Tetrahedron Letters
Easy eco-friendly phenonium ion production from phenethyl
alcohols in dimethyl carbonate
b
c
a
a
d
e
M. Barontini a, I. Proietti Silvestri b, , V. Nardi , P. Bovicelli , L. Pari , F. Gallucci , R. Spezia , G. Righi
⇑
a CRA-ING, Via della Pascolare 16-00016, Monterotondo (RM), Italy
b Dept. of Chemistry, ‘Sapienza’ University of Rome, p.le A. Moro 5, 00187 Rome, Italy
c CNR ICB-Unity of Sassari, Traversa La Crucca 3, Baldanica I, 07040 Sassari, Italy
d Université d’Evry VAL d’Essone (UEVE), LAMBE, CNRS, UMR 8587, Bd F. Mitterand, 91025 Evry Cedex, France
e CNR ICB-Unity of Rome, c/o ‘Sapienza’ University of Rome, p.le A. Moro 5, 00187 Rome, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and simple one-pot procedure for selective etherification of 2-aryl-ethylalcohols has been
achieved through Amberlyst 15-catalyzed reaction in dimethyl carbonate (DMC). Moreover, the polymer
catalyst could be recovered and reused with no effect on its activity. The reaction mechanism involves the
formation of phenonium ion which has been demonstrated by a C–C bond forming reaction. Theoretical
studies are in agreement with and thus explain experimental results.
Received 21 February 2013
Revised 24 June 2013
Accepted 26 June 2013
Available online 3 July 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Phenonium ion
Dimethyl carbonate
Selective etherification
Heterogeneous catalysis
The phenonium ion was first described by Cram1–3 in the 40s as
an intermediate in the solvolysis reactions of phenethyl chlorides
and tosylates. In the 70s Olah and Porter4,5 characterized via
NMR spectroscopy some stable phenonium ions prepared from
their chloride precursors in SbF5/SO2ClF solution. The lifetime of
these cations strictly depends on the ring substitution.6 After the
pioneering work of Cram and Olah, little attention has been paid
to the exploitation of new synthetic routes to generate the pheno-
nium ion.7,8
In the last three decades the interest in dimethyl carbonate
(DMC) as an eco-sustainable reagent has grown.9,10 Recently it
has been largely used as an environmentally friendly and safe med-
ium for its low toxicity and biodegradability. As reagent, DMC has
been widely employed as an electrophile in the methylation
reaction.11
In recent years, the use of solid acidic catalyst has attracted con-
siderable attention.12 In this regard, Amberlyst 15 possesses un-
ique properties such as environmental compatibility, nontoxic,
reusability, chemical, physical stabilities, and durability. Owing
to the numerous advantages associated with this cheap and non-
hazardous polymer, Amberlyst 15 has been explored as a powerful
catalyst in various organic reactions.13
reactivity of b-phenethyl carbonates. We have already reported
that selective protection can be achieved by using DMC with basic
or acid catalysis,14,15 obtaining the corresponding carboxymethyl
esters in excellent yield (Fig. 1).
Herein we describe a one-pot synthesis of 4-hydroxyphenethyl
methyl ether (1b) and its related compounds (Scheme 1).
Initial attempts to prepare 4-hydroxyphenethyl methyl ether
(1b) were performed by reacting 1 in the presence of H2SO4. How-
ever, a large excess of H2SO4 was necessary for a full conversion of
the substrate due to the contemporary formation of dimethyl sul-
fate as the by-product.16 In order to avoid this side reaction, H2SO4
was replaced by Amberlyst 15. Catalysis via Amberlyst 15 is con-
sidered inexpensive and eco-sustainable conditions due to the
possibility of recycling the heterogeneous catalyst. In our case up
to five cycles can be performed without apparent loss of efficiency.
In the procedure using Amberlyst 15 as the catalyst a cascade reac-
tion can be promoted when 1 is refluxed in DMC in the presence of
Amberlyst 15 leading directly to 1b with no need to isolate the
carboxymethyl ester (1a) (Scheme 1). The reported procedure is,
OH
OCOOMe
In the course of our research on the selective protection of pri-
mary alcohol in tyrosol (1), we became interested in exploring the
DMC
DBU or H2SO4
reflux
OH
OH
⇑
Corresponding author. Tel.: +39 0649913632; fax: +39 0649913628.
Figure 1. Selective carboxymethylation of primary alcohols.
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.