12 research outputs found
Meta-Selective C<sub>Ar</sub>–H Nitration of Arenes through a Ru<sub>3</sub>(CO)<sub>12</sub>-Catalyzed Ortho-Metalation Strategy
The
first example of transition metal-catalyzed meta-selective C<sub>Ar</sub>–H nitration of arenes is described. With the use of Ru<sub>3</sub>(CO)<sub>12</sub> as the catalyst and CuÂ(NO<sub>3</sub>)<sub>2</sub>·3H<sub>2</sub>O as the nitro source, a wide spectrum
of arenes bearing diversified <i>N</i>-heterocycles or oximido
as the directing groups were nitrated with meta-selectivity exclusively.
Mechanism studies have demonstrated the formation of a new 18e-octahedral
ruthenium species as a key <i>ortho</i>-C<sub>Ar</sub>–H
metalated intermediate, which may be responsible for the subsequent
meta-selective electrophilic aromatic substitution (S<sub>E</sub>Ar).
Moreover, this approach provides a fast-track strategy for atom/step
economical synthesis of many useful pharmaceutical molecules
Meta-Selective C<sub>Ar</sub>–H Nitration of Arenes through a Ru<sub>3</sub>(CO)<sub>12</sub>-Catalyzed Ortho-Metalation Strategy
The
first example of transition metal-catalyzed meta-selective C<sub>Ar</sub>–H nitration of arenes is described. With the use of Ru<sub>3</sub>(CO)<sub>12</sub> as the catalyst and CuÂ(NO<sub>3</sub>)<sub>2</sub>·3H<sub>2</sub>O as the nitro source, a wide spectrum
of arenes bearing diversified <i>N</i>-heterocycles or oximido
as the directing groups were nitrated with meta-selectivity exclusively.
Mechanism studies have demonstrated the formation of a new 18e-octahedral
ruthenium species as a key <i>ortho</i>-C<sub>Ar</sub>–H
metalated intermediate, which may be responsible for the subsequent
meta-selective electrophilic aromatic substitution (S<sub>E</sub>Ar).
Moreover, this approach provides a fast-track strategy for atom/step
economical synthesis of many useful pharmaceutical molecules
Cobalt-Catalyzed Carbonylation of C(sp<sup>2</sup>)–H Bonds with Azodicarboxylate as the Carbonyl Source
A novel and efficient
approach for the CÂ(sp<sup>2</sup>)–H
bond carbonylation of benzamides has been developed using stable and
inexpensive CoÂ(OAc)<sub>2</sub>·4H<sub>2</sub>O as the catalyst
and the commercially available and easily handling azodicarboxylates
as the nontoxic carbonyl source. A broad range of substrates bearing
diverse functional groups were tolerated. This is the first example
where cobalt-catalyzed CÂ(sp<sup>2</sup>)–H bond carbonylation
occurs with azodicarboxylate as the carbonyl source
Ru(II)-Catalyzed Direct C(sp<sup>2</sup>)–H Activation/Selenylation of Arenes with Selenyl Chlorides
A new
ruthenium catalytic system was developed for the construction
of a CÂ(sp<sup>2</sup>)–Se bond with the assistance of directing
groups. This protocol features mild reaction conditions, wider substrate
scope, and convenient late-stage selenylation of bioactive molecules
Highly Stereoselective Assembly of Polycyclic Molecules from 1,6-Enynes Triggered by Rhodium(III)-Catalyzed C–H Activation
An
RhÂ(III)-catalyzed C–H activation of pyrazolones with
1,6-enynes was investigated. The regioselectivity of the C–H
activation/alkyne insertion is readily solved by using symmetric enyne
coupling partners, and a C–H activation-triggered cascade reaction
is realized, which involves alkyne insertion, tautomerization, and
double cyclization to offer a class of structurally complex polycyclic
architectures. This cascade reaction tolerates a broad substrate scope
in high regioselectivity and stereospecificity and furnishes three
new chemical bonds and four chiral centers in a single operation.
Various derivatizations of the polycyclic scaffolds are conducted,
providing products with ample space for further functional transformations
Difluorination of Furonaphthoquinones
An
unprecedented difluorination reaction was developed based on
the furonaphthoquinone skeleton of natural products tanshinones and
their analogues. By using Selectfluor as the fluorinating source and
H<sub>2</sub>O as the hydroxyl source, a wide range of unique polycyclic
α,α-difluoro β,β-dihydroxyl <i>para</i>-quinone products were achieved with yields up to 90%. The mechanistic
studies revealed that the reaction might undergo tandem multiple electrophilic
and nucleophilic substitutions, as well as cleavages of C–O
and C–C bonds. This approach not only provides a new method
to synthesis of α,α-difluoro ketones, but also affords
a series of unique chemotypes for biological activity screening
Ligand-Promoted Pd(II)-Catalyzed Functionalization of Unactivated C(sp<sup>3</sup>)–H Bond: Regio- and Stereoselective Synthesis of Arylated Rimantadine Derivatives
Stereoselective
functionalization of the adamantyl bridge methylene CÂ(sp<sup>3</sup>)–H bonds is a rather appealing, yet challenging strategy
due to the bulky and unactivated nature. Here we present a palladium-catalyzed
CÂ(sp<sup>3</sup>)–H arylation/hetereoarylation of the antivirus
drug rimantadine with the picolinamide moiety as the bidentate directing
group and a mono-<i>N</i>-protected amino acid (MPAA) as
the ligand. Multisubstituted rimantadine substrates and diverse aryl/heteroaryl
iodides are well tolerated, and a series of optically pure arylated
rimantadine derivatives have been synthesized in high regio- and diastereoselectivity
that provides ample compound space for further pharmaceutical research
Rh(III)-Catalyzed Intermolecular C–H Amination of 1‑Aryl‑1<i>H</i>‑pyrazol-5(4<i>H</i>)‑ones with Alkylamines
An
intermolecular C–H amination of 1-aryl-1<i>H</i>-pyrazol-5Â(4<i>H</i>)-ones was achieved under mild reaction
conditions, using a low catalyst loading and with a broad scope of
aminating reagents. This protocol not only provides the first example
of rhodiumÂ(III)-catalyzed intermolecular aromatic C–H amination
directed by an intrinsic functionality of the substrate/product but
also features aminating an existing drug with either primary or secondary <i>N</i>-benzoate alkylamines as the coupling partners
Rh(III)-Catalyzed Intermolecular C–H Amination of 1‑Aryl‑1<i>H</i>‑pyrazol-5(4<i>H</i>)‑ones with Alkylamines
An
intermolecular C–H amination of 1-aryl-1<i>H</i>-pyrazol-5Â(4<i>H</i>)-ones was achieved under mild reaction
conditions, using a low catalyst loading and with a broad scope of
aminating reagents. This protocol not only provides the first example
of rhodiumÂ(III)-catalyzed intermolecular aromatic C–H amination
directed by an intrinsic functionality of the substrate/product but
also features aminating an existing drug with either primary or secondary <i>N</i>-benzoate alkylamines as the coupling partners
Substituent-Enabled Oxidative Dehydrogenative Cross-Coupling of 1,4-Naphthoquinones with Alkenes
A Rh-catalyzed
oxidative dehydrogenative cross-coupling of 1,4-naphthquinones
with alkenes was achieved by using a substituent-enabled CÂ(sp<sup>2</sup>)–H functionalization (SEF) strategy. The method shows
high functional group tolerance, broad substrate scope, and great
potential for further functional transformations