Efficient access to triarylmethanes through decarboxylation

Article abstract of DOI:10.1039/c6ra25429b

A new synthetic approach has been developed for efficient access to triarylmethanes by palladium catalyzed decarboxylative cross coupling reactions. The reaction features sp²-sp³ coupling where benzoic acids upon decarboxylation reac

Full text of DOI:10.1039/c6ra25429b

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Efficient access to triarylmethanes through
decarboxylation†
Cite this: RSC Adv., 2017, 7, 6966
Tiash Saha,a M. Srinivas Lavanya Kumar,a Saurav Bera,a Bidhu Bhusan Karkaraa
ab
*
and Gautam Panda
Received 18th October 2016
Accepted 2nd January 2017
A new synthetic approach has been developed for efficient access to triarylmethanes by palladium
catalyzed decarboxylative cross coupling reactions. The reaction features sp2–sp3 coupling where
benzoic acids upon decarboxylation reacted with diaryl methyl iodides having both electron donating
and withdrawing functionalities, leading to the synthesis of diverse triarylmethanes.
DOI: 10.1039/c6ra25429b
www.rsc.org/advances
functionalized in the quest for new therapeutic agents and
unexplored biologically relevant chemical spaces.3 Several triar-
Introduction
ylmethane based dyes were also developed as sensitizers, exhib-
iting selective phototoxicity towards cancerous cell lines and thus
forms the basic principle of photodynamic therapy.4 These tri-
arylmethanes exhibit interesting properties like photo lability,
photo ionization which were successfully exploited for the
development of many organic based dyes, photochromatic
devices and uorescent probes.4b,5 Apart from this, these class of
compounds oen found their explosive growth in the construc-
tion of supramolecular architectures.6
The triarylmethane class of molecules contains several biologi-
cally signicant motifs displaying a wide range of pharmaceutical
proles.1 It forms the basic skeleton of several antitubercular,2a
anticancer,2b,c antidiabetic2d and other medicinally important
molecules, Fig. 1. These privileged architectures can be diversely
Conventionally, triarylmethanes are synthesized through
typical Friedel–Cras alkylation of diarylcarbinols with aromatic
ring as nucleophile7 or hydroarylation of arenes with aromatic
aldehydes or imines in the presence of either suitable Bronsted or
Lewis acid systems.1a Recently, Crudden et al. reported the
synthesis of triarylmethanes through arylative desulfonation8
whereas Chakravarty et al. reported Friedel–Cras reaction on
benzylic phosphates for the synthesis of triarylmethanes.9a These
procedures oen suffer from lack of selectivity, involves multi-
step synthesis and moreover is limited to only electron rich arene
systems.9b,c
Due to this, cross coupling based strategies emerged as
promising avenue for the short and efficient synthesis of triaryl-
methanes.10 Oshima et al. reported palladium catalyzed direct C–H
bond activation11 of aryl(azaaryl)methanes for synthesis of
´
triarylmethanes. L. A. Lopez et al. reported zinc catalyzed cascade
reaction between enynones and azoles resulting in the diversely
substituted triarylmethanes synthesis.12 A reductive cross coupling
was developed by Zhang et al. using benzophenone tosylhy-
drazones using palladium catalyst.13 Jarvo et al. synthesized
enantioenriched triarylmethanes by stereospecic cross coupling
in presence of nickel catalyst.14 Similarly, palladium catalysed C–
H/C–O coupling of oxazoles with diarylmethanol derivatives have
also been reported for synthesis of triarylmethanes.15
Fig. 1 Representative triarylmethane containing architectures.
aMedicinal and Process Chemistry Division, CSIR-Central Drug Research Institute, BS
10/1, Jankipuram Extension, Sitapur Road, Lucknow 226031, India. E-mail: gautam.
panda@gmail.com; gautam_panda@cdri.res.in; Fax: +91-522-2771941; Tel: +91-
522-2772450 ext. 4661; +91-522-2772550 ext. 4662
bAcademy of Scientic and Innovative Research, New Delhi 110001, India
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra25429b
Decarboxylative cross coupling reaction has been emerged as
a powerful strategy for C–C bond formation16 in the recent past
6966 | RSC Adv., 2017, 7, 6966–6971
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and had been largely explored. Organometallic species formed architectures. For the test reaction, we have chosen 2,6 dime-
via expulsion of CO2 from commercially available arene thoxy benzoic acid and diphenylmethyl iodide21 as model
carboxylic acids were ventured in this cross coupling strategy. substrates. Preliminary screening using Pd(OAc)2 and dppp as
Goossen et al. synthesized arylalkenes via decarboxylative cross a ligand in the presence of Ag2CO3 (Table 1, entries 1 and 2) was
coupling.17 Palladium catalyzed decarboxylative cross coupling, unsuccessful. Then changing the palladium catalyst to
as demonstrated by Becht and coworkers18 were used in the Pd2(dba)3 (Table 1, entry 3) resulted in 22% yield. Altering the
synthesis of biaryl motifs. Even industrial scale production of bases to Cs2CO3, Li2CO3, Cs2CO3, AgOAc, DBU and K2CO3 were
commercially important biaryls like intermediates of agro- unable to increase the yield of the desired product to signicant
chemicals boscalid, bixafen has been demonstrated by this level. Employing additive such as CuI, resulted in trace amount
strategy.19 Decarboxylation reactions were well explored in sp– of product. Keeping palladium source intact, varying the
sp2, sp2–sp2 cross couplings whereas sp2–sp3 coupling was ligands to triphenyl phosphine and 1,10-phenanthroline resul-
hardly explored.20 In our quest for highly desirable triar- ted in more or less comparable yields but xantphos gave
ylmethanes,1b,2b,7 we here reported an efficient palladium cata- promising yields (Table 1, entries 4–6). Some by-products due to
lyzed decarboxylative sp2–sp3 cross coupling for the access to protodecarboxylation of carboxylic acids and deiodination of
triarylmethanes with both electron demanding and donating diphenyl methyl iodides were also isolated.22,23 Then surveying
substitutions using commercially available benzoic acids with various palladium catalysts like Pd(CH3CN)2Cl2 and Pd(Cl)2(-
tailor made diarylmethyl iodides.
PPh3)2, Pd(acac)2, PdCl2 and careful solvent screening revealed
that PdCl2 along with xantphos ligand, Ag2CO3 as base in
presence of DMSO offered the ideal conditions for the reaction
(Table 1, entry 11).
Results and discussion
Aer optimizing the catalyst system for decarboxylative
coupling reactions, the scopes of substrates were evaluated with
reference to both the coupling partners (Table 2). Poor yields
were obtained in the case of diphenylmethyl bromide (38%) and
In principle, we presumed that aromatic carboxylic acids16a can
be used as boronic acid surrogate and palladium catalyst could
synchronize coupling16b between decarboxylated benzoic
species with diarylmethyl iodides leading to these valuable
Table 1 Optimization of conditions for decarboxylative cross coupling
Entrya
Catalyst
Ligand
Solvent
Yieldf (%)
1b
2
3
4
5
6
7
8
9
10
11
12
13
Pd(OAc)2
Pd(OAc)2
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
PdCl2
Pd(acac)2
Pd(Cl)2(PPh3)2
Pd(OAc)2
PdCl2
Dppp
Dppp
Dppp
THF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
0
Ndg
22 (trace)c
Ndg
42
1,10-Phenanthroline
Xantphos
PPh3
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
Xantphos
34
59 (47)d
31
DMF
DMF
40
42
DMSO
NMP : mesitylene (1 : 1)
Diglyme
62 (68)e
Trace
15
PdCl2
PdCl2
a
Reaction conditions: Pd source (0.1 equiv.), ligand (0.2 equiv.), Ag2CO3 (1.5 equiv.), arene carboxylic acid (1.2 equiv.), methyl iodide (1.0 equiv.),
b
c
d
e
100 ꢀC. Reaction was performed at 65 ꢀC. CuI additive (0.2 eq.) is used. Pd catalyst (0.2 eq.) was used. Reaction was performed at 120 ꢀC.
f
Overall isolated yield. g Nd means not determined.
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Table
2 Substrate scope for decarboxylative cross coupling of
aromatic carboxylic acid
Fig. 2 Synthesis of heteroaryl substituted triarylmethanes.
reaction failed when performed with diphenylmethyl chloride.
The electron rich 2,6 dimethoxy benzoic acid 1a was success-
fully coupled with various diphenylmethyl iodides which
provided sterically hindered triarylmethanes 3aa–3ae, 3ah in
good yields. Similarly, 2-methoxy benzoic acid 1b was success-
fully cross coupled with diphenylmethyl iodide derivatives 2a,
2f, 2g and even with the substrate 2i resulting in triarylmethane
derivatives 3ba, 3bf, 3bg and 3bi. Thus, the reaction was also
compatible with unsubstituted benzene carboxylic acids
affording the products 3ca, 3cj in 67% and 56% yield, respec-
tively. Even sterically demanding benzoic acid 1e also worked
well in this strategy leading to cross coupled product 3ef. In
order to explore the feasibility of this reaction further, cross
coupling reaction was performed between electron poor coun-
terparts. Slight modication in the reaction conditions needed
for the elaboration of this cross coupling reaction to electron
poor triaryl methanes. Doubling the amount of catalyst and
ligand and changing the solvent system to DMSO : DMF
(90 : 10) resulted the coupling of 2-uoro 5-nitro benzoic acid
1d and 2-nitrobenzoic acid 1f with the methyl iodide 2k
successfully in moderate yields leading to 3dk and 3
respectively.
Electron density on aromatic backbone showed strong inu-
ence on reactivity and yields. Thus, the catalyst system showed its
suitability for wide variety of diphenylmethyl iodides and both
electron rich and electron poor benzoic acids successfully
underwent decarboxylation to yield diverse triarylmethanes.
Aer establishing the decarboxylative cross coupling reac-
tion with arenes, we veried the methodology towards synthe-
sizing heteroaryl containing triarylmethanes. Attempted
decarboxylative cross coupling (Fig. 2) between phenyl thio-
phenyl methyl iodide and benzoic acid was also successful
using 0.2 equiv. PdCl2, 0.4 equiv. xantphos, 2.0 equiv. Ag2CO3 at
ꢀ
140 C in DMSO : DMF (90 : 10) for 24 h. Agreeably, the cross
coupling product 5 was observed in good yield and it provided
a new horizon in the synthesis of antitubercular analogue of
CDRI-830 using sp2–sp3 decarboxylative cross coupling.2a
Experimental section
General
a
All the reactions were carried out in oven-dried glassware under
argon atmosphere. Carboxylic acids were purchased from Sigma
Aldrich. Palladium catalysts were purchased from Sigma Aldrich.
Phosphine ligands were bought from Sigma-Aldrich or Alfa Aesar
and used as such. DMSO and DMF was dried according to
Reaction conditions: substituted diphenylmethyl iodide (1 equiv.), aryl
carboxylic acid (1 equiv.), PdCl2 (0.1 equiv.), xantphos (0.2 equiv.),
Ag2CO3 (1.5 equiv.), DMSO. Substituted diphenylmethyl iodide (1
equiv.), aryl carboxylic acid (1 equiv.), PdCl2 (0.2 equiv.), xantphos (0.4
equiv.), Ag2CO3 (1.5 equiv), DMSO : DMF (90 : 10). Isolated yields
b
c
aer column chromatography in silica gel.
˚
standard procedure and stored on molecular sieves 4 A. All the
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other reagents and solvents mentioned in this text were bought degassed with argon thrice and stirred in preheated oil bath at
from Sigma Aldrich or Alfa Aesar or spectrochem and puried if requisite temperature and was monitored by TLC. Aer the
necessary. NMR spectra were recorded on 300, 400 or 500 MHz completion of reaction, mixture was cooled to room tempera-
1
spectrometer for H NMR, 75 or 100 or 125 MHz for 13C NMR ture and ltered through a bed celite with ethyl acetate. The
spectroscopy. Chemical shis are reported in parts per million (d) organic layer was washed with saturated NH4Cl solution and
downeld relative to the residual signals of tetramethylsilane in dried on sodium sulphate and concentrated in vacuo. It was
CDCl3. Spin multiplicities are indicated by the following later puried by column chromatography on silica gel to obtain
symbol: s (singlet), d (doublet), t (triplet) and m (multiplet).
corresponding triarylmethanes.
General procedure for synthesis of diphenyl carbinols
Spectroscopic data of synthesized compounds
((2,6-Dimethoxyphenyl)methylene)dibenzene
A 100 ml double-necked round bottom ask was charged with
magnesium (2 equiv.), pinch of iodine and aer ushing with
nitrogen, dried THF was added and stirred. Then corresponding
bromoarene (1.5 equiv.) was added, the colour of iodine dis-
appeared slowly on time, indicating the generation of Grignard
reagent. It was stirred for one hour followed by addition of
corresponding carbaldehye (1 equiv.). Completion of reaction
was determined by TLC. Reaction was quenched by saturated
NH4Cl solution. Organic layer was extracted thrice with ethyl
acetate and concentrated in vacuo. Compound was puried by
column chromatography.
(3aa).
Prepared following the general procedure A. Rf: 0.35 (2% EtOAc
in Hex). Isolated as pale brown, oily liquid (yield: 68%). 1H NMR
(400 MHz, CDCl3): d 7.27–7.06 (m, 10H), 6.73–6.71 (m, 1H),
6.46–6.37 (m, 2H), 5.82 (s, 1H), 3.78 (s, 3H), 3.68 (s, 3H) ppm. 13
C
NMR (100 MHz, CDCl3): 158.2 (2C), 143.0 (2C), 129.5 (4C), 128.1
(4C), 126.8 (2C), 124.6, 102.5 (2C), 97.4, 54.3, 54.0, 47.9 ppm. IR
(lm, cmꢁ1): 2817, 1726, 1582, 1231, 814, 770, 637. MS (ESI): m/z
305 (M + H)+. HRMS (ESI): m/z calcd for C21H21O2 [M + H]+
305.1536, found 305.1542.
1,3-Dimethoxy-2-(phenyl(o-tolyl)methyl)benzene
(3ab).
Prepared following the general procedure A. Rf: 0.4 (2% EtOAc
in Hex). Isolated as yellow oily liquid (yield: 70%). 1H NMR (400
General procedure for synthesis of diphenyl methyl iodide
To oven dried round bottom ask under nitrogen, the alcohol (1 MHz, CDCl3): d 7.22–7.02 (m, 8H), 6.79–6.35 (m, 4H), 5.89 (s,
equiv.) and KI (1 equiv.) were added and dissolved in dry 1,4- 1H), 3.78 (s, 3H), 3.68 (s, 3H), 2.18 (s, 3H) ppm. 13C NMR (100
dioxane and stirred for 5 min. Then BF3$Et2O (1 equiv.) was MHz, CDCl3): 159.3, 158.0, 143.6, 142.6, 136.7, 130.6, 130.1,
added and stirred at room temperature. Completion of reaction 129.5 (2C), 128.9, 128.0 (2C), 126.0, 125.8, 125.4, 124.7, 103.7,
was monitored by TLC. The reaction mixture was poured in cold 98.6, 55.6, 55.2, 45.9, 19.6 ppm. IR (lm, cmꢁ1): 2828, 1631,
water and extracted with dichloromethane. The organic layer 1536, 1483, 1284, 1171, 823, 772, 656. MS (ESI): m/z 319 (M + H)+.
was washed with water and dried by sodium sulphate; solvent HRMS (ESI): m/z calcd for C22H23O2 [M + H]+ 319.1693, found
was evaporated under reduced pressure. The crude was puried 319.1691.
by quickly passing through short pad of silica using hexane/
1-Methoxy-2-(phenyl(p-tolyl)methyl)benzene (3bf). Prepared
ethyl acetate (8 : 2) as eluent to obtain diphenylmethyl iodides following the general procedure A. Rf: 0.6 (1.5% EtOAc in Hex).
1
and should be used immediately.
Yield: 72%. H NMR (400 MHz, CDCl3): d 7.23–6.80 (m, 11H),
6.43–6.34 (m, 2H), 5.69 (s, 1H), 3.70 (s, 3H), 2.27 (s, 3H) ppm. 13
C
NMR (100 MHz, CDCl3): 156.2, 144.4, 141.1, 141.0, 135.1, 135.0,
132.7, 132.6, 129.1, 129.0, 129.0, 128.6, 127.8, 125.6, 125.5,
124.1, 103.7, 98.6, 55.8, 48.6, 21.0 ppm. IR (lm, cmꢁ1): 1689,
1276, 948, 879, 847, 716. MS (ESI): m/z 289 (M + H)+. HRMS (ESI):
m/z calcd for C21H21O [M + H]+ 289.1587, found 289.1594.
1,3-Dimethoxy-2-(phenyl(4-propylphenyl)methyl)benzene (3ac).
Prepared following the general procedure A. Rf: 0.3 (2% EtOAc in
Hex). Yield: 80%, 1H NMR (400 MHz, CDCl3): d 7.25–6.96 (m, 9H),
6.75–6.73 (m, 1H), 6.45–6.37 (m, 2H), 5.79 (s, 1H), 3.77 (s, 3H), 3.68
(s, 3H), 2.54 (t, 2H, J ¼ 7.83 Hz), 1.64–1.59 (m, 2H), 0.92 (t, 3H, J ¼
7.32 Hz) ppm. 13C NMR (100 MHz, CDCl3): 159.3, 157.9, 144.5,
141.3, 140.1, 130.7, 129.3 (2C), 129.1 (2C), 128.1 (2C), 128.0 (2C),
125.8, 125.5, 103.7, 98.6, 55.5, 55.2, 48.6, 37.6, 24.4, 13.9 ppm. IR
(lm, cmꢁ1): 3248, 1692, 1452, 1268, 910, 880, 730, 633. MS (ESI):
m/z 347 (M + H)+. HRMS (ESI): m/z calcd for C24H27O2 (M + H)+
347.2006, found 347.2003.
General procedure A for synthesis of various substituted
triarylmethanes by decarboxylative cross coupling
To the oven dried round bottom ask was charged with aryl
carboxylic acid (1 equiv.), Ag2CO3 (1.5 equiv.), PdCl2 (0.1 equiv.),
xantphos (0.2 equiv.), diphenyl methyl iodides (1 equiv.) were
dissolved in DMSO. The reaction mixture was degassed with
argon thrice and stirred in preheated oil bath. Reaction as
monitored by TLC aer completion, the reaction mixture was
cooled to room temperature and ltered through celite bed. The
organic layer was washed with saturated NH4Cl solution and
dried on sodium sulphate and concentrated under reduced
pressure. It was later puried by column chromatography on
silica gel to obtain corresponding triarylmethanes.
General procedure B for synthesis of substituted
triarylmethanes by decarboxylative cross coupling
1,3-Dimethoxy-2-((4-methoxyphenyl)(phenyl)methyl)benzene
To the oven dried round bottom ask was charged with aryl (3ad). Prepared following the general procedure A. Rf: 0.2 (3%
1
carboxylic acid (1 equiv.), Ag2CO3 (1.5 equiv.), PdCl2 (0.2 equiv.), EtOAc in Hex). Yield: 74%, H NMR (400 MHz, CDCl3): d 7.35–
xantphos (0.4 equiv.), diphenyl methyl iodides (1 equiv.) were 6.36 (m, 12H), 5.76 (s, 1H), 3.76 (s, 3H), 3.76 (s, 3H), 3.67 (s,
dissolved in DMSO : DMF 90 : 10. The reaction mixture was 3H) ppm. 13C NMR (100 MHz, CDCl3): 159.3, 158.9, 157.9, 144.6,
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136.3, 130.6, 130.3, 129.3, 128.5, 128.3, 128.0, 127.1, 127.0, 125.8, 747, 615. MS (ESI): m/z 309 (M + H)+. HRMS (ESI): m/z calcd for
125.5, 113.4, 103.7, 98.6, 55.6, 55.2, 55.2, 48.3 ppm. IR (lm, C20H18ClO [M + H]+ 309.1041, found 309.1050.
cmꢁ1): 2802, 1664, 1596, 1327, 932, 815, 804, 730, 623. MS (ESI):
((4-(Triuoromethyl)phenyl)methylene)dibenzene
m/z 335 (M + H)+. HRMS (ESI): m/z calcd for C22H23O3 (M + H)+ Prepared following the general procedure A. Rf: 0.5 (1% EtOAc
335.1642, found 335.1632.
in Hex). Yield: 56%. 1H NMR (400 MHz, CDCl3): d 7.54–7.52 (m,
1,3-Dimethoxy-2-((4-methoxyphenyl)(o-tolyl)methyl)benzene 2H), 7.31–7.21 (m, 8H), 7.10–7.08 (m, 4H), 5.59 (s, 1H) ppm. 13
(3cj).
C
(3ae). Prepared following the general procedure A. Rf: 0.3 (4% NMR (100 MHz, CDCl3): 148.0, 142.9 (2C), 129.7, 129.3 (6C),
1
EtOAc in Hex). Yield: 72%, H NMR (400 MHz, CDCl3): d 7.17– 128.5 (6C), 126.6, 125.2, 125.2, 56.6. IR (lm, cmꢁ1): 2812, 1664,
6.28 (m, 11H), 5.76 (s, 1H), 3.70 (s, 6H), 3.60 (s, 3H), 2.10 (s, 1543, 1320, 932, 815. MS (ESI): m/z 313 (M + H)+. HRMS (ESI): m/
3H) ppm. 13C NMR (100 MHz, CDCl3): 159.3, 157.9, 157.7, 143.0, z calcd for C20H16F3 [M + H]+ 313.1199, found 313.1198.
136.6, 135.6, 130.5, 130.3, 130.1 (2C), 128.7 (2C), 125.9, 125.4,
4-((2-Fluoro-5-nitrophenyl)(phenyl)methyl)-1,10-biphenyl (3dk).
125.0, 113.4, 103.7, 98.6, 55.6, 55.2, 55.1, 45.1, 19.5 ppm. IR Prepared following the general procedure B. Rf: 0.5 (3% EtOAc in
(lm, cmꢁ1): 2902, 1685, 1536, 1347, 911, 776. MS (ESI): m/z 349 Hex). Yield: 42%, 1H NMR (400 MHz, CDCl3): d 7.58–7.54 (m, 4H),
(M + H)+. HRMS (ESI): m/z calcd for C23H25O3 (M + H)+ 349.1798, 7.45–7.32 (m, 6H), 7.29–7.25 (m, 7H), 5.48 (s, 1H) ppm. 13C NMR
found 349.1810.
(100 MHz, CDCl3): 145.2, 142.1, 140.8, 140.0, 137.8, 132.3, 130.7,
1-((4-Ethoxyphenyl)(phenyl)methyl)-2-methoxybenzene (3bg). 130.0, 128.9, 128.7, 128.4, 128.3 (4C), 128.1 (2C), 127.6 (2C), 127.3,
Prepared following the general procedure A. Rf: 0.3 (2% EtOAc in 127.2, 127.1, 127.0, 126.9, 79.8. IR (lm, cmꢁ1): 2883, 1904, 1684,
Hex). Yield: 68%, 1H NMR (400 MHz, CDCl3): d 7.08–6.29 (m, 13H), 1892, 1543, 871, 810, 742, 613. MS (ESI): m/z 384 (M + H)+. HRMS
5.62 (s, 1H), 3.90 (m, 2H), 3.62 (s, 3H), 1.31 (t, 3H, J ¼ 5.4 Hz) ppm. (ESI): m/z calcd for C25H19FNO2 [M + H]+ 384.1394, found
13C NMR (100 MHz, CDCl3): 157.0, 156.2, 144.6, 136.2, 136.1, 132.6, 384.1402.
132.5, 130.0 (2C), 129.1 (3C), 127.9 (2C), 125.6, 124.3, 113.9, 95.5,
2-((4-Methoxyphenyl)(o-tolyl)methyl)-1,3-dimethylbenzene (3ef).
63.3, 55.8, 48.2, 14.9 ppm. IR (lm, cmꢁ1): 2815, 1664, 1592, 1585, Prepared following the general procedure A. Rf: 0.5 (2% EtOAc
1320, 1104, 932, 812, 730, 623. MS (ESI): m/z 319 (M + H)+. HRMS in Hex). Yield: 74%. 1H NMR (400 MHz, CDCl3): d 7.42–7.40 (m,
(ESI): m/z calcd for C22H23O2 [M + H]+ 319.1693, found 319.1693.
1H), 7.31–7.12 (m, 10H), 5.40 (s, 1H), 3.38 (s, 3H), 2.26 (s,
2-((3,4-Dimethoxyphenyl)(phenyl)methyl)-1,3-dimethoxyben- 9H) ppm. 13C NMR (100 MHz, CDCl3): 144.6, 141.8, 141.4,
zene (3ah). Prepared following the general procedure A. Rf: 0.3 141.0, 139.9, 139.6, 136.4, 136.0, 130.6, 130.5, 128.3, 128.2,
(5% EtOAc in Hex). Yield: 79%, 1H NMR (400 MHz, CDCl3): 127.9, 127.6, 127.4, 126.2, 126.1 (2C), 57.1, 47.4, 19.5 (2C),
d 7.18–6.29 (m, 11H), 5.68 (s, 1H), 3.76 (s, 3H), 3.70 (s, 3H), 3.67 19.3 ppm. IR (lm, cmꢁ1): 2984, 1683, 1317, 981, 823, 728, 604.
(s, 3H), 3.61 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): 158.2, HRMS (ESI): m/z calcd for C23H25O [M + H]+ 317.1900, found
156.8, 147.4, 146.0, 143.3, 135.6, 129.4 (2C), 128.1 (2C), 126.8, 317.1898.
124.7, 124.2, 120.1, 111.7, 109.5, 102.6, 97.5, 54.6, 54.6, 54.4,
4-((2-Nitrophenyl)(phenyl)methyl)-1,10-biphenyl
(3).
54.1, 47.5 ppm. IR (lm, cmꢁ1): 2805, 1664, 1587, 1523, 1320, Prepared following the general procedure A. Rf: 0.4 (2% EtOAc
1104, 897, 816. MS (ESI): m/z 365 (M + H)+, HRMS (ESI): m/z calcd in Hex). Yield: 49%, 1H NMR (400 MHz, CDCl3): d 7.58–7.54 (m,
for C23H25O3 [M + H]+ 365.1747, found 365.1756.
5H), 7.46–7.40 (m, 7H), 7.36–7.28 (m, 6H), 5.48 (s, 1H) ppm. IR
((2-Methoxyphenyl)methylene)dibenzene (3ba). Prepared (lm, cmꢁ1): 2873, 1796, 1676, 1579, 1544, 923, 815, 794, 745,
following the general procedure A. Rf: 0.5 (1% EtOAc in Hex). 631. HRMS (ESI): m/z calcd for C25H20NO2 [M + H]+ 366.1489,
1
Yield: 71%, H NMR (400 MHz, CDCl3): d 7.27–6.79 (m, 14H), found 366.1499.
5.48 (s, 1H), 3.75 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): 158.0,
1-((4-Methoxyphenyl)(3-(triuoromethyl)phenyl)methyl)-3-
144.3 (2C), 136.1, 130.4 (2C), 129.4 (5C), 128.3 (4C), 126.2 9 (2C), nitrobenzene (3gl). Prepared following the general procedure B.
113.7, 56.0, 55.2 ppm. IR (lm, cmꢁ1): 2943, 1685, 1576, 1280, Rf: 0.4 (3% EtOAc in Hex). Yield: 51%. 1H NMR (400 MHz,
810, 730. MS (ESI): m/z 275 (M + H)+. HRMS (ESI): m/z calcd for CDCl3): d 7.85–7.79 (m, 1H), 7.56–7.51 (m, 2H), 7.42–7.36 (m,
C20H19O [M + H]+ 275.1430, found 275.1439.
3H), 7.09–7.06 (m, 2H), 7.01–7.00 (m, 2H), 6.85–6.82 (m, 2H),
Triphenylmethane (3ca). Prepared following the general 5.85 (s, 1H), 3.80 (S, 3H) ppm. IR (lm, cmꢁ1): 2907, 1886, 1673,
1
procedure A. Rf: 0.5 (1% EtOAc in Hex). Yield: 67%, H NMR 1584, 1543, 1281, 942, 881, 634. HRMS (ESI): m/z calcd for
(400 MHz, CDCl3): d 7.33–7.09 (m, 15H), 5.54 (s, 1H) ppm. 13C
C
21H17F3NO3 [M + H]+ 388.1155, found 388.1149.
NMR (100 MHz, CDCl3): 143.9 (3C), 129.5, 128.3 (6C), 128.3 (6C),
1-Chloro-3-((4-methoxyphenyl)(3-(triuoromethyl)phenyl)-
128.2, 126.3, 56.9 ppm. IR (lm, cmꢁ1): 2987, 1642, 1586, 1572, methyl)benzene (3hl). Prepared following the general procedure
1121. MS (ESI): m/z 245 (M + H)+. HRMS (ESI): m/z calcd for B. Rf: 0.2 (2% EtOAc in Hex). Yield: 56%. H NMR (400 MHz,
1
C
19H17O [M + H]+ 245.1325, found 245.1329.
CDCl3): d 7.24–7.22 (m, 1H), 7.04–6.98 (m, 2H), 6.95–6.93 (m,
1-((4-Chlorophenyl)(phenyl)methyl)-2-methoxybenzene (3bi). 3H), 6.89–6.88 (m, 2H), 6.85–6.84 (m, 1H), 6.82–6.79 (m, 2H),
Prepared following the general procedure A. Rf: 0.3 (2% EtOAc in 6.63–6.62 (m, 1H), 5.82 (s, 1H), 3.78 (S, 3H) ppm. IR (lm, cmꢁ1):
Hex). Yield: 62%. 1H NMR (400 MHz, CDCl3): d 7.25–7.19 (m, 6H), 2928, 1691, 1564, 1298, 911, 828, 804. HRMS (ESI): m/z calcd for
7.07–6.99 (m, 4H), 6.87–6.79 (m, 3H), 5.87 (s, 1H), 3.69 (s,
C
21H17ClF3O [M + H]+ 377.0915, found 377.0919.
2-Benzhydrylthiophene (5). Prepared following the general
3H) ppm. 13C NMR (100 MHz, CDCl3): 157.0, 143.3, 142.5, 132.1,
1
131.8, 130.7, 130.2, 129.4 (2C), 128.2 (5C), 127.8, 126.2, 120.3, procedure A. Rf: 0.6 (1% EtOAc in Hex). Yield: 50%. H NMR
110.7, 55.5, 49.0 ppm. IR (lm, cmꢁ1): 2763, 1675, 1297, 981, 824, (400 MHz, CDCl3): d 7.30–7.17 (m, 11H), 6.92 (m, 1H), 6.68 (m,
1H), 5.67 (s, 1H) ppm. 13C NMR (100 MHz, CDCl3): 147.9, 143.8
6970 | RSC Adv., 2017, 7, 6966–6971
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(2C), 128.8 (4C), 128.4 (4C), 126.7, 126.6, 126.4 (2C), 124.5, 52.1.
IR (lm, cmꢁ1): 1592, 1585, 1365, 623. MS (ESI): m/z 251 (M +
H)+. HRMS (ESI): m/z calcd for C17H15S [M + H]+ 251.0889, found
251.0892.
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Conclusion
In conclusion, we reported an efficient pathway for synthesizing
various triarylmethanes using sp2–sp3 decarboxylative cross
coupling reactions. These reactions showed functional group
tolerance, providing moderate to good yields of diverse triaryl-
methanes in less complicated steps. Decarboxylative cross
coupling on heteroaryl methyl iodide provides an opportunity
for accessing diverse biologically important triarylmethanes
and work in this direction is currently underway.
Acknowledgements
´
´
12 J. Gonzalez, C. P. Calleja, L. A. Lopez and R. Vicente, Angew.
This research project was partly supported by DST project (SB/
S1/OC-93/2013). SLKM and SB thank Council of Scientic and
Industrial Research (CSIR), India for research fellowship.
Instrumental facilities from SAIF, CDRI is acknowledged (CDRI
Communication No. 9408).
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