Hydroalumination of phenylthioacetylenes. Synthesis and reactions of (Z)- and (E)-1-butyltelluro-1-phenylthio-1-alkenes

Article abstract of DOI:10.1016/S0040-4039(01)01511-8

Hydroalumination of phenylthioacetylenes with the Zweifel's reagent as reducing agent followed by the addition of C₄H₉TeBr afforded (Z)-telluro(thio)ketene acetals (Z >80-93%). The (E)-isomers were obtained with 100% stereoselectivit

Full text of DOI:10.1016/S0040-4039(01)01511-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 7167–7172
Hydroalumination of phenylthioacetylenes. Synthesis and
reactions of (Z)- and (E)-1-butyltelluro-1-phenylthio-1-alkenes
Miguel J. Dabdoub* and Palime´cio G. Guerrero, Jr.
Laborato´rio de S´ıntese de Compostos Organocalcogeˆnios, Departamento de Qu´ımica, FFCLRP, Universidade de Sa˜o Paulo,
Av. Bandeirantes, 3900 Ribeira˜o Preto, SP, Brazil
Received 14 August 2001; accepted 17 August 2001
Abstract—Hydroalumination of phenylthioacetylenes with the Zweifel’s reagent as reducing agent followed by the addition of
C4H9TeBr afforded (Z)-telluro(thio)ketene acetals (Z >80–93%). The (E)-isomers were obtained with 100% stereoselectivity by
reduction of thioacetylenes with DIBAL-H, followed by the addition of n-BuLi and subsequent treatment with C4H9TeBr.
Reaction of the (E)-telluro(thio)ketene acetals with n-BuLi followed by the addition of valeraldehyde afforded the (Z)-phenylthio
allylic alcohol as the main product and traces of the (E)-isomer, while the mixture of (Z)- and (E)-telluro(thio)ketene acetals
under similar reaction conditions gave the (E)-phenylthio allylic alcohol exclusively. © 2001 Elsevier Science Ltd. All rights
reserved.
Organotellurium compounds have been the subject of
intense research due to their applications in organic
synthesis.1,2 The chemistry of vinyl tellurides2–4 has
received special attention because these compounds can
be used as intermediates in carbonꢀcarbon bond forma-
tion, resulting in carbon chain elongation by different
processes such as transition metal-catalyzed cross-cou-
pling reactions5 or by the stereo-retentive Te/metal
exchange reactions like Te/Li,6 Te/Cu,7 Te/Zn,5c,d,8 or
Te/Mg.9
groups such as organotellurium and organosulfur moie-
ties in their structure, with the aim to study the
selectivity in the reactivity of each of these groups in
different reactions like transmetallations, metal-cata-
lyzed cross-coupling reactions and others. With this in
mind, a novel methodology for the synthesis of disub-
stituted 1,2-dichalcogene alkenes with opposite regio-
chemistry to the telluro(thio)ketene acetals was recently
developed by our group.4b The hydrotelluration of
thioacetylenes was performed, and the (Z)-1-butyltel-
luro-2-phenylthio-1-alkenes with total control on the
regio- and stereochemistry were obtained in good
yields.4b
Our group developed some methodologies for the syn-
thesis of vinylic compounds containing two het-
eroatoms directly attached to the same carbonꢀcarbon
double bond as telluroketene acetals,10 (E)-telluro(stan-
nyl)ketene acetals2b and (E)-telluro(seleno)ketene
acetals,11 using bis(cyclopentadienyl) chloro zirconium
hydride (Schwartz’s reagent) as reducing agent. In a
previous study (1999),12 we published the synthesis of
telluro(thio)ketene acetals by reaction of methylthio
phosphonates with aryl (or butyl) tellurenyl halides and
aldehydes under basic conditions. However, this
methodology produced mixtures of (Z)-, (E)-tel-
luro(thio)ketene acetals and vinyl sulfides as by-prod-
ucts. To date, this is the first and only known method
for the synthesis of this kind of compounds. Of particu-
lar importance is the regio- and stereocontrol to obtain
pure alkenes containing two different organochalcogene
The reaction of selenoacetylenes with DIBAL-H fol-
lowed by the addition of C4H9TeBr results in the
(E)-teluro(seleno)ketene acetal formation with total
control of the regio- and stereochemistry, as described
by us recently.13 However, the desired products were
obtained in low to moderate yields (22–50%), probably
because the Al/Te exchange reactions are less efficient
in the vinyl alanes13 than in the corresponding ate
complexes, as will be disclosed in the present
communication.
Now, we devoted our efforts to the development of
methodologies for the synthesis of telluro(thio)ketene
acetals with high regio- and stereoselectivity. In this
way, we envisioned two related routes for the synthesis
of each isomer (E)- and (Z)-butyltelluro-1-phenylthio-
1-alkene. First, we studied the reduction of phenyl-
* Corresponding author. E-mail: migjodab@usp.br
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01511-8

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thioacetylenes 1a–d with DIBAL-H which is a syn-
stereospecific addition process, with the hydride and the
organoaluminum moiety being added to the triple bond
on the same side. It is noteworthy that the aluminum
atom is exclusively attached to the sp2 carbon bearing
the phenylthio group, affording exclusively the a-alumi-
nated phenylthio alkene intermediate 2 (Scheme 1).
Subsequent addition of n-BuLi to the a-aluminum
vinylsulfide intermediate 2 allows the generation of the
corresponding ate complex 3 that is more reactive than
2 toward the Al/Te exchange reaction. In this way, the
capture of 3 with C4H9TeBr gave the (E) compounds
4a–d14 in good yields, with 100% regio- and stereoselec-
tivity (Scheme 1; Table 1).
On the other hand, the synthesis of (Z)-tel-
luro(thio)ketene acetals with high stereoselectivity was
performed employing the Zweifel’s reagent as an anti-
stereoespecific reducing agent.15 The lithium di(iso-
butyl)-n-butyl aluminate hydride (Zweifel’s reagent)
was generated in situ by adding n-BuLi in hexanes to a
solution of DIBAL-H in THF at 0°C. Thioacetylenes
1a–d were reacted with the formed ate complex, result-
ing in an anti-addition of the hydride and the organo-
aluminum moiety with the last group being transferred
to the sp2 carbon bearing the phenylthio group, as
depicted in the proposed structure for the lithium
phenylthio vinyl alanate intermediate 5 (Scheme 2).
This intermediate was trapped with C4H9TeBr and
Scheme 1.
Table 1. (Z)-Telluro(thio)ketene acetals obtained
Thioacetylene
Producta
Reaction time (min)
Yield (%)b
60
75
60
40
40
80
50
60
a Fully characterized by NMR, MS, elemental analyses and IR.
b Isolated yields and purified by PTLC.

M. J. Dabdoub, P. G. Guerrero, Jr. / Tetrahedron Letters 42 (2001) 7167–7172
7169
Scheme 2.
Table 2. (Z)- and (E)-Telluro(thio)ketene acetals obtained
Productsa
Thioacetylene
Ratio 6:4b
Reaction time (min)
Yield (%)c
93:7
60
63
85:15
80:20
60
40
65
57
90:10
40
60
a Fully characterized by NMR, MS, elemental analyses and IR.
b Ratio obtained by 1H NMR.
c Isolated yields and purified by PTLC.
mixtures of stereoisomers (Z)-telluro(thio)ketene
acetals 6a–d (major products; 80–93%) and (E)-
neither syn- nor anti-hydroalumination of phenyl-
thioalkynes to generate phenylthio vinyl aluminate
complex intermediates 3 and 5 were ever reported.
telluro(thio)ketene
acetals
4a–d
(by-products;
7–20%) were obtained in good yields (Scheme 2; Table
2).
The importance of the chemistry described here lies in
the established synthetic utility of the vinyl tellurides1–11
and vinyl sulfides.11,16 The Te/Li exchange reaction is
one of the most powerful tools for the regio- and
stereocontrolled synthesis of olefinic systems.1a,6,10
However, only very few examples of this reaction
employing trisubstituted vinyl tellurides have been
described in the literature.4b
Although the syn-hydroalumination reaction of com-
mon terminal alkynes using DIBAL-H have been exten-
sively studied by others, the anti-hydroalumination
employing the DIBAL-H/n-BuLi complex (Zweifel’s
reagent) have been scarcely studied to date15 and only
in specific substrates. To the best of our knowledge

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M. J. Dabdoub, P. G. Guerrero, Jr. / Tetrahedron Letters 42 (2001) 7167–7172
diate 8. This intermediate undergoes a partial inversion
of configuration due to the steric interaction between
the phenylthio and the butyl groups, furnishing the
(E)-a-lithiated vinyl sulfide 7. However, the reaction of
the (Z)-8 intermediate with valeraldehyde occurs faster
than the complete isomerization to 7, allowing the
formation of 10 as the major product (Scheme 4).
In the present communication, we also describe our
preliminary results concerning the chemical reactivity of
the trisubstituted 1-butyltelluro-1-phenylthio-1-alkenes
obtained (4 and 6) and their synthetic applications.
Employing a mixture of stereoisomers (Z)- and (E)-1-
butyltelluro-1-phenylthio-2-hexene 6b and 4b as a rep-
resentative example, we studied the chemoselectivity in
the reaction with n-BuLi at −78°C. To make possible
the capture of the generated intermediates, they were
subsequently treated with valeraldehyde and the (E)-6-
phenylthio-6-undecen-5-ol 9 was obtained exclusively in
77% yield. The reaction with n-BuLi produced exclu-
sively the detellurated intermediates as a mixture of
(Z)- and (E)-a-lithiated vinyl sulfides 7 and 8. After
formation of these two intermediates, we believe that
the steric interaction between the phenylthio and the
butyl moieties in the (Z)-a-lithiated vinylsulfide 8 pro-
motes the complete isomerization to the (E)-a-lithiated
vinyl sulfide 7 which was trapped with valeraldehyde
(Scheme 3).
Several attempt to transform intermediates 3b and 5b
into compounds (Z)-10 and (E)-9, respectively, by
direct condensation with valeraldehyde (up to 3.0
equiv.) failed completely. The major products obtained
in these cases were the corresponding (Z)-11 or the
(E)-12 phenylthio hexenes (Scheme 5), together with
mixtures of saturated alcohols formed because the alkyl
groups (from the aluminate intermediates) were prefer-
entially transferred to the aldehyde.
As a consequence, it is important to mention that the
whole routes described here to reach the stereodefined
phenylthio allylic alcohols (Z)-10 and (E)-9 (from
phenylthioacetylenes) are synthetically important even
being necessary converting the aluminate intermediate
to the tellurium compound, and then to a lithium
compound before condensation.
In the same way, the reaction of the isomerically pure
(E)-1-butyltelluro-1-phenylthio-1-hexene 4b with n-
BuLi was performed in THF at −78°C, followed by the
addition of valeraldehyde, and the (Z)-6-phenylthio-6-
undecen-5-ol 10 was obtained in 76% yield as the major
product. However, traces of the (E)-6-phenylthio-6-
In summary, as stated above, we have developed two
new methodologies that permit the high stereoselective
synthesis of (Z)- and (E)-telluro(thio)ketene acetals.
The stereospecificity of tellurium compound formation
1
undecen-5-ol 9 were detected by H NMR. We believe
that in this case the reaction of n-BuLi with 4b fur-
nished initially the (Z)-a-lithiated vinyl sulfide interme-
Scheme 3.
Scheme 4.

M. J. Dabdoub, P. G. Guerrero, Jr. / Tetrahedron Letters 42 (2001) 7167–7172
7171
Scheme 5.
depends on that of the initial aluminate complexes that
are described here for the first time. Our studies con-
firmed the expected highest reactivity of the butyltel-
lurium group because the phenylthio group remained
untouched in reactions of the telluro(thio)ketene acetals
with n-BuLi. This last reaction allowed us to obtain the
corresponding stereodefined phenylthio allylic alcohols.
Other synthetic applications of these mixed 1,1-bis(or-
ganylchalcogeno)-1-alkenes are now under development
in our laboratory.
6. (a) Hiiro, T.; Mogami, T.; Kambe, N.; Fujiwara, S. I.;
Sonoda, N. Angew. Chem., Int. Ed. Engl. 1987, 26, 1187;
(b) Dabdoub, M. J.; Dabdoub, V. B.; Comasseto, J. V.
Tetrahedron Lett. 1992, 33, 7353; (c) Ogawa, A.; Tsuboi,
Y.; Obayashi, R.; Yokoyama, K.; Ryu, I.; Sonoda, N. J.
Org. Chem. 1994, 59, 1600; (d) Dabdoub, M. J.; Dab-
doub, V. B. Tetrahedron 1995, 51, 9830; (e) Dabdoub, M.
J.; Begnini, M. L.; Cassol, T. M.; Guerrero, Jr., P. G.;
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Acknowledgements
rous, Sulfur Silicon 1992, 67, 103.
This work was supported by grants from CNPq and
FAPESP. Thanks are due to Mr. Djalma Batista
Gianetti for assistance in obtaining infrared and mass
spectra.
10. Dabdoub, M. J.; Begnini, M. L.; Guerrero, Jr., P. G.
Tetrahedron 1998, 54, 2371.
11. Dabdoub, M. J.; Begnini, M. L.; Guerrero, Jr., P. G.;
Baroni, A. C. M. J. Org. Chem. 2000, 65, 61.
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14. Typical procedure for the synthesis of (E)-1-butyltelluro-
1-phenylthio-1-alkenes 4: To DIBAL-H (2.0 mL, 2.0
mmol, 1 M in hexanes) in hexanes (5.0 mL) under N2, a
solution of 1-phenylthio-1-hexyne (0.2 g, 1.0 mmol) in
hexanes (2.0 mL) was added via syringe at rt. The
reaction was refluxed for 60 min, then n-BuLi (1.53 mL,
2.0 mmol, 1.3 M in hexanes) was added dropwise at 0°C
and stirring was continued for 30 min. A solution of
C4H9TeBr/LiCl obtained in a different flask was trans-
ferred via syringe [4.0 mmol, obtained by the addition of
Br2 (0.32 g, 2.0 mmol) in benzene or CCl4 (10 mL) to a
solution of (C4H9Te)2 (2.0 mmol, 0.73 g) in THF (10 mL)
at 0°C, under stirring for 10 min followed by the addition
of LiCl (1.3 g)]. Stirring was continued for an additional
30 min and the mixture was transferred to an Erlenmeyer
flask and diluted with ethyl acetate (20 mL), 95% ethanol
(10 mL) and water (20 mL). Butylbromide (0.64 mL, 6.0
mmol) and finally NaBH4 (0.18 g, 6.0 mmol) were added
to transform the (C4H9Te)2 to the corresponding tel-
luride, which is more easily removed by distillation. After
the usual work-up the product was dried (MgSO4) and
the solvent evaporated under vacuum. The (C4H9)2Te
was removed by distillation from the crude product using
a Kugelro¨hr oven. The residue was purified by PTLC,
using hexane as mobile phase. (E)-1-Butyltelluro-1-
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P. Tetrahedron Lett. 2000, 41, 437.

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M. J. Dabdoub, P. G. Guerrero, Jr. / Tetrahedron Letters 42 (2001) 7167–7172
phenylthio-1-hexene 4b. Yield: 0.25 g (80%); CG/MS m/z
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378 (27.23), 239 (11.90), 191 (30.59), 149 (100.00), 116
(25.19), 81 (57.69); 1H NMR (300 MHz) (l in CDCl3) 0.86
(t, J=7.5 Hz, 3H), 0.90 (t, J=7.5 Hz, 3H), 1.16–1.46 (m,
8H), 1.70 (quint., J=7.5 Hz, 2H), 2.40 (q, J=7.5 Hz, 2H),
2.73 (t, J=7.5 Hz, 2H), 6.71 (t, J=7.5 Hz, 1H), 7.26 (m,
5H); 13C NMR 9.7, 13.4, 13.9, 22.3, 25.1, 31.1, 33.7, 36.4,
101.5, 126.3, 128.8, 129.4, 136.8, 152.9. Anal. calcd for
C16H24TeS: C, 50.82; H, 6.40. Found: C, 50.82; H, 6.08.