Two-step regio- and stereoselective synthesis of cis-vinylstannanes

Article abstract of DOI:10.1021/ol801251m

(Figure Presented) Herein we describe a novel stereoselective synthesis of cis-vinylstannanes employing the widely established Li/Te exchange pathway. In contrast to previously reported methods of cis-selective hydrostannation (i.e., ZrCI₄), th

Full text of DOI:10.1021/ol801251m

ORGANIC
LETTERS
2008
Vol. 10, No. 17
3861-3863
Two-Step Regio- and Stereoselective
Synthesis of cis-Vinylstannanes
Paul Malek Mirzayans, Rebecca H. Pouwer, and Craig M. Williams*
School of Molecular and Microbial Sciences, UniVersity of Queensland,
Brisbane, 4072 Queensland, Australia
c.williams3@uq.edu.au
Received June 3, 2008
ABSTRACT
Herein we describe a novel stereoselective synthesis of cis-vinylstannanes employing the widely established Li/Te exchange pathway. In
contrast to previously reported methods of cis-selective hydrostannation (i.e., ZrCl4), this method demonstrates compatibility toward oxygenated
substrates.
The Stille coupling1 of vinyltin reagents with vinyl2 and aryl
halides2 and triflates2 is a synthetically useful means for
obtaining conjugated double bonds with defined geometry.1
Unfortunately, methods to access cis-vinylstannanes are
somewhat limited and often exhibit poor stereoselectivity.
To date, cis-vinylstannanes have been most commonly
synthesized by radical,3 Lewis acid,4 and transition metal5
mediated hydrostannation of alkynes, hydrozirconation6 of
stannyl alkynes, and the transmetalation of vinyl metallic
substrates.7 The use of ZrCl4 as a Lewis acid catalyst in the
hydrostannation of alkynes has proven especially valuable,4b
mainly because the reaction proceeds in an entirely cis-
selective manner. However, the reaction is not compatible
with oxygen-containing functionality, possibly due to coor-
dination to the Lewis acid, as it requires bulky substituents
(e.g., TBDMS) on oxygen to facilitate reaction.4b The use
of bulky substituents on oxygen, however, has not proven
to be a general method in order to circumvent this problem.8,9
Furthermore, in the case of di- and tristannylation the high
control over stereochemistry is lost.4c
The hydrometalation of alkynes tends to occur in a syn
fashion to give trans-organometallics. However, isomeriza-
tion often leads to mixtures of cis and trans isomers. An
exception is found in the hydrotelluration of alkynes, which
occurs in a highly selective anti fashion to give cis-
vinyltellurides, which are not susceptible to isomerization.10
Vinyl tellurides are also known to undergo transmetalation
to give, for example, vinyl lithium, copper, zinc, magnesium,
aluminum, calcium, and sodium reagents with retention of
configuration.11
With a view to finding a method to selectively synthesize
cis-vinylstannanes that could also accommodate oxygen
functionality, a two-step hydrotelluration lithium-tin ex-
change protocol was investigated, the results of which are
presented herein.
(1) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
(2) Mee, S. P. H.; Lee, V.; Baldwin, S. E. Chem. Eur. J. 2005, 11, 3294.
(3) Smith, N. D.; Mancuso, J.; Lautens, M. Chem. ReV. 2000, 100, 3257.
(4) (a) Gevorgyan, V.; Liu, J. X.; Yamamoto, Y. Chem. Commun. 1998,
1, 37. (b) Asao, N.; Liu, J. X.; Sudoh, T.; Yamamoto, Y. J. Org. Chem.
1996, 61, 4568. (c) Rim, C.; Son, D. Y. Org. Lett. 2003, 5, 3443.
(5) Kikukawa, K.; Umekawa, H.; Wada, F.; Matsuda, T. Chem. Lett.
1988, 881.
(8) L’opez, S.; Montenegro, J.; Sa’a, C. J. Org. Chem. 2007, 72, 9572
.
(9) To the best of our knowledge, only one isolated example of trans-
hydrostannylation employing B(C6F5)3 as a Lewis acid catalyst compatible
with oxygen functionality has been reported. See ref 4a.
(10) Barross, S. M.; Dabdoub, M. J.; Dabdoub, V. M. B.; Comasseto,
J. V. Organometallics 1989, 8, 1661.
(6) (a) Bickley, J. F.; Roberts, S. M.; Santoro, M. G.; Snape, T. J.
Tetrahedron 2004, 60, 2569. (b) Bialy, L.; Waldmann, H. Chem. Eur. J.
2004, 10, 2759. (c) Lipshutz, B.; Keil, R.; Barton, J. Tetrahedron Lett. 1992,
33, 5861.
(11) (a) Huang, X.; Liang, C.; Qing, X.; He, Q. J. Org. Chem. 2001,
66, 74, and references therein. (b) Zeni, G.; Lu¨dtke, D. S.; Panatieri, R. B.;
Braga, A. L. Chem. ReV. 2006, 106, 1032. (c) Petragnani, N.; Stefani, H. A.
Tellurium In Organic Chemistry, 2nd, Updated and Enlarged Edition;
Academic Press: Amsterdam, The Netherlands, 2007.
(7) Cochran, J. C.; Philips, H. K.; Tom, S.; Hurd, A. R.; Bronk, B. S.
Organometallics 1994, 13, 947.
10.1021/ol801251m CCC: $40.75
Published on Web 08/14/2008
2008 American Chemical Society

The cis-vinyl tellurides were uneventfully transmetalated
with n-butyllithium to the corresponding vinyl lithium, which
were subsequently quenched with trimethyltin chloride
affording the cis-vinylstannanes in 40-68% yield without
any detectable trans-vinylstannane (Table 2, entries 1-9)
(Scheme 1).
Table 1. Hydrotelluration of Alkynes 1 Affording
cis-Vinyltellurides 3
Table 2. Transmetalation of cis-Vinyl Telluride 3 Affording
cis-Vinylstannanes 4
a Isolated yields. b Inseparable mixture (ratio 2:1).
Alkynes (i.e., 1) (Table 1, entries 1-10) were treated with
dibutyl ditelluride 2 and sodium borohydride under standard
conditions11 to give cis-vinyltellurides (i.e., 3) in 48-90%
yield (Table 1) (Scheme 1). In all conjugated alkyne cases,
a Isolated yields.
Vinylstannanes 4 were accompanied by small amounts of
the corresponding protonated alkenes, which were readily
removed under vacuum. The removal of dibutyltelluride 5,
however, proved very difficult by distillation or by column
chromatography of the nonpolar and/or low molecular weight
compounds (i.e., Table 2, entries 4-7, 914). Hence, an
efficient method for separation of nonpolar cis-vinylstannanes
4 from dibutyl telluride 5 was required. Capitalizing on the
fact that dibutyl telluride 5 reacts with methyl iodide to give
methyl di-n-butyltelluronium iodide 6 under catalyzed (Ag-
NO3, AgBF4)15 and noncatalyzed conditions,16 excess methyl
iodide (6 equiv) was added to the reaction mixture after
Scheme 1
.
Synthesis of cis-Vinyl Tellurides 3 and
cis-Vinylstannanes 4
regio- and stereoselectivity were maintained. Isolated alkynes
(Table 1, entry 10), however, posed regioselectivity problems
yielding mixtures of 1,2- and 2,2-disubstituted vinylic
tellurides, in favor of the 1,2-disubstituted vinylic tellurides,
as previously documented.12,13
(13) Vieira, M. L.; Zinn, F. K.; Comasseto, J. V. J. Braz. Chem. Soc.
2001, 12, 586.
(12) Stefani, H. A.; Costa, I. M.; Zeni, G. Tetrahedron Lett. 1999, 40,
(14) Purification by silica column chromatography was achieved;
however, the general procedure should be followed for ease.
9215.
3862
Org. Lett., Vol. 10, No. 17, 2008

trimethyltin chloride. This workup additive reacted selec-
tively with the dibutyl telluride 5 affording telluronium salt
6, which could be readly separated from the cis-vinylstannane
4 by trituration followed by column chromatography (Scheme
2).
of conjugated cis double bond systems is of considerable
importance, for example, construction of cis-configured 1,3,5-
trienes for 6π-electrocyclization.17,18 This body of work
demonstrates that access to cis-vinylstannanes containing
oxygen functionality is now readily achievable allowing
further utilization of the Stille reaction to incorporate cis
double-bond conjugation.
Scheme 2. Removal of Dibutyl Telluride From 4
Acknowledgment. We thank the University of Queensland
for financial support.
Supporting Information Available: Copies of 1H and 13C
NMR spectra for all compounds, including experimental
conditions and characterization data. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
In conclusion, developing new methods that access cis
double bonds selectively for application to the construction
OL801251M
(17) Branda¨nge, S.; Leijonmarck, H. J. Chem. Soc., Chem. Commun.
(15) Lenarda˜o, E. J.; Mendes, S. R.; Ferreira, P. C.; Perin, G.; Silveira,
C. C.; Jacob, R. G. Tetrahedron Lett. 2006, 47, 7439.
2004, 292
(18) Pouwer, R. H.; Schill, H.; Williams, C. M. Eur. J. Org. Chem.
2007, 4699
.
(16) Balfe, M. P.; Chaplin, C. A.; Phillips, H. J. Chem. Soc. 1938, 341.
.
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