. The NMR

as a white solid. H NMR (500 MHz, CDCl

): δ 7.68 (d, J = 8.0 Hz,

1H), 7.43−7.24 (m, 11H), 7.17 (t, J = 7.7 Hz, 1H), 4.55 (s, 2H),

12b

data of 3aj are in accordance with the literature.

H NMR (400

4.47−4.44 (m, 4H), 3.43 (t, J = 8.0 Hz, 2H). C{ H} NMR (126

MHz, CDCl ): δ 160.3, 141.8, 140.8, 137.8, 135.7, 135.1, 130.6,

130.4, 128.5, 128.12, 128.10, 127.98, 127.94, 124.92, 123.3, 122.7,

MHz, CDCl ): δ 7.51 (d, J = 8.1, 1H), 7.44−7.40 (m, 2H), 7.35−7.31

(

m, 2H), 7.26−7.24 (m, 2H), 7.17 (t, J = 7.7 Hz, 1H), 4.43 (t, J = 8.3

Hz, 2H), 3.41 (t, J = 8.1 Hz, 2H), 2.67 (q, J = 7.6 Hz, 2H), 1.14 (t, J =

117.8, 73.0, 66.9, 47.3, 27.9. HRMS: calcd for C25

H22NO [M + H] ,

.6 Hz, 3H). ¹³C{ H} NMR (101 MHz, CDCl ): δ 160.7, 148.3,

368.1651; found, 368.1654. IR (neat): 2920, 1633, 1614, 1605, 1054,

−

41.9, 136.5, 133.4, 131.0, 129.9, 128.4, 127.5, 124.7, 123.1, 121.7,

17.7, 47.1, 27.3, 22.9, 14.6. IR (neat): 3523, 2923, 1631, 1594, 770,

699 cm . Mp: 119−121 °C.

6-(Hydroxymethyl)-5-phenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-

one (3ap). Compound 3ap was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

−

08 cm . Mp: 112−114 °C.

-Butyl-5-phenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (3ak).

Compound 3ak was prepared according to the general procedure A

and was puriﬁed by ﬂash column chromatography (EtOAc/hexane

(EtOAc/hexane 40/60) to aﬀord 30.0 mg of 3ap in 54% yield as a

white solid. H NMR (400 MHz, DMSO-d

): δ 7.75 (d, J = 7.9 Hz,

5/85) to aﬀord 41.3 mg of 3ak in a 68% yield of the major

1H), 7.42−7.33 (m, 4H), 7.30−7.28 (m, 2H), 7.16 (t, J = 7.7 Hz,

1H), 5.26 (t, J = 5.1 Hz, 1H), 4.43 (t, J = 5.0 Hz, 2H), 4.28 (t, J = 8.0

Hz, 2H), 3.37−3.33 (m, 2H) (overlapped with DMSO peak).

regioisomer as a white solid. The NMR data of 3ak are in accordance

12c

with the literature.

Hz, 1H), 7.45−7.42 (m, 2H), 7.38−7.33 (m, 2H), 7.27−7.25 (m,

H), 7.18(t, J = 7.6 Hz, 1H), 4.45 (t, J = 8.1 Hz, 2H), 3.43 (t, J = 8.1

H NMR (400 MHz, CDCl ): δ 7.51 (d, J = 7.9

C{ H} NMR (101 MHz, DMSO-d ): δ 159.2, 143.7, 141.3, 135.5,

133.0, 130.8, 130.4, 127.7, 127.4, 128.8, 122.8, 127.7, 117.0, 58.2,

Hz, 2H), 2.68−2.64 (m, 2H), 1.57−1.50 (m, 2H), 1.32−1.23 (m,

47.1, 26.6. HRMS: calcd for C H NO [M + H] , 278.1181; found,

−1

H), 0.80 (t, J = 7.3 Hz, 3H). C{ H} NMR (101 MHz, CDCl ): δ

278.1176. IR (neat): 3277, 2922, 1635, 1610, 1022, 759, 704 cm .

Mp: 210−213 °C.

60.6, 147.1, 141.8, 136.5, 133.6, 131.0, 130.0, 128.3, 127.5, 124.6,

23.0, 121.8, 118.0, 47.1, 32.3, 29.4, 27.2, 23.0, 13.8. IR (neat): 2954,

930, 1633, 1611, 700, 770 cm . Mp: 121−124 °C.

4-Methyl-N-((4-oxo-5-phenyl-2,4-dihydro-1H-pyrrolo[3,2,1-ij]-

quinolin-6-yl)methyl)benzenesulfonamide (3aq). Compound 3aq

was prepared according to the general procedure A and was puriﬁed

by ﬂash column chromatography (EtOAc/hexane 50/50) to aﬀord

−

-Methyl-5-(naphthalen-2-yl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-

one (3al). Compound 3al was prepared according to the general

procedure A. The crude reaction mixture was puriﬁed by ﬂash column

chromatography (EtOAc/hexane 15/85) to aﬀord 46.1 mg of 3al in

53.4 mg of 3aq in 62% yield as a white solid. H NMR (500 MHz,

DMSO-d ): δ 7.98 (t, J = 5.3 Hz, 1H), 7.62 (d, J = 8.1 Hz, 1H), 7.46

4% yield as a white solid. The NMR data of 3al are in accordance

(d, J = 8.2 Hz, 2H), 7.42 (d, J = 7.2 Hz, 1H) 7.31−7.26 (m, 5H),

12c

with the literature.

H NMR (400 MHz, CDCl ): δ 7.92 (d, J = 8.4

7.21−7.18 (m, 3H), 4.29 (t, J = 8.0 Hz, 2H), 3.87 (d, J = 5.3 Hz, 2H),

Hz, 1H), 7.90−7.84 (m, 2H), 7.77 (s, 1H), 7.54−7.48 (m, 3H), 7.44

3.40−3.35 (m, 2H), 2.37 (s, 3H). C{ H} NMR (126 MHz, DMSO-

(dd, J = 8.3, 1.4 Hz, 1H), 7.38 (d, J = 7.3 Hz, 1H), 7.21 (t, J = 7.6 Hz,

d ): δ 158.8, 142.7, 141.1, 139.1, 136.2, 134.9, 134.7, 130.8, 130.1,

H), 4.49 (t, J = 8.1 Hz, 2H), 3.45 (t, J = 8.1 Hz, 2H), 2.35 (s, 3H).

129.4, 127.5, 127.2, 126.4, 124.9, 122.8, 122.0, 116.4, 47.0, 41.5, 26.6,

C{ H} NMR (101 MHz, CDCl ): δ 160.5, 142.8, 141.3, 134.0,

20.9. HRMS: calcd for C H N O S [M + H] , 431.1249; found,

25 23

−

33.5, 133.4, 132.8, 130.8, 129.4, 128.4, 128.1, 127.7 (overlapped),

26.0, 125.9, 124.9, 123.2, 121.7, 119.0, 47.2, 27.3, 16.3. IR (neat):

431.1434. IR (neat): 3255, 1644, 1615, 1323, 1165, 712 cm . Mp:

218−221 °C.

6-Butyl-5-(hex-1-ynyl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

(3ar). Compound 3ar was prepared according to the general

procedure B and was puriﬁed by ﬂash column chromatography

−

924, 1638, 1601, 812, 746 cm . Mp: 146−149 °C.

-Ethyl-5-(naphthalen-2-yl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-

one (3am). Compound 3am was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

(EtOAc/hexane 20/80) to aﬀord 25.8 mg of 3ar in 42% yield as a

(EtOAc/hexane 15/85) to aﬀord 42.3 mg of 3am in a 65% yield of

white solid. H NMR (500 MHz, CDCl ): δ 7.43 (d, J = 8.0 Hz, 1H),

the major regioisomer as a white solid. H NMR (400 MHz, CDCl ):

δ 7.93 (d, J = 8.4 Hz, 1H), 7.90−7.84 (m, 2H), 7.75 (s, 1H), 7.56 (d,

7.28 (d, J = 6.8 Hz, 1H), 7.13 (t, J = 7.7 Hz, 1H), 4.40 (t, J = 8.1 Hz,

2H), 3.37 (t, J = 8.1 Hz, 2H), 3.05−3.02 (m, 2H), 2.55 (t, J = 7.0 Hz,

412

J. Org. Chem. 2021, 86, 9407−9417

The Journal of Organic Chemistry

Article

H), 1.67−1.56 (m, 4H), 1.56−1.44 (m, 4H), 0.99−0.94 (m, 6H).

white solid. The NMR data of 3ea are in accordance with the

12c

C{ H} NMR (126 MHz, CDCl ): δ 160.0, 152.9, 141.1, 130.9,

literature.

H NMR (400 MHz, CDCl ): δ 7.44 (d, J = 1.2 Hz,

25.0, 123.2, 121.3, 117.6, 117.2, 100.8, 75.7, 47.1, 31.4, 31.0, 30.5,

1H), 7.29−7.26 (m, 3H), 7.23 (br s, 1H), 7.17−7.08 (m, 7H), 4.54

7.2, 23.2, 22.2, 19.9, 14.0, 13.8. HRMS: calcd for C H NNaO [M

(t, J = 8.0 Hz, 2H), 3.46 (t, J = 8.0 Hz, 2H). C{ H} NMR (101

MHz, CDCl ): δ 160.1, 146.1, 140.7, 135.4, 135.1, 134.4, 132.7,

130.9, 129.7, 128.3, 128.1, 128.0, 127.6, 127.2, 126.1, 119.7, 115.8,

Na] , 330.1834; found, 330.1836. IR (KBr): 3439, 2921, 1637,

−

610, 771 cm . Mp: 120−123 °C.

-Cyclohexenyl-5-phenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

3as). Compound 3as was prepared according to the general

procedure B and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 15:85) to aﬀord 30.1 mg of 3as in a 46% yield of the

−

47.6, 27.1. IR (neat): 3057, 3023, 1640, 1619, 861, 709 cm . Mp:

188−190 °C.

(

(E)-5,6-Diphenyl-8-styryl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

(3fa). Compound 3fa was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

(

major regioisomer as a white solid. The crude H NMR analysis

shows the formation of regioisomeric products with a ratio of 6:1. H

(EtOAc/hexane 15/85) to aﬀord 67.0 mg of 3fa in 81% yield as a

NMR (500 MHz, CDCl ): δ 7.45 (d, J = 8.0 Hz, 1H), 7.38−7.23 (m,

white solid. H NMR (500 MHz, CDCl

): δ 7.64 (s, 1H), 7.44 (d, J =

H), 7.13 (t, J = 7.6 Hz, 1H), 5.67−5.65 (m, 1H), 4.50−4.46 (m,

7.4 Hz, 1H), 7.33−7.28 (m, 5H), 7.25−7.13 (m, 10H), 7.05 (d, J =

H), 3.45−3.42 (m, 2H), 2.15−1.87 (m, 4H), 1.72−1.36 (m, 4H).

16.3 Hz, 1H), 6.96 (d, J = 16.2 Hz, 1H), 4.57 (t, J = 8.1 Hz, 2H), 3.50

C{ H} NMR (126 MHz, CDCl ): δ 160.7, 149.6, 142.0, 136.2,

(t, J = 8.0 Hz, 2H). C{ H} NMR (126 MHz, CDCl ): δ 160.3,

33.2, 131.8, 130.6, 130.5, 129.7, 127.6, 127.3, 124.7, 123.3, 122.9,

147.0, 141.7, 137.3, 136.0, 135.6, 133.8, 133.1, 131.3, 131.1, 130.0,

128.8, 128.7, 128.2, 127.82, 127.80, 127.65, 127.60, 127.1, 126.4,

18.1, 47.3, 28.9, 27.3, 25.2, 22.7, 21.9. HRMS: calcd for

C H NNaO [M + Na] , 350.1521; found, 350.1523. IR (neat):

123.1. 122.3, 118.5, 47.8, 27.2. HRMS: calcd for C31

Na] , 448.1677; found, 448.1672.

23NNaO [M +

−

2921, 1638, 1613, 1598, 773, 717, 699 cm . Mp: 169−172 °C.

N-(5-Heptyl-4-oxo-2,4-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-6-yl)-

9-Bromo-5,6-diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

(3ga). Compound 3ga was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

(EtOAc/hexane 20/80) to aﬀord 75.6 mg of 3ga in 94% yield as a

white solid. The NMR data of 3ga are in accordance with the

N-methylmethanesulfonamide (3at). Compound 3at was prepared

according to the general procedure B and was puriﬁed by ﬂash

column chromatography (EtOAc/hexane 30/70) to aﬀord 29.4 mg of

at in 39% yield as an oﬀ-white solid. H NMR (500 MHz, CDCl ): δ

.49 (d, J = 8.1 Hz, 1H), 7.31 (d, J = 7.1 Hz, 1H), 7.19 (t, J = 7.6 Hz,

H), 4.43 (t, J = 8.0 Hz, 2H), 3.42 (t, J = 8.0 Hz, 2H), 3.28 (s, 3H),

.15 (s, 3H), 2.76−2.66 (m, 2H), 1.68−1.61 (m, 3H), 1.47−1.41 (m,

literature.

H NMR (400 MHz, CDCl

): δ 7.28−7.21 (m, 3H),

7.17−7.14 (m, 8H), 6.97 (d, J = 8.6 Hz, 1H), 4.53 (t, J = 8.1 Hz, 2H),

3.40 (t, J = 8.1 Hz, 2H). C{ H} NMR (101 MHz, CDCl ): δ 160.5,

H), 1.38−1.28 (m, 5H), 0.87 (t, J = 6.8 Hz, 3H). C{ H} NMR

146.8, 142.2, 135.6, 135.2, 133.4, 131.0, 130.9, 129.8, 128.2, 127.9,

127.6, 127.2, 126.0, 125.7, 119.6, 117.4, 47.0, 28.7.

(126 MHz, CDCl ): δ 161.0, 143.0, 141.3, 137.7, 130.8, 124.8, 123.8,

21.0, 117.3, 47.2, 40.1, 37.9, 31.9, 30.6, 29.2, 28.6, 28.5, 27.3, 22.8,

2-Methyl-5,6-diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

(3ha). Compound 3ha was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

4.2. HRMS: calcd for C H N NaO S [M + Na] , 399.1718; found,

−

99.1720. IR (KBr): 3431, 2924, 2852, 1635, 1617, 1337, 1159 cm .

(

EtOAc/hexane 20/80) to aﬀord 37.8 mg of 3ha in 56% yield as a

Mp: 102−105 °C.

-Methyl-5,6-diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

3ba). Compound 3ba was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 20/80) to aﬀord 57.4 mg of 3ba in 85% yield as a

white solid. The NMR data of 3ba are in accordance with the

white solid. The NMR data of 3ha are in accordance with the

literature.

12b

(

H NMR (500 MHz, CDCl ): δ 7.33−7.29 (m, 2H),

7.23−7.20 (m, 3H), 7.16−7.04 (m, 7H), 7.01 (d, J = 7.1 Hz, 1H),

(

5.18−5.12 (m, 1H), 3.69 (dd, J = 16.7, 9.4 Hz, 1H), 3.05 (dd, J =

16.7, 3.7 Hz, 1H), 1.69 (d, J = 6.4 Hz, 3H). C{ H} NMR (126

12c

literature.

H NMR (400 MHz, CDCl ): δ 7.30−7.24 (m, 3H),

MHz, CDCl ): δ 160.4, 147.0, 141.2, 136.2, 135.7, 134.0, 131.2,

.19 (s, 1H), 7.16−7.09 (m, 7H), 6.88 (s, 1H), 4.53 (t, J = 8.0 Hz,

130.0, 129.9, 129.2, 128.2, 128.0, 127.7, 127.6, 127.0, 125.0, 123.9,

123.1, 118.6, 57.3, 36.5, 20.8.

H), 3.44 (t, J = 8.0 Hz, 2H), 2.32 (s, 3H). C{ H} NMR (101

MHz, CDCl ): δ 160.3, 146.9, 140.0, 136.1, 135.7, 133.4, 133.0,

1-Methyl-5,6-diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

3ia). Compound 3ia was prepared according to the general

(

31.0, 130.7, 129.9, 128.1, 127.6, 127.5, 126.9, 126.5, 123.1, 118.3,

7.6, 27.2, 21.7.

procedure A and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 20/80) to aﬀord 42.5 mg of 3ia in 63% yield as a

white solid. The NMR data of 3ia are in accordance with the

(

-Methoxy-5,6-diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

3ca). Compound 3ca was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 20/80) to aﬀord 58.7 mg of 3ca in 83% yield as a

white solid. The NMR data of 3ca are in accordance with the

(

12b

literature.

H NMR (500 MHz, CDCl ): δ 7.33 (dd, J = 6.8, 1.1

(

Hz, 1H), 7.28−7.24 (m, 3H), 7.17−7.07 (m, 9H), 4.71 (dd, J = 12.9,

9.5 Hz, 1H), 4.09 (dd, J = 12.8, 5.4 Hz, 1H), 3.88−3.80 (m, 1H), 1.52

12c

literature.

H NMR (400 MHz, CDCl ): δ 7.29−7.24 (m, 3H),

(d, J = 6.9 Hz, 3H). C{ H} NMR (126 MHz, CDCl ): δ 160.4,

.16−7.11 (m, 7H), 7.02 (d, J = 1.3 Hz, 1H), 6.54 (d, J = 1.8 Hz,

147.1, 141.2, 136.2, 135.74, 135.70, 133.6, 131.1, 129.9, 128.1, 127.7,

127.6, 127.0, 124.02, 124.0, 123.2, 118.6, 55.4, 34.9, 21.0.

H), 4.55 (t, J = 7.9 Hz, 2H), 3.68 (s, 3H), 3.40 (t, J = 8.0 Hz, 2H).

C{ H} NMR (101 MHz, CDCl ): δ 159.9, 156.6, 146.6, 136.7,

5-Phenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (5aa). Com-

pound 5aa was prepared according to the general procedure C and

was puriﬁed by ﬂash column chromatography (EtOAc/hexane 10/90)

36.1, 135.8, 133.8, 132.0, 131.1, 129.8, 128.1, 127.7, 127.5, 127.0,

18.4, 115.0, 105.4, 56.1, 47.6, 27.3.

-Chloro-5,6-diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

3da). Compound 3da was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 15/85) to aﬀord 63.0 mg of 3da in 88% yield as a

white solid. The NMR data of 3da are in accordance with the

to aﬀord 34.1 mg of 5aa in 69% yield as a white solid. H NMR (400

(

MHz, CDCl

): δ 7.80 (s, 1H), 7.73 (d, J = 7.3 Hz, 2H), 7.43−7.42

(m, 3H), 7.38 (d, J = 7.0 Hz, 1H), 7.34 (d, J = 7.3 Hz, 1H), 7.16 (t, J

= 7.5 Hz, 1H), 4.53 (m, 2H), 3.47 (m, 2H). C{ H} NMR (101

MHz, CDCl ): δ 160.3, 142.2, 136.8, 135.4, 134.9, 130.5, 129.2,

(

12c

literature.

H NMR (400 MHz, CDCl ): δ 7.31−7.25 (m, 4H),

128.3, 128.2, 124.8, 123.7, 123.4, 117.9, 47.8, 27.5. HRMS: calcd for

.19−7.08 (m, 8H), 4.55 (t, J = 8.0 Hz, 2H), 3.47 (t, J = 8.0 Hz, 2H).

C H NNaO [M + Na] , 270.0895; found, 270.0890. IR (KBr):

−1

C{ H} NMR (101 MHz, CDCl ): δ 160.0, 146.0, 140.2, 135.3,

3431, 2924, 1644, 1618, 1261, 775 cm . Mp: 122−124 °C.

5-p-Tolyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (5ab). Com-

pound 5ab was prepared according to the general procedure C and

was puriﬁed by ﬂash column chromatography (EtOAc/hexane 10/90)

35.0, 134.3, 132.2, 130.8, 129.6, 128.4, 128.2, 127.8, 127.5, 127.1,

25.4, 123.0, 119.0, 47.5, 27.0.

-Bromo-5,6-diphenyl-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

3ea). Compound 3ea was prepared according to the general

procedure A and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 15/85) to aﬀord 50.9 mg of 3ea in 81% yield as a

(

to aﬀord 35.0 mg of 5ab in 67% yield as a white solid. H NMR (400

MHz, CDCl ): δ 7.80 (s, 1H), 7.63 (d, J = 8.1 Hz, 2H), 7.41 (d, J =

(

7.9 Hz, 1H), 7.31 (d, J = 7.2 Hz, 1H), 7.24 (d, J = 7.9 Hz, 2H), 7.15

413

J. Org. Chem. 2021, 86, 9407−9417

The Journal of Organic Chemistry

Article

(

t, J = 7.4 Hz, 1H), 4.50 (t, J = 8.0 Hz, 2H), 3.44 (t, J = 8.0 Hz, 2H),

5-(Naphthalen-2-yl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

(5ah). Compound 5ah was prepared according to the general

procedure C and was puriﬁed by ﬂash column chromatography

.40 (s, 3H). ¹³C{ H} NMR (126 MHz, CDCl ): δ 160.3, 142.1,

38.0, 134.7, 133.9, 130.4, 129.02, 129.0 (overlapped), 124.6, 123.6,

23.3, 117.9, 47.6, 27.4, 21.4. HRMS: calcd C H NO is [M + H] ,

(EtOAc/hexane 10/90) to aﬀord 35.1 mg of 5ah in 59% yield as

62.1232; found, 262.1224. IR (KBr): 3429, 2961, 1642, 1611, 1020,

white solid. H NMR (400 MHz, CDCl

): δ 8.26 (s, 1H), 7.94 (s,

−

H), 7.90−7.84 (m, 4H), 7.51−7.44 (m, 3H), 7.34 (d, J = 7.0 Hz,

19 cm . Mp: 115−118 °C.

-(4-tert-butylphenyl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

5ac). Compound 5ac was prepared according to the general

procedure C and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 7/93) to aﬀord 38.2 mg of 5ac in 63% yield as a

H), 7.17 (t, J = 7.6 Hz, 1H), 4.54 (t, J = 8.0 Hz, 2H), 3.46 (t, J = 8.0

Hz, 2H). C{ H} NMR (101 MHz, CDCl ): δ 160.3, 142.2, 135.6,

(

134.6, 134.3, 133.4, 133.1, 130.5, 128.5, 128.3, 127.6, 127.0, 126.3,

(

126.1, 124.8, 123.7, 123.4, 117.8, 47.6, 27.4. HRMS: calcd for

white solid. H NMR (400 MHz, CDCl ): δ 7.82 (s, 1H), 7.68 (d, J =

15NNaO [M + Na] , 320.1051; found, 320.1054. IR (KBr):

−

.2 Hz, 2H), 7.45 (d, J = 8.1 Hz, 2H), 7.41 (d, J = 7.9 Hz, 1H), 7.32

3436, 2928, 1644, 1615, 737 cm . Mp: 158−161 °C.

(

d, J = 7.2 Hz, 1H), 7.15 (t, J = 7.6 Hz, 1H), 4.52 (t, J = 8.0 Hz, 2H),

.45 (t, J = 8.0 Hz, 2H), 1.35 (s, 9H). C{ H} NMR (101 MHz,

Procedure D for the Reduction of 5-Phenyl-1H-pyrrolo-

[3,2,1-ij]quinolin-4(2H)-one (5aa). An oven-dried Schlenk tube

equipped with a magnetic stir bar was charged with 5-phenyl-1H-

pyrrolo[3,2,1-ij]quinolin-4(2H)-one (5aa; 24.7 mg, 0.1 mmol, 1.0

CDCl ): δ 160.3, 151.1, 142.1, 134.8, 134.6, 133.9, 130.4, 128.8,

for C H NNaO [M + Na] , 326.1521; found, 326.1521. IR (neat):

25.3, 124.6, 123.6, 123.3, 117.9, 47.6, 34.7, 31.4, 27.4. HRMS: calcd

equiv) in air followed by addition of Pd(OH) /C (10.0 mg) and

−

EtOAc (1.0 mL). The Schlenk tube was vacuumized and ﬁlled with

959, 2852, 1644, 1618, 1606, 834, 773 cm . Mp: 122−125 °C.

-(4-Methoxyphenyl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one

5ad). Compound 5ad was prepared according to the general

procedure C and was puriﬁed by ﬂash column chromatography

EtOAc/hexane 15/85) to aﬀord 30.0 mg of 5ad in 54% yield as a

H (1−2 atm). The closed Schlenk tube was then placed at 40 °C for

4 h. After completion of the reaction, the reaction mixture was then

(

cooled to room temperature. The crude mixture was puriﬁed by ﬂash

column chromatography (ethyl acetate/hexane) on silica gel,

(

aﬀording 5-phenyl-5,6-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-

white solid. H NMR (500 MHz, CDCl ): δ 7.78 (s, 1H), 7.71−7.69

(

hz, 1H), 6.97−6.95 (m, 2H), 4.50 (t, J = 8.1 Hz, 2H), 3.85 (s, 3H),

one (6) in 69% (17.2 mg) yield. H NMR (500 MHz, CDCl ): δ

m, 2H), 7.40 (d, J = 7.9 Hz, 1H), 7.31−7.29 (m, 1H), 7.14 (t, J = 7.6

.31−7.24 (m, 5H), 7.11 (d, J = 7.5 Hz, 1H), 7.01 (d, J = 7.4 Hz,

1H), 6.95 (t, J = 7.4 Hz, 1H), 4.15−4.11 (m, 2H), 3.93 (t, J = 7.5 Hz,

NMR (126 MHz, CDCl ): δ 168.2, 141.2, 140.0, 129.0, 128.8, 128.1,

.44 (t, J = 8.0 Hz, 2H). C{ H} NMR (126 MHz, CDCl ): δ 160.2,

H), 3.32 (dd, J = 16.4, 7.1 Hz, 1H), 3.24−3.17 (m, 3H). C{ H}

59.5, 141.8, 134.1, 134.0, 130.2 (overlapped), 129.1, 124.3, 123.4,

23.2, 117.8, 113.6, 55.3, 47.4, 27.3. HRMS: calcd for C H NO [M

127.3, 125.5, 123.6, 123.5, 119.9, 48.2, 45.7, 33.1, 28.0. HRMS: calcd

H] , 278.1181; found, 278.1176. IR (KBr): 3436, 2924, 2853, 1647,

−

for C H NNaO [M + Na] , 272.1051; found, 272.1053. IR (neat):

607, 1246, 1176, 830 cm . Mp: 98−100 °C.

−

027, 2924, 1651, 1479, 762, 696 cm . Mp: 114−116 °C.

-(4-Fluorophenyl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (5ae).

Procedure E for the Oxidation of 5-Phenyl-1H-pyrrolo-

Compound 5ae was prepared according to the general procedure C

and was puriﬁed by ﬂash column chromatography (EtOAc/hexane

NMR (400 MHz, CDCl ): δ 7.79 (s, 1H), 7.72−7.69 (m, 2H), 7.41

(

[

3,2,1-ij]quinolin-4(2H)-one (5aa). An oven-dried Schlenk tube

equipped with a magnetic stir bar was charged with 5-phenyl-1H-

pyrrolo[3,2,1-ij]quinolin-4(2H)-one (5aa; 24.7 mg, 0.1 mmol, 1.0

equiv) under an argon atmosphere followed by addition of DDQ

0/90) to aﬀord 36.1 mg of 5ae in 68% yield as a white solid. H

d, J = 7.9 Hz, 1H), 7.33 (d, J = 7.2 Hz, 1H), 7.17 (d, J = 7.6 Hz, 1H),

(

113.5 mg, 0.5 mmol, 5.0 equiv) and 1,4-dioxane (1.0 mL). The

.14−7.08 (m, 2H), 4.50 (t, J = 8.0 Hz, 2H), 3.45 (t, J = 8.0 Hz, 2H).

closed tube was placed in a preheated oil bath at 110 °C, and the

contents were stirred for 12 h. After completion of the reaction, the

reaction mixture was then cooled to room temperature. The crude

mixture was puriﬁed by ﬂash column chromatography (ethyl acetate/

hexane 15/85) on silica gel, aﬀording 5-phenyl-4H-pyrrolo[3,2,1-

C{ H} NMR (126 MHz, CDCl ): δ 162.8 (d, J

= 247.3 Hz),

C−F

60.1, 142.2, 135.1, 133.7, 132.8 (d, J

.1 Hz), 130.5, 124.8, 123.7, 123.4, 117.7, 115.2 (d, J

7.6, 27.4. F (373 Mz, CDCl ): −113.86. HRMS: calcd for

= 3.0 Hz), 130.9 (d, J

C−F

= 21.4 Hz),

C−F

C H FNO [M + H] , 266.0981; found, 266.0966. IR (KBr): 3431,

ij]quinolin-4-one (7) in 62% (15.2 mg) yield. H NMR (500 MHz,

−

923, 1640, 1604, 1233, 776, 831 cm . Mp: 162−164 °C.

-(4-Bromophenyl)-1H-pyrrolo[3,2,1-ij]quinolin-4(2H)-one (5af).

CDCl ): δ 8.04 (d, J = 3.5 Hz, 1H), 7.94 (s, 1H), 7.84 (d, J = 7.5 Hz,

H), 7.74−7.64 (m, 1H), 7.65 (d, J = 7.5 Hz, 1H), 7.49−7.40 (m,

Compound 5af was prepared according to the general procedure C

and was puriﬁed by ﬂash column chromatography (EtOAc/hexane

NMR (500 MHz, CDCl ): δ 7.82 (s, 1H), 7.62 (d, J = 8.4 Hz, 2H),

Hz, 2H). C{ H} NMR (126 MHz, CDCl ): δ 159.9, 142.3, 135.7,

found, 326.0172. IR (KBr): 3431, 2961, 2920, 1617, 1644, 1103, 813

cm . Mp: 150−152 °C.

H), 6.93 (d, J = 3.5 Hz, 1H). C{ H} NMR (126 MHz, CDCl ): δ

58.8, 136.6, 136.4, 135.4, 132.2, 129.2, 128.5, 128.4, 127.6, 125.0,

24.34, 124.30, 117.3, 111.1. HRMS: calcd for C H NNaO [M +

0/90) to aﬀord 34.0 mg of 5af in 52% yield as a brown solid. H

Na] , 268.0738; found, 268.0739. IR (neat): 2922, 1660, 1633, 783

cm . Mp: 115−117 °C.

.55 (d, J = 8.5 Hz, 2H), 7.42 (d, J = 7.9 Hz, 1H), 7.35 (d, J = 7.2 Hz,

H), 7.17 (t, J = 7.6 Hz, 1H), 4.51 (t, J = 8.0 Hz, 2H), 3.46 (t, J = 8.0

−1

Competitive Experiment with Alkynes. An oven-dried Schlenk

tube equipped with a magnetic stir bar was charged with

35.3, 113.6, 131.4, 130.8, 130.6, 125.0, 123.8, 123.6, 122.4, 117.7,

Cp*Co(CO)I (9.5 mg, 0.02 mmol, 10 mol %) and AgOTf (10.2

7.7, 27.4. HRMS: calcd for C H BrNO [M + H] , 326.0181;

mg, 0.04 mmol, 20 mol %) under an argon atmosphere. A small

amount of TFE (0.5 mL) was placed in the Schlenk tube, and the

contents were stirred for 1−2 min. Then, N,N-dimethylindoline-1-

carboxamide (1a; 38.0 mg, 0.2 mmol, 1.0 equiv), 1,2-diphenylethyne

−

-Methyl-N-(3-(4-oxo-2,4-dihydro-1H-pyrrolo[3,2,1-ij]quinolin-5-

yl)phenyl)benzenesulfonamide (5ag). Compound 5ag was prepared

according to the general procedure C and was puriﬁed by ﬂash

column chromatography (EtOAc/hexane 10/90) to aﬀord 54.1 mg of

(

2a; 17.8 mg, 0.1 mmol, 0.5 equiv), and dodec-6-yne (2e; 16.6 mg,

.1 mmol, 0.5 equiv) followed by Zn(OTf) (21.8 mg, 0.06 mmol, 30

mol %) and 1.5 mL of TFE were successively placed in the Schlenk

tube. The closed tube was placed in a preheated oil bath at 110 °C.

After 16 h, the reaction mixture was then cooled to room temperature.

The crude reaction mixture was passed through a short pad of silica,

ag in 65% yield as a gummy solid. H NMR (500 MHz, DMSO-d ):

δ 10.26 (bs, 1H), 7.87 (s, 1H), 7.70 (d, J = 8.2 Hz, 1H), 7.54−7.50

(

m, 2H), 7.39−7.32 (m, 6H), 7.15 (t, J = 7.6 Hz, 1H), 7.08 (d, J = 8.0

Hz, 1H), 4.34 (t, J = 7.9 Hz, 2H), 3.37−3.36 (m, 2H) (overlapped

with DMSO peak), 2.31 (s, 3H). C{ H} NMR (126 MHz, CDCl ):

and the ratio of 3aa and 3ae was calculated from a H NMR analysis

(3aa :3ae = 1.0:1.23) (see the NMR spectra in the Supporting

Information ).

Competitive Experiment with N-Carbamoyl Indoline De-

rivatives. An oven-dried Schlenk tube equipped with a magnetic stir

δ 158.6, 143.2, 141.9, 137.6, 137.5, 136.7, 135.3, 132.7, 130.7, 129.7,

28.7, 126.8, 125.0, 124.5, 123.6, 123.1, 120.5, 119.2, 116.7, 47.4,

6.8, 20.9. HRMS: calcd for C H N O S [M + H] , 326.0181;

found, 326.0172. IR (neat): 3392, 2853, 1640, 1608, 1157, 1003, 761

cm .

bar was charged with Cp*Co(CO)I (9.5 mg, 0.02 mmol, 10 mol %)

−

and AgOTf (10.2 mg, 0.04 mmol, 20 mol %) under an argon

414

J. Org. Chem. 2021, 86, 9407−9417

The Journal of Organic Chemistry

S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonodo, M.;

Article

atmosphere. A small amount of TFE (0.5 mL) was placed in the

Schlenk tube, and the contents were stirred for 1−2 min. Then,

N,N,5-trimethylindoline-1-carboxamide (1b; 20.4 mg, 0.1 mmol, 0.5

equiv), 5-bromo-N,N-dimethylindoline-1-carboxamide (1e; 26.9 mg,

ACKNOWLEDGMENTS

■

Financial support provided by DST (INT/RUS/RFBR/359)

to carry out this research is gratefully acknowledged. R.M. and

B.G. thank the CSIR and PMRF for their fellowships.

.1 mmol, 0.5 equiv) and 1,2-diphenylethyne (2a; 35.6 mg, 0.2 mmol,

.0 equiv) followed by Zn(OTf) (21.8 mg, 0.06 mmol, 30 mol %)

and 1.5 mL of TFE were successively placed in the Schlenk tube. The

closed tube was placed in a preheated oil bath at 110 °C. After 24 h,

the reaction mixture was then cooled to room temperature. The crude

reaction mixture was passed through a short pad of silica, and the ratio

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AUTHOR INFORMATION

■

4) (a) Yoshino, T.; Ikemoto, H.; Matsunaga, S.; Kanai, M. Cp*Co ^I ^I ^I

Corresponding Author

Catalyzed C2-Selective Addition of Indoles to Imines. Chem. - Eur. J.

2013 , 19 , 9142 −9146. (b) Sun, B.; Yoshino, T.; Matsunaga, S.; Kanai,

M. Air-Stable Carbonyl(pentamethylcyclopentadienyl)cobalt Diio-

d i d e C o m p l e x a s

Pentamethylcyclopentadienyl)cobalt(III) Catalysis: Application for

Basker Sundararaju − Fine Chemical Laboratory, Department

of Chemistry, Indian Institute of Technology Kanpur,

Kanpur, Uttar Pradesh, India 208016; orcid.org/0000-

P r e c u r s o r f o r C a t i o n i c

see: (a) Yoshino, T.; Matsunaga, S. (Pentamethylcyclopentadienyl)-

003-1112-137X ; Email: basker@iitk.ac.in

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Authors

2014, 356, 1491−1495.

III

(

5) For reviews on Cp*Co -catalyzed C −H bond functionalization,

Rajib Mandal − Fine Chemical Laboratory, Department of

Chemistry, Indian Institute of Technology Kanpur, Kanpur,

Uttar Pradesh, India 208016

Bholanath Garai − Fine Chemical Laboratory, Department of

Chemistry, Indian Institute of Technology Kanpur, Kanpur,

Uttar Pradesh, India 208016

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Recent Developments in Cobalt Catalyzed Carbon-Carbon and

Carbon-Heteroatom Bond Formation via C-H Bond Functionaliza-

tion. Synthesis 2017 , 49 , 1419 −1443. (d) Moselage, M.; Li, J.;

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.joc.1c00713

Ackermann, L. Cobalt-Catalyzed C-H Activation. ACS Catal. 2016 , 6 ,

Notes

98 −525. (e) Yoshikai, N. Cp *Co Catalyzed C-H Activation of

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