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Synthetic Applications of 3,4-Bis(trimethylsilyl)thiophene: Unsymmetrically 3,4-Disubstituted Thiophenes and 3,4-Didehydrothiophene†,‡
journal contribution
posted on 1997-04-04, 00:00 authored by Xin-Shan Ye, Henry N. C. Wong3,4-Bis(trimethylsilyl)thiophene (1a) was
synthesized by three routes: (a) 1,3-dipolar
cycloaddition;
(b) modification of 3,4-dibromothiophene; and (c) intermolecular
thiazole−alkyne Diels−Alder
reaction. 3,4-Bis(trimethylsilyl)thiophene
(1a) can function as a versatile building block for
the
construction of unsymmetrically 3,4-disubstituted thiophenes utilizing
its stepwise regiospecific
mono-ipso-substitution followed by palladium-catalyzed
cross-coupling reactions. In this manner,
thiophenes 15, 16,
17a−j, 19a,b,
20, 22a−c,
23a,b, 24a−d,
25a−c, and
27a−j were prepared.
The thiophene-3,4-diyl dimer 28 and thiophene-3,4-diyl
tetramer 29 were also realized by palladium-catalyzed self-coupling reaction of organoboroxines. The
stannylthiophene 31, formed by conversion
of the C−Si bond to a C−Sn bond via boroxine
26c underwent both carbonylative coupling and
lithiation followed by quenching with electrophiles to afford
unsymmetrically 3,4-disubstituted
thiophenes 33 and 36a−c
as well. Moreover, 3,4-bis(trimethylsilyl)thiophene
(1a) can be used as
the starting material for the generation of the highly strained cyclic
cumulene 3,4-didehydrothiophene (2), whose existence was substantiated by its
trapping reaction with several alkenes.