A simple synthesis of B-2-(1-trimethylsilyl-1-alkyl)-1,3,2-dioxaborinanes. Isolation and selective oxidation to 1-trimethylsilyl-1-alkanols

Article abstract of DOI:10.1016/S0040-4039(03)01750-7

(Z)-1-Trimethylsilyl-1-alkenes easily prepared by the hydroboration of the corresponding 1-trimethylsilyl-1-alkynes followed by protonolysis with acetic acid, readily react with dibromoborane-methyl sulfide complex in dichloromethane for 6 h. The resulting solution is then treated with 1, 3-propane diol in a 1:1 mixture of dichloromethane and n-pentane at 0°C for half an hour to provide the corresponding gem-dimetalloalkanes containing boron and silicon. These alpha-trimethylsilylalkylboronate esters are purified by vacuum distillation in high yields (72-84%) and the structures of these novel intermediates are further confirmed by selective oxidation with alkaline hydrogen peroxide to provide the corresponding alcohols containing trimethylsilyl group.

Full text of DOI:10.1016/S0040-4039(03)01750-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 6833–6835
A simple synthesis of
B-2-(1-trimethylsilyl-1-alkyl)-1,3,2-dioxaborinanes. Isolation and
selective oxidation to 1-trimethylsilyl-1-alkanols
Narayan G. Bhat* and Amanda Garza
Department of Chemistry, University of Texas-Pan American, 1201 West University Drive, Edinburg, TX 78541, USA
Received 15 June 2003; revised 15 July 2003; accepted 15 July 2003
Abstract—(Z)-1-Trimethylsilyl-1-alkenes easily prepared by the hydroboration of the corresponding 1-trimethylsilyl-1-alkynes
followed by protonolysis with acetic acid, readily react with dibromoborane-methyl sulfide complex in dichloromethane for 6 h.
The resulting solution is then treated with 1,3-propane diol in a 1:1 mixture of dichloromethane and n-pentane at 0°C for half
an hour to provide the corresponding gem-dimetalloalkanes containing boron and silicon. These alpha-trimethylsilylalkylboronate
esters are purified by vacuum distillation in high yields (72–84%) and the structures of these novel intermediates are further
confirmed by selective oxidation with alkaline hydrogen peroxide to provide the corresponding alcohols containing trimethylsilyl
group.
© 2003 Elsevier Ltd. All rights reserved.
1. Introduction
trimethylsilane at −78°C for 1 h and allowed the reac-
tion mixture to stir overnight. The resulting
1-trimethylsilyl-1-alkynes were isolated and kept in
refrigerator under nitrogen atmosphere for further use.
They were characterized by 300 MHz NMR spectral
data.
Hydroboration of 1-trimethylsilyl-1-alkynes with
dicyclohexylborane1 is well documented in literature.
The protonolysis of the resulting boron intermediates
with acetic acid2 provided the corresponding (Z)-1-
trimethylsilyl-1-alkenes in high stereochemical purities.
Different gem-dimetallics containing aluminum and zir-
conium,3 zinc and zirconium,4 zinc and magnesium,5
zinc and lithium,5 zinc and boron,6 copper and boron,6
boron and lithium,7 and boron and zirconium.8 Pelter
and co-workers have reported an example of gem-
dimetalloalkane containing boron and silicon.9 Litera-
ture search revealed that no truly general simple
synthetic procedures were available to prepare gem-
dimetalloalkanes containing boron and silicon. Conse-
The hydroboration of 1-trimethylsilyl-1-alkynes with
dicyclohexylborane10 (freshly prepared by mixing cyclo-
hexene with borane–methyl sulfide complex) in tetra-
hydrofuran proceeded cleanly at 0°C, for 3 h followed
by stirring for 1 h at room temperature. The resulting
clear solution was treated with acetic acid and the
stirring continued for 6 h at room temperature.
quently, we undertook
a methodology involving
Table 1. Synthesis of 1-trimethylsilyl-1-alkenes
(Z)-1-trimethysilyl-1-alkenes via the hydroboration-
alcoholysis sequence to achieve the synthesis of gem-
dimetalloalkanes containing boron and silicon. In this
report, we reveal the results of our investigation.
No.
Eq. (1) R=
Yielda
1
2
3
4
5
6
n-C4H9
82
78
86
78
76
79
n-C5H11
n-C6H13
-(CH2)3Cl
-C(CH3)3
-sec-Bu
2. Results and discussion
We reacted terminal alkynes with n-butyllithium at
−78°C for 1 h followed by treatment with chloro-
a All of the reactions were carried out on a 50 mmol scale. The
compounds were purified by chromatography over alumina fol-
lowed by vacuum distillation.
* Corresponding author.
0040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01750-7

6834
N. G. Bhat, A. Garza / Tetrahedron Letters 44 (2003) 6833–6835
(1)
(2)
(3)
Table 2. The synthesis of gem-dimetalloalkanes containing
boron and silicon
No.
Eq. (2) R=
Yielda
1
2
3
4
5
6
n-C4H9
84
82
78
72
74
80
n-C5H11
n-C6H13
-(CH2)3Cl
-C(CH3)3
-sec-Bu
3. Conclusions
In summation, we have developed for the first time a
simple, and efficient conversion of 1-trimethylsilyl-1-
alkynes into the corresponding gem-dimetalloalkanes
containing boron and silicon in high yields. These
gem-dimetalloalkanes were isolated and characterized
using 300 MHz NMR spectral data for the first time.
The carbon skeletons present in these intermediates are
further confirmed by selective oxidation studies with
alkaline hydrogen peroxide to provide the correspond-
ing alcohols containing trimethylsilyl group. We are
presently utilizing these valuable compounds for further
synthetic applications.
a All of the reactions were carried out on a 10 mmol scale. The
compounds were purified by vacuum distillation. The carbon skele-
tons present in these compounds were confirmed by selective oxida-
tion to alcohols containing trimethylsilyl group (Eq. (3)).
The solvents were removed and replaced by n-pentane.
Monoethanolamine11 was added to remove the boron
by-product. Representative (Z)-1-trimethylsilyl-1-alke-
nes (Table 1) were prepared (Eq. (1)) and characterized
by 300 MHz NMR data.
The (Z)-1-trimethylsilyl-1-alkenes thus prepared were
subjected to hydroboration with dibromoborane–
methyl sulfide complex in dichloromethane at room
temperature for 6 h. The resulting solution was reacted
Acknowledgements
with
1,3-propane
diol
in
1:1
mixture
of
We are highly grateful to the Robert A. Welch Founda-
tion of Texas for generous financial support under
grant number B-1387. Ms. Amanda Garza acknowl-
edges a research fellowship from the University of
Texas-Pan American Louis Stokes Alliance for Minor-
ity Participation.
dichloromethane and n-pentane at 0°C for half an
hour. The supernatant solution was removed by dou-
ble-ended needle technique and the solvents were
pumped off and the resulting liquids were purified by
high vacuum distillation. The representative selection of
gem-dimetalloalkanes were prepared (Table 2, Eq. (2))
using the above procedure.
These novel gem-dimetalloalkanes were reacted with
alkaline hydrogen peroxide at room temperature for 3 h
and the resulting alcohols containing trimethylsilyl
group (Eq. (3)) were purified by column chromatogra-
phy over alumina.
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