External oxidant-free dehydrogenative lactonization of 2-arylbenzoic acids via visible-light photocatalysis

Article abstract of DOI:10.1021/acs.joc.7b03195

An external oxidant-free C-H functionalization/C-O bond formation reaction for constructing benzo-3,4-coumarins accompanied by quantitative H₂ evolution has been developed. High functional group tolerance and excellent reaction efficiency are s

Full text of DOI:10.1021/acs.joc.7b03195

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External Oxidant-Free Dehydrogenative Lactonization
of 2-Arylbenzoic Acids via Visible-Light Photocatalysis
Ailong Shao, Jirui Zhan, Na Li, Chien-Wei Chiang, and Aiwen Lei
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b03195 • Publication Date (Web): 05 Mar 2018
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The Journal of Organic Chemistry
External OxidantꢀFree Dehydrogenative Lactonization of 2ꢀ
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Arylbenzoic Acids via VisibleꢀLight Photocatalysis
Ailong Shao,a Jirui Zhan,a Na Li,a ChienꢀWei Chiang,*a and Aiwen Lei*a,b
a Institute for Advanced Studies (IAS), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P.
R. China
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b National Research Center for Carbohydrate Synthesis, Jiangxi Normal University, Nanchang 330022, Jiangxi, P. R. China
ABSTRACT: An external oxidantꢀfree C–H functionalization/C–O bond formation reaction for constructing benzoꢀ3,4ꢀcoumarins
accompanying with quantitative H2 evolution has been developed. High functional group tolerance and excellent reaction efficiency
is shown in this transformation. Meanwhile, the substrates containing heterocyclic substituents such as thienylꢀ, pyridinylꢀ, pyrrolꢀ
ylꢀbenzoic acids displayed well performance. Importantly, this reaction can be performed with good efficiency on gram scale. CV
study
and
DFT
calculations
could
provide
insights
into
the
mechanism
of
this
reaction.
■ INTRODUCTION
Intramolecular cyclization of tethered carbon atoms or heteroatoms onto proximate CꢀH bonds is one of the most straightforward
and efficient method for numerous ringꢀformations.1 However, these reactions mainly utilized the traditionalꢀmetal catalysis strateꢀ
gy or excess of oxidants to perform the reaction under high temperature, which would limit the practical application of these reacꢀ
tions. Recently, photocatalysis has emerged as the new generation method to perform CꢀH bond functionalization.2 The combinaꢀ
tion of photoꢀredox catalyst and cobaloxime catalyst could achieve oxidative crossꢀcoupling reactions under the oxidantꢀfree condiꢀ
tions, which could satisfy the demand of green chemistry.3 This dual catalytic system provided a great opportunity for the synthesis
of various ringꢀformations through the oxidative intramolecular cyclization reaction without the requirement of stoichiometric oxiꢀ
dants, in which the unexpected chemical waste can be avoided and the H2 served as the only byꢀproduct.
Benzoꢀ3,4ꢀcoumarins possess a privileged structural cores in the natural products and pharmaceuticals such as Cell proliferation
inhibitor,4a Alternariol,4b, 4c and Graphislactones4d, 4e (Scheme 1a). In a view of the important synthetic applications of benzoꢀ3,4ꢀ
coumarins, tremendous efforts have been made to develop methods through the intramolecular CꢀH lactonization of 2ꢀarylbenzoic
acids. Early on, the synthesis of benzoꢀ3,4ꢀcoumarins usually required harsh reaction conditions, such as chromic acid oxidant and
ultraviolet irradiation.5 Recently, transitionꢀmetal catalysed oxidative CꢀH lactonization has been developed to realize this CꢀO
bond formation.6 In addition, Martin and his coꢀworker developed a metalꢀfree CꢀH lactonization process in which the inꢀsitu genꢀ
erated hypervalent iodine spieces was an important intermediate.7 Besides, the photoꢀredox catalysis also provided an alternative
approach for this oxidative intramolecular cyclization reaction. In 2013, Wei et al. reported oxidative lactonization of 2ꢀarylbenzoic
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acids mediated by NIS for the synthesis of dibenzopyranones.8 In 2015, GonzalezꢀGomez et al. also described a visibleꢀlight photoꢀ
catalytic oxidative CꢀO coupling of 2ꢀarylbenzoic acids using NH4S2O8 as stoichiometric oxidant9 and Gilmour et al. reported diꢀ
rect synthesis of coumarins from Eꢀcinnamic acids by using (−)ꢀRiboflavin as photocatalyst and oxygen as terminal oxidant.10 More
recently, Luo et al. and Zhu et al. demonstrated a photoredoxꢀcobalt coꢀcatalyzed system to perform the dehydrogenative lactonizaꢀ
tion of 2ꢀarylbenzoic acids, accompanied by hydrogen evolution.11a,11b We also envisioned that the merge of photoredox catalyst
and cobaloxime catalyst should has the capacity of realizing the dehydrogenative lactonization with hydrogen evolution, which
could provide an alternative avenue to build CꢀO bond (Scheme 1b).
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Scheme 1. (a) Natural and Pharmaceutical Molecules; (b) External Oxidantꢀfree Dehydrogenative Lactonization of 2ꢀ
Arylbenzoic Acids via VisibleꢀLight Photocatalysis.
■ RESULTS AND DISCUSSION
We began our studies by using 2ꢀphenylbenzoic acid (1a) as the model substrate to exam the suitable conditions for this photoꢀ
redox cobaloxime catalyzed CꢀH lactonization reaction. To our delight, the desired product can be isolated in 75% yield and quantiꢀ
tative H2 can be detected by GCꢀTCD in the presence of the Fukuzumi’s acridium photosensitizer and a protonꢀreduction catalyst
Co(dmgH)2(4ꢀMe2NꢀC5H4N)Cl after 10 h irradiation of blue light. Further investigation on photocatalysts demonstrated that only
ꢀ
Acr+ꢀMesClO4 enabled the coumarin product formation, while Ru(bpy)3Cl2, Ru(bpz)3(PF6)2 and Ir(ppy)3 not effective (Table 1,
entry 1 ꢀ 4). Meanwhile, the investigation in protonꢀreduction catalyst showed that the cobalt catalyst C emerged as the best cataꢀ
lysts for this reaction (Table 1, entry 1, 5, 6). Since the redox potential of catalyst A (E°(CoII/I) = ꢀ1.13 V vs SCE) and B (E°(CoII/I) = ꢀ
1.13 V vs SCE) is significantly lower than catalyst C (E°(CoII/I) = ꢀ0.81 V vs SCE),15a which indicates that catalyst A or B would
show a lower oxidative efficiency than C to oxidize radical intermediate. Besides, the reaction was drastic inhibited when the addiꢀ
tive was introduced to this reaction (Table 1, entry 7, 8, 9). Two explanations we proposed: (1) in some degree, we thought that
because of the special structure of acridinium catalyst, the alkaline additives would gradually make it deactivation and then interꢀ
rupt the reaction. Meanwhile, according to the investigation of the reaction conditions of references 11, this reaction could be carꢀ
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ried out smoothly with a moderate yield without adding any alkaline additives. And by using 2,6ꢀlutidine or PhCO2Na as a promotꢀ
er was a well option just to improve the reaction efficiency. However, in our protocol, we just carried out a strict deoxygenation
process of the reaction system; (2) different types of bases might lead to differences in the efficiency of the reaction. For example,
trimethylamine was more basic than 2,6ꢀlutidine11a and could react with the substrate to generate a stable ammonium salt to stop the
reaction. Meanwhile, it also had a strong reducing ability to destroy the structure of the acridinium catalyst. Moreover, chlorine
atoms on the cobalt catalyst C might be replaced by triethylamine to form a new cobalt catalyst, reduced reactivity of original coꢀ
balt catalyst. Finally, control experiments showed that the photocatalyst, cobaloxime catalyst and visible light were indispensable in
this transformation (Table 1, entry 10, 11, 12).
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Table 1. Optimization of the Reaction Conditions.a
Entry [Co]
Photocatalyst
Acr+–Mes ClO4
Ru(bpy)3Cl2
Additive
Yield (%)b
1c
A
A
A
A
B
C
C
C
C
C
ꢀ
ꢀ
75
0
ꢀ
2
ꢀ
3
Ru(bpz)3(PF6)2
Ir(ppy)3
ꢀ
0
4
5c
6c
7c
8c
9c
10c
11c
12c, d
ꢀ
0
Acr+–Mes ClO4
Acr+–Mes ClO4
Acr+–Mes ClO4
Acr+–Mes ClO4
Acr+–Mes ClO4
ꢀ
ꢀ
75
99
15
5
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Na2CO3
Et3N
NH4OAc
30
0
ꢀ
ꢀ
ꢀ
Acr+–Mes ClO4
Acr+–Mes ClO4
0
ꢀ
ꢀ
C
0
a Conditions: 1 (0.20 mmol), Photocatalyst (1.5 mol%) and Co Catalyst (2 mol%) were mixed in CH3CN (1 mL) under nitrogen
b
atmosphere and irradiated with 3W blue LEDs at room temperature for 10 h; H2 was detected by gas chromatography; Isolated
yields were showed. c Through a strict deoxygenation process (for details, see the Experimental Section). d Without light.
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With the optimized condition in hand, we turned to explore the functional group tolerances for the construction of benzoꢀ3,4ꢀ
coumarins (Table 2). The effect of Ar1 will be firstly investigated. For instance, both electronꢀrich and electronꢀpoor 4′ꢀsubstituted
aryl carboxylic acids could furnish the corresponding products in moderate to excellent yields (Table 2, 2a, 2b, 2c, 2f, 2g). Notably,
this reaction could tolerate an unprotected OH group (Table 2, 2h) and halogen groups, such as fluoro, chloro (Table 2, 2d, 2e).
Meanwhile, the corresponding benzocoumarins (Table 2, 2i, 2j) were obtained in moderate yields and with good regioselectivities.
Naphthalene ring and dibenzofuran ring could also be tolerated in this reaction (Table 2, 2k, 2l). Distinct from the prior reports in
reference 11, we found that thiofuran and pyridyl heterocyclic motifs could be incorporated, and with complete regiocontrol (Table
2, 2m, 2n). Interestingly, none of the other regioisomer of 2k, 2m, 2n was observed. Benzoic acid with pyrrolyl heterocyclic motif
could also transform into the corresponding product in good yield (Table 2, 2o). In addition, Ar2, which is bound the carboxylate
group directly, with either electronꢀrich or electronꢀpoor substituents could provide the good reactivity to build benzoꢀ3,4ꢀ
coumarins (Table 2, 2p – 2v). The yields of substrates with electron deficient substituents showed a slightly decrease (Table 2, 2s,
2t vs 2q, 2r). In the meantime, substrates with halogen groups, such as fluoro, chloro, could be transformed into the target products
in good yield
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Table 2. Substrate Scope of the Synthesis of substituted Benzoꢀ3,4ꢀcoumarins.a
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a Conditions: 1 (0.20 mmol), Acr+ꢀMesClO4 (1.5 mol%) and Co(dmgH)2Cl2 (2 mol%) were mixed in CH3CN (1 mL) under niꢀ
ꢀ
trogen atmosphere, and irradiated with 3W blue LEDs at room temperature for 10 h; H2 was detected by gas chromatography; isoꢀ
2
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lated yields were shown. * = Minor regioisomer (NOESY spectra of 2d, see supporting information Figure S2).
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(Table 2, 2u, 2v). Naphthalene was also tolerated in this transformation and gave 75% isolated yield (Table 2, 2p). However, when
the ortho position of Ar1 was substituted, the reaction was significantly inhibited (Scheme 2), indicating that the steric effect on the
ortho position would influence the coupling efficiency.
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Scheme 2. The Reactivity of different 2′ꢀSubstituted Acids.
Cl
Cl
1.5 mol% Acr+-MesClO4
,
,
-
2 mol% Co(dmgH)2Cl2,
OH
O
O
CH3CN, RT,
Blue LEDs, 10 h
O
O
O
Yield: < 5%
Yield: 20%
1.5 mol% Acr+-MesClO4
-
2 mol% Co(dmgH)2Cl2,
OH
O
CH3CN, RT,
Blue LEDs, 10 h
O
O
Yield: < 5%
To explore the synthetic potential of this oxidantꢀfree lactonization, some aryl cinnamic acids such as 1w and 1x, were syntheꢀ
sized and tested under standard conditions (Scheme 3). 2w and 2x could be successfully obtained as the corresponding coumarins in
good yield. Interestingly, orthoꢀenyl benzoic acids such as 1y and 1z, could react to form isocoumarins, which is different from the
recent work that Luo and his coꢀworkers have published.11a A possible explanation is that CF3CH2OH is a protic solvent and probaꢀ
bly used as a Hꢀatom donor, yet CH3CN is considered as a nonꢀprotic solvent, which lead to the difference to the results of two
transformations. According to the proposed mechanism, we suggested that after the radical addition of a carboxyl radical to C=C
bond, the alkyl radical could be obtained. When CF3CH2OH was used as a solvent, the new generated alkyl radical would proceed a
hydrogen atom transfer with CF3CH2OH to give an antiꢀMarkovnikov hydrocarboxylation product. However, in our study, CH3CN
was considered as a nonꢀprotic solvent with a higher BDE, which made it difficult to accomplish the hydrogen atom transfer proꢀ
cess with the new generated alkyl radical. Consequently, the generated alkyl radical was transferred to cation intermediate after
undergoing a single electron transfer (SET) process with Co(II) intermediate and quickly lost a proton to produce the desired prodꢀ
uct.
Scheme 3. Scope of Aryl Cinnamic Acids and orthoꢀenyl Benzoic Acids.
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Furthermore, a gramꢀscale synthesis of this oxidantꢀfree dehydrogenative lactonization was performed (Scheme 4), 6 mmol of 1a
could be cyclized to 2a in 85% yield (1.01 g) and performed the dehydrogenation. This result indicated that the photoredoxꢀcobalt
coꢀcatalyzed dehydrogenation crossꢀcoupling had a great potential in practical synthesis.
Scheme 4. GramꢀScale Synthesis.
In order to gain more insight of the reaction mechanism, we experimentally explored the presence of radical intermediates. Firstꢀ
ly, radical trapping reagents such as BHT and triethyl phosphite have been introduced to the reaction mixture. As the results, the
reaction could be completely quenched by above reagents (Scheme 5a). Thus, we proposed that this transformation might proceed
through a radical pathway. In addition, the competitive intermolecular kinetic isotopic effect has been done (kH/kD = 1.10), this reꢀ
sult suggested that the CꢀH bond cleavage might not be the rateꢀdetermining step in this process (Scheme 5b).
Scheme 5. Mechanistic Studying.
Moreover, cyclic voltammetry (CV) experiments of a series of substrates and their deprotonated salts have been performed (Figꢀ
ure 1a and 1b). In the CV experiments, electronꢀpoor and electronꢀneutral substrates 1 showed a relatively higher redox potential
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(E1/2 red = +2.20 – 2.55 V vs SCE) to an excited state of acridinium (E*1/2 red = +2.08 V vs SCE)12 (Figure 1a), indicating that these
1
2
substrates could not be oxidized directly by the photocatalyst. In contrast, the redox potential of sodium aryl benzoates Na(1ꢀ) (E1/2
3
4
= +1.58 – 1.71 V vs SCE) were apparently lower than photocatalyst (Figure 1b). Therefore, aryl benzoate (1ꢀ) would be an inꢀ
red
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termediate in the catalytic process.
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(a)
(b)
Figure 1. (a) Cyclic voltammetry of a series of arylbenzoic acid 1; (b) a series of sodium arylbenzoates Na(1ꢀ) in CH3CN with nꢀ
Bu4NBF4 (0.2 M) as the electrolyte under nitrogen at a platinumꢀdisk electrode at a scan rate of 100 mVsꢀ1.
In addition, DFT calculation was developed to explain the generation of oxidative species. The spin density map of the oxidative
species was showed in Figure 2. According to the result, we found that when carboxyl acid was deprotonated preliminarily, the
singleꢀelectronꢀoxidative species would be generated an oxygen radical 1a• which mainly located on the oxygen atom of the carꢀ
boxyl group. Then this oxygen radical would perform cyclization through an intramolecular attack with the aryl ring.
Figure 2. The spin density plot of 1a radical. Blue and green represent the spinꢀup and spinꢀdown spinꢀdensity, respectively.
As we all know, acetonitrile is not basic enough to deprotonate benzoic acid. Moreover, the spectroscopy studies (inꢀsitu IR,
UV/Vis and EPR) of this reaction indicated that the catalysts were not able to promote the dissociation of 1a to 1aꢀ. Thus we turned
to consider the solvent effect. Compared to CH3CN as the solvent, when the reaction was proceeded in the solvents such as DCE,
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THF, DMF and DMSO, the results were limited (Table 3). One possible explanation is due to the existence of lone pair electrons on
nitrogen atom of CH3CN, which made it possible to induce the deprotonation of 2ꢀarylbenzoic acids.13 On the other hand, emission
quenching experiments were performed to obtain further insight into the photoredox catalytic cycle and activation of 2ꢀ
phenylbenzoic acid. As shown, the experiments revealed that 2ꢀphenylbenzoic acid could quench the excited state of Acr+ꢀ
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ꢀ
MesClO4 , but the quenching rate shows extremely slow. In addition, CH3CN could not be an emission quencher of 2ꢀ
9
phenylbenzoic acid (for details, see supporting information (Figure S3 and Figure S4)). We proposed that under the combined acꢀ
tion of catalysts and CH3CN, benzoic acid would be given a sufficient energy to perform the deprotonation and oxidation process to
generate carboxyl radical (1a•) straightforwardly.
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Table 3. Solvent Effect.a
ꢀ
a Conditions: 1 (0.20 mmol), Acr+ꢀMesClO4 (1.5 mol%) and Co(dmgH)2Cl2 (2 mol%) were mixed in solvent (1 mL) under nitroꢀ
gen atmosphere, and irradiated with 3W blue LEDs at room temperature for 10 h; H2 was detected by gas chromatography. b Isolatꢀ
ed yields were shown.
Based on the above results and previous report,9 a plausible reaction mechanism was described in Scheme 6. Firstly, acridinium
(6) was excited by visible light to provide an excited state of MesꢀAcr+* (7) (E*1/2 red = +2.08 V vs SCE).12 Through the interaction
with CH3CN, 1a lose one H+ and was then oxidized by 7, generating the carboxyl radical species (3). Meanwhile, 7 was reduced to
MesꢀAcr radical (8) (E1/2 red = ꢀ0.49 V vs SCE),14 which would be oxidized by Co(III) catalyst (9) to complete the cycle of the phoꢀ
tocatalyst. Consequently, through the intramolecular attack by carboxyl radical, the cyclized intermediate 4 could be produced.
After undergoing a single electron transfer (SET) process with Co(II) intermediate (10), 4 would transfer to cation intermediate 5.
Eventually, after a deprotonation process, 5 quickly lose a proton to generate the desired product 2a. At the meantime, Co(I) interꢀ
mediate (11) could capture a proton from the reaction system to reach the Co(III)–H (12).15 As a result, 9 was regenerated via the
protonation of 12 to release H2.
Scheme 6. Proposed Mechanism.
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In conclusion, a green, mild and efficient protocol of visibleꢀlight promoted 2ꢀarylbenzoic acids to accomplish the C–H functionꢀ
alization/C–O bond formation reaction was developed, accompanying with H2 released. Synthetically, this method could tolerate
either electronꢀpoor and electronꢀrich group of 2ꢀarylbenzoic acids to generate benzoꢀ3,4ꢀcoumarins. Meanwhile, heterocyclic subꢀ
strates were also suitable for this reaction. Additionally, this reaction could be conducted with a gram scale and gave a good effiꢀ
ciency. Mechanistically, based on the results of radical trapping experiments, CV experiments and DFT calculations, we could proꢀ
vide a new vision to the reaction mechanism.
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■ EXPERIMENTAL SECTION
1
2
3
General Information. Thin layer chromatography (TLC) employed glass 0.25 mm silica gel plates. 1bꢀ1w,9 1x,16a 1yꢀ1z16b were preꢀ
4
pared according to reported procedures. Flash chromatography columns were packed with 200ꢀ300 mesh silica gel in petroleum (boiling
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6
o
point is between 60ꢀ90 C). Gradient flash chromatography was conducted eluting with a continuous gradient from petroleum to the indiꢀ
7
8
9
cated solvent, and they are listed as volume/volume ratios. NMR spectra were recorded on a Varian Mercury spectrometer on a Bruker
spectrometer at 400 MHz (1H NMR), 101 MHz (13C NMR). Tetramethylsilane was used as an internal standard. All 1H NMR spectra were
reported in delta (δ) units, parts per million (ppm) downfield from the internal standard. Coupling constants are reported in Hertz (Hz).
High resolution mass spectra (HRMS) were obtained by use of a Bruker Compact TOF mass spectrometer in electrospray ionization mode
(ESI+). GCꢀMS spectra were recorded on a Varian GCꢀMS 3900ꢀ2100T and Shimadzu GCMSꢀQP2010SE. Hydrogen gas content was
analyzed by gas chromatography (7890ꢀII, Tianmei, China, TCD, argon as a carrier gas and 5 Å molecular sieve column, a thermal conꢀ
ductivity detector).
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General Procedure for External OxidantꢀFree Dehydrogenative Lactonization of 2ꢀArylbenzoic Acids via VisibleꢀLight Photocaꢀ
talysis. 2ꢀArylbenzoic acid (0.2 mmol), Acr+ꢀMesClO4 (0.003 mmol, 1.2 mg) and Co(dmgH)2Cl2 (0.004 mmol, 1.9 mg) were added in a
ꢀ
clean and dried sealed Schlenk tube equipped with a stir bar. Anhydrous CH3CN (1 mL) was injected in the tube through a syringe. After a
strict deoxygenation process (Note) and fill the Schlenk tube with N2, the reaction mixture was irradiated with 3W blue LEDs lights and
stirred at room temperature for 10 h. After completion of the reaction, as indicated by TLC and GCꢀMS, the mixture was then purified by
column chromatography on silica gel using petroleum ether and ethyl acetate (PE/EA = 3/1 ꢀ 10/1) as eluent to afford pure product.
Detail process of strict deoxygenation: 2ꢀArylbenzoic acid (0.2 mmol), Acr+ꢀMesClO4 (0.003 mmol, 1.2 mg) and Co(dmgH)2Cl2
ꢀ
(0.004 mmol, 1.9 mg) were added in a clean and dried sealed Schlenk tube equipped with a stir bar. Anhydrous CH3CN (1 mL) was injectꢀ
ed in the tube through a syringe. And then, the Schlenk tube was put into a prepared Dewar flask with an appropriate amount of liquid
nitrogen. After the reaction solution was completely frozen, the air in the reaction system was discharged by using a vacuum pump. About
1 minute later, the Schlenk tube was filled with nitrogen, which was allowed to warm to room temperature after removing from liquid niꢀ
trogen. Repeat this operation three times.
ꢀ
Procedure for gram scale synthesis: 2ꢀPhenylbenzoic acid (6.0 mmol, 1.19 g), Acr+ꢀMesClO4 (0.023 mmol, 18.5 mg) and
Co(dmgH)2Cl2 (0.06 mmol, 28.5 mg) were added in a clean and dried sealed Schlenk tube (100 mL) equipped with a stir bar. After flushꢀ
ing the Schlenk tube three times with N2 atmosphere, CH3CN (30 mL) was injected in the tube through a syringe. The reaction mixture
was irradiated with 3W blue LEDs lights and stirred at room temperature for 48 h. After completion of the reaction, as indicated by TLC
and GCꢀMS, the mixture was purified by column chromatography on silica gel using petroleum ether and ethyl acetate (PE/EA = 10/1) as
eluent to afford pure product 2a (1.01 g) in 85% yield.
General procedure for cyclic voltammetry (CV): Cyclic voltammetry was performed in a threeꢀelectrode cell connected to a schlenk
line under nitrogen at room temperature. The working electrode was a glassyꢀcarbon disk electrode (diameter, 1 mm), the counter electrode
a platinum wire. The reference was a Ag/AgCl electrode submerged in saturated aqueous KCl solution, and separated from reaction by a
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n
salt bridge. 10 mL of acetonitrile containing 0.2 M Bu4NBF4 was poured into the electrochemical cell with a series of arylbenzoic acid 1
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and sodium arylbenzoates Na(1ꢀ) in all experiments. The scan rate is 100 mVsꢀ1, ranging from 0 V to 4.0 V.
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Detection of hydrogen gas by GCꢀTCD analysis: 2ꢀPhenylbenzoic acid (0.2 mmol, 39.6 mg), Acr+ꢀMesClO4 (0.003 mmol, 1.2 mg)
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and Co(dmgH)2Cl2 (0.004 mmol, 1.9 mg) were added in a clean and dried sealed Schlenk tube equipped with a stir bar. After flushing the
Schlenk tube three times with N2 atmosphere, anhydrous CH3CN (1 mL) was injected in the tube through a syringe. The reaction mixture
was irradiated with 3W blue LEDs lights and stirred at room temperature for 10 h. After completion of the reaction, the extracted 1000 ꢁL
gas from the reaction system was analyzed by GCꢀTCD. And according to the spectra (Figure 1), the only peak stands for the generation of
hydrogen gas (Nitrogen can’t be detected due to the instrument parameter setting).
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Synthesis of deuterated phenylboronic acid 1aꢀD5 and benzoꢀ3,4ꢀcoumarin 2aꢀD4: Polideuterated bromobencene (5 mmol, 0.81 g)
dissolved in dry THF under N2 atmosphere in an ovenꢀdried 100 mL flask. The solution was then cooled to ꢀ78 ºC and BuLi solution (6
mmol, 2.0 mL, 3.2 M) was slowly injected into the stirred solution. The reaction mixture stirred under N2 atmosphere at ꢀ78 ºC for another
30 min. Then, B(OiPr)3 (13 mmol, 2.5 g) was added dropwisely and the reaction mixture rose to room temperature and stirred overnight.
After that, the reaction mixture was quenched with HCl (10 %, 30 mL) until pH<1 and stirred for another 3 h. The reaction mixture was
concentrated and H2O (10 mL) was added. The aqueous layer was extracted with EtOAc (4 × 10 mL). The combined organic layer was
washed with brine (1 × 5 mL), dried over anhydrous MgSO4 and concentrated under reduced pressure to afford a yellow solid. The yellow
solid turned to white after washing with hexane (10 mL), which was used without further purification at the Suzuki Cross Coupling reacꢀ
tion. The desired deuterated phenyl 2ꢀcarboxylic acid 1aꢀD5 was obtained following the typical procedure described for the synthesis of
acids 1bꢀ1u by using 2 mmol of methyl 2ꢀiodobenzoate. Then, under standard conditions, 1aꢀD5 gave the desired product benzoꢀ3,4ꢀ
coumarin 2aꢀD4 in 65% yield.
Emission quenching experiments for Acr+ꢀMesClO4 : Emission intensities were recorded using a HITACHI Fꢀ4600 Fluorescence
ꢀ
Spectrometer. All Acr+ꢀMesClO4ꢀ solutions were excited at 430 nm and the emission intensity at 607 nm was observed. In a typical experꢀ
iment, the emission spectrum of a 1×10ꢀ4 M solution of Acr+ꢀMesClO4ꢀ in CH3CN was collected. Then, appropriate amount of quencher (a
1×10ꢀ3 M solution of 2ꢀphenylbenzoic acid in CH3CN) was added to the measured solution and the emission spectrum of the sample was
collected.
Emission quenching experiments for 2ꢀphenylbenzoic acid: All 2ꢀphenylbenzoic acid solutions were excited at 306 nm and the emisꢀ
sion intensity at 360 nm was observed. In a typical experiment, the emission spectrum of a 1×10ꢀ4 M solution of 2ꢀphenylbenzoic acid in
THF was collected. Then, appropriate amount of quencher (a 1×10ꢀ3 M solution of CH3CN in THF) was added to the measured solution
and the emission spectrum of the sample was collected.
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6HꢀBenzo[c]chromenꢀ6ꢀone (2a):9 White solid (38.8 mg, 99%, PE/EA = 10/1 as eluent). Melting point: 93 – 94 C. H NMR (400
MHz, CDCl3) δ 8.31 (d, J = 7.9 Hz, 1H), 8.01 (d, J = 8.0 Hz, 1H), 7.95 (d, J = 8.2 Hz, 1H), 7.76 (t, J = 7.6 Hz, 1H), 7.52 (t, J = 7.6 Hz,
1H), 7.42 (t, J = 7.6 Hz, 1H), 7.28 (d, J = 6.1 Hz, 2H). 13C NMR (101 MHz, CDCl3) δ 161.0, 151.0, 134.7, 134.5, 130.3, 128.7, 124.4,
122.6, 121.5, 120.9, 117.8, 117.5.
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3ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2b):6b White solid (41.6 mg, 99%, PE/EA = 10/1 as eluent). Melting point: 117 – 118 C. H
NMR (400 MHz, CDCl3) δ 8.33 (d, J = 7.9 Hz, 1H), 8.01 (d, J = 8.0 Hz, 1H), 7.85 (d, J = 8.5 Hz, 1H), 7.76 (t, J = 7.6 Hz, 1H), 7.51 (t, J =
7.6 Hz, 1H), 7.10 (d, J = 5.0 Hz, 2H), 2.41 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 161.4, 151.1, 141.2, 134.9, 134.7, 130.4, 128.3, 125.6,
122.4, 121.4, 120.7, 117.8, 115.3, 21.4.
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3ꢀ(Tertꢀbutyl)ꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2c):6d White solid (49.9 mg, 99%, PE/EA = 10/1 as eluent). Melting point: 150 – 152 C.
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1H NMR (400 MHz, CDCl3) δ 8.37 (d, J = 7.9 Hz, 1H), 8.07 (d, J = 8.1 Hz, 1H), 7.96 (d, J = 8.9 Hz, 1H), 7.80 (t, J = 7.7 Hz, 1H), 7.54 (t,
J = 7.6 Hz, 1H), 7.37 (dd, J = 4.3, 2.5 Hz, 2H), 1.37 (s, 9H). 13C NMR (101 MHz, CDCl3) δ 161.5, 154.7, 151.2, 134.9, 134.8, 130.5,
128.4, 122.4, 122.0, 121.5, 120.9, 115.3, 114.5, 35.0, 31.1.
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3ꢀFluoroꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2d):9 White solid (34.2 mg, 80%, PE/EA = 10/1 as eluent). Melting point: 152 – 154 C. H
NMR (400 MHz, CDCl3) δ 8.36 (dd, J = 8.0, 1.0 Hz, 1H), 8.05 – 7.99 (m, 2H), 7.87 – 7.77 (m, 1H), 7.60 – 7.53 (m, 1H), 7.11 – 7.03 (m,
2H). 13C NMR (101 MHz, CDCl3) δ 163.4 (d, JC-F = 252.5 Hz), 160.8, 152.1 (d, JC-F = 12.1 Hz), 135.1, 134.2, 130.7, 128.8, 124.4 (d, JC-F
= 9.1 Hz), 121.5, 120.4, 114.6 (d, JC-F = 3.0 Hz), 112.5 (d, JC-F = 22.2 Hz), 105.6 (d, JC-F = 25.3 Hz). 19F NMR (377 MHz, CDCl3) δ ꢀ
108.37.
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3ꢀChloroꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2e):9 White solid (39.1 mg, 85%, PE/EA = 10/1 as eluent). Melting point: 148 – 150 C. H
NMR (400 MHz, CDCl3) δ 8.37 (d, J = 7.9 Hz, 1H), 8.05 (d, J = 8.1 Hz, 1H), 7.96 (d, J = 8.5 Hz, 1H), 7.86 – 7.79 (m, 1H), 7.63 –7.56 (m,
1H), 7.38 – 7.28 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 160.6, 151.5, 135.9, 135.1, 134.0, 130.7, 129.2, 125.0, 123.8, 121.7, 120.9,
117.9, 116.7.
3ꢀ(Trifluoromethyl)ꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2f):9 White solid (34.3 mg, 65%, PE/EA = 10/1 as eluent). Melting point: 138 – 140
oC. 1H NMR (400 MHz, CDCl3) δ 8.41 (dd, J = 7.9, 1.1 Hz, 1H), 8.16 (t, J = 7.8 Hz, 2H), 7.92 – 7.86 (m, 1H), 7.70 – 7.64 (m, 1H), 7.58
(d, J = 9.5 Hz, 2H). 13C NMR (101 MHz, CDCl3) δ 160.3, 150.9, 135.2, 133.3, 132.2 (q, JC-F = 34.3 Hz), 130.8, 130.2, 123.7, 123.3 (q, JC-F
= 272.7 Hz), 122.2, 121.6, 121.1 (q, JC-F = 4.0 Hz), 115.2 (q, JC-F = 4.0 Hz). 19F NMR (377 MHz, CDCl3) δ ꢀ62.78.
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2,4ꢀDimethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2g):6b White solid (44.3 mg, 99%, PE/EA = 10/1 as eluent). Melting point: 188 – 190 C.
1H NMR (400 MHz, CDCl3) δ 8.35 (dd, J = 6.4, 1.5 Hz, 1H), 8.03 (dd, J = 7.7, 3.8 Hz, 1H), 7.76 (ddd, J = 9.7, 3.3, 2.0 Hz, 1H), 7.60 (d, J
= 2.9 Hz, 1H), 7.55 – 7.47 (m, 1H), 7.09 (s, 1H), 2.41 (s, 3H), 2.38 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 161.3, 147.6, 135.0, 134.5,
133.3, 132.7, 130.3, 128.4, 126.5, 121.7, 121.0, 120.3, 117.2, 21.0, 15.9.
3ꢀ(Hydroxymethyl)ꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2h):6b White solid (31.6 mg, 70%, PE/EA = 3/1 as eluent). Melting point: 178 – 179
oC. 1H NMR (400 MHz, DMSOꢀd6) δ 8.41 (d, J = 8.1 Hz, 1H), 8.31 (d, J = 8.1 Hz, 1H), 8.27 – 8.22 (m, 1H), 7.99 – 7.92 (m, 1H), 7.67 (t, J
= 7.5 Hz, 1H), 7.35 (d, J = 9.3 Hz, 2H), 5.49 (t, J = 5.8 Hz, 1H), 4.62 (d, J = 5.8 Hz, 2H). 13C NMR (101 MHz, DMSOꢀd6) δ 160.9, 151.2,
146.6, 135.8, 134.9, 130.2, 129.5, 123.9, 123.1, 122.9, 120.8, 116.5, 114.9, 62.6.
2ꢀMethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2i):6d White solid (31.6 mg, 70%, 15:1 ratio according to 1H NMR, PE/EA = 4/1 as eluent).
1H NMR (400 MHz, CDCl3) δ 8.38 (dd, J = 7.9, 0.9 Hz, 1H), 8.04 (d, J = 8.1 Hz, 1H), 7.84 – 7.78 (m, 1H), 7.57 (t, J = 7.9 Hz, 1H), 7.45
(d, J = 2.9 Hz, 1H), 7.29 – 7.25 (m, 1H), 7.03 (dd, J = 9.0, 2.9 Hz, 1H), 3.90 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 161.3, 156.3, 145.5,
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134.7, 134.6, 130.6, 128.9, 121.7, 121.3, 118.6, 118.5, 117.1, 106.2, 55.8.
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4ꢀFluoroꢀ3ꢀmethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2j): White solid (31.9 mg, 70%, 12:1 ratio according to 1H NMR, PE/EA = 10/1 as
eluent). 1H NMR (400 MHz, CDCl3) δ 8.37 (d, J = 7.9 Hz, 1H), 7.95 (d, J = 8.0 Hz, 1H), 7.81 (dd, J = 11.2, 4.1 Hz, 1H), 7.63 – 7.54 (m,
2H), 7.16 (d, J = 6.5 Hz, 1H), 2.36 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 161.1, 158.0 (d, JC-F = 242.3 Hz), 147.1 (d, JC-F = 2.0 Hz),
134.9, 134.2 (d, JC-F = 2.6 Hz), 130.7, 129.0, 128.4 (d, JC-F = 20.1 Hz), 121.7, 120.9, 120.0 (d, JC-F = 5.4 Hz), 116.8 (d, JC-F = 8.4 Hz),
108.2 (d, JC-F = 25.9 Hz), 14.9 (d, JC-F = 3.2 Hz). Main product: 19F NMR (377 MHz, CDCl3) δ ꢀ121.35. Minor product: 19F NMR (377
MHz, CDCl3) δ ꢀ137.07. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H10FO2: 229.0660; Found: 229.0651.
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5HꢀDibenzo[c,g]chromenꢀ5ꢀone (2k):6b White solid (48.7 mg, 99%, PE/EA = 10/1 as eluent). Melting point: 190 – 192 C. H NMR
(400 MHz, CDCl3) δ 8.46 (d, J = 8.8 Hz, 1H), 8.36 (d, J = 7.7 Hz, 1H), 8.05 (d, J = 8.1 Hz, 1H), 7.90 (d, J = 8.8 Hz, 1H), 7.81 – 7.74 (m,
2H), 7.64 (d, J = 8.8 Hz, 1H), 7.59 – 7.49 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 161.1, 147.0, 135.2, 134.9, 134.1, 130.5, 128.5, 127.8,
127.6, 127.0, 124.4, 123.7, 122.2, 121.9, 121.0, 119.0, 112.8.
6Hꢀbenzo[2,3]benzofuro[6,7ꢀc]chromenꢀ6ꢀone (2l):6b White solid (34.3 mg, 60%, PE/EA = 5/1 as eluent). Melting point: 202 – 204
oC. 1H NMR (400 MHz, CDCl3) δ 8.85 (d, J = 8.1 Hz, 1H), 8.33 (d, J = 7.8 Hz, 1H), 7.86 – 7.74 (m, 3H), 7.55 (t, J = 7.9 Hz, 2H), 7.44 (t,
J = 7.4 Hz, 1H), 7.34 (t, J = 7.4 Hz, 1H), 7.20 (d, J = 8.4 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 160.9, 156.3, 152.0, 150.5, 135.0, 132.7,
130.2, 128.8, 126.9, 126.4, 123.5, 123.0, 121.1, 120.8, 120.7, 120.2, 112.7, 111.7, 105.4.
5HꢀThieno[2,3ꢀc]isochromenꢀ5ꢀone (2m): White solid (26.3 mg, 65%, PE/EA = 10/1 as eluent). Melting point: 110 – 112 oC. 1H NMR
(400 MHz, CDCl3) δ 8.33 (d, J = 7.9 Hz, 1H), 7.82 – 7.77 (m, 1H), 7.74 (d, J = 7.3 Hz, 1H), 7.53 – 7.47 (m, 1H), 7.30 (d, J = 5.9 Hz, 1H),
6.98 (d, J = 5.9 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 161.7, 156.1, 135.4, 134.3, 131.1, 127.6, 122.2, 119.2, 118.3, 117.0, 116.1. HRMS
(ESIꢀTOF) m/z: [M+H]+ Calcd for C11H7O2S: 203.0161; Found: 203.0164.
3ꢀMethoxyꢀ6Hꢀisochromeno[3,4ꢀb]pyridinꢀ6ꢀone (2n): White solid (25.0 mg, 55%, PE/EA = 3/1 as eluent). Melting point: 200 – 202
oC. 1H NMR (400 MHz, CDCl3) δ 8.36 (d, J = 7.9 Hz, 1H), 8.27 (d, J = 8.5 Hz, 1H), 7.96 (d, J = 8.0 Hz, 1H), 7.81 (t, J = 7.5 Hz, 1H), 7.54
(t, J = 7.6 Hz, 1H), 6.80 (d, J = 8.5 Hz, 1H), 4.03 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 164.1, 161.1, 155.4, 135.1, 134.7, 134.2, 130.8,
128.2, 121.2, 120.1, 108.8, 105.9, 54.4. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C13H10NO3: 228.0655; Found: 228.0645.
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5HꢀBenzo[d]pyrrolo[2,1ꢀb][1,3]oxazinꢀ5ꢀone (2o): Yellow solid (31.5 mg, 85%, PE/EA = 8/1 as eluent). Melting point: 112 – 114 C.
1H NMR (400 MHz, CDCl3) δ 8.15 (d, J = 7.9 Hz, 1H), 7.73 (t, J = 7.8 Hz, 1H), 7.43 (d, J = 8.3 Hz, 1H), 7.29 (t, J = 7.8 Hz, 1H), 6.99 –
6.93 (m, 1H), 6.37 (t, J = 3.5 Hz, 1H), 5.80 – 5.73 (m, 1H). 13C NMR (101 MHz, CDCl3) δ 157.9, 139.6, 137.8, 136.6, 131.3, 124.7, 113.4,
111.0, 110.6, 106.6, 89.4. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C11H8NO2: 186.0550; Found: 186.0542.
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3ꢀMethylꢀ6Hꢀnaphtho[2,3ꢀc]chromenꢀ6ꢀone (2p): White solid (39.0 mg, 75%, PE/EA = 10/1 as eluent). Melting point: 228 – 230 C.
1H NMR (400 MHz, CDCl3) δ 8.90 (s, 1H), 8.37 (s, 1H), 8.00 (d, J = 8.1 Hz, 1H), 7.94 (t, J = 9.0 Hz, 2H), 7.63 (t, J = 7.5 Hz, 1H), 7.53 (t,
J = 7.5 Hz, 1H), 7.13 (d, J = 8.1 Hz, 1H), 7.08 (s, 1H), 2.42 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 161.8, 150.8, 141.0, 136.3, 132.8,
132.2, 129.9, 129.6, 129.5, 128.0, 127.0, 125.8, 122.7, 120.2, 119.1, 118.0, 115.6, 21.5. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for
C18H13O2: 261.0910; Found: 261.0901.
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3,9ꢀDimethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2q):9 White solid (44.3 mg, 99%, PE/EA = 10/1 as eluent). Melting point: 138 – 140 oC. 1H
NMR (400 MHz, CDCl3) δ 8.30 – 8.12 (m, 1H), 7.86 (dd, J = 11.7, 5.6 Hz, 1H), 7.80 (d, J = 7.6 Hz, 1H), 7.31 (dd, J = 7.0, 5.3 Hz, 1H),
7.11 (d, J = 5.7 Hz, 2H), 2.52 (s, 3H), 2.43 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 161.5, 151.4, 145.8, 141.1, 134.9, 130.5, 129.6, 125.5,
122.4, 121.6, 118.4, 117.8, 115.4, 22.3, 21.5.
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9ꢀMethoxyꢀ3ꢀmethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2r):6b White solid (45.6 mg, 95%, PE/EA = 4/1 as eluent). Melting point: 196 – 198
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oC. H NMR (400 MHz, CDCl3) δ 8.27 (d, J = 8.8 Hz, 1H), 7.82 (d, J = 8.6 Hz, 1H), 7.38 (d, J = 2.3 Hz, 1H), 7.10 (d, J = 7.0 Hz, 2H),
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7.04 (dd, J = 8.8, 2.3 Hz, 1H), 3.97 (s, 3H), 2.43 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 164.8, 161.3, 151.6, 141.4, 137.1, 132.8, 125.5,
122.5, 117.9, 115.8, 115.4, 114.0, 104.7, 55.7, 21.5. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C15H13O3: 241.0859; Found: 241.0850.
3ꢀMethylꢀ9ꢀ(trifluoromethyl)ꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2s): White solid (47.3 mg, 85%, PE/EA = 10/1 as eluent). Melting point:
152 – 154 oC. 1H NMR (400 MHz, CDCl3) δ 8.49 (d, J = 8.3 Hz, 1H), 8.29 (s, 1H), 7.93 (d, J = 7.9 Hz, 1H), 7.76 (d, J = 8.2 Hz, 1H), 7.19
(d, J = 8.2 Hz, 2H), 2.47 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 160.3, 151.4, 142.6, 136.2 (q, JC-F = 33.3 Hz), 135.6, 131.5, 126.1, 124.6
(q, JC-F = 4.0 Hz), 123.4 (q, JC-F = 273.7 Hz), 123.3, 122.7, 118.8 (q, JC-F = 4.0 Hz), 118.1, 114.4, 21.6. 19F NMR (377 MHz, CDCl3) δ ꢀ
63.34. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C15H10F3O2: 279.0628; Found: 279.0620.
9ꢀAcetylꢀ3ꢀmethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2t): White solid (40.3 mg, 80%, PE/EA = 3/1 as eluent). Melting point: 194 – 196 oC.
1H NMR (400 MHz, CDCl3) δ 8.83 (s, 1H), 8.38 – 8.32 (m, 1H), 8.10 (d, J = 8.4 Hz, 1H), 7.92 (d, J = 8.1 Hz, 1H), 7.20 – 7.11 (m, 2H),
2.70 (s, 3H), 2.46 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 196.3, 160.7, 151.7, 143.0, 138.6, 136.4, 133.5, 131.3, 126.1, 123.2, 122.0,
120.6, 118.0, 114.6, 26.7, 21.6. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C16H13O3: 253.0859; Found: 253.0850.
8ꢀFluoroꢀ3ꢀmethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2u): White solid (40.1 mg, 88%, PE/EA = 10/1 as eluent). Melting point: 180 – 182
oC. 1H NMR (400 MHz, CDCl3) δ 8.05 (dd, J = 8.8, 4.8 Hz, 1H), 7.99 (dd, J = 8.5, 2.7 Hz, 1H), 7.84 (d, J = 8.3 Hz, 1H), 7.54 – 7.48 (m,
1H), 7.14 (d, J = 7.6 Hz, 2H), 2.44 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 162.1, (d, JC-F = 251.5 Hz), 160.5 (d, JC-F = 3.0 Hz), 150.7,
141.3, 131.5 (d, JC-F = 3.0 Hz), 125.9, 124.0 (d, JC-F = 8.1 Hz), 123.0 (d, JC-F = 23.2 Hz), 122.5 (d, JC-F = 7.1 Hz), 122.3, 117.9, 116.0 (d,
JC-F = 23.2 Hz), 114.7, 21.4. 19F NMR (377 MHz, CDCl3) δ ꢀ111.00. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H10FO2: 229.0660;
Found: 229.0652.
8ꢀChloroꢀ3ꢀmethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2v): White solid (34.1 mg, 70%, PE/EA = 10/1 as eluent). Melting point: 184 – 186
oC. 1H NMR (400 MHz, CDCl3) δ 8.29 (d, J = 2.3 Hz, 1H), 7.97 (d, J = 8.6 Hz, 1H), 7.84 (d, J = 8.0 Hz, 1H), 7.71 (dd, J = 8.6, 2.3 Hz,
1H), 7.18 – 7.08 (m, 2H), 2.44 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 160.3, 151.0, 141.8, 135.1, 134.4, 133.4, 129.9, 126.0, 123.2, 122.5,
122.1, 117.9, 114.6, 21.5. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H9ClO2: 245.0364; Found: 245.0357.
3ꢀMethylꢀ7,8,9,10ꢀtetrahydroꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2w): White solid (34.2 mg, 80%, PE/EA = 10/1 as eluent). Melting point:
105 – 106 oC. 1H NMR (400 MHz, CDCl3) δ 7.43 (d, J = 8.0 Hz, 1H), 7.17 – 6.99 (m, 2H), 2.76 (dd, J = 7.0, 5.2 Hz, 2H), 2.57 (t, J = 6.0
Hz, 2H), 2.43 (s, 3H), 1.88 – 1.77 (m, 4H). 13C NMR (101 MHz, CDCl3) δ 162.1, 152.0, 147.2, 141.1, 125.2, 122.9, 122.5, 117.7, 116.9,
25.2, 24.0, 21.7, 21.5, 21.4. HRMS (ESIꢀTOF) m/z: [M+H]+ Caled for C14H15O2: 215.1067; Found: 215.1066.
7ꢀMethylꢀ4ꢀ(pꢀtolyl)ꢀ2Hꢀchromenꢀ2ꢀone (2x):16a White solid (40.0 mg, 80%, PE/EA = 10/1 as eluent). Melting point: 140 – 142 oC. 1H
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NMR (400 MHz, CDCl3) δ 7.40 (d, J = 8.1 Hz, 1H), 7.38 – 7.29 (m, 4H), 7.21 (s, 1H), 7.04 (d, J = 8.1 Hz, 1H), 6.30 (s, 1H), 2.45 (s, 6H).
13C NMR (101 MHz, CDCl3) δ 161.3, 155. 8, 154.3, 143.1, 139.8, 132.5, 129.5, 128.4, 126.8, 125.3, 117.5, 116.7, 113.8, 21.6, 21.4.
4ꢀPhenylꢀ1Hꢀisochromenꢀ1ꢀone (2y):16c White solid (33.3 mg, 75%, PE/EA = 10/1 as eluent). Melting point: 80 – 82 oC. 1H NMR (400
MHz, CDCl3) δ 8.39 (dd, J = 7.9, 0.9 Hz, 1H), 7.73 – 7.66 (m, 1H), 7.58 – 7.53 (m, 1H), 7.52 – 7.45 (m, 3H), 7.43 – 7.38 (m, 3H), 7.26 (s,
1H). 13C NMR (101 MHz, CDCl3) δ 162.1, 142.3, 136.8, 134.7, 133.0, 130.1, 129.8, 128.9, 128.6, 128.5, 124.7, 121.3, 120.7.
4ꢀ(pꢀTolyl)ꢀ1Hꢀisochromenꢀ1ꢀone (2z):16d White solid (35.4 mg, 75%, PE/EA = 10/1 as eluent). Melting point: 129 – 131 oC. 1H NMR
(400 MHz, CDCl3) δ 8.38 (dd, J = 7.9, 0.9 Hz, 1H), 7.73 – 7.62 (m, 1H), 7.60 – 7.47 (m, 1H), 7.42 (d, J = 8.0 Hz, 1H), 7.29 (m, 4H), 7.23
(s, 1H), 2.43 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 162.1, 142.1, 138.4, 136.9, 134.6, 130.0, 129.7, 129.6, 128.5, 124.7, 121.3, 120.5,
21.3.
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[1,1'ꢀbiphenyl]ꢀ2',3',4',5',6'ꢀd5ꢀ2ꢀcarboxylic acid (1aꢀD5):9 White solid. 1H NMR (400 MHz, CDCl3) δ 7.94 (dd, J = 7.8, 1.1 Hz, 1H),
7.56 (td, J = 7.6, 1.3 Hz, 1H), 7.41 (td, J = 7.6, 1.1 Hz, 1H), 7.37 (d, J = 7.6 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 173.5, 143.4, 140.8,
132.1, 131.3, 130.7, 129.3, 127.2.
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6Hꢀbenzo[c]chromenꢀ6ꢀoneꢀ1,2,3,4ꢀd4 (2aꢀD4):9 White solid (26.0 mg, 65%, PE/EA = 10/1 as eluent). H NMR (400 MHz, CDCl3) δ
8.40 (d, J = 7.9 Hz, 1H), 8.11 (d, J = 8.1 Hz, 1H), 7.87 – 7.77 (m, 1H), 7.58 (t, J = 7.6 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 161.2,
151.2, 134.9, 134.7, 130.6, 128.9, 121.7, 121.2, 118.0.
■ ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website. Including the following contents:
1. Detection of hydrogen gas by GCꢀTCD analysis; 2. NOESY spectra of 2d; 3. Emission quenching experiments; 4. DFT calculations;
5. NMR spectra of all products (PDF)
■ AUTHOR SECTION
Corresponding Author
*Email: aiwenlei@whu.edu.cn; cwchiang@whu.edu.cn.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of China (21390402, 21520102003) and the Hubei Province Natural
Science Foundation of China (2017CFA010). The Program of Introducing Talents of Discipline to Universities of China (111 Program) is
also appreciated.
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