to Cu(II) was notable and modification of 3n to make it
water-soluble would be worthwhile.
In summary, we have discovered a novel intermolecular
condensation reaction of 1,3,5-triarylenynols catalyzed by gold
as Lewis acid, which involved a dimerization–fragmentation
process. This reaction could be developed to give a straight-
forward method for the effective synthesis of a new kind of
structurally unique molecules, which have the highly conjugated
dienyne aromatic system. Preliminary experiments showed that
the tandem reaction product 3n can be used as a fluorimetric
probe for mercury. Further study of this new kind of potentially
useful functional molecules in materials chemistry is ongoing in
our group.
Scheme 5 Mechanism of Au(I)-catalyzed coupling of enynols.
Notes and references
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Fig. 1 Fluorescence emission spectra of 3n in the presence of different
metal ions Li+, Na+, K+, Ca2+, Mg2+, Al3+, Cr3+, Mn2+, Co2+
,
Ni2+, Cu2+, Zn2+, Pd2+, Cd2+, Ag+ and Hg2+ (as their ClO4À salts)
in CHCl3. lex = 335 nm, [3n] = 1 Â 10À5 M, [Mn+] = 5 Â 10À4 M.
with the elimination of R1CHO and H2O as well as the release
of AuCl for the next catalytic cycle.10,11 Notably, the stability
of the carbocations in 5 and 6 of this proposed pathway could
be used to rationalize the high efficiency of the condensation
reaction when employing substrates 1 with electron-rich
substituents at the C-1, C-3 and C-5 positions.
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11 The formation of PhCHO was further confirmed by GC-MS
analysis of the crude reaction mixture in the model coupling
reaction of 1a (entry 1 of Table 1).
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As is well known conjugated molecules have been widely
used in the field of organic materials chemistry due to their
interesting optical, electrical, photoelectric and magnetic
properties.12 Moreover, small molecule ligands with conju-
gated systems are attracting strong interest in the detection of
chemical species because of their selective optical sensing.13 In
connection with the highly conjugated molecules obtained by
our condensation reaction and tandem reaction, it is assumed
that these products may be useful in materials chemistry and a
preliminary experiment taking compound 3n as organic
molecular probe (OMP) has been done. As illustrated in
Fig. 1, introduction of 50 equiv. of Hg(II) to a solution of 3n
in CHCl3 resulted in an almost 96% decrease in emission at
388 nm at room temperature. Moreover, less than 5% fluores-
cence change occurred following addition of Li(I), Na(I), K(I),
Ca(II), Mg(II), Al(III), Cr(III), Mn(II), Co(II), Ni(II), Cu(II),
Zn(II), Pd(II), Cd(II) and Ag(I). These experimental results
indicated that the easily synthesized compound 3n can be used
as a ‘‘turn-off’’ fluorimetric molecular probe with high selec-
tivity toward mercury ion, which has deleterious effects on
environment and human health.14 The insensitivity of 3n
14 For a recent review about small-molecular mercury sensors, see:
E. M. Nolan and S. J. Lippard, Chem. Rev., 2008, 108, 3443.
ꢀc
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2708 | Chem. Commun., 2009, 2706–2708