2 research outputs found
Recyclable, Graphite-Catalyzed, Four-Component Synthesis of Functionalized Pyrroles
<div><p></p><p>A facile, convenient, and multicomponent coupling strategy for the synthesis of highly functionalized pyrroles is developed using graphite as a catalyst, but devoid of moisture-sensitive metal catalysts and corrosive acidic reagents. This method involves four-component coupling reactions of ethyl acetoacetate compound or diethyl acetylene dicarboxylate, amines, aromatic aldehydes, and nitromethane without an inert atmosphere. This approach provides easy access to highly substituted pyrroles in good yields via one-pot tandem reaction. The method is very simple, straightforward, and environmentally friendly compared to the existing methods.</p>
<p>[Supplementary materials are available for this article. Go to the publisher's online edition of <i>Synthetic Communications</i>® for the following free supplemental resource(s): Full experimental and spectral details.]</p>
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Cyclocondensation of Arylhydrazines with 1,3-Bis(het)arylmonothio-1,3-diketones and 1,3-Bis(het)aryl-3-(methylthio)-2-propenones: Synthesis of 1‑Aryl-3,5-bis(het)arylpyrazoles with Complementary Regioselectivity
Two
efficient highly regioselective routes for the synthesis of unsymmetrically
substituted 1-aryl-3,5-bis(het)arylpyrazoles with complementary regioselectivity
starting from active methylene ketones have been reported. In the
first protocol, the newly synthesized 1,3-bis(het)aryl-monothio-1,3-diketone
precursors (prepared by condensation of active methylene ketones with
het(aryl) dithioesters in the presence of sodium hydride) were reacted
with arylhydrazines in refluxing ethanol under neutral conditions,
furnishing 1-aryl-3,5-bis(het)arylpyrazoles <b>7</b>, in which
the het(aryl) moiety attached to the thiocarbonyl group of monothio-1,3-diketones
is installed at the 3-position. In the second method, the corresponding
3-(methylthio)-1,3-bis(het)aryl-2-propenones (prepared in situ by
base-induced alkylation of 1,3-monothiodiketones) were condensed with
arylhydrazines in the presence of potassium <i>tert</i>-butoxide
in refluxing <i>tert</i>-butyl alcohol, yielding 1-aryl-3,5-bis(het)arylpyrazoles <b>9</b> with complementary regioselectivity (method A). The efficiency
of this protocol was further improved by developing a one-pot, three-component
procedure for the synthesis of pyrazoles <b>9</b>, directly
from active methylene ketones, by reacting in situ generated 3-(methylthio)-1,3-bis(het)aryl-2-propenones
with arylhydrazines in the presence of sodium hydride (instead of
potassium <i>tert-</i>butoxide as base). The structures
and regiochemistry of newly synthesized pyrazoles were confirmed from
their spectral and analytical data along with X-ray crystallographic
data of three pairs of regioisomers