Chemistry Reference
In-Depth Information
R
R'
R
R'
X
Y
X
Y
Me
3
Al
SnBu
2
+
MeO
2
C
X
Y
X
Y
R
R'
R
R'
Figure 2.7. Scheme of the Me
3
Al-promoted coupling reaction of organotin com-
pounds with esters (strategy S6). X,Y=S,SeandR,R
stand for substituents.
R
R
S
S
+
+ ...
2
R
R
2
CS
2
S
S
R
R
Figure 2.8. Scheme of the preparation of TTF-derivatives from C
2
R
2
and CS
2
(strategy S7).
Strategies S4 (Wittig-Horner type) and S5 (Wittig type) enable a higher degree
of selectivity in discriminating the symmetric products of the reaction. S4 can be
considered as entirely selective while S5 is partially selective. In Fig. 2.5 only the
initial and final products are shown. However, the reactions aremuchmore involved.
Note that two possible paths exist for each strategy. S4 has been employed in the
synthesis of a great number of functionalized TTF derivatives and of TTF partially
substituted with selenium atoms.
An additional entirely selective condensation synthesis for asymmetric TTF
molecules is based on strategy S6, which consists in the reaction of an organ-
otin dichalcogenolate with an ester in the presence of a Lewis acid such as Me
3
Al
(Yamada
et al.
, 2004). A scheme of the reaction is given in Fig. 2.7. The method
applies to the preparation of varied asymmetric TTFs and can also be extended to
the synthesis of selenium-containing analogues.
It is possible to add carbon disulfide to acetylenes having at least one electron-
attracting substituent R (in particular with R
CF
3
) to give the product tetra-R-
TTF (see Fig. 2.8) but in addition other compounds are obtained. This is our strategy
S7. Their relative yields depend on the experimental conditions. However, in the
presence of trifluoroacetic acid, the TTF derivative shown in the figure dominates.
On the other hand, benzyne (C
6
H
6
with a triple bond) is known to cycloadd rapidly
to CS
2
giving DBTTF.
Functionalization of TTF can also be achieved by means of electrophilic sub-
stitution of metalated TTF. This strategy (S8) is based on the substitution of the
hydrogen atoms of TTF by lithium in a metalation reaction with
n
-BuLi or LDA
(see previous example of thiophene). Tetrathiafulvalenyllithium is highly reactive
even at low temperature, and it reacts immediately with various electrophiles to
=
