One-pot synthesis of telluroketene acetals and haloketene acetals using sp2 geminated hetero organobismetallic intermediates

Article abstract of DOI:10.1016/j.tetlet.2012.01.065

A novel one-pot synthesis of 1,1-dihalo-1-alkenes and 1,1-bis(butyltelluro) -1-alkenes was developed from hydrozirconation of alkynylzinc bromide with Cp₂Zr(H)Cl and subsequent capture of the Zn/Zr 1,1-heterodimetallo-1- alkene intermediates wi

Full text of DOI:10.1016/j.tetlet.2012.01.065

Tetrahedron Letters 53 (2012) 1582–1586
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
One-pot synthesis of telluroketene acetals and haloketene acetals using sp2
geminated hetero organobismetallic intermediates
Palimécio G. Guerrero Jr. a, , Paulo R. de Oliveira a, Adriano C.M. Baroni b, Francisco A. Marques c,
⇑
Ricardo Labes c, Miguel J. Dabdoub d
a Department of Chemistry and Biology, DAQBi, Paraná Federal University of Technology, UTFPR, Curitiba, PR, Brazil
b Department of Pharmacy and Biochemistry, Federal University of Mato Grosso do Sul, UFMS, Campo Grande, MS, Brazil
c Department of Chemistry, Federal University of Paraná, UFPR, Curitiba, PR, Brazil
d Department of Chemistry, São Paulo State University, USP, Ribeirão Preto, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel one-pot synthesis of 1,1-dihalo-1-alkenes and 1,1-bis(butyltelluro)-1-alkenes was developed
from hydrozirconation of alkynylzinc bromide with Cp2Zr(H)Cl and subsequent capture of the Zn/Zr
1,1-heterodimetallo-1-alkene intermediates with halogen and tellurium electrophiles. These protocols,
which include multiple reactions in a one-pot procedure, allow the preparation of the potentially useful
haloketene acetals and telluroketene acetals from terminal alkynes, under mild conditions and in a good
yield.
Received 16 December 2011
Accepted 17 January 2012
Available online 28 January 2012
Keywords:
Zn/Zr sp2 organobismetallic
Telluroketene acetals
Haloketene acetals
One-pot
Ó 2012 Elsevier Ltd. All rights reserved.
New strategies for generation of 1,1-bisanions such as 1,1-sp3
and 1,1-sp2 bismetallic reagents have been the target of intense
research, as reflected in a plethora of articles published in recent
decades.1,2 Vinyl geminated organobismetallic derivatives contain-
ing lithium,3 boron,4 magnesium,5 aluminum,6 copper,7 titanium,8
gallium,9 and indium10 have been applied as an efficient and useful
alternative to prepare functionalized substituted olefins. The total
synthesis of molecules with retinoidal activities11a such as
Temarotene11b,c was performed by palladium catalyzed cross-cou-
pling reactions of gem-borazirconocene alkenes.4b The synthesis
and recent applications of trisubstituted olefins containing two
functional groups attached to the same C-sp2 such as haloketene
acetals (1,1-dibromo-1-alkenes 1 and 1,1-diiodo-1-alkenes 2)12
and telluroketene acetals (1,1-bis(organylchalcogene)-1-alkenes)13
3 were investigated by our group and others. As representative
examples, telluroketene acetals and haloketene acetals can be
obtained by the hydrozirconation of telluroacetylenes13a and
stannylacetylenes12d followed by subsequent quenching of the
sp2 1,1-heterobismetallic intermediates using butyltellurenyl
bromide (C4H9TeBr) and halogen electrophiles, respectively. The
1,1-diiodo-1-alkenes can also be obtained by carbometalation of
alkynyl alanate6a with (CH3)3Al and Cl2ZrCp2 as catalyst. However,
the published methodology to synthesize telluroketene acetals and
haloketene acetals requires the preliminary preparation of
R
R
H
1) C6H5MgBr
2) ZnBr2
THF/0 o
C
ZnBr
4
Cp2Zr(H)Cl
CH2Cl2/ 25 o
10 min.
C
R
ZnBr
R
I
I
TeC4H9
TeC4H9
R
I2
C4H9TeBr
THF/CCl4/0 o
THF/0 oC
5
C
ZrCp2Cl
2a-g
65 %- 80 %
3a-c, g, i,j
60%- 75 %
NBS/THF/CH2Cl2/0oC
R
Br
Br
1a-g
63 %-78 %
R = Alkyl, aryl, alkenyl, CH2OBn, CH2(CH2)2Cl, CH2OTBS for compounds 1 and 2
R = Alkyl, aryl, alkenyl, CH2OCH3 for compounds 3
Scheme 1.
⇑
Corresponding author. Tel./fax: +55 41 3310 4661.
E-mail address: pali@utfpr.edu.br (P.G. Guerrero).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2012.01.065

P. G. Guerrero Jr. et al. / Tetrahedron Letters 53 (2012) 1582–1586
1583
Table 1
Table 2
Iodonolysis of C-Zr or C-Zn of 1,1-bismetallic-1-alkenes
Bromonolysis of C-Zr or C-Zn of 1,1-bismetallic-1-alkenes
C4H9
C4H9
C4H9
ZnBr
I
C4H9
C4H9
C4H9
C4H9
Br
Br
ZnBr
C4H9
I
Br
NBS
I2
+
+
+
+
THF/CH2Cl2
THF
I
I
ZrCp2Cl
Br
ZrCp2Cl
5a
6
7
2
5a
8
9
1a
Ratioa
Entry
Reactions and conditions
Ratioa
Entry
Reactions and conditions
6:
7:
2:
8:
9:
1a:
1
2
3
4
5
6
7
8
1.0 equiv of I2/THF, À78 °C
1.0 equiv of I2/THF, 0 °C
1.5 equiv of I2/THF, À78 °C
1.5 equiv of I2/THF, 0 °C
2.0 equiv of I2/THF, -78 °C
2.0 equiv of I2/THF, 0 °C
2.5 equiv of I2/THF, À78 °C
2.5 equiv of I2/THF, 0 °C
78
61
50
48
10
09
05
—
15
30
35
30
05
07
05
—
07
09
15
22
85
84
90
100
1
2
3
4
5
6
7
8
1.0 equiv of NBS/THF/CH2Cl2, À78 °C
1.0 equiv of NBS/THF/CH2Cl2, 0 °C
1.5 equiv of NBS/THF/CH2Cl2, À78 °C
1.5 equiv of NBS/THF/CH2Cl2, 0 °C
2.0 equiv of NBS/THF/CH2Cl2, À78 °C
2.0 equiv of NBS/THF/CH2Cl2, 0 °C
2.5 equiv of NBS/THF/CH2Cl2, À78 °C
2.5 equiv of NBS/THF/CH2Cl2, 0 °C
91
90
75
75
08
08
05
—
09
10
25
25
05
05
—
—
—
—
—
87
87
95
100
—
a
Ratio determined by 1H NMR.
a
Ratio determined by 1H NMR.
Table 3
Synthesis of 1,1-dihalo-1-alkenes
Entry
1,1-Bimetallic reagent
Electrophile
I2
Time (h)a
1.0
1,1-Dihalo-1-alkeneb
Yield (%)c
76
C4H9
C4H9
ZnBr
I
2a
ZrCp2Cl
I
Br
5a
5b
5c
1
C4H9
NBS
I2
1.5
1.0
1.5
1.0
1.5
72
73
75
65
70
Br
I
1a
2b
C6H13
C6H13
C6H13
ZnBr
I
ZrCp2Cl
2
Br
NBS
I2
Br
I
1b
2c
C6H5
C6H5
C6H5
ZnBr
I
Br
ZrCp2Cl
3
NBS
Br
1c
ZnBr
I
BnO
BnO
Cl
I2
2.5
3.0
2.0
76
75
80
2d
I
Br
ZrCp2Cl
5d
4
BnO
Cl
NBS
I2
Br
1d
ZnBr
I
I
Br
ZrCp2Cl
2e
1e
5e
5
6
Cl
NBS
2.5
2.5
78
78
Br
ZnBr
I
I
TBSO
TBSO
I2
2f
ZrCp2Cl
5f
(continued on next page)

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P. G. Guerrero Jr. et al. / Tetrahedron Letters 53 (2012) 1582–1586
Table 3 (continued)
Entry
1,1-Bimetallic reagent
Electrophile
NBS
Time (h)a
3.0
1,1-Dihalo-1-alkeneb
Yield (%)c
75
Br
Br
TBSO
1f
I
ZnBr
I2
3.0
4.0
70
63
I
ZrCp2Cl
2g
5g
7
Br
NBS
Br
1g
a
Reaction time of the electrophile and 1,1-bismetallic-1-alkene reagent.
Fully characterized by NMR (1H and 13C), HRMS.
Isolated yields after purification by chromatography using silica gel (230–400 mesh). Mobile phase: hexane for 1a–c, 1g; 2a–c, 2g and a mixture of ethyl acetate/hexane
b
c
(2:8 v/v) for 1d–f, 2d–f.
Table 4
Synthesis of telluroketene acetals21
R
TeC4H9
TeC4H9
R
ZnBr
C4H9TeBr (3.0 equiv.)
THF/CCl4 /0oC
ZrCp2Cl
3a-c, g,h-j
5a-c,g,h-j
60% - 75%
(1.0 equiv)
Entry
1
1,1-Bimetallic reagent
Electrophile
Time (min)a
30
Productb
Yieldc (%)
70
C4H9
C6H13
C6H5
C4H9
TeC4H9
ZnBr
C4H9TeBr
C4H9TeBr
C4H9TeBr
TeC4H9
TeC4H9
ZrCp2Cl
ZnBr
3a
5a
C6H13
2
3
30
50
73
67
ZrCp2Cl
ZnBr
TeC4H9
TeC4H9
3b
5b
C6H5
ZrCp2Cl
ZnBr
TeC4H9
5c
3c
TeC4H9
4
5
C4H9TeBr
C4H9TeBr
60
20
60
65
ZrCp2Cl
TeC4H9
5g
ZnBr
3g
TeC4H9
ZrCp2Cl
TeC4H9
5h
C3H7
3h
C3H7
TeC4H9
ZnBr
6
7
C4H9TeBr
C4H9TeBr
30
45
75
65
TeC4H9
ZrCp2Cl
ZnBr
5i
3i
TeC4H9
CH3O
CH3O
TeC4H9
ZrCp2Cl
3j
5j
a
b
c
Reaction time of the electrophile and 1,1-bismetallic-1-alkene.
Fully characterized by NMR (1H and 13C), GC/MS and microanalysis.
Isolated yields after purification by chromatography using silica gel (230–400 mesh). Mobile phase: hexane for 3a-c, g, h–i and a mixture of ethyl acetate/hexane (2:8 v/v)
for 3j.

P. G. Guerrero Jr. et al. / Tetrahedron Letters 53 (2012) 1582–1586
1585
telluroacetylenes13a or stannylacetylenes12d as starting material
and the carbometalation of the alkynyl alanate6a to afford the
iodoketene acetals, is carried out using the dangerous and pyro-
phoric reagent trimethyl-aluminum.
1H NMR, 13C NMR, HRMS, GC/MS and microanalysis published pre-
viously by our group.
In summary, we describe a novel, efficient, and general one-pot
synthesis of the useful 1,1-bis(organyltelluro)-1-alkenes, 1,
1-diiodo-1-alkenes and 1,1-dibromo-1-alkenes by the reactions
of Zn/Zr 1,1-bismetallic-1-alkenes with tellurium and halogen
electrophiles. To the best of our knowledge, this is the first report
in which telluroketene acetals and haloketene acetals are obtained
directly from 1-alkynes via double halogenolysis reactions involv-
ing Zn/Zr 1,1-bismetallic-1-alkenes type 5 under mild conditions.
This procedure tolerates various functional groups that are not
compatible with some published procedures.
Further studies applying the telluroketene acetals and
haloketene acetals toward rapid total synthesis of molecules with
medicinal and biological activities, such as gem-enedyines, which
have anticancer properties, and insect sex pheromones are
presently underway in our laboratories.
Knochel and co-workers14 published a long time ago, the syn-
thesis of polyfunctional olefins and allenes using Zn/Zr 1,1-sp2
bismetallic reagents 5. However, to the best of our knowledge,
studies concerning the chemical reactivity involving the powerful
intermediate type 5 with other electrophiles such as chalcogenes
and halogen have not yet been reported. Considering that 1,1
-dihalo-1-alkenes have been applied as important substrates in
cross-coupling reactions,12e,f to prepare therapeutic agents such
as heteroaryl ketones12g and anticancer polyketides,12h we de-
scribe herein our detailed study toward the one-pot synthesis of
telluroketene acetals and haloketene acetals using a wide range
of Zn/Zr alkylidene species.
Corey and Fuchs demonstrated that various aldehydes can be
converted into 1,1-dibromo-1-alkenes using a Wittig-type reaction
with carbon tetrabromide.12a Recently, the use of phosphorus
reagents has been avoided because of their high toxicity and the te-
dious procedures involved in product purification which limits this
protocol.15 Bismetallic vinyl species of Sn16 and In17 generated
from terminal acetylenes have been used to obtain 1,1-dihalo-1-
alkenes of type 1, 2. However, these methodologies are not effi-
cient, since only specific alkynes containing oxygen were used.
Therefore, the development of new, versatile, and general alterna-
tives to afford the synthesis of the useful 1,1-dihalo-alkenes and
telluroketene acetals has been the target of great interest in organ-
ic synthesis.
Acknowledgments
The authors are grateful to CNPq and Fundação Araucária for
financial support. Thanks are also due to Dr. Janet W. Reid
(JWR Associates) for the English revision and to Dr. Andersson
Barison (UFPR) for the NMR spectra facilities.
References and notes
1. Marek, I.; Normant, J. F. Chem. Rev. 1996, 96, 3241.
2. Marek, I. Chem. Rev. 2000, 100, 2887.
3. (a) Maercker, A.; Bos, B. Main Group Met. Chem. 1991, 14, 67; (b) Maercker, A. In
Lithium Chemistry; Sapse, A. M., Schelyer, P., Eds.; Wiley & Sons: New York,
1995; p 490; (c) Seyferth, D.; Langer, P.; Doering, M. Organometallics 1995, 14,
4457.
4. (a) Cooke, M. P., Jr. J. Org. Chem. 1994, 59, 2930; (b) Deloux, L.; Srebnik, M.;
Sabat, M. J. Org. Chem. 1995, 60, 3276; (c) Desurmont, G.; Dalton, S.; Giolando,
D. M.; Srebnik, M. J. Org. Chem. 1997, 62, 8907.
5. (a) Duboudin, J. G.; Jousseaume, B. Synth. Comm. 1979, 9, 53; (b) Duboudin, J. G.;
Jousseaume, B.; Saux, A. J. Organometal. Chem. 1979, 168, 1.
6. (a) Van Horn, D. E.; Valente, L. F.; Idacavage, M. J.; Negishi, E. I. J. Organometal.
Chem. 1978, 156, C20; (b) Pelter, A.; Smith, K.; Parry, D. E.; Jones, K. D. Aust. J.
Chem. 1992, 45, 57.
7. Janssen, M. D.; Kohler, K.; Herres, M.; Dedieu, A.; Smeets, W. J. J.; Spek, A. L.;
Grove, D. M.; Lang, H.; van Koten, G. J. Am. Chem. Soc. 1996, 118, 4817.
8. (a) Urabe, H.; Hamada, T.; Sato, F. J. Am. Chem. Soc. 1999, 121, 2931; (b) Urabe,
H.; Sato, F. J. Am. Chem. Soc. 1999, 121, 1245.
9. Yamaguchi, M.; Tsukagoshi, T.; Arisawa, M. J. Am. Chem. Soc. 1999, 121, 4074.
10. Fujiwara, N.; Yamamoto, Y. J. Org. Chem. 1999, 64, 4095.
11. (a) Mangelsdorf, D. J.; Umesono, K.; Evans, R. M. The Retinoid Receptors. In The
Retinoids; Academic Press: Orlando, FL, 1994; (b) Ritter, S. J.; Smith, J. E.
Biochim. Biophys. Acta 1996, 1291, 228; (c) Nankervis, R.; Davis, S. S.; Day, N. H.;
Shaw, P. N. Int. J. Pharm. 1996, 130, 57.
12. For the synthesis of 1,1-dihalo-1-alkenes see: (a) Corey, E. J.; Fuchs, P. L.
Tetrahedron Lett. 1972, 13, 3769; (b) Desai, N. B.; McKelvie, N.; Ramirez, F. J. Am.
Chem. Soc. 2002, 84, 1745; (c) Bonnet, B.; Le Gallic, Y.; Plé, G.; Duhamel, L.
Synthesis 1993, 1071; (d) Dabdoub, M. J.; Dabdoub, V. B.; Baroni, A. C. M. J. Am.
Chem. Soc. 2001, 123, 9694; For the applications of 1,1-dihalo-1-alkenes see (e)
Rao, M. L. N.; Jadhav, D. N.; Dasgupta, P. Org. Lett. 2010, 12, 2048; (f) Chelucci,
G.; Capitta, F.; Baldino, S. Tetrahedron 2008, 64, 10250; (g) Fan, X.; He, Y.;
Zhang, X.; Guo, S.; Wang, Y. Tetrahedron 2011, 67, 6369; (h) Paterson, I.; Paquet,
T.; Dalby, S. M. Org. Lett. 2011, 13, 4398.
Our approach to synthesize 1,1-dihalo-1-alkenes and telluroketene
acetals from 1-alkynes using a one-pot procedure, which is described
in Scheme 1, was realized as an extension of the work developed by
Knochel,14 who reported the reduction of alkynylzinc bromide 4 with
Cp2Zr(H)Cl (Schwarts reagent)18 in CH2Cl2.
´
We examined the chemical reactivity of the in situ generated
1,1-bismetallic-1-alkenes species 5a as toward I2 and NBS under
several reaction conditions (Tables 1 and 2). A predominance of
(Z)-vinyl halides 6, 8 and low amounts of 1,1-dihalo-1-alkenes 1,
2 (Tables 1 and 2, entries 1–4) were detected when a solution con-
taining iodine in THF or NBS in THF/CH2Cl2 (1.0 and 1.5 equiv) was
added at either 0 °C or À78 °C to a solution of the 1,1-bismetallic-
1-alkenes 5 (1.0 equiv). These results allow us to observe that the
halogenolysis of C-Zn is faster than C-Zr. Larger amounts of 1,1-
dihalo-1-alkenes 1, 2 and traces of vinyl halides 6–9 were observed
after the addition of 2.0 equiv of I2 or NBS to a solution of the
intermediate 5 (Tables 1 and 2, entries 5–6).
The (Z) and (E)-vinyl halides 6–9 are formed by hydrogen
capture during the aqueous workup.
By adding 2.5 equiv of NBS in THF/CH2Cl2 or I2 in THF at 0 °C to
alkylidene species 5, the 1,1-dibromo-1-alkenes19 1, and 1,1-diio-
do-1-alkenes20 2 were obtained exclusively and in good yields
(Tables 1, 2 entry 8 and Table 3).
13. For the synthesis of telluroketene acetals see: (a) Dabdoub, M. J.; Begnini, M. L.;
Guerrero, P. G., Jr. Tetrahedron 1998, 54, 2371; (b) Silveira, C. C.; Perin, G.; Jacob,
R. G.; Braga, A. L. Phosphorus, Sulfur and Silicon 2001, 172, 55; For the
applications of telluroketene acetals see: (c) Zeni, G.; Perin, G.; Cella, R.; Jacob,
R. G.; Braga, A. L.; Silveira, C. C.; Stefani, H. A. Synlett 2002, 975.
14. (a) Tucker, C. E.; Knochel, P. J. Am. Chem. Soc. 1991, 113, 9888; (b) Tucker, C. E.;
Greve, B.; Klein, W.; Knochel, P. Organometallics 1994, 13, 94.
15. Wang, Z.; Campagna, S.; Yang, K.; Xu, G.; Pierce, M. E.; Fortunak, J. M.;
Confalone, P. N. J. Org. Chem. 2000, 65, 1889.
16. Quayle, P.; Wang, J.; Xu, J.; Urch, C. J. Tetrahedron Lett. 1998, 39, 481.
17. Klaps, E.; Schmid, W. J. Org. Chem. 1999, 64, 7537.
Exploiting our previous results to prepare the 1,1-dihalo-1-al-
kenes 1–2, we studied the one-pot synthesis of telluroketene ace-
tals type 3 by using butyltellurenyl bromide (C4H9TeBr) instead of
iodine or NBS as electrophile. However, the addition of 2.5 equiv of
C4H9TeBr to 1,1-hetero bismetallic intermediate 5a–b leads to
telluroketene acetals in low yields (15–20%), and an appreciable
amount of telluroacetylene (50–65%) was detected.
To overcome these problems, the best result, as shown in Table 3,
was achieved by the addition of butyltellurenyl bromide (C4H9TeBr;
3.0 equiv) at 0 °C to the Zn/Zr 1,1-dimetallo 1-alkenes 5 (1.0 equiv),
leading to the one-pot preparation of the telluroketene acetals 3 in a
good yield (Scheme 1, Table 4).
18. Buchwald, S. L.; LaMarie, S. J.; Nielsen, R. B.; Watson, B. T.; King, S. M.
Tetrahedron Lett. 1987, 28, 3895.
19. Typical procedure for the preparation of 1,1-dibromo-1-alkenes
To a two-neck flask under nitrogen atmosphere and equipped with a magnetic
stirring bar, containing 1-alkyne (1.0 mmol) in THF (5.0 mL), a solution of
phenyl magnesium bromide (1.1 mL; 1.1 mmol; 1.0 M in THF) was added
dropwise at 0 °C. After 10 min, ZnBr2 (0.22 g; 1.1 mmol) in THF (3.0 mL) was
Assignments of the 1,1-dihalo-1-alkenes (Table 3)12d and
1,1-bis(butyltelluro)-1-alkenes (Table 4)13a are consistent with

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P. G. Guerrero Jr. et al. / Tetrahedron Letters 53 (2012) 1582–1586
added at -78 °C and the mixture was stirred for an additional 15 min. Next, the
1,1-Diiodo-1-octene 2b. Yield (73%). IR (cmÀ1) 3166, 2924, 2854, 1589, 1464,
715. 1H NMR (300 MHz) (d in CDCl3) 0.95 (t, J = 7.2 Hz, 3H), 1.0-1.5 (m, 6H),
1.45 (quint, J = 7.5 Hz, 2H), 6.60 (t, J = 7.5 Hz, 1H); 13C NMR (75 MHZ) 11.5,
14.1, 22.5, 27.4, 28.5, 31.5, 39.7,153.2. HMRS Calc for C8H14I2 (M+): 363.9186.
Found: 363.9190.
system was warmed to 25 °C and the THF was totally removed under vacuum
and replaced by dry CH2Cl2 (5.0 mL). Then, Cp2Zr(H)Cl (0.26 g; 1.0 mmol) in
CH2Cl2 (5.0 mL) was added slowly at 25 °C and the mixture was stirred for
10 min for generation of the 1,1-bismetallic intermediate 5. Finally, the
reaction mixture was cooled to 0 °C and NBS (0.44 g, 2.5 mmol) dissolved in
THF (5.0 mL) and CH2Cl2 (5.0 mL) was transferred via syringe and the solution
stirred for the time needed, as indicated in Table 2. The mixture was diluted
with ethyl acetate (50.0 mL) the organic phase was washed with brine
(4 Â 20.0 mL) and dried over anhydrous magnesium sulfate. After filtration,
the solvent was removed under vacuum by rotary evaporation and the crude
products were purified by flash chromatography (using silica gel 230–400
mesh and the appropriate mobile phase as shown in Table 1), furnishing the
1,1-dibromo-1-alkenes as a pale yellow oil.
21. Typical procedure for the preparation of 1,1-bis(butyltelluro)-1-alkenes
The reaction mixture containing the 1,1-bismetallic
5 intermediate was
performed as described in the Ref19, and cooled to 0 °C. Then, butyltellurenyl
bromide [(C4H9TeBr; 3.0 mmol, prepared separately by the addition of bromine
(0.24 g; 1.5 mmol) in CCl4 (5.0 mL) to a solution of dibutyl ditelluride22 (0.55 g;
1.5 mmol) in THF (10.0 mL)], was added dropwise via syringe. The stirring was
continued for 30 min. at 0 °C, and the mixture was transferred to an
Erlenmeyer flask (500 mL) and diluted with ethyl acetate (20.0 mL), water
(50.0 mL) and 95% (v/v) ethanol (20.0 mL). Finally, butyl bromide (1.0 mL) and
NaBH4 (until the mixture turned pale yellow) were added to transform dibutyl
ditelluride to the corresponding telluride, which is easily removed by
distillation. After this treatment, the crude product was extracted with ethyl
acetate (3 Â 20.0 mL) and washed with brine (4 Â 15.0 mL). The organic phase
was dried over anhydrous MgSO4, and the solvent was evaporated. After
filtration through Celite using hexane as the eluent, the product was
concentrated under vacuum. Dibutyl telluride was removed by distillation
from the crude product using a Kugelrohr apparatus (80 °C/0.01 mmHg). Flash
column chromatography (using silica gel 230–400 mesh and the appropriate
mobile phase as shown in Table 1) of the residue furnished the telluroketene
acetals as a yellow oil.
1,1-Dibromo-1-hexene 1a. Yield (72%). IR (cmÀ1) 2958, 2929, 1623, 1465, 808.
1H NMR (300 MHz) (d in CDCl3) 0.91 (t, J = 7.5 Hz, 3H), 1.2–1.7 (m, 4H), 2.12 (q,
J = 7.2 Hz, 2H), 6.42 (t, J = 7.5 Hz, 1H); 13C NMR (75 MHz) 13.8, 22.2, 29.9, 32.6,
88.5, 138.9. HMRS Calcd for C6H10Br2 (M+): 239.9150 Found: 239.9143.
1,1-Dibromo-1-octene 1b. Yield (75%). IR (cmÀ1) 2928, 2856, 1623, 1465, 779.
1H NMR (300 MHz) (d in CDCl3) 0.90 (t, J = 7.5 Hz, 3H), 1.3-1.6 (m, 8H), 2.10 (q,
J = 7.5 Hz, 2H), 6.40 (t, J = 7.5 Hz, 1H); 13C NMR (75 MHz) 14.1, 22.5, 27.8, 28.2,
31.6, 33.0, 88.5, 138.9. HMRS Calcd for C8H14Br2 (M+): 267.9465. Found:
267.9453.
20. Typical procedure for the preparation of 1,1-diiodo-1-alkenes
The reaction mixture containing the 1,1-bismetallic
5 intermediate was
performed as described in the Ref19, and cooled to 0 °C. Then, iodine (0.63 g;
2.5 mmol) dissolved in THF (5.0 mL) was transferred via syringe and the
resulting dark-red solution was stirred for the time needed as indicated in
Table 2. The resulting solution was transferred to an Erlenmeyer flask and a
solution of sodium thiosulfate (5 g/100 mL) was added under stirring until the
solution turned pale yellow. The mixture was diluted with ethyl acetate
(50.0 mL) and the organic phase was washed with brine (4 Â 20.0 mL) and
dried over anhydrous magnesium sulfate. After filtration, the solvent was
removed under vacuum by rotary evaporation and the crude products were
purified by flash chromatography (using silica gel 230–400 mesh and the
appropriate mobile phase as shown in Table 1), furnishing the 1,1-diiodo-1-
alkenes as a yellow oil.
1,1-Bis(butyltelluro)-1-hexene 3a. Yield (70%). GC/MS m/z 456 (12.15), 454
(20.24), 452 (23.00), 315 (40.47), 313 (42.45), 258 (22.38), 169 (19.63), 81
(100.00), 57(61.38). 1H NMR (300 MHz) (d in CDCl3) 0.93 (t, J = 7.0 Hz, 9H), 1.3–
1.5 (m, 6H), 1.7–1.9 (m, 4H), 2.26 (q, J = 7.0 Hz, 2H), 2.79 (t, J = 7.0 Hz, 1H), 6.72
(t, H = 7.0 Hz, 1H); 13C NMR (75 MHz) 14.2, 15.8, 23.2, 25.7, 26.2, 29.0, 32.3,
34.2, 39.9, 49.2, 126.5, 155.6. Anal. Calcd for C14H28Te2: C 35.29, H 5.93. Found:
C 35.41, H 5.77.
1,1-Bis(butyltelluro)-1-octene 3b. Yield (73%). GC/MS m/z 482 (3.00), 480 (3.19),
406 (2.04), 315 (2.30), 313 (2.99), 109 (39.37), 57 (100.00). 1H NMR (300 MHz)
(d in CDCl3) 0.8–1.0 (m, 9H), 1.2–1.5 (m, 12H), 1.78 (quint, J = 7.2 Hz, 2H), 1.82
(quint, J = 7.2 Hz, 2H), 2.24 (q, J = 7.2 Hz, 3H), 2.78 (t, J = 7.2 Hz, 4H), 6.71 (t,
J = 7.2 Hz, 1H); 13C NMR (75 MHz) 11.8, 13.4,13.5, 13.7, 14.1, 22.6,25.0, 25.2,
28.8, 31.7, 33.4, 33.9, 34.2, 39.4, 102.4, 145.6. Anal. Calcd for C16H32Te2: C
40.07, H 6.72. Found: C 40.45, H 6.70.
1,1-Diiodo-1-hexene 2a. Yield (76%). IR (cmÀ1) 2955, 2925, 2856, 1589, 1463,
715. 1H NMR (300 MHz) (d in CDCl3) 0.92 (t, J = 7.5 Hz, 3H), 1.38 (sext.,
J = 7.5 Hz, 2H), 1.43 (quint, J = 7.5 Hz, 2H), 1.92 (quart, J = 7.5 Hz, 2H), 7.01 (t,
J = 7.5 Hz, 1H); 13C NMR (75 MHZ) 11.5, 13.9, 22.1, 29.5, 39.3, 154.1. HRMS.
Calc for C6H10I2 (M+) 335.8875. Found 335.8872.
22. (a) Engman, L.; Cava, M. Synth. Commun. 1982, 12, 163; (b) de Araujo, M. A.;
Raminelli, C.; Comasseto, J. V. J. Braz. Chem. Soc. 2004, 15, 358.