41 research outputs found
Synthesis of Indeno[1′,2′:4,5]imidazo[1,2‑<i>a</i>]pyridin-11-ones and Chromeno[4′,3′:4,5]imidazo[1,2‑<i>a</i>]pyridin-6-ones through Palladium-Catalyzed Cascade Reactions of 2‑(2-Bromophenyl)imidazo[1,2‑<i>a</i>]pyridines
A novel and efficient synthesis of
11<i>H</i>-indenoÂ[1′,2′:4,5]ÂimidazoÂ[1,2-<i>a</i>]Âpyridin-11-one, a hybrid structure of indenone with imidazoÂ[1,2-<i>a</i>]Âpyridine, from the reaction of 2-(2-bromophenyl)ÂimidazoÂ[1,2-<i>a</i>]Âpyridine with carbon monoxide through palladium-catalyzed
CO insertion and C–H bond activation, has been developed. Intriguingly,
under similar conditions but in the presence of CuÂ(OAc)<sub>2</sub>, the reaction selectively afforded 6<i>H</i>-chromenoÂ[4′,3′:4,5]ÂimidazoÂ[1,2-<i>a</i>]Âpyridin-6-one, a hybrid structure of chromenone with imidazoÂ[1,2-<i>a</i>]Âpyridine, via a more sophisticated cascade process including
acetoxylation, deacetylation, CO insertion, and C–H bond activation
Synthesis of Naphtho[1′,2′:4,5]imidazo[1,2‑<i>a</i>]pyridines and Imidazo[5,1,2-<i>cd</i>]indolizines Through Pd-Catalyzed Cycloaromatization of 2‑Phenylimidazo[1,2‑<i>a</i>]pyridines with Alkynes
In
this paper, palladium-catalyzed oxidative cycloaromatization
of 2-phenylimidazoÂ[1,2-<i>a</i>]Âpyridine (PIP) with internal
alkyne is studied. From this reaction, two classes of fused <i>N</i>-heterocycle, naphthoÂ[1′,2′:4,5]ÂimidazoÂ[1,2-<i>a</i>]Âpyridine (NIP) and imidazoÂ[5,1,2-<i>cd</i>]Âindolizine
(IID), were formed through dehydrogenative coupling featured with
cleavage of the C–H bonds located on different moiety of the
PIP substrates. Moreover, when 5-methyl-2-phenylimidazo [1,2-<i>a</i>]Âpyridine or 2-mesitylimidazoÂ[1,2-<i>a</i>]Âpyridine
was used, either NIP or IID could be obtained as an exclusive product
with good efficiency. Intriguingly, PdÂ(II) showed different action
mode in promoting this reaction compared with RhÂ(III) and led to the
formation of NIP with reversed regio-selectivity for the reaction
of asymmetrical alkyne
Synthesis of Naphthoquinolizinones through Rh(III)-Catalyzed Double C(sp<sup>2</sup>)–H Bond Carbenoid Insertion and Annulation of 2‑Aryl-3-cyanopyridines with α‑Diazo Carbonyl Compounds
An unprecedented
RhÂ(III)-catalyzed double CÂ(sp<sup>2</sup>)–H
bond carbenoid insertion and annulation of 2-aryl-3-cyanopyridines
with α-diazo carbonyl compounds is presented. Through this cascade
reaction, a series of naphthoquinolizinone derivatives with a large
Ď€-system were efficiently prepared. The reactions could selectively
afford naphthoquinolizinones with either an amine or an amide unit
attached on the 11-position depending on the nature of the solvent
and the additive used. Compared with literature methods, this is a
more efficient, convenient, and atom-economic way to provide polycyclic
heteroaromatic compounds through direct π-extension of simple
aromatics via inert C–H bond activation and functionalization
Synthesis of 3‑Cyano‑1<i>H</i>‑indoles and Their 2′-Deoxyribonucleoside Derivatives through One-Pot Cascade Reactions
An
efficient and economical synthetic approach toward 3-cyano-1<i>H</i>-indoles through the reactions of 2-(2-bromophenyl)Âacetonitriles
with aldehydes and aqueous ammonia is presented. Mechanically, this
novel protocol involves a one-pot cascade procedure consisting of
an aldol-type condensation, a copper-catalyzed amination by using
aqueous ammonia as a cheap and safe nitrogen source, and an intramolecular
Michael addition followed by a dehydrogenative aromatization. Interestingly,
the indole products thus obtained were found to be ready substrates
for the preparation of indole 2′-deoxyribonucleosides through
an unprecedented and highly practical glycosylation procedure in which
the required C–N bond formation and toluoyl protecting group
removal were accomplished efficiently in one pot
Metal-Free Synthesis of 2‑Aminobenzothiazoles via Iodine-Catalyzed and Oxygen-Promoted Cascade Reactions of Isothiocyanatobenzenes with Amines
In
this paper, a highly efficient and sustainable synthesis of
2-aminobenzothiazoles through the cascade reactions of isothiocyanatobenzenes
with primary or secondary amines by using iodine as a catalyst and
oxygen as an oxidant is presented. Mechanistically, the formation
of the title compounds involves the in situ formation of the required
benzothiourea intermediate followed by its intramolecular cross dehydrogenative
coupling of a CÂ(sp<sup>2</sup>)–H bond and a S–H bond.
To our knowledge, this should be the first example in which 2-aminobenzothiazoles
are efficiently prepared from simple and cheap isothiocyanates and
amines under metal-free conditions by using iodine as a catalyst and
molecular oxygen as an oxidant with water as the byproduct. Compared
with literature protocols, this method eliminates the use of <i>ortho</i>-halo-substituted precursors, expensive transition-metal
catalysts, and hazardous oxidants
One-Pot Cascade Reactions Leading to Pyrido[2′,1′:2,3]imidazo[4,5‑<i>c</i>][1,2,3]triazolo[1,5‑<i>a</i>]quinolines under Bimetallic Relay Catalysis with Air as the Oxidant
In this paper, we report an efficient
one-pot synthesis of 1,2,3-triazole/quinoline-fused
imidazoÂ[1,2-<i>a</i>]Âpyridines starting from 2-(2-bromophenyl)ÂimidazoÂ[1,2-<i>a</i>]Âpyridines, alkynes, and sodium azide. This novel method
involves a one-pot bimetallic relay-catalyzed cascade process combining
azide–alkyne cycloaddition, C–N coupling between 1,2,3-triazole
and aryl bromide, and intramolecular cross dehydrogenative C–C
coupling between 1,2,3-triazole and imidazoÂ[1,2-<i>a</i>]Âpyridine. Notable features of this protocol include simple starting
materials, sustainable oxidants, reduced synthetic steps, and high
efficiency
Synthesis of Ketones through Microwave Irradiation Promoted Metal-Free Alkylation of Aldehydes by Activation of C(sp<sup>3</sup>)–H Bond
In
this paper, a novel methodology for the synthesis of ketones
via microwave irradiation promoted direct alkylation of aldehydes
by activation of the inert CÂ(sp<sup>3</sup>)–H bond has been
developed. Notably, the reactions were accomplished under metal-free
conditions and used commercially available aldehydes and cycloalkanes
as substrates without prefunctionalization. By using this novel method,
an alternative synthetic approach toward the key intermediates for
the preparation of the pharmaceutically valuable oxaspiroketone derivatives
was successfully established
Tunable Synthesis of Functionalized Cyclohexa-1,3-dienes and 2‑Aminobenzophenones/Benzoate from the Cascade Reactions of Allenic Ketones/Allenoate with Amines and Enones
A TEMPO-dependent tunable synthesis
of functionalized cyclohexa-1,3-dienes
and 2-aminobenzophenones/benzoate from the one-pot cascade reactions
of allenic ketones/allenoate with amines and enones is presented.
Mechanistically, the construction of the entitled six-membered carbocycles
involves the in situ generation of an enaminone intermediate via the
conjugate addition of allenic ketone with amine followed by its catalyst-
and base-free [3+3] annulation with enone along with the simultaneous
introduction of the valuable amino and carbonyl groups
Synthesis of Functionalized Pyridines via Cu(II)-Catalyzed One-Pot Cascade Reactions of Inactivated Saturated Ketones with Electron-Deficient Enamines
In
this paper, a novel and efficient synthesis of 3-acylpyridines
and pyridine-3-carboxylates through the oxidative one-pot sequential
reactions of inactivated saturated ketones with electron-deficient
enamines is presented. Mechanistically, the formation of the title
compounds involves the in situ formation of an enone intermediate
through an oxidative dehydrogenation of the saturated ketone substrate,
followed by its [3+3] annulation with β-enaminone or β-enaminoester
via a cascade process, including Michael addition, aldol type condensation,
and oxidative aromatization
Tunable Synthesis of Functionalized Cyclohexa-1,3-dienes and 2‑Aminobenzophenones/Benzoate from the Cascade Reactions of Allenic Ketones/Allenoate with Amines and Enones
A TEMPO-dependent tunable synthesis
of functionalized cyclohexa-1,3-dienes
and 2-aminobenzophenones/benzoate from the one-pot cascade reactions
of allenic ketones/allenoate with amines and enones is presented.
Mechanistically, the construction of the entitled six-membered carbocycles
involves the in situ generation of an enaminone intermediate via the
conjugate addition of allenic ketone with amine followed by its catalyst-
and base-free [3+3] annulation with enone along with the simultaneous
introduction of the valuable amino and carbonyl groups