Paper
Dalton Transactions
may continue with attack on a second alkyne monomer. A
slightly slower 1,1-alkenylboration reaction takes place con-
secutively to give the persubstituted butadiene derivatives 4.
This is in contrast to the usual behaviour of alkyne 1,1-carbo-
boration products featuring the more bulky –B(C6F5)2 substitu-
ent which proved unreactive toward further 1,1-alkenylboration
under these typical conditions.6 We assume that the unusual
1,1-alkenylboration behaviour of the compounds 3 is due to
both steric [the B(X)C6F5 group is less bulky than B(C6F5)2] and
electronic reasons [the B(X)C6F5 groups are sufficiently strong
Lewis acids]. However, a limiting situation seems to be
reached with the formation of the dienyl products 4. Although
these also constitute alkenylborane functionalities, we have
not observed any further 1,1-alkenylboration reactivities with
these products. We assume that steric hindrance at the con-
gested central position is responsible for this lack of further
carboboration activity. Nevertheless, some typical borane reac-
tions could be achieved, such as the oxidative cleavage
described in the last section of our report.
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Commun., 1978, 402; (b) C. Bihlmayer, S. Kerschl and
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The here reported series of 1,1-carboboration reactions has
made highly substituted, highly functionalized conjugated ole-
finic systems available in a very simple way, some even featur-
ing further extended π-systems. We shall see how this easily
performed coupling/rearrangement sequence will be devel-
oped into methods for the synthesis of interesting advanced
target molecules.
10 For examples of metal catalyzed 1,1-carboboration reac-
tions see: (a) M. Suginome, A. Yamamoto, T. Sasaki and
M. Murakami, Organometallics, 2006, 25, 2911;
(b) T. Ohmura and M. Suginome, Bull. Chem. Soc. Jpn.,
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Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
Financial support from the DAAD (postdoctoral stipend to
K. Š.) is gratefully acknowledged.
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Dalton Trans.
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