Photocatalytic Decarboxylative Hydroxylation of Carboxylic Acids Driven by Visible Light and Using Molecular Oxygen

Article abstract of DOI:10.1021/acs.joc.6b01360

This paper discloses the first example of photocatalytic direct decarboxylative hydroxylation of carboxylic acids. It enables the conversion of a variety of readily available carboxylic acids to alcohols in moderate to high yields. This unprecedented protocol is accomplished under extremely mild reaction conditions using molecular oxygen (O₂) as a green oxidant and using visible light as a driving force.

Full text of DOI:10.1021/acs.joc.6b01360

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Article
Photocatalytic Decarboxylative Hydroxylation of Carboxylic
Acids Driven by Visible Light and Using Molecular Oxygen
Hai-Tao Song, Wei Ding, Quan-Quan Zhou, Jing Liu, Liang-Qiu Lu, and Wen-Jing Xiao
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01360 • Publication Date (Web): 06 Jul 2016
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Photocatalytic Decarboxylative Hydroxylation of
Carboxylic Acids Driven by Visible Light and Using
Molecular Oxygen
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HaiꢀTao Song, Wei Ding, QuanꢀQuan Zhou, Jing Liu, LiangꢀQiu Lu* and WenꢀJing Xiao
Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry,
Central China Normal University, 152 Luoyu Road, Wuhan, Hubei 430079, China
*Email: luliangqiu@mail.ccnu.edu.cn
Abstract:
This paper discloses the first example of photocatalytic direct decarboxylative hydroxylation of
carboxylic acids. It enables the conversion of a variety of readily available carboxylic acids to
alcohols in moderate to high yields. This unprecedented protocol is accomplished under extremely
mild reaction conditions using molecular oxygen (O2) as a green oxidant and using visible light as a
driving force.
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Introduction
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Decarboxylative hydroxylation is an important transformation in organisms and synthetic chemistry.
In Nature, this process is catalysed by various hydroxylases in a highly efficient and specific way
(Scheme 1a).1 For example, salicylate hydroxylase (SALH) which was isolated from Pseudomonas
putida S-1 can selectively break the CꢀCO2H bond of a carboxylic acid and forge a new CꢀO bond in
the conversion of salicylate to catechol, accompanied by the release of CO2.1d In contrast to
enzymatic methods using molecular oxygen (O2) as green oxidant, many chemical methods for
decarboxylative hydroxylations require the use of stoichiometric highꢀvalent metal reagents as
oxidants, such as Pb(IV), Mn(III), Tl(III) and Ce(IV), which result in much metal waste (Scheme
1b).2,3 In addition, Barton and coworkers developed an indirect method for the decarboxylative
hydroxylation of carboxylic acids, in which corresponding thiohydroxamate esters need to be
preformed (Scheme 1c).4,5 Though being favorable due to its mild reaction condition, green oxidant
and wide substrate scope, this protocol suffers from the twoꢀstep operation, the stability of
thiohydroxamate esters and the utilization of toxic agents (e.g., Bu3SnH or tꢀBuSH).6 Thus, the
search of new, direct and green decarboxylative hydroxylation reactions of carboxylic acids is still a
significant task for synthetic chemists. Herein, we describe a visibleꢀlight photocatalytic
decarboxylative hydroxylation of carboxylic acids, which can be conducted under metal catalystꢀfree
conditions at room temperature and by using O2 as a favorable oxidant (Scheme 1d).
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Scheme 1. Decarboxylative Hydroxylation of Carboxylic Acids
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In the past years, visibleꢀlightꢀinduced decarboxylative transformations of carboxylic acids have
received increasing research interests for its prominent advantages.7,8 First, carboxylic acids are
readily available, highly stable and inexpensive feedstocks. Second, the cleavage of CꢀCO2H bonds
allows the subsequent functionalizations in a siteꢀspecific way. Third, the application of visible light
photocatalysis9 in decarboxylative transformations of carboxylic acids enables the reaction to
proceed under extremely mild condition. Last year, our group10 developed a decarboxylative
carbonylative alkynylation of carboxylic acids through visible light photoredox catalysis (Figure 1,
left).8c Critical to this success is the capture of a radical by the small molecule CO. Therefore, we
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expect that the same radical might react with the small molecule O2 and the resulting intermediate
could be further converted into an alcohol product (Figure 1, right).
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Figure 1. Hypothesis: O2ꢀcapture of radicals for photocatalytic decarboxylative hydroxylation.
Results and Discussion
To test the above hypothesis, we initially examined the feasibility of this photocatalytic
decarboxylative hydroxylation reaction using 2,2ꢀdiphenylacetic acid 1a as the model substrate.
After examining a wide array of reaction conditions,11 we determined that the alcohol 2a can be
produced in a good yield (80%) in the presence of photocatalyst PC-I (Mes-AcrClO4, 2 mol%),
K2HPO4 (1.5 equiv.) and O2 in CHCl3 under irradiation of 7W blue LEDs at room temperature (r.t.),
followed by a reduction operation (Table 1, entry 1).11 The data in Table 1 illuminated the effect of a
variety of parameters on the reaction efficiency. For example, results of control experiments showed
that photocatalyst, visible light, base and molecular oxygen are essential for this reaction (entries
2–5). Replacing of PC-I with other commercially available ruthenium and iridium photocatalysts
(i.e., PC-II~IV), which have been previously proved to be efficient photocatalysts for the
visibleꢀlightꢀinduced decarboxylative functionalization of carboxylic acids, did not give alcohol 2a
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(entries 6ꢀ8). Photocatalysts PC-II, PC-III and PC-IV possess lower oxidation potential [e.g.
E1/2(PC*/PCꢀ) = +0.66 V for PC-II; E1/2(PC*/PCꢀ) = + 0.77 V for PC-III; E1/2(PC*/PCꢀ) = +1.27 for
PC-IV]9c than the Fukuzumi catalyst PC-I [E1/2(PC*/PCꢀ) = +2.06].9g Obviously, PC-II and PC-III
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are difficult to oxidize the carboxylic ion 1a (E1/2 = +1.07 for 1a)8j in this reaction. However, the
reason why PC-IV [E1/2(PC*/PCꢀ) = +1.27] is not an efficient photocatalyst for this transformation is
not clear at current stage. In addition to K2HPO4, other inorganic and organic bases (e.g., Na2CO3
and 2,6ꢀlutidine) were also suitable for this transformation with comparable reaction efficiency
(entries 9 and 10). When DCE or CH3CN was employed as the reaction media to replace CHCl3, a
notable decrease of yield was observed (entries 11 and 12).
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Table 1. Effect of Reaction Parameters on the Photocatalytic Decarboxylative Hydroxylationa
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variation from the standard conditions
entry
yield/%b
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2
none
78 (80c)
no PC-I
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no visible light
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no K2HPO4
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Ar, instead of O2
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PC-II, instead of PC-I
PC-III, instead of PC-I
PC-IV, instead of PC-I
Na2CO3, instead of K2HPO4
2,6ꢀlutidine, instead of K2HPO4
DCE, instead of CHCl3
CH3CN, instead of CHCl3
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aStandard conditions: 1a (0.5 mmol), PC-I (0.01 mmol, 2 mol%), K2HPO4 (0.75 mmol, 1.5
equiv.), O2 balloon and CHCl3 (5.0 mL) at r.t. under the irradiation of 7 W blue LEDs for 36 h;
then NaBH4 (1.0 mmol, 2.0 eq.) and MeOH (2 mL) were added and stirred for 0.5 h.
bDetermined by H NMR analysis using 1, 3, 5ꢀtrimethoxybenzene as an internal standard.
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cIsolated yield. Mes-AcrClO4: 9ꢀmesitylꢀ10ꢀmethylacridinium perchlorate. DCE:
1,2ꢀdichloroethane.
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R2
2(PF6)-
(PF6)-
R1
tBu
tBu
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N
Ir
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PC-III:
N
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R1 = R2 = H
PC-IV:
R1 = F, R2 = CF3
N
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-
ClO4
N
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R1
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PC-I: Mes-AcrClO4
PC-II
With the optimum conditions in hand, we started to probe the generality of this photocatalytic
decarboxylative hydroxylation. As highlighted in Table 2, a wide range of substituted benzylic
carboxylic acids were suitable for the current reaction, producing corresponding benzyl alcohols in
moderate to good yields. In addition to phenyl group, carboxylic acids bearing alkyl groups (i.e.,
methyl, ethyl, cyclohexyl, benzyl and allyl) at the benzylic position were proven feasible, providing
the structurally varied alcohol products 2b-2f in 17ꢀ93% yields. However, the reaction with the
esterꢀsubstituted substrate 2g only gave a complex mixture, presumably due to its instability under
this condition. Moreover, phenyl acetic acids bearing electronꢀdonating groups were also efficient
substrates for this transformation (2j, 64% yield and 2k, 42% yield). Subquently, the electronic effect
on this photocatalytic decarboxylative hydroxylation was investigated with 2ꢀaryl propanoic acids as
examples. We found that, incorporation of either electronꢀdonating groups (Me and MeO) or
electronꢀwithdrawing groups (Br and Cl) on the benzene ring had no obvious impact on the reaction
efficiency and the corresponding products 2l-2o were obtained in 69–75% yields. Notably,
heteroarylꢀsubstituted carboxylic acids, such as thiophene, can readily undergo this reaction to
provide the alcohol product 2p in a moderate yield. Interestingly, drug molecules Ibuprofen,
Naproxen and Carprofen which belong to the family of nonꢀsteroidal antiꢀinflammatory (NSAI)
agents,12 can also undergo this decarboxylative hydroxylation process smoothly, affording the
corresponding hydroxylation products in moderate yields (2q-2s).
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Table 2. Generality of the Photocatalytic Decarboxylative Hydroxylationa
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a Reaction conditions: 1 (0.5 mmol), PC-I (0.01 mmol, 2 mol%), K2HPO4 (0.75 mmol, 1.5 equiv.),
O2 balloon and CHCl3 (5.0 mL) at r.t. under the irradiation of 7 W blue LEDs; then NaBH4 (1.0
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mmol, 2.0 eq.) and MeOH (2 mL) were added and stirred for 0.5 h. Yields of isolated products.
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Beyond these benzylic carboxylic acids, other substrates were tested for this photocatalytic
reaction. For example, when cyclohexanecarboxylic acid 1t and adamantaneꢀ1ꢀcarboxylic acid 1u
were subjected to the standard conditions, to our delight, these reaction proceeded well, delivering
the corresponding alcohols in moderate yields (eq. 1: 2t, 56% yield; eq. 2: 2u, 40% yield).
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Following, we performed more decarboxylative hydroxylation reactions to demonstrate the
utility of this method. Replacing the blue LEDs with the ambient sunlight, the reaction of carboxylic
acid 1d still proceeded very well under the photocatalytic condition, providing
cyclohexyl(phenyl)methanol product 2d in a shortened reaction time and excellent yield (Scheme 2a,
9 h, 98% yield). Additionally, a gramꢀscale decarboxylative hydroxylation reaction of substrate 1d
was carried out under the standard condition, we were pleased to find that the desired product 2d can
be afforded in good yield, albeit at a prolonged time (Scheme 2b, 1.14g, 75% yield).
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Scheme 2. Demonstration of Synthetic Utility
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Despite the success of this photocatalytic system, there are some patterns of carboxylic acids that
fail to proceed with the decarboxylic hydroxylation reaction. As exemplified in Figure 2, when
branched acyclic fatty acid 1v, heteroatomꢀcontaining carboxylic acids 1x and 1y were used as
substrates, only complex reaction mixtures were observed instead of the corresponding alcohol
products. In the case of primary aliphatic acid 1w, no reaction occurs under the standard conditions.
Presumably, the active radicals are not easy to form or apt to decompose before its capture by
molecular oxygen.
Figure 2. Unsuccessful substrates for this photocatalytic decarboxylative hydroxylation reaction.
Furthermore, two control experiments were carried out to shed light on the reaction mechanism.
As indicated in the literature,2 the oxygen atom comes from H2O or the anion of metal salts (i.e.,
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AcOꢀ) in the decarboxylative hydroxylations of carboxylic acids mediated by high valent metals.
That is because the radicals generated from carboxylic acids through these oxidative decarboxylation
processes are prone to be overꢀoxidized; the resulting carbon cation intermediates facilely react with
nucleophilic species H2O or AcOꢀ to deliver the final hydroxylation products. To rule out this
possibility in our transformation, the 18Oꢀlabeling experiments were performed using carboxylic acid
1a as the substrate. When 18Oꢀlabeling oxygen was used, corresponding 18Oꢀlabeling alcohol 2a was
isolated in 82% yield and definitively confirmed by MS (eq. 3); when 18Oꢀlabeling H2O (10 eq.) was
added to the standard conditions, no 18Oꢀlabelled alcohol 2a was observed (eq. 4). According to these
results, the pathway in which the radicals generated from carboxylic acids were captured by O2 was
believed to be more favorable. Meanwhile, it is well known that DABCO can be used to quench the
singlet oxygen.13 The model reaction, however, worked very well even with the addition of two
equivalents of DABCO and affords product 2a in 85% yield (eq. 5). Therefore, the singlet oxygen
pathway could be ruled out from the current reaction.
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Thus, a possible mechanism was proposed to illustrate this photocatalytic decarboxylative
hydroxylation according to the experimental evidences and published literatures (Scheme 3).8d,14ꢀ16
Firstly, the carboxylate A [E1/2(1aꢀ/1a•) = +1.07V vs. SCE] which is generated in situ from
carboxylic acid 1 under the basic conditions is oxidized to afford carboxyl radical B by the excited
state of photocatalyst (Acr•-Mes•+) [E1/2(PC-I*/ PC-Iꢀ) =+2.06V vs. SCE].14,15 Then, radical C which
comes from the photooxidized product B through release of CO2 is captured by soluble O2 to deliver
peroxyl radical D.16 Finally, the mixture of intermediates E and F (confirmed by MS)，which is
generated from D16b is reduced in situ by sodium borohydride and the alcohol 2 is produced. In
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ꢀ.
addition to the capture of the carbon radical C, O2 [E1/2(O2/O2 ) = +0.99V vs. SCE] is also believed
to function as a oxidant to regenerate the ground state of photocatalyst (Acr+-Mes) from the reduced
state of photocatalyst (Acr•-Mes) [E1/2(PC-Iꢀ/PC-I) = ꢀ0.57V vs. SCE].15d
Scheme 3. Proposed Mechanism
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Conclusions
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In summary, we have developed a novel and direct decarboxylative hydroxylation reaction of
carboxylic acids through visibleꢀlightꢀinduced photocatalysis. This protocol enables the conversion
of a variety of readily available carboxylic acids to alcohols in moderate to high yields. It is also
favorable for its green and mild reaction conditions, such as the use of metalꢀfree catalyst, green
oxidants (O2) and sustainable energy (visible light or sunlight).
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Experimental Section
General Information. All reagents and catalysts were purchased from commercial suppliers and
used without further purification. All the solvents were treated according to general methods before
use. NMR spectra were recorded on NMR spectrometers (400/600 MHz) in CDCl3 or DMSO-d6.
Data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q =
quartet, dd = doublet of doublets, m = multiplet, br = broad signal), coupling constants (Hz) and
integration. Mass spectra were measured on a MS spectrometer. IR spectra were recorded on an IR
spectrophotometer. All characterized data of products are coordinate with reported literatures.17
General Procedure for Photocatalytic Decarboxylative Hydroxylations. Carboxylic acid 1
(0.5 mmol), MesꢀAcrClO4 (2 mol%) and K2HPO4 (0.75 mmol, 1.5 eq.) and CHCl3 (5 mL) were
added to 10 mL of Schlenk tube. After charged with O2 using a balloon, the reaction mixture was
stirred under irradiation of 7W blue LEDs (400ꢀ500 nm; max. absorption: 432 nm) (distance app. 5
cm) at room temperature. When the reaction finished (monitored by TLC), NaBH4 (1.0 mmol, 2.0 eq.)
and MeOH (2 mL) were added to the mixture and stirred for 30 min. Then, the reaction mixture was
quenched with saturated aq. NH4Cl, and extracted with DCM for three time (3 x 10 mL). The
combined organic layers were washed with brine and dried over anhydrous Na2SO4. Finally, the
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solvent was removed in vacuo and the crude reaction mixture was purified by flash chromatography
on silica gel [silica: 200ꢀ300; eluent: petroleum ether/ethyl acetate (30:1 – 20:1)] to afford the pure
product.
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o
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Diphenylmethanol (2a). 36 h, white solid: 73.7 mg, yield: 80%, mp. 70 C. H NMR (600 MHz,
CDCl3) δ 7.38 (d, J = 6.6 Hz, 4H), 7.34 (t, J = 7.8 Hz, 4H), 7.30 (m, 2H), 5.85 (s, 1H), 2.22 (br, 1H).
13C NMR (100 MHz, CDCl3) δ 143.7, 128.3, 127.4, 126.5, 76.0. IR (in KBr): 3588, 3332, 1591,
1395, 1181, 1113 cmꢀ1. MS m/z (EI): calcd for [C13H12O]+: 184.2, found: 184.3.
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1-Phenylethanol (2b). 24 h, colourless oil: 42.8 mg, yield: 70%. H NMR (600 MHz, CDCl3) δ
7.42 – 7.32 (m, 4H), 7.29 – 7.26 (m, 1H), 4.91 (dd, J = 6.6, 2.5 Hz, 1H), 1.72 (br, 3H), 1.50 (d, J =
6.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 145.7, 128.4, 127.4, 125.3, 70.3, 25.1. IR (in KBr):
3620, 3339, 1593, 1400, 1115 cmꢀ1. MS m/z (EI): calcd for [C8H10O]+: 122.1, found: 122.2.
1-Phenylpropan-1-ol (2c). 24 h, colourless oil: 42.9 mg, yield: 63%. 1H NMR (600 MHz, CDCl3)
δ 7.40 – 7.25 (m, 5H), 4.61 (t, J = 6.7 Hz, 1H), 1.86 – 1.73 (m, 2H), 1.69 (br, 1H), 0.93 (q, J = 6.0
Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 144.5, 128.3, 127.4, 125.9, 76.0, 31.8, 10.1. IR (in KBr):
3646, 3444, 3326, 1590, 1397, 1113 cmꢀ1. MS m/z (EI): calcd for [C9H12O]+: 136.1, found: 136.0.
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Cyclohexyl(phenyl)methanol (2d). 36 h, white solid: 88.5 mg, yield: 93%, mp. 53 C. H NMR
(600 MHz, CDCl3) δ 7.49 – 7.09 (m, 4H), 4.36 (d, J = 7.2 Hz, 1H), 1.98 (d, J = 13.0 Hz, 1H), 1.78 –
1.72 (m, 2H), 1.70 – 1.57 (m, 3H), 1.37 (d, J = 13.2 Hz, 1H), 1.24 – 1.21 (m, 1H), 1.14 – 1.10 (m,
13
2H), 1.09 – 1.01 (m, 1H), 0.97 – 0.90 (m, 1H). C NMR (100 MHz, CDCl3) δ 143.5, 128.1, 127.3,
126.6, 79.3, 44.8, 29.2, 28.8, 26.4, 26.0, 25.9. IR (in KBr): 3524, 3338, 2926, 1593, 1449, 1080 cmꢀ1.
MS m/z (EI): calcd for [C13H18O]+: 190.2, found: 190.2.
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1,2-Diphenylethanol (2e). 36 h, white solid: 43.6 mg, yield: 44%. H NMR (600 MHz, CDCl3) δ
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7.36 (d, J = 6.5 Hz, 4H), 7.30 (q, J = 5.9, 4.3 Hz, 3H), 7.24 (d, J = 7.2 Hz, 1H), 7.21 (d, J = 7.4 Hz,
2H), 4.91 (dd, J = 8.7, 4.7 Hz, 1H), 3.07 – 2.97 (m, 2H), 1.91 (br, 1H). 13C NMR (100 MHz, CDCl3)
δ 143.7, 138.0, 129.5, 128.5, 128.4, 127.6, 126.6, 125.9, 75.3, 46.0. IR (in KBr): 3658, 3316, 1707,
1495, 1369, 1197 cmꢀ1. MS m/z (EI): calcd for [C14H15O]+: 199.2, found: 199.6.
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1-Phenylbut-3-en-1-ol (2f). 72 h, pale yellow oil: 12.6 mg, yield: 17%. H NMR (600 MHz,
CDCl3) δ 7.39 – 7.27 (m, 4H), 7.27 – 7.23 (m, 1H), 5.87 – 5.71 (m, 1H), 5.13 (m, J = 3.5, 1.4 Hz,
1H), 4.78 – 4.67 (m, 1H), 2.51 (m, J = 8.8, 7.5, 6.2, 1.2 Hz, 2H), 2.03 (br, 1H). 13C NMR (100 MHz,
CDCl3) δ 143.5, 134.1, 128.0, 127.1, 125.5, 117.8, 73.2, 43.6. IR (in KBr): 3666, 3311, 1707, 1494,
1368, 1201, 1045 cmꢀ1. MS m/z (EI): calcd for [C10H13O]+:149.2, found: 149.2.
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1,2,3,4-Tetrahydronaphthalen-1-ol (2h). 48 h, colourless oil: 32.6 mg, yield: 44%. H NMR (600
MHz, CDCl3) δ 7.47 – 7.39 (m, 1H), 7.24 – 7.16 (m, 2H), 7.11 (d, J = 5.1 Hz, 1H), 4.79 (t, J = 4.7
Hz, 1H), 2.83 (m, J = 16.5, 5.5 Hz, 1H), 2.76 – 2.70 (m, 1H), 1.99 (m, J = 11.2, 4.0 Hz, 2H), 1.94 –
1.90 (m, 1H), 1.78 (m, J = 9.7, 6.8, 3.4 Hz, 1H), 1.70 (br, 1H). 13C NMR (100 MHz, CDCl3) δ 138.7,
137.1, 129.0, 128.6, 127.5, 126.1, 68.1, 32.2, 29.2, 18.7. IR (in KBr): 3662, 2938, 1695, 1486, 1372,
1036 cmꢀ1. MS m/z (EI): calcd for [C10H12O]+: 148.2, found: 148.4.
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9H-Fluoren-9-ol (2i). 72 h, white solid: 46.5 mg, yield: 51%, mp. 158 C. H NMR (600 MHz,
CDCl3) δ 7.66 (dd, J = 7.4, 4.4 Hz, 4H), 7.40 (t, J = 7.5 Hz, 2H), 7.33 (t, J = 7.5 Hz, 2H), 5.59 (s,
1H), 1.93 – 1.45 (br, 3H). 13C NMR (100 MHz, CDCl3) δ 145.5, 139.9, 129.0, 127.7, 125.0, 119.9,
75.1. IR (in KBr): 3662, 3310, 1711, 1500, 1291, 1190 cmꢀ1. MS m/z (EI): calcd for [C13H10O]+:
182.2, found: 182.5.
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(3,4-Dimethoxyphenyl)methanol (2j). 24 h, pale yellow oil: 53.8 mg, yield: 64%. H NMR (600
MHz, CDCl3) δ 6.94 (s, 1H), 6.90 (d, J = 8.1 Hz, 1H), 6.87 – 6.84 (m, 1H), 4.63 (s, 2H), 3.90 (s, 3H),
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3.88 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 148.8, 148.3, 133.5, 119.2, 110.8, 110.2, 64.9, 55.7,
55.6. IR (in KBr): 3523, 3442, 3338, 1596, 1514, 1458, 1328, 1142 cmꢀ1. MS m/z (EI): calcd for
[C9H12O3]+: 168.2, found: 168.5.
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(4-(Dimethylamino)phenyl)methanol (2k). 35 h, pale yellow oil: 31.8 mg, yield: 42%. H NMR
(600 MHz, CDCl3) δ 7.24 (d, J = 8.7 Hz, 2H), 6.73 (d, J = 8.3 Hz, 2H), 4.56 (s, 2H), 2.94 (s, 6H).
13C NMR (100 MHz, CDCl3) δ 150.2, 128.9, 128.5, 112.6, 65.2, 40.6. IR (in KBr): 3645, 2878,
1678, 1523, 1348, 1163 cmꢀ1. MS m/z (EI): calcd for [C9H13NO]+: 151.2, found: 151.5.
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1-(p-Tolyl)ethanol (2l). 36 h, colourless oil: 51.1 mg, yield: 75%. H NMR (400 MHz, CDCl3) δ
7.30 – 7.25 (m, 2H), 7.17 (s, 2H), 4.89 – 4.84 (m, 1H), 2.34 (s, 3H), 1.71 (br, 1H), 1.48 (d, J = 6.3 Hz,
3H). 13C NMR (100 MHz, CDCl3) δ 142.9, 137.0, 129.1, 125.4, 70.1, 25.1, 21.1. IR (in KBr): 3622,
3330, 1592, 1392, 1115 cmꢀ1. MS m/z (EI): calcd for [C9H12O]+: 136.2, found: 136.1.
1-(4-Methoxyphenyl)ethanol (2m). 48 h, colourless oil: 52.5 mg, yield: 69%. 1H NMR (600 MHz,
CDCl3) δ 7.30 (d, J = 8.2 Hz, 2H), 6.88 (d, J = 8.1 Hz, 2H), 4.85 (q, J = 6.5 Hz, 1H), 3.80 (s, 3H),
1.80 (br, 1H), 1.48 (d, J = 6.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 159.0, 137.9, 126.6, 113.8,
70.0, 55.3, 25.0. IR (in KBr): 3652, 3328, 1598, 1512, 1244, 1173 cmꢀ1. MS m/z (EI): calcd for
[C9H12O2]+: 152.2, found: 152.2.
1-(4-Bromophenyl)ethanol (2n). 48 h, white solid: 73.4 mg, yield: 73%, mp. 40 oC. 1H NMR (600
MHz, CDCl3) δ 7.47 (d, J = 8.1 Hz, 2H), 7.25 (s, 2H), 4.88 (q, J = 6.5 Hz, 1H), 1.80 (br, 1H), 1.48 (d,
J = 6.5 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 144.70, 131.50, 127.10, 121.10, 69.73, 25.21. IR (in
KBr): 3663, 3310, 1711, 1489, 1201, 1066 cmꢀ1. MS m/z (EI): calcd for [C8H9BrO]+: 201.1, found:
201.4.
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1-(4-Chlorophenyl)ethanol (2o). 36 h, colourless oil: 54.8 mg, yield: 70%. H NMR (400 MHz,
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CDCl3) δ 7.37 – 7.28 (m, 4H), 5.05 – 4.69 (m, 1H), 1.76 (br, 2H), 1.48 (d, J = 6.0 Hz, 3H). 13C NMR
(100 MHz, CDCl3) δ 143.9, 132.5, 128.1, 126.5, 69.3, 25.1. IR (in KBr): 3594, 3336, 1593, 1491,
1402, 1086 cmꢀ1. MS m/z (EI): calcd for [C8H9ClO]+: 156.6, found: 156.2.
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1-(Thiophen-2-yl)ethanol (2p). 36 h, colourless oil: 29.5 mg, yield: 46%. H NMR (600 MHz,
CDCl3) δ 7.24 (d, J = 4.7 Hz, 1H), 7.01 – 6.95 (m, 2H), 5.14 (d, J = 6.9 Hz, 1H), 1.79 (br, 2H), 1.61
(d, J = 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 149.8, 126.6, 124.4, 123.1, 66.2, 25.2. IR (in
KBr): 3647, 3329, 1592, 1389, 1119 cmꢀ1. MS m/z (EI): calcd for [C6H8OS]+: 128.2, found: 128.0.
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1-(4-Isobutylphenyl)ethanol (2q). 36 h, colourless oil: 49.9 mg, yield: 56%. H NMR (400 MHz,
CDCl3) δ 7.25 (d, J = 8.0 Hz, 2H), 7.10 (d, J = 8.0 Hz, 2H), 4.86 (q, J = 6.5 Hz, 1H), 2.46 (d, J = 7.2
Hz, 2H), 1.85 (m, J = 13.5, 6.8 Hz, 1H), 1.49 (d, J = 6.5 Hz, 3H), 0.90 (d, J = 6.6 Hz, 6H). 13C NMR
(100 MHz, CDCl3) δ 143.0, 141.0, 129.2, 125.2, 70.3, 45.1, 30.2, 25.0, 22.4. IR (in KBr): 3646,
3313, 3018, 1672, 1513, 1366,1008 cmꢀ1. MS m/z (EI): calcd for [C12H18O]+: 178.3, found: 178.2.
1-(6-Methoxynaphthalen-2-yl)ethanol (2r). 36 h, white solid: 74.8 mg, yield: 74%, mp. 115oC. H
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NMR (400 MHz, CDCl3) δ 7.73 (t, J = 7.0 Hz, 3H), 7.48 (d, J = 8.6 Hz, 1H), 7.18 – 7.10 (m, 2H),
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5.04 (q, J = 6.6 Hz, 1H), 3.92 (s, 3H), 1.69 (br, 2H), 1.57 (d, J = 6.4 Hz, 3H). C NMR (100 MHz,
CDCl3) δ 157.5, 140.9, 133.9, 129.3, 128.6, 127.1, 124.3, 123.7, 118.9, 105.6, 70.4, 55.2, 25.0. IR
(in KBr): 3627, 3523, 3334, 1594, 1392, 1116, 1025 cmꢀ1. MS m/z (EI): calcd for [C13H14O2]+: 202.3,
found: 202.5.
1-(6-Chloro-9H-carbazol-2-yl)ethanol (2s). 72 h, white solid: 62.7 mg, yield: 51%. 1H NMR (600
MHz, DMSOꢀd6) δ 11.28 (s, 1H), 8.10 (d, J = 2.1 Hz, 1H), 8.00 (d, J = 8.1 Hz, 1H), 7.41 (d, J = 8.6
Hz, 2H), 7.28 (m, J = 8.6, 2.1 Hz, 1H), 7.08 (d, J = 8.1 Hz, 1H), 5.18 (s, 1H), 4.85 – 4.77 (m, 1H),
1.33 (d, J = 6.4 Hz, 3H). 13C NMR (100 MHz, DMSOꢀd6) δ 146.8, 141.1, 138.9, 125.4, 124.3, 123.3,
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120.8, 120.7, 120.1, 117.5, 112.8, 108.2, 69.2, 26.9. IR (in KBr): 3405, 2971, 1719, 1503, 1155 cmꢀ1.
MS m/z (EI): calcd for [C14H13ClNO]+: 246.7, found: 246.7.
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Cyclohexanol (2t). 24 h, colourless oil: 28.1 mg, yield: 56%. 1H NMR (600 MHz, CDCl3) δ 3.61
(d, J = 9.0 Hz, 1H), 1.89 (d, J = 10.1 Hz, 2H), 1.76 – 1.71 (m, 2H), 1.55 (br, J = 13.3 Hz, 1H), 1.28
(m, J = 10.8, 9.6 Hz, 5H), 1.17 (d, J = 11.5 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 70.2, 35.4, 25.4,
24.1. IR (in KBr): 3614, 3443, 1591, 1392, 1113 cmꢀ1. MS m/z (EI): calcd for [C6H12O]+: 100.2,
found: 100.3
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1-Adamantanol (2u). 48 h, colourless solid: 30.4 mg, yield: 40%, mp. 245oC. 1H NMR (400 MHz,
CDCl3) δ 2.14 (s, 3H), 1.71 (d, J = 2.8 Hz, 6H), 1.62 (q, J = 12.7 Hz, 6H). 13C NMR (100 MHz,
CDCl3) δ 68.2, 45.3, 36.0, 30.7. IR (in KBr): 3666, 3310, 2911, 1504, 1349, 1113 cmꢀ1. MS m/z (EI):
calcd for [C10H16O]+: 152.1, found: 152.2.
Acknowledgment We are grateful to the National Natural Science Foundation of China (NO.
21232003, 21202053, 21472058 and 21572074) and other financial supports (NO. 201422,
CCNU15A02007 and 2015CFA033) for support of this research.
Supporting Information
1
Details for condition optimizations, copies of H NMR and 13C NMR spectra of products 2,
references for known compounds and the mechanism study. This material is available free of charge
via the Internet at http://pubs.acs.org.
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(11) See Supporting Information for details of condition optimization.
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(17) Please see the references of known compounds in the Supporting Information.
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