Graphene Oxide Promotes Site-Selective Allylic Alkylation of Thiophenes with Alcohols

Article abstract of DOI:10.1021/acs.orglett.8b01531

The graphene oxide (GO) assisted allylic alkylation of thiophenes with alcohols is presented. Mild reaction conditions and a low GO loading enabled the isolation of a range of densely functionalized thienyl and bithienyl compounds in moderate to high yields (up to 90%). The cooperative action of the Br?nsted acidity, epoxide moieties, and π-surface of the 2D-promoter is highlighted as crucial in the reaction course of the present Friedel-Crafts-type protocol.

Full text of DOI:10.1021/acs.orglett.8b01531

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Graphene Oxide Promotes Site-Selective Allylic Alkylation of
Thiophenes with Alcohols
Laura Favaretto,‡ Juzeng An,† Marco Sambo,† Assunta De Nisi,† Cristian Bettini,‡ Manuela Melucci,‡
Alessandro Kovtun,‡ Andrea Liscio,‡,§ Vincenzo Palermo,‡ Andrea Bottoni,† Francesco Zerbetto,†
Matteo Calvaresi,† and Marco Bandini*,†
†Dipartimento di Chimica “G. Ciamician”, Alma Mater Studiorum - Universita
̀
di Bologna, via Selmi 2, 40126 Bologna, Italy
‡Istituto per la Sintesi Organica e Fotoreattivita
̀
(ISOF) - CNR, via Gobetti 101, 40129 Bologna, Italy
§Istituto per la Microelettronica e Microsistemi (IMM) - CNR, via del Fosso del Cavaliere 100, 00133 Rome, Italy
S
* Supporting Information
ABSTRACT: The graphene oxide (GO) assisted allylic alkylation of thiophenes with alcohols is presented. Mild reaction
conditions and a low GO loading enabled the isolation of a range of densely functionalized thienyl and bithienyl compounds in
moderate to high yields (up to 90%). The cooperative action of the Brønsted acidity, epoxide moieties, and π-surface of the 2D-
promoter is highlighted as crucial in the reaction course of the present Friedel−Crafts-type protocol.
he site-selective functionalization of the thiophene nucleus
Tis still of undoubted importance due to their ubiquitous
use in the realization of functionalized molecular materials for
organic electronics and photonics.1 Catalysis represents an
ultimate synthetic tool for the chemical “decoration” of this
class of heteroarenes, enabling critical aspects such as
selectivity, simplicity, and sustainability to be satisfied
simultaneously. In this context, the Friedel−Crafts (FC) allylic
alkylation reaction is still receiving growing attention, since it
makes feasible further chemical manipulations of the aromatic
core due to the installation of carbon−carbon double bonds.2
The synthetic interest for this approach can be further amplified
by adopting cheap, readily available, and user-friendly π-
alcohols (i.e., allylic, propargylic, and allenylic alcohols) as
alkylating agents.3 However, important synthetic challenges
such as regioselectivity and mono- vs polyalkylation, with
specific reference to electron-rich aromatic rings, are still not
fully addressed.
composite materials, GO has already found elegant applications
in several synthetic organic transformations such as oxidation of
alcohols/amines,6a−e hydrogenation of alkenes,6f click chemis-
try,6g and aminolysis.6h Contrarily, and unexpectedly, the use of
GO in carbon−carbon bond forming reactions is still limited.7
In this context, He and Szostak have recently reported an
elegant GO-assisted alkylation of arenes that caught our
attention. In detail, the benzylation of electron-activated
aromatic compounds with styrenes was discussed by using
GO (200 wt %) as the promoting agent (Figure 1a).8
Bearing all that in mind, we envisioned the emerging
“carbocatalytic” approach4 as a promising tool to overcome
these difficulties. In particular, we identified graphene oxide
(GO)5 as a mediating agent for site-selective allylation of
functionalized thiophenes with readily accessible alcohols.
Moreover, due to its moderate Brønsted acidity, diversified
surface functionalization, and possible implementation into
Figure 1. Previous study on GO-based Friedel−Crafts-type alkylation
of alkenes (a) and the present work (b).
Received: May 16, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b01531
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
In combination with our ongoing interest in catalytic
methodologies for the direct functionalization of arenes with
alcohols,9 we envisioned the possibility of implementing a
metal-free GO-assisted allylating protocol on thiophenes
(Figure 1b). In this letter, preliminary findings and mechanistic
investigations on the topic are documented.
Scheme 1. Scope of the Reaction: Alcohols
At the outset of our investigation, we considered the
commercially available 2-methyl-thiophene 1a and 1-phenyl-
prop-2-en-1-ol 2a as model substrates with the specific intent to
assess the reliability of the protocol toward (a) polyalkylation,
(b) α- vs β-regioselectivity, (c) an SN vs SN′ mechanism (i.e.,
regiochemistry toward the allylic framework), and (d) the
stereochemistry of the newly formed CC. A range of
carbocatalysts and reaction conditions were screened (Table 1).
a
Table 1. Optimization of the Reaction Conditions
b
c
run
additive (wt %)
solvent/time (h)
yield (%)
3aa:3aa’
1
GO (50)
GO (25)
CHCl3/16
CHCl3/16
CHCl3/16
THF/4
36
86:14
85:15
−
72:28
75:25
−
78:22
78:22
86:14
−
2
23
a
b
0.2 mmol of 2 (1a:2 = 3:1) unless otherwise specified. With 1a:2g =
d
3
GOaq (25)
traces
34
c
6:1 and GO loading of 50 wt %. t = 80 °C. In some specific cases,
minor amounts of branched 3 were also detected by NMR (see SI).
4
GO (25)
GO (25)
GO (25)
GO (25)
GO (25)
GO (25)
graphene (25)
rGO (25)
5
ACN/4
51
6
DMF/4
NR
77
very good yield (30−85%). 1-Aryl-propen-1-ols carrying both
electron-donating (e.g., OH, OR) and electron-withdrawing
(e.g., Cl, Br) groups are proven efficient under optimal
conditions. Additionally, synthetically useful alkyne (3ag) and
azide (3ah) groups were effectively tolerated. It is worth noting
that the unprotected phenolic group was also tolerated in the
process, underlying that the FC-based C−C bond forming
product 3ae was favored with respect to the C−O bond
formation under GO-assistance. The synthetic approach was
also applied to the moderately site-selective functionalization of
1a with concomitant formation of products (3ai and 3ak). The
reactivity of aliphatic allylic alcohols was also demonstrated by
condensing 2j with 1a under optimal conditions. Interestingly,
the corresponding C(2)-alkylated thienyl compound 3aj was
isolated in 45% yield as a single regio- and stereoisomer.
Finally, the protocol also enabled the incorporation of
chromophoric units (e.g., fluorenyl and 1-pyrenyl) into the
model aromatic compound in moderate to good yields (56−
70%) with a very short reaction time (45 min−1 h)
Therefore, we turned our attention toward the generality of
the method related to thiophene derivatives. 2-nHex-thiophene
1b displayed feasibility for the present methodology furnishing
the corresponding alkylated compound 3ba in 51% yield.
Analogously, differently substituted bithienyl compounds 1c−h
underwent the FC-allylative process in a satisfying manner
(yields up to 64%) by means of 50 wt % of GO. In all cases,
monosubstituted linear α-allylated compounds 3 were obtained
as the predominant arene (Scheme 2). β-Functionalized linear
allyl-thiophenes were also observed in a non-negligible amount
in the case of 3ca−3ea. Differently, α-branched isomers b-3
were formed only in traces with the exception of substituted
bithiophenes 1d and 1e.13 Additionally, also widely employed
rigid “cores” in organic electronics such as dithienothiophene
1g14a and dithienopyrrole 1h14b underwent allylic alkylation
with alcohols 2a and 2f resulting in a moderate yield (32%) and
very high regioselectivity (up to 95:5).
7
(CH2Cl)2/4
DCE/8
8
89
9
dioxane/4
dioxane/4
Dioxane/4
90
10
11
NR
NR
−
a
All the reactions were carried out in reagent-grade solvents without
b
any moisture exclusion (1a:2a = 3:1). Isolated yield after flash
c
chromatography. Both 3aa and 3aa′ were isolated as E-stereoisomers
d
and resulted in being inseparable via flash chromatography. Aqueous
solution (5 mg/mL) of GO was employed. NR: no reaction. ACN:
acetonitrile.
Interestingly, a promising isolated yield of the 3aa/3aa′
mixture was recorded by using only 50 wt % of catalyst in
CHCl3 at 90 °C (entry 1) that was subsequently reduced to 25
wt % (entry 2) with a decrease of the overall performance (23%
yield). Contrarily, the use of an aqueous solution of GO failed
in producing the final product. DCE and 1,4-dioxane were
elected as the best solvents providing comparable outcomes
(yields 89−90% and up to 86:14 3aa/3aa′ ratio). However, the
shorter reaction time (4 h vs 8 h) led us to choose 1,4-dioxane
for the reaction scope investigation.10 It is worth mentioning
that while the blank reaction clearly emphasized the pivotal role
of the GO11 (entry 10), graphene and reduced graphene oxide
(rGO) proved completely ineffective in the present protocol.
Finally, only the thermodynamically more stable linear
compounds 3aa and 3aa′ were isolated (SN’ vs SN) along
with the exclusive formation of the (E)-isomer. Furthermore,
only in sporadic cases, traces of branched 3aa (i.e., b-3aa) were
also observed in the reaction crude.12
The optimized reaction conditions were applied to a range of
diversely substituted allylic alcohols (2b−m; see Supporting
Information) in the Friedel−Crafts alkylation of 1a (Scheme
1). In all cases, SN2′-type allylation compounds 3 were obtained
exclusively with the (E)-CC configuration in moderate to
B
DOI: 10.1021/acs.orglett.8b01531
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Organic Letters
Letter
a
acid and styryl oxide (both at 100 wt %), 3aa was formed in
30% conversion (1H NMR), providing preliminary evidence of
the synergistic action of the Brønsted acidity and the oxirane
units in promoting the condensation of the thiophene ring and
the allylic alcohol.
Scheme 2. Scope of the Reaction: Thiophenes
To further prove the direct involvement of epoxide units in
the reaction mechanism, X-ray Photoelectron Spectroscopy
(XPS) analysis was carried out in samples of GO before and
after the catalytic protocol (Figure 2).
a
Isolated yields after flash chromatography. Regioselectivity was
1
determined by GC-MS and/or H NMR on the reaction crudes.
In order to obtain mechanistic insight, some control
experiments were performed. First, when branched or linear
allylic alcohols 2a and 2a′ were utilized, comparable chemical
and stereochemical outcomes in (E)-3aa were recorded (90%
and 76% yields, respectively, Scheme 3a). Additionally, the
Figure 2. C 1s XPS spectra of (a) pristine GO, (b) GO after 4 h at 90
°C in dioxane, and (c) GO after the allylic alkylation of thiophenes
with alcohols.
Scheme 3. Control Experiments for the Present GO-Assisted
a
Friedel−Crafts Condensation
The fitting of the high-resolution C 1s peak quantified the
relative amounts of aromatic carbon (C−C sp2, 284.4 eV),
aliphatic carbon (C−C sp3, 285.0 eV), hydroxyl (C−OH, 285.7
eV), epoxy (C−O−C, 286.7 eV), carbonyl (CO, 288.0 eV),
and carboxyl (O−CO, 290.1 eV).15
Figure 2 shows the C 1s spectra of (a) pristine GO, (b) GO
after 4 h at 90 °C in dioxane, and (c) GO after the site-selected
allylic alkylation of thiophenes with alcohols. First, it is possible
to exclude any reaction between GO and dioxane at 90 °C
since GO (a) and GO after 4 h at 90 °C in dioxane (b) have no
remarkable differences. In contrast, after reaction (Figure 2c)
the relative abundance of the epoxy groups decreased
substantially from 40.3
hydroxyl groups increased from 7.6
0.8% to 27.4
0.6%, while the
0.3%
0.3% to 11.9
a
0.2 mmol of 2a/2a′ (1a:2 = 3:1).
suggesting that a partial ring opening of the epoxide units of the
promoting agent took place concomitantly to the reaction
course. As expected, aromatic carbons are not affected by the
reaction (see SI for details).
impact of the sole Brønsted acidity conferred by the GO
solution in dioxane (∼5 mg/mL → pH = 3.70) was assessed by
running the model process in the presence of several organic
Brønsted acids (loading = 75−100 wt %), namely, benzoic acid
(pH = 5.10, 5 mg/mL), pNO2-benzoic acid (pH = 3.82, 1 mg/
mL), and n-hexenoic acid (pH = 4.22, 5 mg/mL), but no
formation of 3aa was observed. Analogously, when ( )-styryl
epoxide (100 wt %) was employed the reaction did not procede
at all (Scheme 3b). The control experiment carried out with
stoichiometric amounts of styrene oxides was intended to verify
the potential role of the oxiranes moieties present in the GO
surface on the reaction mechanism. Such evidence unambig-
uously highlights the concerted action of the GO skeleton and
the functional groups present in the 2D-material in making the
C−C bond formation process effective. In contrast, when 1a
and 2a were reacted with the simultaneous presence of benzoic
We combined all spectroscopic and experimental information
with the QM/MM study to elucidate in detail the reaction
mechanism.16 We used 1a and 2a as model substrates. The
reaction mechanism resulted in being a three-step process, as
depicted in Figure 3. In step 1 the allylic alcohol grafts to the
GO surface. The reaction follows an SN1 mechanism where the
protonation (proton source could rely on the intrinsic Brønsted
acidity of GO) of the epoxide ring on the GO surface leads to
an unstable oxonium unit that opens without overcoming any
barrier (Rx). This gives a reactive α-carbocation that undergoes
a nucleophilic attack by the allylic alcohol (Ts1). From this
picture emerges the crucial role of the GO π-system in
stabilizing the carbocation generated by the epoxide ring
opening event. The concerted action of the GO π-system and
C
DOI: 10.1021/acs.orglett.8b01531
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Organic Letters
Letter
Figure 3. (a) Schematic representation of the reaction mechanism; (b) energy profiles for the three steps; (c) 3D representation of the identified
transition states.
the functional groups present in the 2D-material is highlighted
in agreement with experimental observations. The obtained
protonated allyl ether may undergo a Friedel−Crafts-type allylic
alkylation providing the observed allyl-thiophene (Pd1). Step 2
follows a concerted mechanism where the α-carbon of the 2-
methyl-thiophene attacks the allylic position (Ts2), inducing a
reorganization of the π-system (Figure 3c). The leaving O−H
group remains grafted on the GO surface (Pd2). Such a
mechanism justifies the overall increase of alcoholic moieties
versus the oxirane ones spectroscopically observed by XPS.
The GO catalyst also played a role in the regioselectivity of
the attack carried out by the α carbon of the thiophene
derivatives (3aa vs 3aa′). In fact, if the attack is carried out by
the α carbon (major regioisomer, Figure SI1) the sulfur atom of
the thiophene points toward the graphene sheet, while if the
attack is carried out by the β-carbon there is no interaction
between the S atom and GO. It is well-known that sulfur−π
interactions are strongly stabilizing,17 favoring the attack in α by
6.5 kcal mol−1 (Figure SI1). The final step, namely the
deprotonation of the Wheland-like intermediate (Ts3), is a fast
process (a barrier of only 2.9 kcal mol−1 was computed) carried
out by other epoxide groups present on the GO surface. The
recorded drop in catalytic performance (isolated yields in 3aa)
by the recovered GO (I run: 88%, II run: 66%, III run: 45%, IV
run: 29%) supports the current mechanistic hypothesis. In
particular, the lower the content of epoxide units is on the GO
surface, the less effective the carbocatalysis is.18
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b01531.
■
S
Synthetic procedures, XPS analysis and NMR spectra of
unknown compounds and computational detail (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: marco.bandini@unibo.it.
ORCID
Vincenzo Palermo: 0000-0002-0168-9693
Andrea Bottoni: 0000-0003-2966-4065
Francesco Zerbetto: 0000-0002-2419-057X
Matteo Calvaresi: 0000-0002-9583-2146
Marco Bandini: 0000-0001-9586-3295
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Acknowledgements are made to University of Bologna for
financial support. The research leading to these results has
received funding from the European Union’s Horizon 2020
research and innovation programme (Grant Agreement No.
696656 Graphene Flagship). J.A. is grateful to CSC Programme
No. 201608310110.
In conclusion, the regioselective allylic alkylation of
thiophenes with alcohols is documented under the assistance
of readily available and chemically unmodified graphene oxide.
The protocol features unique key aspects such as high
functional group tolerance, mild reaction conditions, and low
to moderate GO loading. The extension of the present GO-
based protocol to other C−C bond forming functionalizations
of π-systems is currently under investigation in our laboratories.
REFERENCES
■
(1) (a) Mishra, A.; Ma, C.-Q.; Bauerle, P. Chem. Rev. 2009, 109,
̈
1141−1276. (b) Barbarella, G.; Melucci, M.; Sotgiu, G. Adv. Mater.
2005, 17, 1581−1593. (c) Roncali, J.; Leriche, P.; Blanchard, P. Adv.
Mater. 2014, 26, 3821−3838.
(2) (a) Poulsen, T.; Jørgensen, K. A. Chem. Rev. 2008, 108, 2903−
2915. (b) You, S.-L.; Cai, Q.; Zeng, M. Chem. Soc. Rev. 2009, 38,
D
DOI: 10.1021/acs.orglett.8b01531
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
2190−2201. (c) Terrasson, V.; de Figueiredo, R. M.; Campagne, J. M.
Eur. J. Org, Chem. 2010, 2010, 2635−2655. (d) Zeng, M.; You, S.-L.
Synlett 2010, 2010, 1289−1301. (e) Mishra, N. K.; Sharma, S.; Park, J.;
Han, S.; Kim, I. S. ACS Catal. 2017, 7, 2821−2847.
(3) (a) Bandini, M.; Tragni, M. Org. Biomol. Chem. 2009, 7, 1501−
1507. (b) Bandini, M.; Cera, G.; Chiarucci, M. Synthesis 2012, 2012,
504−512. (c) Huang, F.; Liu, Z.; Yu, Z. Angew. Chem., Int. Ed. 2016,
55, 862−875.
(11) GO was used in flakes, and it exfoliated during the reaction. In a
comparative experiment, GO was exfoliated for 10 h in the reaction
solvent and the suspension used as-is for the catalysis. No differences
in reaction performances were recorded.
(12) Additionally, other “conventional” Lewis acids were tested in the
model reaction providing unsatisfying results in terms of yields or
3aa:3aa′ regioselectivity: pTSA (10 mol %) → 18% yield; FeCl3 (10
mol %) → NR; In(OTf)3 → 84% yield (2:1).
(13) Attempts to extend the protocol to longer thiophene oligomers
such as quaterthiophene failed in performing the FC-type process.
(14) (a) Santato, C.; Favaretto, L.; Melucci, M.; Zanelli, A.; Gazzano,
M.; Monari, M.; Isik, D.; Banville, D.; Bertolazzi, S.; Loranger, S.;
Cicoira, F. J. Mater. Chem. 2010, 20, 669−676. (b) Zhou, E.;
Nakamura, M.; Nishizawa, T.; Zhang, Y.; Wei, Q.; Tajima, K.; Yang,
C.; Hashimoto, K. Macromolecules 2008, 41, 8302−8305.
(4) For general reviews, see: (a) Pyun, J. Angew. Chem., Int. Ed. 2011,
50, 46−48. (b) Dreyer, D. R.; Bielawski, C. W. Chem. Sci. 2011, 2,
1233−1240. (c) Navalon, S.; Dhakshinamoorthy, A.; Alvaro, M.;
Garcia, H. Chem. Rev. 2014, 114, 6179−6212. (d) Deng, D.;
Novoselov, K. S.; Fu, Q.; Zheng, N.; Tian, Z.; Bao, X. Nat.
Nanotechnol. 2016, 11, 218−230. (e) Haag, D.-R.; Kung, H. H. Top.
Catal. 2014, 57, 762−773. (f) Chua, C. K.; Pumera, M. Chem. - Eur. J.
2015, 21, 12550−12562. (g) Serp, P.; Figueiredo, J. L. Carbon
Materials in Catalysis; Wiley: 2004. (h) Albero, J.; Garcia, H. J. Mol.
Catal. A: Chem. 2015, 408, 296−309.
(15) (a) Maccaferri, G.; Zanardi, C.; Xia, Z. Y.; Kovtun, A.; Liscio, A.;
Terzi, F.; Palermo, V.; Seeber, R. Carbon 2017, 120, 165−175. (b)
̀
Kovtun, A. PhD Thesis, Universita di Modena e Reggio Emilia, 2017.
(16) (a) Froudakis, G. E. Nano Lett. 2001, 1, 179−182. (b) Giacinto,
P.; Bottoni, A.; Calvaresi, M.; Zerbetto, F. J. Phys. Chem. C 2014, 118,
5032−5040. (c) Spyrou, K.; Calvaresi, M.; Diamanti, E. K.; Tsoufis, T.;
Gournis, D.; Rudolf, P.; Zerbetto, F. Adv. Funct. Mater. 2015, 25, 263−
269. (d) Giacinto, P.; Zerbetto, F.; Bottoni, A.; Calvaresi, M. J. Chem.
Theory Comput. 2016, 12, 4082−4092. (e) Marforio, T. D.; Bottoni,
A.; Giacinto, P.; Zerbetto, F.; Calvaresi, M. J. Phys. Chem. C 2017, 121,
27674−27682.
(5) (a) Jia, H.-P.; Dreyer, D. R.; Bielawski, C. W. Tetrahedron 2011,
67, 4431−4434. (b) Dreyer, D. R.; Todd, A. D.; Bielawski, C. W.
Chem. Soc. Rev. 2014, 43, 5288−5301.
(6) (a) Dreyer, D. R.; Jia, H. P.; Bielawski, X. W. Angew. Chem., Int.
Ed. 2010, 49, 6813−6816. (b) Jia, H. P.; Dreyer, D. R.; Bielawski, C.
W. Adv. Synth. Catal. 2011, 353, 528−532. (c) Su, C.; Acik, M.; Takai,
K.; Lu, J.; Hao, S.; Zheng, Y.; Wu, P.; Bao, Q.; Enoki, T.; Chabal, Y. J.;
Loh, K. P. Nat. Commun. 2012, 3, 1298. (d) Lv, G.; Wang, H.; Yang,
Y.; Deng, T.; Chen, C.; Zhu, Y. ACS Catal. 2015, 5, 5636−5646.
(e) Su, S.; Tandiana, R.; Balapanuru, J.; Tang, W.; Pareek, K.; Nai, C.
T.; Hayashi, T.; Loh, K. P. J. Am. Chem. Soc. 2015, 137, 685−674.
(f) Primo, A.; Neatu, F.; Florea, M.; Parvulescu, V.; Garcia, H. Nat.
Commun. 2014, 5, 5291. (g) Reddy, V. H.; Reddy, Y. V. R.; Sridhar, B.;
Reddy, B. V. S. Adv. Synth. Catal. 2016, 358, 1088−1092. (h) Acocella,
M. R.; D’Urso, L.; Maggio, M.; Guerra, M. ChemCatChem 2016, 8,
1915−1920.
(17) (a) Zauhar, R. J.; Colbert, C. L.; Morgan, R. S.; Welsh, W. J.
Biopolymers 2000, 53, 233−248. (b) Calvaresi, M.; Zerbetto, M. Acc.
Chem. Res. 2013, 46, 2454−2463.
(18) Boukhvalov, D. W.; Dreyer, D. R.; Bielawski, C. W.; Son, Y.-W.
ChemCatChem 2012, 4, 1844−1849.
(7) (a) Kumar, A. V.; Rao, K. R. Tetrahedron Lett. 2011, 52, 5188−
5191. (b) Acocella, M. R.; Mauro, M.; Guerra, G. ChemSusChem 2014,
7, 3279−3283. (c) Wirtanen, T.; Makela, M. K.; Sarfraz, J.; Ihalainen,
̈
̈
P.; Hietala, S.; Melchionna, M.; Helaja, J. Adv. Synth. Catal. 2015, 357,
3718−3726. (d) Acocella, M. R.; De Pascale, M.; Maggio, M.; Guerra,
G. J. Mol. Catal. A: Chem. 2015, 408, 237−241. (e) Gao, Y.; Tang, P.;
Zhou, H.; Zhang, W.; Yang, H.; Yan, N.; Hu, G.; Mei, D.; Wang, J.;
Ma, D. Angew. Chem., Int. Ed. 2016, 55, 3124−3128. (f) Kausar, N.;
Mukherjee, P.; Das, A. R. RSC Adv. 2016, 6, 88904−88910.
(8) Hu, F.; Patel, M.; Luo, F.; Flach, C.; Mendelsohn, R.; Garfunkel,
E.; He, H.; Szostak, M. J. Am. Chem. Soc. 2015, 137, 14473−14480. In
this work, the efficiency of benzyl alcohol as well as 1-phenyl-1-ethanol
was also demonstrated in the sole condensation with resorcinol.
(9) (a) Bandini, M.; Tragni, M.; Umani-Ronchi, A. Adv. Synth. Catal.
2009, 351, 2521−2524. (b) Bandini, M.; Eichholzer, A. Angew. Chem.,
Int. Ed. 2009, 48, 9533−9537. (c) Bandini, M.; Eichholzer, A.;
Gualandi, A.; Quinto, T.; Savoia, D. ChemCatChem 2010, 2, 661−665.
(d) Bandini, M.; Gualandi, A.; Tragni, M.; Savoia, D. J. Organomet.
Chem. 2011, 696, 338−347. (e) Cera, G.; Crispino, P.; Monari, M.;
Bandini, M. Chem. Commun. 2011, 47, 7803−7805. (f) Chiarucci, M.;
Cera, G.; Bandini, M. Pure Appl. Chem. 2012, 84, 1673−1684.
(g) Cera, G.; Chiarucci, M.; Mazzanti, A.; Mancinelli, M.; Bandini, M.
Org. Lett. 2012, 14, 1350−1353. (h) Cera, G.; Piscitelli, S.; Chiarucci,
́
M.; Fabrizi, G.; Goggiamani, A.; Ramon, R. S.; Nolan, S. P.; Bandini,
M. Angew. Chem., Int. Ed. 2012, 51, 9891−9895. (i) Bandini, M.;
Bottoni, A.; Chiarucci, M.; Cera, G.; Miscione, G. J. Am. Chem. Soc.
2012, 134, 20690−20700. (j) Chiarucci, M.; Matteucci, E.; Cera, G.;
Fabrizi, G.; Bandini, M. Chem. - Asian J. 2013, 8, 1776−1779.
(k) Chiarucci, M.; Mocci, R.; Syntrivanis, L.-D.; Cera, G.; Mazzanti, A.;
Bandini, M. Angew. Chem., Int. Ed. 2013, 52, 10850−10853.
(l) Giacinto, P.; Cera, G.; Bottoni, A.; Bandini, M.; Miscione, G. P.
ChemCatChem 2015, 7, 2480−2484.
(10) The flakes of GO tended to dissolve completely during the
heating and reaction time.
E
DOI: 10.1021/acs.orglett.8b01531
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