Synthesis of β-organotelluro vinylphosphine oxides by hydrotelluration of 1-alkynylphosphine oxides and their palladium-catalyzed cross-coupling with alkynes

Article abstract of DOI:10.1016/S0040-4039(02)00778-5

β-Organotelluro vinylphosphine oxides 2 can be prepared by treatment of 1-alkynylphosphine oxides 1 with tellurolate anions in satisfactory yields. Compound 2d undergoes direct coupling reaction with terminal alkynes in the presence of PdCl₂/Cu

Full text of DOI:10.1016/S0040-4039(02)00778-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 4399–4402
Synthesis of b-organotelluro vinylphosphine oxides by
hydrotelluration of 1-alkynylphosphine oxides and their
palladium-catalyzed cross-coupling with alkynes
Antonio L. Braga,* Fabr´ıcio Vargas, Gilson Zeni, Claudio C. Silveira and Leandro H. de Andrade
Departamento de Qu´ımica, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil
Received 25 January 2002; revised 11 March 2002; accepted 8 April 2002
Abstract—b-Organotelluro vinylphosphine oxides 2 can be prepared by treatment of 1-alkynylphosphine oxides 1 with tellurolate
anions in satisfactory yields. Compound 2d undergoes direct coupling reaction with terminal alkynes in the presence of PdCl2/CuI,
triethylamine and methanol at room temperature to give b-alkynyl vinylphosphine oxides 3 with retention of configuration in
good yields. © 2002 Elsevier Science Ltd. All rights reserved.
The synthesis of stereospecifically substituted alkenes is
one of the major challenges in organic synthesis. This
remarkable interest in the preparation of these com-
pounds together with the possibility to prepare enynes
from them have attracted researches in this field.1
The b-organotelluro vinylphosphine oxides 2 were pre-
pared by addition of alkynylphosphine oxides 1 to a
solution of sodium organyl tellurolate, prepared by
reduction of ditellurides with sodium borohydride in
ethanol at room temperature12 (Scheme 2).
We have prepared several functionalized vinylic
compounds2 and also described the use of palladium-
catalyzed reactions to prepare some types of enynes and
enediynes by using cross-coupling of a-bromo-vinyl
chalcogenides,3 a-thio-vinyl tosylates4 and vinyl
tellurides5 with terminal alkynes.
The products 2a–f were obtained in satisfactory yields
with high Z-stereoselectivity (Table 1). In the case of
Ph2Te2, only b-organotelluro vinylphosphine oxides 2a,
On the other hand, unsaturated phosphorus com-
pounds represent a class of important synthetic inter-
mediates.6,7 For example, vinyl phosphine oxides have
been used to synthesize functionalized phosphine oxides
by adding nucleophiles to the electrophilic double
bound8 and also undergo cycloaddition reactions.9
Previously, we have shown that 1-alkynylphosphonates
can be used to prepare b-organochalcogeno
vinylphosphonates10 by hydrochalcogenation and
enynephosphonates from cross-coupling reaction of b-
organotelluro vinylphosphonates with alkynes.11 In
connection with our continued work on this class of
compounds, we decided to expand the scope of these
methodologies to phosphine oxides derivatives (Scheme
1).
Scheme 1.
Keywords: phosphine oxide; tellurium; enyne; palladium; cross-cou-
pling.
* Corresponding author. E-mail: albraga@quimica.ufsm.br
Scheme 2.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00778-5

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A. L. Braga et al. / Tetrahedron Letters 43 (2002) 4399–4402
Table 1. Synthesis of b-organotelluro vinylphosphine oxides 2 according to Scheme 2
for the cross-coupling reaction was the use of PdCl2/
2c and 2e with (Z)-configuration were obtained, while
b-butyltelluro vinylphosphine oxides 2b, 2d and 2f, with
predominant (Z)-stereoselectivity, were isolated using
n-Bu2Te2. The regiochemistry and the exclusive or pre-
dominant Z-stereochemistry of compounds 2 obtained
were readily determined by NMR spectral analysis,
especially NOESY experiments.
CuI (20 mol% each), Et3N (1 mmol), methanol (10
mL), b-organotelluro vinylphosphine oxide 2d (1 mmol)
and the appropriated 1-alkyne (2 mmol) at room tem-
perature,15 as recently described by us in the prepara-
tion of enynephosphonates.11 Compounds 3a–d were
isolated as oils or solids after flash chromatography on
silica gel, using a mixture of hexane–ethyl acetate as
eluent.
The required starting 1-alkynylphosphine oxides 113
were prepared in
a
one-pot procedure from
As indicated by NMR analysis, only the Z-isomer of
the enynes 3 was obtained and no signal of E-isomer
was observed. Also, none of the starting E-isomer of
b-organotelluro vinylphosphine oxide 2d was recovered
at the end of reaction.
diphenylphosphinic chloride and alkynyllithium, in a
method similar to the preparation of alkynylphos-
phonate.14
With the b-organotelluro vinylphosphine oxides 2 in
hand, we chose one of them to study the coupling
reaction with 1-alkynes. The selected compound 2d (as
a mixture of isomers Z:E 85:15) was treated with
appropriated alkynes under cross-coupling conditions5
to give the b-alkynyl vinylphosphine oxides 3 (70–78%
yields, Scheme 3, Table 2).
We do not know with certainty what the fate of the
E-isomer is, since it is consumed in the reaction but
does not furnish the corresponding coupling product.
We suppose that the E-isomer decomposes and does
not isomerize under the coupling conditions. For exam-
ple, the treatment of an 85:15 mixture of isomers of 4d,
Our initial goal in the study of this reaction was to
investigate the effects of a variety of reaction conditions
including solvent (THF, dichloromethane, benzene,
methanol and N,N-dimethylformamide), amine (pyri-
dine, pyrrolidine, diethylamine, triethylamine and diiso-
propylamine) and catalysts [Pd(OAc)2, Pd(PPh3)4,
PdCl2 and CuI]. We found that the optimum condition
Scheme 3.

A. L. Braga et al. / Tetrahedron Letters 43 (2002) 4399–4402
4401
Table 2. Synthesis of b-alkynyl vinylphosphine oxides 3 according to Scheme 3
References
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same previous ratio. To address correctly the problem,
a good alternative would be using 4d in a different ratio
than the 85:15, as isolated. Unfortunately, even after
several different experiments, such as isomerizations,
changing of reaction conditions or inverse addition of
reagents, we always obtained basically the same ther-
modynamic ratio. Because of this, experiments with
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of (E)-b-organotelluro vinylphosphine oxides have not
been described.
In summary, we have demonstrated by our studies the
hydrotelluration of alkyne bearing diphenylphosphoryl
group and disclosed a new class of vinylphosphine
oxide and its synthetic application. The synthesized
b-organotelluro vinylphosphine oxide 2d was used to
prepare b-alkynyl vinylphosphine oxides 3, an impor-
tant class of enynes. It is expected that this class of
vinylphosphine oxides and enynes will find considerable
application in organic synthesis, since the phosphine
oxides are well-known to be a good ligand for transi-
tion metal complexes16 and some derivatives of
vinylphosphine oxides can be used as biologically active
compounds.6,7e,17
Acknowledgements
The authors thank the following agencies for support:
CNPq, FAPERGS, CAPES. L.H.A. thanks CAPES for
a Ph.D. fellowship.
3. Braga, A. L.; Zeni, G.; de Andrade, L. H.; Silveira, C. C.;
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4402
A. L. Braga et al. / Tetrahedron Letters 43 (2002) 4399–4402
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Hz), 133.04 (d, JPꢀC=103.3 Hz, Ph2PO), 131.49, 130.89
(d, 3JPꢀC=9.9 Hz, Ph2PO), 128.35 (d, 2JPꢀC=12 Hz,
Ph2PO), 128.07, 127.75, 126.42, 119.24 (d, 1JPꢀC=105.5
Hz), 118.13, 29.20, 24.52, 21.41, 21.21; IR (KBr; cm−1
)
3052, 2922, 2915, 1546, 1476, 1434 (PꢀPh), 1176 (PꢁO),
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CuI (20 mol%, 0.038 g), Et3N (1 mmol) in MeOH (10
mL) at 25°C under an argon atmosphere, was added
i-butyltelluro vinylphosphine oxide 2d (1 mmol) and the
appropriate alkyne (2 mmol). The mixture was stirred at
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68–70°C; H NMR (400 MHz, CDCl3): l 7.87–7.69 (m,
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5.79–5.75 (m, 1H), 2.36 (t, 2H, J=7.6 Hz), 2.09–2.00 (m,
2H), 1.80–1.75 (m, 2H), 1.65–1.33 (m, 8H), 0.91 (t, 3H,
J=7.6 Hz); 13C NMR (100 MHz, CDCl3): l 144.75,
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(d, JPꢀC=12.1 Hz, Ph2PO), 125.14 (d, JPꢀC=102.5 Hz),
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3JPꢀC=13.8 Hz), 30.08, 28.12, 25.64, 22.01, 21.93, 21.19,
13.80; IR (KBr; cm−1) 2934, 2859, 2190 (CꢂC), 1570, 1435
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