Solvent-free, microwave-assisted conversion of tosylates into iodides

Article abstract of DOI:10.1071/CH14242

A highly efficient method for the conversion of primary tosylates into the corresponding iodides is outlined. The method involves heating a neat mixture of the tosylate and solid sodium iodide in a microwave cavity. Reaction times are short, usually about 60 minutes, delivering high yields. This procedure is especially useful for the in situ generation of volatile primary iodides, and for most of the primary iodides, the crude product is sufficiently pure.

Full text of DOI:10.1071/CH14242

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 1360–1361
Communication
http://dx.doi.org/10.1071/CH14242
Solvent-Free, Microwave-Assisted Conversion
of Tosylates into Iodides*
A
A B
,
Jia Cao and Patrick Perlmutter
A
School of Chemistry, Monash University, Wellington Road,
Clayton, Vic. 3800, Australia.
B
Corresponding author. Email: patrick.perlmutter@monash.edu
A highly efficient method for the conversion of primary tosylates into the corresponding iodides is outlined. The method
involves heating a neat mixture of the tosylate and solid sodium iodide in a microwave cavity. Reaction times are short,
usually about 60 minutes, delivering high yields. This procedure is especially useful for the in situ generation of volatile
primary iodides, and for most of the primary iodides, the crude product is sufficiently pure.
Manuscript received: 15 April 2014.
Manuscript accepted: 19 May 2014.
Published online: 12 June 2014.
We recently reported a new approach to chiral isoprenoid
natural product synthesis based on the reductive alkylation of
chiral lactones.[1] From this work it transpired that we required
a method for the rapid conversion of tosylates into iodides.
The current method involves treatment of a tosylate with excess
sodium iodide in refluxing acetone solution.[2] Reaction times
are typically around 12 hours. It seemed likely that the use of
microwave irradiation would reduce the reaction time. Indeed
we found this to be the case and also discovered that no solvent
was required.
3 equiv. NaI, neat
R
OTs
R
I
The conversion of tosylates into iodides employing, for
example, a modified Finkelstein reaction[3] (i.e. refluxing tosy-
lates and NaI in acetone for several hours) is a well-established
procedure.[2] In order to reduce the reported reaction times, we
1a–g
2a–g
Scheme 1. Conversion of tosylates to iodides.
Table 1. Conversion of tosylates to iodides under solvent-free microwave irradiation
Each tosylate was reacted with 3 equiv. of NaI
Tosylate
Temperature [8C]
Power [W]
100
Time [min]
30
Scale [mmol]
0.4
Yield [%]
OTs
120
.99
(1a)
OTs
(1b)
120
140
120
150
45
30
0.3
0.2
95
95
OTs
(1c)
OTs
(1d)
115
120
100
120
90
45
0.2
0.3
94
98
O
OTs
(1e)
TsO
120
115
110
100
45
60
0.2
0.3
94
75
(1f)
OTs
(1g)
*In memory of Professor Roger Brown, a great scientist, artist, and a wonderful friend.
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

Microwave-Assisted Conversion of Tosylates to Iodides
1361
explored the use of microwave irradiation (Scheme 1). After
some exploration of conditions an optimised set of conditions
was developed. This involved heating a tosylate with three
equiv. of NaI at 100–150 W in a sealed 10 mL microwave vial
in a microwave reactor irradiating for 0.5–2 h, during which
time the temperature was maintained at 100–1408C. A variety of
tosylates were subjected to this treatment and the results are
collected in Table 1.
microwave irradiation in a CEM DiscoverTM microwave
reactor, and subjected to 100–150 W irradiations for 30–
90 min. Following reaction, CH2Cl2 was added to the mixture,
and the solid was removed by filtration. The solvent was
removed under vacuum to yield the product. Primary iodides
were mostly pure according to NMR spectroscopy, while for
the secondary iodide, the yield was somewhat reduced due to
by-product formation.
It was found all the primary tosylates gave iodides in .94 %
yields, whilst conversion of a secondary tosylate to the corre-
sponding iodide, also succeeded although competing elimina-
tion reduced the yield to 75 %.
Thus the conversion of primary tosylates to iodides under
solvent-free, microwave irradiation condition gives the corre-
sponding iodides in high yields with relatively short reaction
time. This procedure is especially useful for the in situ genera-
tion of volatile primary iodides in excellent yields (.94 %),
because the solids (remaining NaI and the by-product sodium
p-toluenesulfonate) can be easily filtered off and the liquid
iodide products could be collected easily.
Supplementary Material
Experiment procedures and characterisations of the products are
available on the Journal’s website.
References
[1] C. Jia, P. Perlmutter, Org. Lett. 2013, 15, 4237.
[2] N. M. O’Connell, Y. C. O’Callaghan, N. M. O’Brien, A. R. Maguire,
F. O. McCarthy, Tetrahedron 2012, 68, 4995. doi:10.1016/J.TET.2012.
04.060
[3] H. Finkelstein, Ber. Dtsch. Chem. Ges. 1910, 43, 1528. doi:10.1002/
CBER.19100430257
Experimental
NaI (3 equiv.) was added to neat primary tosylate in a
10 mL microwave vial, which was sealed and heated under