Rapid formation of diphenylmethyl ethers and thioethers using microwave irradiation and protic ionic liquids

Article abstract of DOI:10.1016/j.tetlet.2012.02.011

Using microwave irradiation and protic ionic liquids (pIL) as co-solvent and catalyst for the synthesis of several diphenylmethyl ethers was achieved. The desired ethers were isolated simply by filtration through a silica plug to remove the pIL and proceeded in high yields (60-98%). These reactions were extremely rapid (10-30 min) and occurred under mild conditions (80 °C). This protocol was also successfully applied to the synthesis of thioethers.

Full text of DOI:10.1016/j.tetlet.2012.02.011

Tetrahedron Letters 53 (2012) 2035–2039
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Rapid formation of diphenylmethyl ethers and thioethers using microwave
irradiation and protic ionic liquids
Jarrad M. Altimari a, Joshua P. Delaney a, Linden Servinis a, Jennifer S. Squire a, Megan T. Thornton a,
Simren K. Khosa a, Benjamin M. Long a, Mark D. Johnstone a, Cassandra L. Fleming a, Frederick M. Pfeffer a,
Shane M. Hickey a, Matthew P. Wride a, Trent D. Ashton a, Bronwyn L. Fox b, Nolene Byrne b,
Luke C. Henderson a,
⇑
a Deakin University, Strategic Research Center for Biotechnology, Chemistry and Systems Biology, Pigdons Road, Waurn Ponds Campus, Waurn Ponds, Victoria 3216, Australia
b Institute of Technology and Research Innovation, Deakin University, Pigdons Road, Waurn Ponds Campus, Waurn Ponds, Victoria 3216, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Using microwave irradiation and protic ionic liquids (pIL) as co-solvent and catalyst for the synthesis of
several diphenylmethyl ethers was achieved. The desired ethers were isolated simply by filtration
through a silica plug to remove the pIL and proceeded in high yields (60–98%). These reactions were
extremely rapid (10–30 min) and occurred under mild conditions (80 °C). This protocol was also success-
fully applied to the synthesis of thioethers.
Received 16 November 2011
Revised 21 January 2012
Accepted 3 February 2012
Available online 17 February 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Protic ionic liquid
Microwave irradiation
Diphenylmethyl ether
Ether
Thioether
The use of protecting groups is ubiquitous within synthetic or-
ganic chemistry. Therefore, novel and efficient means of installing
and removing these groups are in constant demand.1
groups DPM ethers have been of use in small molecular therapeu-
tics as anti-addiction drugs.3
Protic ionic liquids (pILs) are a class of ionic liquids that are
formed by mixing strictly equimolar amounts (1:1) of Brønsted
acids and bases.4 The strength of acid and base combination deter-
mines the degree to which the acidic proton is transferred, a
parameter known as the proton-activity. A number of organic
transformations have recently been carried out with pILs as a sub-
stitute for strong mineral acids with excellent results.5 The use of a
pIL for the formation of DPM ethers or thioethers has not been
investigated. To the best of our knowledge, the only similar appli-
cation is the use of [pmIm]Br as a reaction medium for the SN2
reaction of thiols with bromodiphenylmethane.6
The DPM group can be removed in similar fashion to other ben-
zylic-type protecting groups.1,7 For ethers, removal is typically car-
ried out by hydrogenolysis, however cleavage of the DPM thioether
is not feasible due to palladium poisoning from the resultant thiol.
Nevertheless, treatment of thioethers with strong acids (e.g., triflu-
oroacetic or sulfuric acid) generates the diphenylmethyl carbocat-
ionic species, which can then be scavenged by phenol, thiophenol
or anisole.1a Additionally, single electron transfer mediated
deprotection protocols involving metallic sodium or electrolytic
processes have also been reported for thioethers and ethers,
respectively.1a,8
The diphenylmethyl (DPM) moiety has been used to alkylate
and protect alcohols, carboxylates and thiols, though in recent
years the use of this group has lost favor. Nevertheless, the DPM
ether and thioether functionalities represent an alternative to com-
monly used benzyl-based protecting groups with protection/
deprotection of orthogonality. The installation of the DPM group
has been demonstrated using a variety of reagents. Two recent
examples of DPM ether formation have been published by Pale2a,b
and Yadav2c who used PdCl2 (10 mol %) and NbCl5 (20 mol %),
respectively. In addition, Brønsted acids (both in solution and solid
supported), Lewis acids and carbenes (from their corresponding
diazo-derivatives) have also proven successful. In addition to these
methodology is a standard Williamson ether synthesis protocol
using DPM bromide or chloride.2 It is worth noting that, in the case
of thioethers, the use of acid is crucial; the absence of a proton
source reduces the overall yield of the DPM thioether (typically
reducing the yield to 40–50%).1a Besides their use as protecting
⇑
Corresponding author.
E-mail address: luke.henderson@deakin.edu.au (L.C. Henderson).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2012.02.011

2036
J. M. Altimari et al. / Tetrahedron Letters 53 (2012) 2035–2039
Herein, we present rapid, clean, methodology to install the
3. A reaction time of 10 min was trialed (Table 1, entry 6) and gave
the desired product 2a in similar ratio to 3 as above (Table 1, entry
6) and the yield was only mildly sacrificed (89%), thus offering no
real improvement from previous methods. Overall, we were
pleased with this outcome as it highlighted the ability of pILs to
form DPM ethers in a very short time-frame and high yields.
Proton-activity of a pIL is a key parameter influencing reaction
outcome therefore even though TeaH2SO4 initially proved success-
ful in facilitating the formation of the ethyl-DPM ether 2a, a range
of commonly used pILs were also tested. Repeating the reaction at
80 °C for 10 min using TeaMs (triethylamine-methane sulfonic
acid, Table 1, entry 7) as the pIL gave the desired compound 2a
in a very high yield (93%) with a minimum of dimer 3 [ratio of
2a:3 (47:1)]. Indeed for this transformation TeaMs were far supe-
rior to TeaH2SO4. Reinforcing the notion that identifying a pIL with
the correct proton-activity is critical, only starting material was re-
turned when TeaFM (triethylamine-formic acid) and TeaTFA (tri-
ethylamine-trifluoroacetic acid) were used as the pILs under the
same reaction conditions (Table 1, entries 8 and 9).
diphenylmethyl (DPM) group from diphenylmethanol (1) (DPM-
OH), using microwave irradiation and protic ionic liquids as cosol-
vent and catalyst.
The proton-activity of a protic ionic liquid has been previously
shown to be a key parameter when identifying a suitable pILs to car-
ry out rearrangements or cyclizations.5 In our experience,5b,c TeaH2-
SO4, which possesses a very high proton-activity, has proven to be
the most successful. As such, this pIL was chosen as the starting
point for our investigations into determining the optimal time,
temperature, and ultimately pIL, to be used for the desired
transformation.
Initial experiments used ethanol (0.1 mL, 3.2 equiv) in TeaH2-
SO4 (0.25 mL). Heating the reaction to 130 °C (Table 1, entry 1) ef-
fected excellent conversion (91%) to the desired ethyl-DPM ether 2.
In addition to the desired product, symmetric ether 3 was also ob-
tained, presumably arising from the dimerization of 1, in a moder-
ately good ratio of 2a:3 (8:1). In an attempt to minimize the
formation of the dimer, the amount of ethanol was increased from
0.1 to 0.3 mL and improved conversion into the desired product
was realized (88%, Table 1, entry 2) with only traces of 3 observed
by means of 1H NMR spectroscopy. It is worth noting that in all the
cases discussed here, any unaccounted for material in the reaction
conversion was found to be unreacted 1 as determined by 1H NMR
spectroscopy.
Based on steric grounds the formation of dimer 3 should re-
quire more energy than the simple ethyl-DMP ether 2a. Thus,
the reaction was repeated at lower temperature (100 °C, Table
1, entry 3) and 2a was obtained in an excellent yield (92%) with
only a trace of dimer 3 observed in the 1H NMR spectrum of the
reaction product. At even lower temperatures (80 °C, 0.3 mL of
ethanol, Table 1, entry 4) no evidence of dimer 3 could be found
and the desired ethyl-DMP ether was isolated in an excellent
yield (95%).
Though these results were encouraging, the requirement to
have a large excess of alcohol (i.e., 0.3 mL) to minimize the forma-
tion of 3 was not optimal, therefore, we repeated the reaction using
the original amount of ethanol (0.1 mL) at 80 °C. The reaction affor-
ded the desired product 2a in an excellent yield (93%), but in ratio
of 2a:3 (18:1), respectively.
The most suitable pIL was identified as TeaMs (0.25 mL) and the
optimal reaction conditions were 80 °C for 10 min with 0.1 mL of
alcohol. As such, this set of conditions was subsequently employed
for investigations into the substrate scope of the etherification
reaction (Table 2).
Primary alcohols were tested first and when methanol was used
(Table 2, entry 1) the corresponding methyl ether 2b was produced
in an excellent yield (93%), with no trace of dimer 3 observed in the
1H NMR spectrum. Similarly, n-propanol (Table 2, entry 2), was
converted into the desired propyl ether 2c in a high yield (82%)
with only traces of 3 observed in the 1H NMR spectrum of the reac-
tion product. Continuing this avenue of investigation, n-butanol
was employed as the alcoholic reaction partner but only moderate
conversion into 2d (59%) was realized. The low conversion for n-
butanol was surprising, therefore, the reaction was repeated by
doubling the reaction time (20 min), to give the desired product
2d in a good yield (75%) with only trace amounts of dimer 3. A sim-
ilar scenario arose when iso-amyl alcohol was used; the original
reaction conditions gave only a moderate yield (62%, Table 2, entry
5). Extending the reaction time to 20 min gave an improved yield
of 73% (Table 2, entry 6) while in both cases only trace amounts
of 3 were detected by 1H NMR spectroscopy.
It was also considered that the rate of dimerization of 1 would
be slower at lower temperatures, and as such reducing the reaction
time may serve as another way to minimize the process leading to
Secondary and tertiary alcohols were next examined. For iso-
propanol (Table 2, entry 7) a good yield of the target ether was
Table 1
Reaction optimization9
Ph
Ph
OH
OEt
O
pIL, Temp, Time, EtOH
+
MW
1
2a
3
Entry
pILa
Temp (°C)
Time (min)
Ratio 2a:3
Conversionb (%)
1
TeaH2SO4
TeaH2SO4
TeaH2SO4
TeaH2SO4
TeaH2SO4
TeaH2SO4
TeaMs
130
130
100
80
80
80
80
80
80
20
20
20
20
20
10
10
20
20
8:1
91
88
92
95
93
89
93
—
2c
3
53:1
16:1
100:0
18:1
14:1
47:1
4c
5
6
7
8
d
TeaFM
TeaTFA
—
—
d
9
—
a
b
c
Reaction and conditions: 0.25 mL of pIL and 0.1 mL of EtOH.
Determined by integration of key signals in the 1H NMR spectrum.
0.3 mL EtOH used instead of 0.1 mL.
d
Recovered material was unreacted DPM-OH (1).

J. M. Altimari et al. / Tetrahedron Letters 53 (2012) 2035–2039
2037
Table 2
Reaction scope
protic nature of the ionic liquids may be assisting the formation
of a tert-butyl carbocationic species concurrently with the diphe-
nylmethylene carbocation. Thus in this scenario it is not surprising
that only poor yields were observed.
OH
OR
pIL, Temp, Time, ROH (0.1 mL)
MW
+ 3
Other alcohols were also tested. For benzyl alcohol (Table 2, en-
try 10) smooth conversion (91%) into the desired ether 2h was
noted and again, the ratio of 2h:3 was very good (49:1). This reac-
tion was also repeated using the pIL (TeaH2SO4) and conditions
used initially (Table 1). As suspected (Table 2, entry 11) a poor ratio
of 2h:3 and a drastic reduction in yield (50%) were clearly evident
thus reinforcing the chosen conditions as optimal. Propargyl alco-
hol was also examined (Table 2, entry 12), and using the optimized
conditions was converted to the desired DPM ether in an excellent
yield (97%) with no trace of dimer 3 present in the 1H NMR spec-
trum of the reaction product. The longer chain terminal alkynes,
but-3-yn-1-ol (Table 2, entry 13) was also smoothly converted into
the desired ether 2j in a 92% yield. It is worth noting that unsatu-
rated alcohols proved troublesome for Pale et al,2a but in our hands,
alcohols bearing a terminal alkyne were excellent substrates.
Following this, we used N-Cbz protected amino alcohols to test
functional group tolerance. These substrates (Table 2, entry 14)
were converted into the desired ether 2k but in a moderate yield
(46%, respectively). With diethylene glycol as substrate a mixture
of the mono-DPM ether 2l and the bis-DPM ether analogue
(approximately 78% 2l and 11% bis-ether, Table 2, entry 15) was
produced. It was pleasing that a large quantity of the mono-ether
2
1
Entry
Product
Alcohola
Yield 2b (%)
Yield 3b
1
2b
2c
2d
2d
MeOH
93
82
59
75
Tracec
Trace
Trace
Trace
OH
2
OH
OH
OH
3
4d
5
2e
2e
2f
62
73
75
55
19
Trace
Trace
5%
OH
6d
7
OH
OH
8e
9
2f
33%
16%
2g
OH
OH
10
2h
2h
91
50
Trace
45%
OH
11e
12
2l, as it has
a free alcohol moiety available for further
functionalization.
2i
2j
97
92
Trace
Trace
The generation of DPM ethers from phenol has proven to be
very problematic; for example Pale et al.2a,b reported only a 4%
yield after 96 h. In our hands, this reaction (Table 1, entry 16) gave
a complex mixture of products. Purification by column chromatog-
raphy afforded the para-substituted phenol 2m and not the ex-
pected O-alkylated product 4 (Fig. 1). This product was obtained
in a reasonable yield (48%), and presumably arose due to quench-
ing of the diphenylmethylene carbocation by the electron-rich
arene ring of the phenol. A similar C–C bond forming reaction
was observed by Yadav and co-workers,2c in which the same carb-
ocationic species was scavenged with resorcinol to give the corre-
sponding C–C bonded product.
OH
13
14
OH
O
2k
2l
46h
89f
Trace
Trace
CbzHN
HO
OH
O
f
15
OH
OH
g
16
2m
2n
OH
48h
Trace
Trace
HO
17g
29h
Similarly, 4-hydroxyphenethyl alcohol (Table 2, entry 17), bear-
ing phenolic alcohol and primary alcohol moieties, was converted
into a complex mixture of products. Purification of this mixture
identified the major component as 2n, bearing the DPM ether
g
18
2o
2o
30
80
24%
N/A
HO
HO
i
19
OH
a
b
c
0.1 mL of alcohol was used in each case.
Calculated by integrating key signals in the 1H NMR spectrum (See ESI).
Trace is here defined as <5% of crude mixture as determined by 1H NMR
spectroscopy.
d
Reaction time was increased to 20 min.
O
e
f
Reaction carried out at 130 °C using TeaH2SO4.
11% of the bisdiphenylmethyl ether was observed by 1H NMR spectroscopy.
When the alcohol was a solid, 0.35 mL of pIL was used for solvation.
Isolated yield.
Ph
Ph
g
h
i
2m
4
Reaction time was increased to 30 min.
Figure 1. Products from the reaction of phenol and TMP-OH (1).
realized (75%), but a higher quantity of 3 was noted. Steric effects
were presumably slowing the formation of the desired DPM ether
2f and as such the dimerization of 1 can occur to a more apprecia-
ble extent. This theory was supported when tert-butanol (Table 2,
entry 9) was used in the reaction as the yield of the product was
very poor (19%) and the ratio of 2g:3 was much higher (23:20).
In addition to steric bulk there is a second consideration which
could account for the poor results observed for t-butanol. The
OH
CHO
1.TeaMs, 80 °C, 10 min
Propargyl alcohol, MW
Ph
Ph
O
2. Pd(PPh3)2Cl2, NEt , DMF,
100 °C, 40 min,3MW
1
5
(1.1 eq)
63% over 2 steps
para-bromobenzaldehyde
Scheme 1. Formation of DPM ethers using the alcohol as the limiting reagent.

2038
J. M. Altimari et al. / Tetrahedron Letters 53 (2012) 2035–2039
OH
SR
TeaMs, 80 °C, 10 min
MW
+ 3
+
RSH
1
6a
7a 3
= 61%, Yield = 21%
R = CH3(CH2)7
Yield
6b R = Ph
Yield 7b = 71%, Yield 3 = <3%
Scheme 2. Generation of thioethers using pILs.
group at the primary alcohol, though in a low yield (29%). For men-
thol, the reaction gave only a low yield of the desired DPM ether 2o
(30%, Table 1, entry 18) with an almost equal amount (24%) of di-
mer 3 present in the reaction mixture. The alcohol of menthol is in
a conformationally locked ring structure and adjacent to an isopro-
pyl substituent, thus this poor result was attributed to steric ef-
fects. Considering our previous success with secondary alcohols
the reaction with menthol was repeated using excess DPM-OH
(1) (1.1 equiv) and the reaction time was extended to 30 min (Ta-
ble 2, entry 19). In this case the conversion of ( )-menthol into the
desired DPM ether 2o was excellent (80%) but was accompanied by
formation of the dimer 3 (ꢀ10%) which was not unexpected due to
the use of excess DPM-OH (1) (note that the dimeric ether 3 could
be easily removed from 2o by column chromatography).10
Although the results from Table 2 are promising, the use of ex-
cess alcohol is not an ideal situation if the DPM group is to be used
as a protecting group. The final entry of Table 2, proved that sub-
stoichiometric amounts of DPM-OH (1) could be used. In the case
of DPM ether 2o, the menthol framework offers little in terms of
further structural elaboration after etherification. Therefore, prop-
argyl ether 2g was chosen to highlight the versatility of this meth-
odology, as this compound has very high synthetic utility given the
terminal alkyne can undergo cycloadditions with azides11 or in
Sonogashira12 cross-coupling reactions.
Treating propargyl alcohol with 1.1 equiv of DPM-OH (1) and
subjecting the mixture to our optimal conditions gave the desired
ether 2g in an excellent isolated yield of 92%. These conditions also
resulted in less than 10% formation of the dimer 3, which was eas-
ily separated from the desired product using column chromatogra-
phy. To demonstrate the potential synthetic applications of this
transformation, the DPM propargyl ether 2g was then treated un-
der Sonogashira conditions with para-bromobenzaldehyde, giving
aldehyde 5 in a good yield (68%) and in a short time-frame
(40 min) (Scheme 1). As such, novel aldehyde 5 was successfully
synthesized in a high yield (63% over two steps) in less than 1 h
of total reaction time, thus highlighting the practicality of this
methodology in a multistep synthetic protocol.
Next, our attention turned to the application of the pIL medi-
ated protocol to generate C–S bonds. Initially the optimal method-
ology for the alcohol substrates was used. Both 1-octane thiol 6a
and thiophenol 6b gave the corresponding thioethers 7a and 7b
(Scheme 2). Surprisingly, thiophenol was converted in higher yield
(71% compared to 61%) and with less dimer side product. This
apparently counterintuitive result may be due to poor solubility
of the octanethiol in the TeaMs pIL, leading to slower thioether for-
mation and enhanced dimerization.
Nevertheless, these thiols gave yields which are acceptable,
especially in light of the rapid timeframe of the reaction. The in-
creased nucleophilicity of sulfur compared to oxygen was believed
to be the reason for the exclusive formation of 7b, rather than the
aromatic substitution product (thiol analogue of 2m Fig. 1).
In conclusion, a combination of microwave irradiation and pILs
has been used to facilitate the rapid installation of the diphenyl-
methyl ether functionality to both alcohols and thiols. The reaction
uses a minimal amount of organic solvent and products which re-
quire little or no purification. In these cases, the pIL is removed by
simple filtration through a silica plug, thus providing a safe alter-
native to the neutralization of strong acids.
Acknowledgments
The authors would like to thank the Strategic Research Center
for Biotechnology, Chemistry and Systems Biology for financial
support and the Australian Research Council for an APD for N.B.
Supplementary data
Supplementary data (for spectra and general procedures please
refer to the supplementary information) associated with this arti-
cle can be found, in the online version, at doi:10.1016/
j.tetlet.2012.02.011.
References and notes
1. (a) Greene, T. W.; Wuts, P. G. M. Protective groups in Organic Synthesis, 3rd ed.; J.
Wiley & Sons: New York, 1999; (b) Kocienski, P. J. Protecting Groups, 3rd ed.; G.
Thieme: Stuttgart: New York, 2004.
2. (a) Bikard, Y.; Weibel, J.-M.; Sirlin, C.; Dupuis, L.; Loeffler, J.-P.; Pale, P.
Tetrahedron Lett. 2007, 48, 8895–8899; (b) Mezaache, R.; Dembelé, Y. A.; Bikard,
Y.; Weibel, J.-M.; Blanc, A.; Pale, P. Tetrahedron Lett. 2009, 50, 7322–7326; (c)
Yadav, J. S.; Bhunia, D. C.; Krishna, K. V.; Srihari, P. Tetrahedron Lett. 2007, 48,
8306–8310; (d) Stanescu, M. A.; Varma, R. S. Tetrahedron Lett. 2002, 43, 7307–
7309; (e) Namboodiri, V. V.; Varma, R. S. Tetrahedron Lett. 2002, 43, 4593–4595;
(f) Suzuki, T.; Kobayashi, K.; Noda, K.; Oriyama, T. Synth. Commun. 2001, 31,
2761–2766; (g) Kolovos, M.; Froussios, F. Tetrahedron Lett. 1984, 25, 3909–
3912; (h) Sharma, G. V. M.; Rajendra Prasad, T.; Mahalingam, A. K. Tetrahedron
Lett. 2001, 41, 759–761; (i) Paredes, R.; Perez, R. L. Tetrahedron Lett. 1998, 39,
2037–2038; (j) Iranpoor, N.; Firouzabadi, H.; Farahi, S. J. Sulfur Chem. 2007, 28,
581–587; (k) Naik, S.; Kavala, V.; Gopinath, R.; Patel, B. K. Arkivoc 2006, 1, 119–
127; (l) Rao, K. T. V.; Rao, P. S. N.; Sai Prasad, P. S.; Lingaiah, N. Catal. Commun.
2009, 10, 1394–1397; (m) Bickard, Y.; Mezaache, R.; Weibel, J.-M.; Benkouider,
A.; Sirlin, C.; Pale, P. Tetrahedron 2008, 64, 10224–10232; (n) Ali, I. A. I.; Ashry,
E. S. H.; Schmidt, R. R. Eur. J. Org. Chem. 2003, 4121–4131; (o) Lapatsanis, L.
Tetrahedron Lett. 1978, 19, 3943–3944; (p) Salehi, P.; Lranpoor, N.; Behbahani,
F. K. Tetrahedron 1998, 54, 943–948; (q) Romanellia, G.; Ruiz, D.; Vázquez, P.;
Thomas, H.; Autino, J. C. Chem. Eng. J. 2010, 161, 355–362; (r) Srihari, P.; Bhunia,
D. C.; Sreedhar, P.; Yadav, J. S. Synlett 2008, 7, 1045–1049; (s) Best, D.;
Jenkinson, S. F.; Rule, S. D.; Higham, R.; Mercer, T. B.; Newell, R. J.; Weymouth-
Wilson, A. C.; Fleet, G. W. J.; Petursson, S. Tetrahedron Lett. 2008, 49, 2196–
2199.
3. (a) Htils, A.; Purand, K.; Stark, H.; Ligneau, X.; Arrang, J.-M.; Schwartz, J. C.;
Schunack, W. Bioorg. Med. Chem. Lett. 1996, 6, 2013–2018; (b) Lewis, D. B.;
Matecka, D.; Zhang, Y.; Hsin, L.-W.; Dersch, C. M.; Stafford, D.; Glowa, J. R.;
Rothman, B. R.; Rice, K. C. J. Med. Chem. 1999, 42, 5029–5042; (c) Richardson, J.
L.; Nett, I. R. E.; Jones, D. C.; Abdille, M. H.; Gilbert, I. H.; Fairlamb, A. H.
ChemMedChem 2009, 4, 1333–1340.
4. (a) Hajipour, A. R.; Rafiee, F. Org. Prep. Proced. Int. 2010, 42, 285–362; (b) Akbari,
J.; Heydari, A.; Ma’mani, L.; Hassan, H. Comptes. Rendus. Chim. 2010, 13, 544–
547; (c) Atkin, R.; Warr, G. J. Phys. Chem. B 2008, 112, 4164–4166; (d) Angell, C.
A.; Byrne, N.; Belieres, J.-P. Acc. Chem. Res. 2007, 40, 1228–1236; (e) Belieres, J.-
P.; Angell, C. A. J. Phys. Chem. B 2007, 111, 4926–4937; (f) Greaves, T. L.;
Weerawardena, A.; Fong, C.; Krodkiewska, I.; Drummond, C. J. Chem. Commun.
2006, 110, 22479–22487; (g) Luo, H.; Baker, G. A.; Lee, J. S.; Pagni, R. M.; Dai, S. J.
Phys. Chem. B 2009, 113, 4181–4183; (h) Debeljuh, N.; Barrow, C. J.; Henderson,
L. C.; Byrne, N. Chem. Commun. 2011, 47, 6371–6373.
5. (a) Gordon, C. P.; Byrne, N.; McCluskey, A. Green Chem. 2010, 12, 1000–1006;
(b) Henderson, L. C.; Byrne, N. Green Chem. 2011, 13, 813–816; (c) Thornton, M.
T.; Henderson, L. C.; Byrne, N.; Pfeffer, F. M. Curr. Org. Chem. 2012, 16, 121–126.
6. Ranu, B. C.; Jana, R. Adv. Synth. Catal. 2005, 347, 1811–1818.
7. Screttas, C. G.; Micha-Screttas, M. J. Org. Chem. 1982, 47, 3008–3011.
8. Mairanovsky, V. G. Angew. Chem., Int. Ed. 1976, 15, 281–292.
9. Representative procedure: alcohol (0.1 mL) was added to a microwave vial
charged with DPM-OH (1) (100 mg, 0.54 mmol) and a stirrer bar. To this

J. M. Altimari et al. / Tetrahedron Letters 53 (2012) 2035–2039
suspension was added pIL (0.25 mL) and the reaction heated to the desired 10. See ESI for full details.
2039
temperature under microwave irradiation. Once complete the contents of the
vial cooled and diluted with diethylether (2 mL) and filtered under vacuum
through a silica plug. The microwave vial and silica plug were thoroughly
washed with Et2O. The filtrate was then collected and solvent removed in
vacuo to give clear oil.
11. Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 11, 2004–
2021.
12. (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 16, 4467–
4470; (b) Chinchilla, R.; Nájera, C. Chem. Rev. 2007, 107, 874–922; (c) Negishi,
E.; Anastasia, L. Chem. Rev. 2003, 103. 1979–201.