ORGANIC
LETTERS
2008
Vol. 10, No. 9
1727-1730
Hexafluoroisopropanol as a Unique
Solvent for Stereoselective
Iododesilylation of Vinylsilanes
Elizabeth A. Ilardi, Craig E. Stivala, and Armen Zakarian*
Department of Chemistry and Biochemistry, Florida State UniVersity,
Tallahassee, Florida 32306-4390
Received February 14, 2008
ABSTRACT
Stereoselective preparation of iodoalkenes from vinylsilanes is described. 1,1,1,3,3,3-Hexafluoroisopropanol serves as a unique solvent that
ensures high yields and stereoselectivities in the iododesilylation of a variety of functionalized substrates.
Iodoalkenes are versatile intermediates that have found
widespread use in organic synthesis. Alkynes can often serve
as covenient starting materials for their preparation. Among
a variety of transformations that can be employed for this
purpose, hydrometalation of triple bonds followed by iodi-
nolysis provides a direct one-step route from alkynes to
iodoalkenes.1 Hydrozirconation of alkynes followed by
iodination of intermediate vinylzirconium species is an
important example of this process.2 Mildness of the reaction
conditions and excellent regio- and stereocontrol with
terminal alkynes make it useful for hydroiodination of triple
bonds in complex substrates. Occasionally, however, dif-
ficulties in handling and storing of HZrCp2Cl,3 overhydrozir-
conation, and protonolysis of vinylzirconium species detract
from the utility of this method. In addition, poor regiose-
lectivity is typically observed with internal alkynes.4
Stannyl-5 and silylcupration6 followed by iododestanny-
lation or iododesilylation provides an attractive, two-step
alternative for functionalization of alkynes under mild
conditions.7 Previously, we used this approach effectively
when the hydrozirconation-iodination was unproductive.8
The advantages of silylcupration are that it does not require
toxic tin reagents and the intermediate vinylsilanes are more
stable and less toxic and thus more easily handled in
multistep reaction sequences.
Several reagents and reaction conditions have been used
for iododesilylation. These include I2 in CH2Cl2,7,9
I2-AgO2CCF3 in CH2Cl2 followed by KF·2H2O, I2/Lewis
(4) Useful level of regioselectivity is usually achieved with 2-alkynes.
For examples, see ref.3
(5) Sharma, S.; Oehlschlager, A. C. J. Org. Chem. 1989, 54, 5064–
5073.
(6) (a) Fleming, I.; Roessler, F. J. Chem. Soc., Chem. Commun. 1980,
276–277. (b) Fleming, I.; Newton, T. W.; Roessler, F. J. Chem. Soc., Perkin
Trans. 1 1981, 2527. (c) Fleming, I.; Newton, T. W. J. Chem. Soc., Perkin
Trans. 1 1984, 1805. (d) Fleming, I.; Marigorta, E. M. Tetrahedron Lett.
1985, 38, 4629–4632. (e) Archibald, S. C.; Barden, D. J.; Bazin, J. F. Y.;
Fleming, I.; Foster, C. F.; Mandal, A. K.; Mandal, A. K.; Parker, D.; Takaki,
K.; Ware, A. C.; Williams, A. R. B.; Zwicky, A. B. Org. Biomol. Chem.
2004, 2, 1051–1064.
(1) Labinger, J. A. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: New York 1996; Vol. 8, Chapter 3.9,
pp 667-702..
(2) (a) Schwartz, J.; Labinger, J. A. Angew. Chem., Int. Ed. Engl. 1976,
15, 333–340. (b) Negishi, E. In Organometallics in Synthesis: A Manual,
2nd ed.; Schlosser, M., Ed.; Wiley: New York, 2002; Chapter 8, pp
925-1002. (c) Wipf, P.; Jahn, H. Tetrahedron 1996, 52, 12853–12910. (d)
Lipshutz, B. H.; Pfeiffer, S. S.; Noson, K.; Tamioka, T. In Titanium and
Zirconium in Organic Synthesis; Marek, I., Ed.; Wiley-VCH: Weinheim,
Germany, 2002; Chapter 4, pp 110-148.
(7) For another alternative, see: Arefolov, A.; Langille, N. F.; Panek,
J. S. Org. Lett. 2001, 3, 3281–3284.
(8) (a) Lu, C.-D.; Zakarian, A Org. Lett. 2007, 9, 3161–3163. For other
applications, see: (b) Coleman, R. S.; Walczak, M. C.; Campbell, E. L.
J. Am. Chem. Soc. 2005, 127, 16038–16039. (c) Zakarian, A.; Batch, A.;
Holton, R. A. J. Am. Chem. Soc. 2003, 125, 7822–7824.
(3) A practical solution to this problem has been described recently.
Huang, Z.; Negishi, E. Org. Lett. 2006, 8, 3675–3678.
10.1021/ol800341z CCC: $40.75
Published on Web 04/03/2008
2008 American Chemical Society