5 research outputs found
One-Pot Synthesis of Functionalized Benzo[<i>b</i>]thiophenes and Their Hetero-Fused Analogues via Intramolecular Copper-Catalyzed S‑Arylation of In Situ Generated Enethiolates
An
efficient one-pot synthesis of highly functionalized multisubstituted
benzoÂ[<i>b</i>]Âthiophenes and their hetero-fused analogues,
such as thienoÂ[2,3-<i>b</i>]Âthiophenes, indoloÂ[2,3-<i>b</i>]Âthiophenes, and pyrazoloÂ[3,2-<i>c</i>]Âthiophenes,
has been reported. The overall strategy involves sequential base-mediated
condensation of 2-bromohetÂ(aryl)Âacetonitrile precursors with (het)Âaryl/alkyl
dithioesters or other thiocarbonyl species such as dimethyl trithiocarbonate,
<i>S</i>-methyl xanthates, methyl <i>N</i>-imidazolyl
dithioate, <i>N</i>-alkyl dithiocarbamate, and phenyl isothiocyanate,
followed by intramolecular copper-catalyzed arylthiolation of in situ
generated enethiolates, furnishing a broad range of 2-functionalized
3-cyanobenzoÂ[<i>b</i>]- and/hetero-fused thiophenes in high
yields
Sequential One-Pot Synthesis of Tri- and Tetrasubstituted Thiophenes and Fluorescent Push–Pull Thiophene Acrylates Involving (Het)aryl Dithioesters as Thiocarbonyl Precursors
An efficient, one-pot three component
synthesis of highly functionalized
tri- and tetrasubstituted thiophenes has been reported involving (het)Âaryl
dithioesters as thiocarbonyl precursors. Thus, sequential base mediated
condensation of readily available (het)Âaryl active methylene ketones
with (het)Âaryl dithioesters followed by <i>S</i>-alkylation
of the resulting enethiolate salts with activated halomethylene compounds
and concurrent intramolecular aldol-type condensation of <i>S</i>-alkylated compounds affords substituted thiophenes in excellent
yields. The methodology has also been extended for the synthesis of
highly fluorescent push–pull substituted thiophene-5-acrylates
by using bromocrotonate as the activated methylene alkylating agent
Synthesis of 2‑Phenyl-4,5-Substituted Oxazoles by Copper-Catalyzed Intramolecular Cyclization of Functionalized Enamides
An efficient two-step synthesis of 2-phenyl-4,5-substituted
oxazoles
involving intramolecular copper-catalyzed cyclization of highly functionalized
novel β-(methylthio)Âenamides as the key step has been reported.
These enamides are obtained by nucleophilic ring-opening of newly
synthesized 4-[(methylthio)ÂheteroÂ(aryl)Âmethylene]-2-phenyl-5-oxazolone
precursors by alkoxides, amines, amino acid esters and aryl/alkyl
Grignard reagents, thus leading to the introduction of an ester, N-substituted
carboxamide or acyl functionalities at 4-position of the product oxazoles.
Synthesis of two naturally occurring 2,5-diaryloxazoles, i.e., texamine
and uguenenazole, via two-step hydrolysis–decarboxylation of
the corresponding 2,5-diaryloxazole-4-carboxylates has also been described.
Similarly, three of the serine-derived oxazole-4-carboxamides were
elaborated to novel trisubstituted 4,2′-bisoxazoles through
DAST/DBU-mediated cyclodehydration–dehydrohalogenation sequence.
The present protocol is complementary and an improvement to our previously
reported silver carbonate-induced cyclization of β-bisÂ(methylthio)Âenamides
to 2-phenyl-5-(methylthio)-4-substituted oxazoles
Synthesis of N‑Functionalized/NH-Multisubstituted Indoles, Thienopyrroles, Pyrroloindoles, and Pyrazolopyrroles via Sequential One-Pot Base-Mediated and Copper-Catalyzed Inter- and Intramolecular Amination of 2‑[2-Bromo(het)aryl]-3-(het)aryl-3-(methylthio)acrylonitriles
A novel,
efficient route to substituted 1-<i>N</i>-(het)Âaryl/NH-2-(het)Âaryl-3-cyanoindoles
and related pyrrolo-fused heterocycles such as thienopyrroles, pyrroloindoles,
and pyrazolopyrroles has been reported. The overall protocol involves
sequential cycloamination of readily available 2-[2-bromoÂ(het)Âaryl]-3-(het)Âaryl-3-(methylthio)Âacrylonitrile
precursors with primary amines or amides via two key C–N bond-forming
processes, one base-mediated intermolecular and the other Cu-catalyzed
intramolecular arylamination leading to N(1)–C(2) and N(1)–CÂ(7a)
bond formation, respectively, in a two-step one-pot procedure
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-bisÂ(het)Âarylpyrazoles with complementary regioselectivity
starting from active methylene ketones have been reported. In the
first protocol, the newly synthesized 1,3-bisÂ(het)Âaryl-monothio-1,3-diketone
precursors (prepared by condensation of active methylene ketones with
hetÂ(aryl) dithioesters in the presence of sodium hydride) were reacted
with arylhydrazines in refluxing ethanol under neutral conditions,
furnishing 1-aryl-3,5-bisÂ(het)Âarylpyrazoles <b>7</b>, in which
the hetÂ(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-bisÂ(het)Âaryl-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-bisÂ(het)Âarylpyrazoles <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-bisÂ(het)Âaryl-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