TETRAHEDRON
LETTERS
Tetrahedron Letters 44 (2003) 5883–5887 Pergamon
6-(Arylvinylene)-3-pyridinylboronic esters. Part 2: Versatile
building blocks for push–pull nonlinear optical chromophores
Nicolas Leclerc, Laurent Galmiche and Andre ´-Jean Attias*
Laboratoire de Chimie des Polyme `res (CNRS, UMR 7610), Universite ´P. et M. Curie, 4 place Jussieu, F -75252 Paris Cedex 05,
France
Received 2 June 2003; revised 3 June 2003; accepted 3 June 2003
Abstract—This paper describes a general approach for the synthesis of push–pull 6,6-disubstituted-3,3-bipyridine chromophores.
As examples, 6-(4-ethanol-2-thienylvinylene)-5-methyl-3-bromopyridine, 6-(4-hydroxy-phenylvinylene)-5-methyl-3-bromopyridine,
and the corresponding 3-pyridinylboronic esters have been prepared as building blocks end-capped with electron donor groups
(D). 6-(4-Cyano-phenylvinylene)-5-methyl-3-bromopyridine, and 6-(4-cyano-phenylvinylene)-3-bromopyridine have been synthe-
sized as building blocks end-capped with electron acceptor groups (A). {AxD} type cross-couplings via Suzuki reaction gave the
push–pull chromophores (I) and (II) in high yields and multigram scales.
© 2003 Elsevier Ltd. All rights reserved.
Organic second-order nonlinear optical (NLO) poly-
meric materials have been intensively studied for many
years.
1,2
In these systems NLO noncentrosymmetric
chromophores are either covalently attached to the
backbone as side-groups, or are made part of the
polymer backbone itself. A typical NLO chromophore
consists of an electron-accepting group and an electron-
donating group connected by a -conjugated bridge
(push–pull structure). The structure–property relation-
ships of the molecular NLO property ( ) of these
one-dimensional dipolar chromophores have been theo-
retically and experimentally established.
3–5
In previous papers,
6–9
we have described a novel class
of conjugated molecules.
These compounds are either symmetric molecules (a) or
asymmetric push–pull molecules (b). They were pre-
pared by a one-step ((a) series) or a two-steps ((b)
series) Knoevenagel type condensation, under acidic
conditions, of 6,6-dimethyl-3,3-bipyridine derivatives
with corresponding aromatic aldehydes: thienyl ring as
donor group, or benzene ring para -substituted with
electron-donor (D) or electron-acceptor (A) groups. By
lateral substitutions of the -conjugated bridge and by
varying the nature of the acceptor/donor pair, we were
able to tune the mesogenic,
6,7
electrochemical,
6,7
photo-
luminescent,
6,7
and second- as well as third-order NLO
properties of the chromophores.
7–9
However, despite
the above-mentioned attractive features, the previous
two-step synthetic route, in the case of the nonsymmet-
ric chromophores, restricts the yield because of separa-
tion and purification difficulties. Consequently, it was
difficult to access many combinations of donor/accep-
tor pairs. This is the reason why it was necessary to
define a new more efficient synthetic route to obtain
such unsymmetrical conjugated chromophores. More-
over, we were interested in synthesizing chromophores
with reactive functionalities (e.g. hydroxyl groups) at
one end to covalently couple the chromophores to a
polymer backbone.
Concerning substituted 3,3-bipyridines, few general
routes have been described whatever the symmetry of
the molecule: besides the synthesis of symmetrical 6,6-
disubstituted-3,3-bipyridines by a Ni(0)-coupling of 3-
halopyridines,
10
only, to our knowledge, the synthesis
of 3-heteroarylpyridines,
11
and unsubstituted symmetric
3,3-bipyridines,
12
by Pd(0)-catalyzed cross-coupling of
3-stannylpyridines or 3-pyridylboranes with heteroaryl
halides or 3-bromopyridine respectively, have been
reported in the literature.
* Corresponding author. Tel.: +33-1-44-27-53-02; fax: +33-1-44-27-
70-89; e-mail: attias@ccr.jussieu.fr
0040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01427-8