L. J. Charbonnie`re et al. / Tetrahedron Letters 42 (2001) 659–662
661
Scheme 2. (i) (a) NaH, THF, rt, 1 h; (b) 7 (1.3 equiv.), 80°C, 12 h (84%); (ii) [Pd(PPh3)2Cl2] (0.05 equiv. per Br atom), EtOH,
Et3N, CO (1 atm), 80°C, 12 h (39% for 11 and 33% for 13); (iii) (a) NaOH, MeOH, H2O, 100°C, 2 h; (b) HCl dil. (89% for 2
and 51% for 3); (iv) 7 (2.2 equiv.), Na2CO3, CH3CN, 80°C, 48 h (87%).
References
bipyridine fragments on pre-organised platforms. Spe-
cifically, as examples of such reactions, compounds 8
and 9 can be used in nucleophilic substitution reactions
with 7 to generate the ether bridged compound 11 and
the podand 13 (Scheme 2). Furthermore, applying the
previously described carboalkoxylation process to these
brominated bipyridines allowed the synthesis of their
ethyl ester derivatives 12 and 14 which, upon basic
treatment and subsequent neutralisation, afforded the
quasi-linear bis-bidentate and podand type tris-triden-
tate ligands 29 and 3,10 respectively. Interestingly, in the
case of the tertiary amine 14, the ester functions are
easily hydrolysed to their corresponding acid, explain-
ing the relative low yield obtained for the preparation
of 14. Applying the saponification process directly on
a crude sample of 14 obtained by evaporation of
the solvents after the carboalkoxylation reaction allow
us to isolate the tripod 3 in a far better yield
(90%).
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8. 5%-Methyl-2,2%-bipyridine-6-carboxylic acid (1): mp=250–
251°C. 1H NMR (DMSO-d6): l 2.65 (s, 3H), 8.16–8.30
(m, 2H), 8.49 (dd, 1H, 3J=7.5 Hz, 4J=1.5 Hz), 8.56–8.77
(m, 3H). 13C NMR (DMSO-d6): l 18.9, 125.4, 126.8,
128.9, 141.4, 142.2, 143.2, 145.8, 147.8, 149.0, 149.7,
167.8. IR (KBr pellets, cm−1): 1744 (wCO), 1551, 1465
(wCꢀC, wCꢀN). Anal. calcd for C12H10N2O2·0.1H2O: C,
66.72; H, 4.76; N, 12.97. Found: C, 66.82; H, 4.95; N,
12.63.
In summary, the development of asymmetrically disub-
stituted bipyridines such as 7, 8 and 9 opens the way to
a potentially large family of tridentate ligands, among
which 2 and 3 are archetypal members. Our interest is
currently directed toward the chemical and photophysi-
cal behaviours of their lanthanide complexes, as well as
to the anchoring of the 2,2%-bipyridine-6-carboxylic acid
fragment on extended pre-organised architectures. It is
acknowledged that anionic derivatives (e.g. diethylene-
triaminetetraacetic)11 strongly stabilise trivalent lan-
thanides salts and also that a,a%-bipyridine units effec-
tively act as molecular transformers.12 The ligands
described here combined both skills within the same
9. Bis-[(6-carboxy-2,2%-bipyridine-5-yl)methyl]ether (2): mp=
217–218°C. 1H NMR (DMSO-d6): l 4.75 (s, 4H), 8.08
(dd, 2H, 3J=8.5 Hz, 4J=2.0 Hz), 8.15 (t, 2H, 3J=7.5
3
3
Hz), 8.58 (d, 2H, J=8.0 Hz), 8.60 (d, 2H, J=7.0 Hz),
8.61 (d, 2H, 3J=7.0 Hz), 8.75 (s, br, 2H). 13C NMR
(DMSO-d6): l 69.0, 121.3, 123.8, 125.1, 135.0, 137.9,
139.0, 147.6, 148.0, 152.8, 153.8, 165.8. Anal. calcd
frame.
.