Modulating the Reactivity
of Functionalized <i>N</i>,<i>S</i>-Ketene Acetal
in MCR: Selective Synthesis
of Tetrahydropyridines and Thiochromeno[2,3-<i>b</i>]pyridines
via DABCO-Catalyzed Tandem Annulation
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Abstract
An efficient and straightforward three-component synthetic
protocol
was developed to synthesize 1,2,3,4-tetrahydropyridine derivatives
or thiochromeno[2,3-<i>b</i>]pyridine derivatives from β-aroylthioacetanilides
or β-(2-haloaroyl)thioacetanilides, aldehydes, and aroyl acetonitriles
via DABCO-catalyzed tandem [3 + 2 + 1] annulation and S<sub>N</sub>Ar reaction. This synthetic approach has the prominent features of
high chemo-, stereo- (or enantio-), and unusual regioselectivity.
In the domino processes, at least seven reactive sites were involved,
and up to three covalent bonds and one functionalized pyridine ring
were generated. This facile and efficient reaction is a quite general
for the preparation of tetrahydropyridine derivatives or thiochromeno[2,3-<i>b</i>]pyridine derivatives