P. G. Guerrero Jr. et al. / Tetrahedron Letters 49 (2008) 3872–3876
3875
Finally, these vinyl alanate intermediates were cap-
tured with C4H9TeBr (4.0 mmol) in THF/benzene at
0 °C furnishing exclusively the (E)-1-butyltelluro-1-butyl-
seleno-2-organoyl ethenes 5a–g13 with good yields
(Table 1).
uro(seleno)ketene acetals are under development in our
laboratory.
Acknowledgments
The stereochemistry of the (E)-telluro(seleno)ketene ace-
tals was determined by the gNOESY in the 1H NMR spec-
tra of 5b. An enhancement of the methylenic protons next
to tellurium was observed as the vinylic proton of 5b was
irradiated.
The authors thank to FAPESP and FUNDUNESP for
financial support and Dr. Janet W. Reid (J.W.R. Associ-
ates) for revising the English text.
References and notes
The NOE effect was also observed between the allylic
protons and the CH2 of the butylseleno group. Futher-
more, correlations were not observed between the vinylic
hydrogen and the CH2 attached at the selenium atom.
These NMR experiments indicate that the butylseleno
group is situated close to the alkyl group attached to the
adjacent carbon (E configuration).
In the context of our strong interest in exploring a con-
venient access to (Z)-telluro(seleno)ketene acetals we stud-
ied the hydroalumination of butylseleno acetylenes using
the lithium di-(isobutyl)-n-butyl aluminate hydride 6
(Zweifel’s reagent)14 obtained ‘in situ’ by the addition of
n-butyllithium (1.0 equiv) to a solution of DIBAL-H
(1.0 equiv.) in diglyme (10 mL) at 0 °C.
1. (a) Wirth, T. Organoselenium Chemistry, Modern Developments in
Organic Synthesis, Vol. 208; Springer: Berlin, 2000; (b) Denmark, S.
E.; Edwards, M. G. J. Org. Chem. 2006, 71, 7293.
2. (a) Petragnani, N. Best Synthetic Methods — Tellurium in Organic
Synthesis; Academic Press: London, 1994; (b) Petragnani, N.; Stefani,
H. A. Tetrahedron 2005, 61, 1613.
3. (a) Comasseto, J. V.; Ling, L. W.; Petragnani, N.; Stefani, H. A.
Synthesis 1997, 373; (b) Yang, J.; Cohn, S. T.; Romo, D. Org. Lett.
2000, 2, 763; (c) Dabdoub, M. J.; Rotta, J. C. Synlett 1996, 526; (d)
Barrientos-Astigarraga, R. E.; Castelani, P.; Comasseto, J. V.;
Formiga, H. B.; Da Silva, N. C.; Sumida, C. Y.; Vieira, M. L. J.
Organomet. Chem. 2001, 623, 43.
4. (a) Marino, J. P.; McClure, M. S.; Holub, D. P.; Comasseto, J. V.;
Tucci, F. C. J. Am. Chem. Soc. 2002, 124, 1664; (b) Oliveira, J. M.;
Zeni, G.; Malvestiti, I.; Menezes, P. H. Tetrahedron Lett. 2006, 47,
8183.
The first attempt at trans-stereoselective reaction of the
1-selenobutyl-1-hexyne 2b failed, and the hydroalumina-
tion afforded a mixture of alkylselenides as product due
to Csp–Se cleavage from the starting material.
However, when we reacted the phenylseleno acetylenes
(1.0 mmol.) 7a–g and lithium di-(isobutyl)-n-butyl alumi-
nate hydride 6 (1.5 mmol) in diglyme (10 mL) under reflux,
the (E)-phenylseleno vinyl alanate intermediates 8a–g were
generated by the anti-addition of the hydride from Zwei-
fel’s reagent to the triple bond.
5. (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. Tetrahedron 1995, 51, 9830.
6. (a) Dabdoub, M. J.; Dabdoub, V. B.; Marino, J. P. Tetrahedron Lett.
2000, 41, 433; (b) Dabdoub, M. J.; Dabdoub, V. B.; Marino, J. P.
Tetrahedron Lett. 2000, 41, 437.
7. Larock, R. C. Comprehensive Organic Transformations; VCH: New
York, 1989.
8. Yoshimatsu, M.; Oguri, K.; Ikeda, K.; Gotoh, S. J. Org. Chem. 1998,
63, 4475.
9. Dabdoub, M. J.; Begnini, M. L.; Guerrero, P. G., Jr. Tetrahedron
1998, 54, 2371.
Consequently, the organoaluminium moiety was trans-
ferred to the carbon sp2 bearing the phenylseleno group
and finally these intermediates 8a–g were trapped with
C4H9TeBr furnishing the (Z)-telluro(seleno)ketene acetals
9a–g15 exclusively and good yields (Table 2).
10. Dabdoub, M. J.; Guerrero, P. G., Jr. Tetrahedron Lett. 2001, 42,
7167.
11. Dabdoub, M. J.; Cassol, T. M.; Barbosa, S. L. Tetrahedron Lett.
1996, 37, 831.
12. Dabdoub, M. J.; Begnini, M. L.; Guerrero, P. G., Jr.; Baroni, A. C.
M. J. Org. Chem. 2000, 65, 61.
The stereochemistry of the (Z)-telluro(seleno)ketene
acetals was also determined by the gNOESY experiments.
For example we utilised compound 9c to demonstrate the
(Z)-configuration of the trisubstituted olefins 9a–g. NOE
effects from allylic CH2 to the CH2 directly attached to
the tellurium atom and between vinyl hydrogen and CH
aromatic from phenyl group bonded to the selenium atom
were observed. On the other hand, correlations were not
observed between the vinylic hydrogen and CH2 bonded
directly at the tellurium atom.
In summary, we developed two new methodologies that
permit the exclusive synthesis of (E)- and (Z)-tell-
uro(seleno)ketene acetals with total control of regio and
stereochemistry. The vinyl aluminates complexes described
here for the first time are responsible for the stereospecific-
ity of tellurium compounds formation which were obtained
by NOE experiments. Synthetic applications involving the
Te/Li exchange and cross coupling reactions of these tell-
13. Typical procedure for the synthesis of(E)-telluro(seleno)ketene acetals
5a–g: To a solution of butylseleno acetylene (1.0 mmol) in hexanes
(5 mL) under a nitrogen atmosphere, DIBAL-H (1.5 mL; 1.0 mmol;
1.5 M in toluene) was added at room temperature and stirred for the
time shown in Table 1. The mixture was cooled at 0 °C, n-butyllithium
(0.4 mL; 1.0 mmol; 2.5 M in hexanes) was added dropwise and the
reaction was stirred for 30 min. Then, a solution of C4H9TeBr
prepared separately [4.0 mmol; by the addition of Br2 (0.32 g,
2.0 mmol) in benzene (10 mL) to a solution of (C4H9Te)2 (2.0 mmol,
0.73 g) in THF (10 mL) at 0 °C] was transferred via syringe. Stirring
was continued for an additional 30 min and the solution was diluted
with ethyl acetate (100 mL), the organic phase washed with brine
(3 Â 50 mL), dried over anhydrous MgSO4, and the solvent evapo-
rated under vacuum. The residue containing the (E)-telluro(seleno)-
ketene acetals was obtained as a yellow liquid after purification by
silica flash (230–400 mesh). (E)-1-Butyltelluro-1-butylseleno-1-hexene
5b. Yield: 87% (0.35 g); GC/MS m/z 402 (5.65), 279 (10.2), 267 (11.5),
202 (16.4),149 (90.1), 83 (17.2), 81 (98.9), 57 (100.0); 1H NMR
(300 MHz) (d in CDCl3) 0.85–0.95 (m, 9H), 1.3–1.5 (m, 8H), 1.62
(quint, J = 7.3 Hz, 2H), 1.78 (quint, J = 7.0 Hz, 2H), 2.33 (q,
J = 7.3 Hz, 2H), 2.73 (t, J = 7.3 Hz, 2H), 2.79 (t, J = 7.3 Hz, 2H),