13 research outputs found
Rh[III]-Catalyzed C–H Amidation Using Aroyloxycarbamates To Give <i>N</i>‑Boc Protected Arylamines
The Rh(III)-catalyzed amidation of C(sp<sup>2</sup>)–H bonds by the use of electron-deficient aroyloxycarbamates as efficient electrophilic amidation partners is reported. The reaction proceeded under mild conditions with broad functional group tolerance, and pyridine and <i>O</i>-methyl hydroxamic acids serve as efficient directing groups, giving access to valuable <i>N</i>-Boc protected arylamines (also Fmoc and Cbz). Preliminary mechanistic experiments are discussed
Manganese(I)-Catalyzed Direct C–H Allylation of Arenes with Allenes
Polysubstituted allyl
groups, for example, the prenyl group, are
valuable synthetic handles and widely encountered in bioactive compounds.
Reported herein is a manganeseÂ(I)-catalyzed direct C–H coupling
with allenes for the efficient assembly of allylated arenes. The protocol
offers an extremely high level of atom-economy and is particularly
suited for the introduction of 1,1-disubstitiuted allyl groups, as
exemplified by the quantitative syntheses of a variety of prenylated
indoles. The practicality of this method was evidenced by a gram-scale
synthesis with a lower catalyst loading of manganeseÂ(I) (2.5 mol %,
95% yield). Experimental mechanistic studies were conducted, and a
possible reaction mechanism was proposed
Mild Rh(III)-Catalyzed C–H Activation and Annulation with Alkyne MIDA Boronates: Short, Efficient Synthesis of Heterocyclic Boronic Acid Derivatives
Taking advantage of RhÂ(III)-catalyzed
C–H activation reactions,
we have developed a mild, short, and efficient method for the synthesis
of bench-stable 3-isoquinolone MIDA boronates. The reaction is practical
and scalable. The product formed has been applied in the Suzuki–Miyaura
reaction with high efficiency. This strategy has also been successfully
expanded to the synthesis of MIDA boronate functionalized heterocycles
such as isoquinoline, pyrrole, and indole
Mild Mn(OAc)<sub>3</sub>‑Mediated Aerobic Oxidative Decarboxylative Coupling of Arylboronic Acids and Arylpropiolic Acids: Direct Access to Diaryl 1,2-Diketones
A simple and efficient
method for the synthesis of diaryl 1,2-diketones
has been developed. The reaction represents the first example of diaryl
1,2-diketones that are synthesized directly from arylboronic acids
and arylpropiolic acids by a radical pathway in moderate to good yields.
This reaction proceeds under mild reaction conditions and with good
tolerance of a variety of functional groups. Preliminary mechanistic
studies were conducted
N–O Bond as External Oxidant in Group 9 Cp*M(III)-Catalyzed Oxidative C–H Coupling Reactions
Group 9 Cp*MÂ(III) (M = Co, Rh, Ir)
complexes have been extensively
investigated as catalysts in a variety of C–H activation reactions.
Typically, late metal-based silver or copper salt was used (while
needed) as oxidant in these catalytic systems. Herein, we report our
discovery of a potentially general type of N–O bond-containing
oxidants, which allowed the mild and efficient syntheses of isocoumarins,
isoquinolines, isoquinolinone, and styrenes via C–H activation
catalyzed by group 9 Cp*MÂ(III) complexes. By using Cp*RhÂ(III)-catalyzed
isocoumarin synthesis as a model reaction, experimental and theoretical
mechanistic studies were conducted. The results concluded that the
RhÂ(III)–RhÂ(I)–RhÂ(III) rather than the RhÂ(III)–RhÂ(V)–RhÂ(III)
pathway is more likely involved in the mechanism, and both the C–H
activation and oxidation of the Cp*RhÂ(I) species were involved in
the turnover-limiting step
Regioselective Synthesis of 5‑Aminooxazoles via Cp*Co(III)-Catalyzed Formal [3 + 2] Cycloaddition of <i>N</i>‑(Pivaloyloxy)amides with Ynamides
A simple
and efficient protocol for the regioselective synthesis
of 5-aminooxazoles is disclosed. The reaction, catalyzed by a cheap
Cp*CoÂ(III) catalyst, starts from easily accessible <i>N</i>-(pivaloyloxy)Âamides and ynamides. Mild reaction conditions, a broad
substrate scope, good functional group tolerance, and good to excellent
yields were observed
Cp*Co(III)-Catalyzed Annulations of 2‑Alkenylphenols with CO: Mild Access to Coumarin Derivatives
Cp*CoÂ(III)-catalyzed annulations
of 2-alkenylphenols with CO for
the synthesis of coumarin derivatives have been developed. The reaction
features mild reaction conditions, broad substrate scope, and good
functional group tolerance. Preliminary mechanistic studies were conducted,
suggesting that C–H activation is the turnover limiting step.
Furthermore, the efficiency of this reaction was demonstrated by the
rapid total synthesis of three natural products herniarin, xanthyletin,
and seselin
Synthesis of Alkylated Monofluoroalkenes via Fe-Catalyzed Defluorinative Cross-Coupling of Donor Alkenes with <i>gem</i>-Difluoroalkenes
A reductive
cross-coupling of <i>gem</i>-difluoroalkenes
with diverse unactivated and heteroatom substituted olefins through
a Fe-catalyzed hydrogen atom transfer (HAT) strategy is reported.
Different from the previous HAT-type olefin cross-coupling reactions,
the presence of a fluorine atom in the molecule results in a stereoselective
β-F cleavage, leading to a CÂ(sp<sup>2</sup>)–CÂ(sp<sup>3</sup>) bond formation. A wide variety of alkylated monofluoroalkenes
were obtained in good efficiency with excellent <i>Z</i> selectivity under air- and water-tolerant reaction conditions. A
similar defluorinative coupling reaction of monofluoroalkenes was
also realized
From Indoles to Carbazoles: Tandem Cp*Rh(III)-Catalyzed C–H Activation/Brønsted Acid-Catalyzed Cyclization Reactions
A tandem Cp*RhÂ(III)-catalyzed C–H
activation/Brønsted
acid-catalyzed intramolecular cyclization allows a facile synthesis
of carbazoles from readily available indoles. The reaction proceeds
under rather mild reaction conditions with the generation of water
and N<sub>2</sub> as the only byproducts. Broad substrate scope, excellent
functional group tolerance, and high yields were observed. The benzannulation
of pyroles for the synthesis of indoles is also feasible using the
same protocol
Three-Component Catalytic Carboxygenation of Activated Alkenes Enabled by Bimetallic Rh(III)/Cu(II) Catalysis
A novel cascade Cp*RhÂ(III)-catalyzed
C–H alkylation/CuÂ(II)-promoted
α-oxygenation which enabled a three-component carboxygenation
of activated alkene is reported. Mild reaction conditions, broad substrate
scope, and good functional group tolerance were observed. The synthetic
utility of the protocol was showcased by the facile transformations
of the product to a variety of structurally diverse molecules. Preliminary
mechanistic studies were conducted