A new, mild, general and efficient route to aryl ethyl carbonates in solvent-free conditions promoted by magnesium perchlorate

Article abstract of DOI:10.1002/ejoc.200600366

A new, general and mild method for the direct synthesis of aryl and alkyl ethyl carbonates promoted by a Lewis acid is reported. The reaction proceeds smoothly with diethyl dicarbonate in the presence of Mg(ClO₄) ₂, a specific activator of 1,3-dicarbonyl compounds, and shows general applicability. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejoc.200600366

FULL PAPER
DOI: 10.1002/ejoc.200600366
A New, Mild, General and Efficient Route to Aryl Ethyl Carbonates in
Solvent-Free Conditions Promoted by Magnesium Perchlorate
Giuseppe Bartoli,[a] Marcella Bosco,[a] Armando Carlone,[a] Manuela Locatelli,[a]
Enrico Marcantoni,[b] Paolo Melchiorre,[a] Paolo Palazzi,[a] and Letizia Sambri*[a]
Keywords: Alcohols / Alkyl aryl carbonates / Lewis acids / Perchlorates / Solvent-free conditions
A new, general and mild method for the direct synthesis of
aryl and alkyl ethyl carbonates promoted by a Lewis acid is
reported. The reaction proceeds smoothly with diethyl dicar-
bonate in the presence of Mg(ClO4)2, a specific activator of
1,3-dicarbonyl compounds, and shows general applicability.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
Therefore, we thought to explore the efficiency of
Mg(ClO4)2 to activate diethyl dicarbonate for preparing
alkyl and aryl ethyl carbonates under Lewis acid catalysis.
The remarkable importance of aryl and alkyl carbonates
in various chemical fields is well documented by the pres-
ence of a large number of patents[11] and papers in the lit-
erature.[12] Organic carbonates, in fact, have found employ-
ment as fuel additives, lubricating oils, herbicides, pesti-
cides, plastics and solvents and for medicinal and biological
applications. Moreover they can act as useful protecting
groups of alcohols and phenols, since they are more stable
than the corresponding esters under basic conditions.[13]
The traditional methods for the preparation of organic
carbonates require the use of basic conditions and toxic rea-
gents,[12a,14] such as phosgene, pyridine and carbon mon-
oxide. Thus, much effort has been recently devoted to the
development of more environmentally friendly procedures
for organic carbonate synthesis.[15]
The organic carbonate interchange[12a] has probably been
the most pursued approach and has given rise to the devel-
opment of a large number of protocols, most of which are
patented.[16] This is an equilibrium reaction, which follows
thermodynamic rules; the more nucleophilic alcohol should
displace the less nucleophilic one. From these considera-
tions, phenols are expected to have difficulty in reacting
with dialkyl carbonates. However, sophisticated procedures,
high temperatures and appropriate catalysts allow the equi-
librium to be shifted towards the desired product, even if
the reactions proceed at relatively slow rates with generally
low yields. Moreover, besides mixed carbonates, appreciable
amounts of symmetrical carbonates are always ob-
tained.[11f,12a]
For a long time, the chemical community has avoided the
use of metal perchlorates out of fear that they can work as
explosives.[1] However, recently Long asserted that the
scarce consideration of perchlorates in commercial pro-
cesses was due to “the mistaken association of perchlorate
salts with the oxidizing potential of perchloric acid and the
pyrotechnic performances of ammonium perchlorate”.[2]
Actually, perchlorate salts are only dangerous if heated over
their decomposition temperature (300–500 °C)[3] in the
presence of oxidizable materials or under highly acidic con-
ditions. The National Fire Protection Association (NFPA)
ranks magnesium perchlorate as barely hazardous for
health and as an oxidizing product, but not as an explosive
one.[4] Suppliers inform us that magnesium perchlorate is
stable under ordinary conditions of use and storage, but
contact with heat and reducing agents must be avoided.[5]
In conclusion, the scarce use of perchlorate salts under mild
conditions in organic chemistry is mainly due to a bad
name rather than true chemical hazard.
On the other hand, because metal perchlorates are highly
dissociated ion pairs,[6] they can act as powerful Lewis ac-
ids, exploiting their ability to activate mainly bidentate
compounds. In particular, metal perchlorates can promote
various acylation and esterification reactions,[7] the synthe-
sis of β-enamino esters,[8] the protection of amines as Boc-
derivatives[9] and the synthesis of aryl and alkyl tert-butyl
ethers.[10]
[a] Università di Bologna, Dipartimento di Chimica Organica “A.
Mangini”,
V.le Risorgimento 4, 40136 Bologna, Italy
Fax: +39-051-2093654
E-mail: letizia.sambri@unibo.it
The selective synthesis of mixed aryl or alkyl carbonates
was also performed by using toxic ethyl chloroformate.[17]
However, sometimes tertiary amines did not survive the re-
[b] Università di Camerino, Dipartimento di Scienze Chimiche,
Via S. Agostino 1, 62032 Camerino (Mc), Italy
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L. Sambri et al.
FULL PAPER
action conditions.[17e] Moreover, this reagent also requires of the addition process, while Cu(OTf)2 drastically lowers
basic conditions, and pyridine, which is the most commonly the reaction rate. Other common Lewis acid catalysts, such
used reaction partner, can displace the reactive halide as iron and indium chloride, gave poor results (Table 1, En-
groups in an SNAr fashion.[17f]
tries 9–10). Finally, p-toluenesulfonic acid (PTSA), a protic
In conclusion, an efficient and simple protocol for the acid, was completely unable to catalyse the reaction
direct synthesis of mixed aryl alkyl carbonates under acidic (Table 1, Entry 11). In conclusion, among the examined ac-
conditions is still lacking. We wish to report herein the pe- ids, our original choice was revealed as the most efficient
culiar reactivity of diethyl dicarbonate[18] in the presence of one.
Mg(ClO4)2, which allowed us to set up a new, simple and
mild approach to aryl ethyl carbonates.
Moreover, some further comments on the advantages of
this catalyst can be made. The almost quantitative yields of
the recovered product demonstrate that, under the adopted
experimental conditions, none of the possible side reactions
occur [(Scheme 1, Equation (1)]. In fact, as will be detailed
later in the text, the possible addition of the by-product
ethanol to unreacted diethyl dicarbonate (2) [Scheme 1,
Equation (2)] is slower than the addition of phenol to 2, so
that only the desired ethyl phenyl carbonate (3a) is success-
fully obtained. Moreover, the transesterification-type pro-
cess depicted in Equation (3) of Scheme 1, although ther-
modynamically favoured, is actually very slow. On the other
hand, when 3a was added to 1 equiv. of EtOH and 10 mol-
% of Mg(ClO4)2, it was recovered unaltered after 24 h of
stirring at 40 °C. This experiment demonstrates that, under
mild conditions, Mg(ClO4)2 is able to activate only 1,3-di-
carbonyl compounds and does not catalyse the transesterifi-
cation-type process generally promoted by basic cata-
lysts.[12a]
Results and Discussion
When phenol (1a) is left to react with diethyl dicarbonate
(2, 1.2 equiv.) in the presence of a 10 mol-% of Mg(ClO4)2 at
40 °C under solvent-free conditions (SFC), a smooth ad-
dition occurs within 5 h, giving the expected ethyl phenyl
carbonate (3a) in almost quantitative yield (Table 1, Entry
1).[19]
Table 1. Comparison between various Lewis acid catalysts in the
reaction of phenol (1a) with diethyl dicarbonate (2, 1.2 equiv.) at
40 °C.
Entry
Catalyst
Yield [%]
1
2
3
4
5
6
7
8
9
Mg(ClO4)2
Ͼ99
68
90
83
13
90
46
13
80
39
56
0
Mg(ClO4)2·6H2O
[a]
Mg(ClO4)2
LiClO4
Al(ClO4)3·9H2O
Zn(ClO4)2·6H2O
Sc(OTf)3
Cu(OTf)2
InCl3
FeCl3
Ti(OiPr)4
PTSA
10
11
12
Scheme 1.
[a] 1 mol-%.
A low catalyst amount (1 mol-%, Table 1, Entry 3) re-
The same experimental conditions can be used to convert
sulted in a lower conversion (90% instead of almost quanti- various phenols into aryl ethyl carbonates (Table 2). The
tative). Longer reaction times did not improve the conver- best reaction conditions require 10 mol-% of the catalyst.
sion, since the competitive decomposition of diethyl dicar- The use of lower catalyst amounts (1 mol%) involves longer
bonate began to be important. In order to demonstrate that reaction times, except in the case of the more reactive p-
Mg(ClO4)2 is the best choice, we tested other Lewis acid nitro phenol (Table 2, Entry 9).
catalysts commonly used to activate carbonyls. Other per-
The nature of the substituent on the aromatic ring seems
chlorates, though they are among the most powerful Lewis not to dramatically influence the reaction rate. In fact, com-
acids, are less efficient (Table 1, Entries 4–6).[6] For example, plete conversion was observed in almost all cases.
Zn(ClO4)2·6H2O, which was demonstrated to be more ef-
All reactions were carried out under SFC in order to
ficient than magnesium perchlorate in the acetylation of minimize solvent waste, since the solid alcohols dissolved in
alcohols,[20] gave a lower yield. Moreover, scandium and dicarbonate 2 at 40 °C. Only 1q was not soluble in the reac-
copper triflates, which are able to convert carboxylic acids tion medium, making the addition of dichloromethane as
into esters by reaction with pyrocarbonates,[7a] led to very solvent necessary.
unsatisfactory results under the same experimental condi-
The reaction is highly chemoselective. In fact, various
tions (Table 1, Entries 7–8). In particular, with Sc(OTf)3, functionalities present in the substrates are tolerated under
decomposition of 2 occurs at a rate comparable with that the adopted reaction conditions, including aldehyde, ketone
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Aryl Ethyl Carbonate Synthesis Promoted by Magnesium Perchlorate
FULL PAPER
Table 2. Reaction of aromatic alcohols 1 with diethyl dicarbonate (2, 1.2 equiv.) in the presence of Mg(ClO4)2 at 40 °C.
Catalyst amount
Entry
Ar
Time [h]
Product
Yield [%]
[mol-%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
o-CH3O–C6H4-
m-CH3O–C6H4-
p-CH3O–C6H4-
p-CH3O–C6H4-
m-Cl–C6H4-
m-Cl–C6H4-
p-F–C6H4-
p-NO2–C6H4-
p-NO2–C6H4-
p-CHO–C6H4-
p-CHO–C6H4-
m-CH3C=O–C6H4-
m-N(CH3)2–C6H4-
m-N(CH3)2–C6H4-
p-CN–C6H4-
o-CN–C6H4-
4-[HO(CH2)3]–C6H4-
3-pyridyl
10
10
10
1
10
1
10
10
1
10
1
10
10
none
10
10
10
10
none
10
10
10
3
2
3
3
5
5
5
1.5
1.5
4.5
4.5
4.5
4.5
6
4.5
20
6
5.5
7
3
3
7.5
3b
3c
3d
3d
3e
3e
3f
3g
3g
3h
3h
3i
3j
3j
3k
3l
3m
3n
3n
3o
3p
3q
Ͼ99
98
Ͼ99
98
98
93
85
Ͼ99
Ͼ99
Ͼ99
88
Ͼ99
85
80
97
82[a]
89[b,c]
Ͼ99
98
3-pyridyl
1-naphthyl
2-naphthyl
8-quinolyl
Ͼ99
Ͼ99
93[b]
[a] 15% of unreacted starting material was also recovered. [b] Reaction carried out in dichloromethane. [c] Reaction carried out with
1.05 equiv. of 2.
and cyano substituents and heterocyclic functionalities
This result prompted us to extend this procedure to the
(Table 2, Entries 10, 12, 15, 16, 18 and 22). Tertiary amines synthesis of alkyl ethyl carbonates. The reaction succeeded
are not cleaved, in contrast to mixed carbonate formation with primary alkyl alcohols, which smoothly reacted with
with ethyl chloroformate.[17e]
diethyl dicarbonate to give the corresponding mixed car-
Unlike neutral substrates, which were recovered unal- bonates in good yields (Table 3, Entries 1–7). However, the
tered in the absence of the catalyst, basic substrates reacted reaction with aliphatic alcohols proved to be slower than
without any catalyst but in fairly lower yields (Table 2, En- that with phenols, and the ethanol by-product competed in
tries 14 and 19). These results can be rationalized by classi- the addition to 2 [Scheme 1, Equation (2)]. Thus, to com-
cal base catalysis or by an attack of the nitrogen on the plete the reaction, it was necessary to use 2.2 equiv. of di-
carbonyl group followed by migration.
ethyl dicarbonate. Diethyl carbonate is formed as a by-
We also investigated the chemoselectivity of the reaction. product, but it generally can be easily separated from the
Initially, 3-(4-hydroxyphenyl)propanol (1m) was allowed to desired carbonate by column chromatography.
react under standard reaction conditions, and a mixture of
Even with aliphatic alcohols, various functional groups
products was obtained, in which the monocarbonate 3m are tolerated, including bromide, the triisopropylsilyloxy
was the major product, and minor products were identified group and carbon–carbon double bonds in various posi-
as 3-{4-[(ethoxycarbonyl)oxy]phenyl}propyl ethyl dicarbon- tions and geometries (Table 3, Entries 3–7).
ate, ethyl 3-(4-hydroxyphenyl)propyl carbonate and the
Under the same conditions, less reactive secondary
starting material. Since the reaction mixture was syrupy, we alcohols give the mixed carbonates in a maximum yield of
thought that the medium viscosity was very likely to be re- 55% (Table 3, Entries 8–10). A complete conversion of 2-
sponsible for the incomplete chemoselectivity. Therefore, al- octanol into 6h could not be obtained, even by using
most equimolar amounts of 1m and 2 were dissolved in 4 equiv. of diethyl dicarbonate. On the other hand, tertiary
dichloromethane (0.3  solution of 1m) and were allowed alcohols are totally unreactive under the adopted reaction
to react in the presence of the catalyst (Table 2, Entry 17). conditions, as demonstrated by the recovery of 2-methyl-2-
After 6 h, the reactants disappeared, and the regioselectivity hexanol (5k) unaltered after 15 h at 40 °C in the presence
was complete, since ethyl 4-(3-hydroxypropyl)phenyl car- of 2.2 equiv. of 2.
bonate (3m) was the only isolated product. Only trace
Some considerations on the reaction mechanism are nec-
amounts of the dicarbonate were detected by NMR analy- essary to explain the observed reactivity. The results ob-
sis.
tained suggest that the reaction rate depends on the acidity
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L. Sambri et al.
FULL PAPER
Table 3. Reaction of aliphatic alcohols (5) with diethyl dicarbonate duces EtOH and CO2. The irreversibility of the last two
(2, 2.2 equiv.) in the presence of 10 mol-% of Mg(ClO4)2 at 40 °C.
steps drives the overall process towards 3. This explanation
accounts for the formation of the mixed carbonate 3 as the
major product of the reaction. However, this is a speculative
hypothesis, supported only by the analysis of the experi-
mental results. Unfortunately, at the moment, all attempts
to follow the reaction by NMR analysis failed to identify
the presence of any intermediate, and only the starting ma-
terials and the reaction products were observed. Neverthe-
less, studies are in progress to find experimental evidence to
elucidate the reaction mechanism.
However, since the release of the alcoholic proton in 8
seems to be the key step of the process, an easy shift of the
proton will accelerate the overall reaction. In other words,
a higher acidity of the starting alcohol will result in a faster
formation of 3. Aryl alcohols are therefore more reactive
than aliphatic ones. Among alkyl alcohols, steric hindrance,
together with the relative acidity, probably influences the
reactivity, primary alcohols being more reactive than sec-
ondary ones and tertiary alcohols being completely unreac-
tive.
of the starting hydroxy compound, and not on its nucleo-
Conclusions
philicity, as in the transesterification process. In fact, the
more acidic and less nucleophilic phenols react faster than
In conclusion, we have developed a new, mild and gene-
aliphatic alcohols, and the p-nitrophenol 3g is the most re- ral method for the direct synthesis of ethyl aryl carbonates
active among the aromatic substrates. Therefore, the release catalysed by a Lewis acid. Mixed carbonates are generally
of the alcoholic proton should be involved in the rate-de- prepared under basic catalysis, but side reactions often oc-
termining step. A similar dependence of the reaction rate cur. With the aim of avoiding the formation of by-products,
on alcohol acidity was already demonstrated by Gooßen in we explored the efficiency of Lewis acid catalysis. Our
the esterification of carboxylic acids with dicarbonates.[7a] original idea was to activate diethyl dicarbonate with
A
reasonable mechanistic hypothesis is depicted in Mg(ClO4)2, a specific coordinating agent for dicarbonyl
Scheme 2.
compounds. This approach proved to be effective in focus-
ing the reaction exclusively towards the desired product.
In addition, the reaction proceeds under mild conditions
at 40 °C with a slight excess of dicarbonate under SFC.
Various functional groups are tolerated, and the protocol
can be successfully applied to primary alcohols, allowing
for a new, simple approach to alkyl ethyl carbonates. Fi-
nally, an easy tuning of the reaction conditions allows a
simple and chemoselective formation of alkyl aryl carbon-
ates in the presence of aliphatic hydroxyl groups.
Experimental Section
1
General Remarks: H and 13C NMR spectra were recorded at 400
or 300 MHz and 100 or 75 MHz, respectively. The chemical shifts
(δ) are given in ppm relative to the signals of the solvent (CHCl3)
or TMS. Coupling constants are given in Hz. Carbon types were
determined by DEPT 13C NMR experiments. The following ab-
breviations are used to indicate the multiplicity: s (singlet), d (doub-
let), t (triplet), q (quartet), m (multiplet) and bs (broad signal).
The purification of the reaction products was carried out by flash
chromatography on silica gel (230–400 mesh).
Scheme 2. A possible mechanistic explanation.
Owing to its ability to coordinate 1,3-dicarbonyl com-
pounds, Mg(ClO4)2 reacts with diethyl dicarbonate to form
complex 7, which can undergo the addition of the alcohol
to form intermediate 8. An internal proton shift in 8 can
produce intermediate 9, which can irreversibly decompose
to the mixed carbonate 3 and to the carbonic acid mono-
Materials: Commercial grade reagents and solvents were used with-
out further purification. All starting alcohols, anhydrous Mg-
(ClO4)2 and diethyl dicarbonate were purchased from Aldrich and
ester 10. Owing to its high instability, 10 immediately pro- used as received.
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Aryl Ethyl Carbonate Synthesis Promoted by Magnesium Perchlorate
FULL PAPER
1
General Procedure for the Synthesis of Aryl Ethyl Carbonates (3):
In a two-necked flask equipped with a magnetic stirring bar,
Mg(ClO4)2 (0.10 mmol), the phenol 1 (1.0 mmol) and diethyl dicar-
bonate 2 (1.2 mmol) were added. The mixture was stirred at 40 °C
until the GM-MS analysis revealed the presence of 1. The crude
reaction mixture was diluted with water and extracted with Et2O.
The organic layer was separated, dried with MgSO4 and filtered,
and the solvent was removed by rotary evaporation. The aryl ethyl
carbonate 3 was purified by flash chromatography on silica gel with
a mixture of petroleum ether/Et2O = 95:5. Ethyl phenyl carbonate
(3a) and ethyl 4-nitrophenyl carbonate (3g) are commercial prod-
ucts. Ethyl 2-methoxyphenyl carbonate (3b),[21] ethyl 4-meth-
oxyphenyl carbonate (3d)[22] and ethyl 4-formylphenyl carbonate
(3h)[23] are completely characterized known compounds. Ethyl 3-
methoxyphenyl carbonate (3c),[24] ethyl 3-chlorophenyl carbonate
(3e),[25] ethyl 4-fluorophenyl carbonate (3f),[26] ethyl 3-(dimeth-
ylamino)phenyl carbonate (3j)[27] ethyl 4-cyanophenyl carbonate
(3k),[28] ethyl 2-cyanophenyl carbonate (3l)[29] ethyl pyrid-3-yl car-
bonate (3n),[30] ethyl naphth-1-yl carbonate (3o),[31] ethyl naphth-2-
yl carbonate (3p)[24] and ethyl quinol-8-yl carbonate (3q)[32] are
known compounds.
9-Bromononyl Ethyl Carbonate (6c): H NMR (300 MHz, CDCl3):
δ = 1.20–1.50 (m, 13 H), 1.60–1.75 (m, 2 H), 1.80–1.90 (m, 2 H),
3.41 (t, JHH = 6.9 Hz, 2 H), 4.12 (t, JHH = 6.2 Hz, 2 H), 4.19 (t,
JHH = 7.4 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 14.7
(CH3), 26.0 (CH2), 28.4 (CH2), 29.0 (CH2), 29.4 (CH2), 29.6 (CH2),
33.0 (CH2), 34.4 (CH2), 64.2 (CH2), 68.3 (CH2), 155.7 (C) ppm.
IR: ν = 2929 (s), 2855 (s), 1747 (vs), 1258 (vs) cm–1. ESI-MS: (m/z)
˜
= 319–317 [M+Na]+, 295–297 [M+H]+. C12H23BrO3 (295.21):
calcd. C 48.82, H 7.85, Br 27.07, O 16.26; found C 48.90, H 7.85.
Ethyl 4-(Triisopropylsilyloxy)butyl Carbonate (6d): 1H NMR
(400 MHz, CDCl3): δ = 1.00–1.10 (m, 21 H), 1.31 (t, JHH = 7.3
Hz, 3 H), 1.55–1.70 (m, 2 H), 1.70–1.85 (m, 2 H), 3.73 (t, JHH = 6.2
Hz, 2 H), 4.15–4.25 (m, 4 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 11.9 (CH), 14.2 (CH3), 18.0 (CH3), 25.2 (CH2), 29.2 (CH2), 62.3
(CH ), 63.6 (CH ), 67.8 (CH ), 155.3 (C) ppm. IR: ν = 2942 (s),
˜
2
2
2
2866 (s), 1747 (vs), 1258 (vs), 1105 (s), 1012 (s) cm–1. ESI-MS:
(m/z) = 341 [M+Na]+, 319 [M+H]+. C16H34O4Si (318.52): calcd.
C 60.33, H 10.76, O 20.09, Si 8.82; found C 60.30, H 10.75.
Acknowledgments
1H and 13C NMR spectroscopic data for uncharacterized com-
pounds follow.
Work carried out in the framework of the National Project “Stereo-
selezione in Sintesi Organica. Metodologie e Applicazioni” sup-
ported by MIUR, Rome, by the University of Bologna, in the
framework of “Progetto di Finanziamento Pluriennale, Ateneo di
Bologna” and by National Project FIRB “Progettazione, prepara-
zione e valutazione biologica e farmacologica di nuove molecole
organiche quali potenziali farmaci”.
Ethyl 3-Acetylphenyl Carbonate (3i): 1H NMR (300 MHz, CDCl3):
δ = 1.40 (t, JHH = 7.4 Hz, 3 H), 2.60 (s, 3 H), 4.33 (q, JHH = 7.4
Hz, 2 H), 7.35–7.40 (m, 1 H), 7.45–7.55 (m, 1 H), 7.75–7.80 (m, 1
H), 7.80–7.85 (m, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 14.1
(CH3), 26.6 (CH3), 64.9 (CH2), 120.8 (CH), 125.7 (CH), 125.8
(CH), 129.6 (CH), 138.5 (C), 151.4 (C), 153.3 (C), 196.7 (C) ppm.
IR: ν = 1759 (s), 1686 (s), 1234 (vs) cm–1. EI–MS: m/z (%) = 208
˜
(3), 164 (4),149 (19), 136 (32), 121 (100), 93 (19), 65 (10), 43 (24).
HRMS: calcd. for C11H12O4 208.07356; found 208.07312.
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Ethyl 4-(3-Hydroxypropyl)phenyl Carbonate (3m): 1H NMR
(400 MHz, CDCl3): δ = 1.37 (t, JHH = 7.3 Hz, 3 H), 1.79–1.81 (m,
2 H), 2.02 (bs, 1 H, OH, exchange with D2O), 2.67 (t, JHH = 7.3
Hz, 2 H), 3.62 (t, JHH = 6.3 Hz, 2 H), 4.29 (q, JHH = 7.3 Hz, 2 H),
7.07 (d, JHH = 8.2 Hz, 2 H), 7.18 (d, JHH = 8.2 Hz, 2 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 14.0 (CH3), 31.3 (CH2), 34.0 (CH2),
61.8 (CH2), 64.7 (CH2), 120.8 (CH), 129.2 (CH), 133.5 (C), 149.1
(C), 153.7 (C) ppm. IR: ν = 3379 (vs), 2937 (s), 1758 (vs), 1255 (vs)
˜
cm–1. EI–MS: m/z (%) = 224 (3), 206 (17), 135 (23), 134 (100), 133
(52), 107 (49), 91 (11), 77 (10). HRMS: calcd. for C12H16O4
224.10486; found 224.10474.
General Procedure for the Synthesis of Alkyl Ethyl Carbonates (6):
In a two-necked flask equipped with a magnetic stirring bar,
Mg(ClO4)2 (0.10 mmol), the alcohol 5 (1.0 mmol) and diethyl di-
carbonate (2) (2.2 mmol) were added. The mixture was stirred at
40 °C until the GM-MS analysis revealed the presence of 1. The
crude reaction mixture was diluted with water and extracted with
Et2O. The organic layer was separated, dried with MgSO4 and fil-
tered, and the solvent was removed by rotary evaporation. The
alkyl ethyl carbonate 6 was separated from the residual alcohol by
flash chromatography on silica gel with a mixture of petroleum
ether/Et2O = 95:5. Ethyl octyl carbonate (6a),[33] benzyl ethyl car-
bonate (6b),[34] (E)-ethyl hex-2-enyl carbonate (6g),[35] ethyl octan-
2-yl carbonate (6h),[36] ethyl (R)-menthyl carbonate (6i)[27] and (S)-
ethyl 2-(ethoxycarbonyloxy) propanoate (6j)[37] are completely
characterized known compounds. (E)-ethyl hex-3-enyl carbonate
(6e)[38] and (Z)-ethyl hex-3-enyl carbonate (6f)[31] are known com-
pounds.
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Jung, Tetrahedron 2000, 56, 8207.
1H and 13C NMR spectroscopic data for uncharacterized com-
pounds follow.
Eur. J. Org. Chem. 2006, 4429–4434
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4433

L. Sambri et al.
FULL PAPER
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[19] The anhydrous form worked better than the hydrated one
(Table 1, entries 1–2). However, the presence of small amounts
of water did not lower the reaction efficiency, and hence
Mg(ClO4)2 can be used as supplied.
Received: April 27, 2006
Published Online: July 25, 2006
4434
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4429–4434