Improved procedure for the hydrotelluration of alkynes

Article abstract of DOI:10.1016/S0040-4039(99)02297-2

Z-Vinylic tellurides were prepared by hydrotelluration of alkynes with lithium butyl tellurolate generated by reaction of n-butyllithium with elemental tellurium. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(99)02297-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 1311–1313
Improved procedure for the hydrotelluration of alkynes
Gilson Zeni, Henrique B. Formiga and João V. Comasseto ∗
Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748 Cx.P. 26077, 05599-970, São Paulo, Brazil
Received 29 October 1999; accepted 8 December 1999
Abstract
Z-Vinylic tellurides were prepared by hydrotelluration of alkynes with lithium butyl tellurolate generated by
reaction of n-butyllithium with elemental tellurium. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: vinylic tellurides; hydrotelluration; lithium butyl tellurolate.
Vinylic tellurides are valuable synthetic intermediates and have recently been used in total synthesis.1
The hydrotelluration of alkynes is the method of choice to prepare Z-vinylic tellurides, in view of the easy
access to the starting materials,2 the high regio- and stereoselectivity of the reaction and the practicality
of the experimental procedure. The organo tellurolate 2 is generated by reduction of diorgano ditellurides
1 with sodium borohydride in ethanol at room temperature, and reacts with the appropriate alkyne 3 to
give the vinylic telluride of the Z configuration 4 in good yields.3 As Z-vinylic tellurides 4 are used to
generate Z-vinylorganometallics 5 by transmetallation,3 an alkyl group, usually n-butyl, has to be linked
to tellurium to avoid the formation of mixture of products in the transmetallation step (Scheme 1).
Scheme 1.
The use of dibutyl ditelluride 1 to generate the butyl tellurolate anion 2 constitutes a limitation of this
methodology, since dibutyl ditelluride is not commercially available. In addition, this reagent is not stable
for long periods of time, and has a very unpleasant smell, which impregnates skin and clothes. In this
communication we report a practical and safe method to perform the hydrotelluration of alkynes, which
avoids the use of dibutyl ditelluride.
∗
Corresponding author. E-mail: jvcomass@quim.iq.usp.br (J. V. Comasseto)
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(99)02297-2
tetl 16225

1312
Reaction of n-butyllithium with elemental tellurium in THF at room temperature under nitrogen gives
lithium butyl tellurolate 6, as indicated by the consumption of the gray tellurium powder and formation
of a yellow solution. To this solution is added the appropriate alkyne 3 in deoxygenated dry ethanol. Then
the mixture is heated under reflux until the consumption of the alkyne, monitoring the reaction by TLC
(Eq. (1)).4
(1)
The Z-vinylic tellurides 4 are obtained in yields similar to those observed in the hydrotelluration
reaction using the dibutyl ditelluride/NaBH4 method,3a,5 as shown in Table 1. These vinylic tellurides
are stable enough to be purified by column chromatography on a laboratory bench, and are no more
unpleasant to handle than many standard reagents found in organic chemistry laboratories. Some of them
Table 1
Vinylic tellurides prepared

1313
are almost odorless. With the improvement described in this communication, the hydrotelluration of
alkynes becomes a routine practice, and can be performed with no need for special safety precautions.
This should stimulate the synthetic organic chemists to include Z-vinylic tellurides in their synthetic
plans.
Acknowledgements
The authors thank FAPESP and CNPq for support. FAPESP is acknowledged for PhD (G.Z.) and
undergraduate (H.B.F.) fellowships.
References
1. (a) Zeni, G.; Comasseto, J. V. Tetrahedron Lett. 1999, 40, 4619, and references cited therein; (b) Stefani, H. A.; Costa, I. M.;
Zeni, G. Tetrahedron Lett. 1999, 40, 9215.
2. Brandsma, L. Preparative Acetylenic Chemistry; Elsevier: Amsterdan, 1988.
3. (a) Tucci, F. C.; Chieffi, A.; Comasseto, J. V.; Marino, J. P. J. Org. Chem. 1996, 61, 4975; for reviews, see: (b) Comasseto,
J. V. Reviews on Heteroatom Chem. 1993, 9, 61; (c) Comasseto, J. V.; Lo, W. L.; Petragnani, N.; Stefani, H. Synthesis 1997,
373.
4. Typical procedure for the hydrotelluration with n-BuLi/Te: n-BuLi (0.66 mL, 1 mmol of a 1.5 M solution in hexane) is added
dropwise to a stirred suspension of elemental tellurium (0.127 g, 1 mmol) in THF (5 mL) at room temperature under N2. A
clear solution is formed after 5 min of stirring. Then phenylacetylene (0.122 g, 1.2 mmol) in deoxygenated ethanol (10 mL)
is added and the solution is refluxed for 4 h, monitoring by TLC. After this time the mixture is diluted with ethyl acetate (20
mL) and washed with brine (2×20 mL). The organic layer is separated, dried (MgSO4) and the solvent is evaporated. The
residue is purified by silica gel column chromatography eluting with hexane to give 0.215 g (75%) of the vinylic telluride
4a.3a When the reaction is performed in a 40 mmol scale, the yield rises to 88%.
5. Barros, S. M.; Comasseto, J. V.; Berriel, J. Tetrahedron Lett. 1989, 30, 7533.