8 research outputs found
Diastereoselective Synthesis of Dibenzoazepines through Chelation on Palladium(IV) Intermediates
Joint palladium/norbornene organometallic
catalysis allows for
straightforward access to dibenzoÂ[<i>c,e</i>]Âazepines. These
synthetically challenging polycyclic frameworks form in one pot via
a three-component coupling of an aryl iodide, a bromobenzylamine,
and an olefin. A key, atroposelective arylâaryl coupling from
chelated PdÂ(IV) intermediates dictates the outcome of the cascade.
DFT modeling sheds light on the complex mechanism that allows the
complete diasteroselectivity to be observed
Diastereoselective Synthesis of Dibenzoazepines through Chelation on Palladium(IV) Intermediates
Joint palladium/norbornene organometallic
catalysis allows for
straightforward access to dibenzoÂ[<i>c,e</i>]Âazepines. These
synthetically challenging polycyclic frameworks form in one pot via
a three-component coupling of an aryl iodide, a bromobenzylamine,
and an olefin. A key, atroposelective arylâaryl coupling from
chelated PdÂ(IV) intermediates dictates the outcome of the cascade.
DFT modeling sheds light on the complex mechanism that allows the
complete diasteroselectivity to be observed
Acid-Catalyzed Formal Cycloaddition of α,ÎČ-Unsaturated Carbonyls with Epoxides: Dioxepines or Acetals?
It
has been recently reported that the reaction of α,ÎČ-unsaturated
carbonyl derivatives with epoxides in the presence of a homogeneous
acid catalyst readily delivers the corresponding dioxepines via formal
(4 + 3) cycloaddition. We report herein that the same apparent reactivity
can be triggered via heterogeneous catalysis. Characterization of
products by means of NMR correlation experiments and DFT modeling
revealed, however, that products are the acetals of the unsaturated
reagent rather than the desired heterocycles
Pd-Catalyzed/Iodide-Promoted 뱉Arylation of Ketones for the Regioselective Synthesis of Isocoumarins
A variety of isocoumarins
have been synthesized directly from 2-halobenzoates
and ketones through a palladium-catalyzed α-arylation step followed
by an intramolecular cyclization process. The addition of iodide anions
to the reaction mixture increased yields and selectivities especially
when 2-bromobenzoates were employed. This phosphine-free one-pot synthesis
features a high functional group tolerance and gives access to richly
decorated isocoumarins. This general methodology was successful in the total synthesis of Xyridin
A, an important natural product with antibacterial and antifungal
activity
Rearrangements of <i>N</i>âAcyl Isothioureas. Alternate Access to Acylguanidines from Cyanamides
We report a tin-free one-pot radical approach to the synthesis of <i>N</i>-acyl isothioureas and acylguanidines from <i>N</i>-acyl cyanamides. Photoactivated reduction of aromatic disulfides in the presence of HuÌnigâs base results in hydrothiolation of the cyanamide moiety, followed by spontaneous 1,3-migration of the acyl group. Onward reaction of the isothioureas obtained with amines led to the corresponding <i>N</i>-acylguanidines, where the acyl group is attached to the nitrogen atom formerly at the cyano-end of the starting material
Alternative Routes to Tricyclic Cyclohexenes with Trinuclear Palladium Complexes
Highly
symmetric all-metal aromatic Pd<sub>3</sub><sup>+</sup> complexes
can catalyze the cycloisomerization of terminal 1,6-enynes and internal
dienynes under mild conditions. Modification of substrates dictates
the mechanism and steers the reaction toward different polycyclic
frameworks, enabling the development of complex cascades. The reactivity
of PdÂ(<sup>4</sup>/<sub>3</sub>) complexes is complementary to that
of mononuclear Pd(0) and PdÂ(II) ones
Pd Catalysis in Cyanide-Free Synthesis of Nitriles from Haloarenes via Isoxazolines
A method to obtain
aryl nitriles from the corresponding halides
by Pd catalysis, in the absence of any cyanide source, is reported.
The reaction of an aryl halide, ethyl nitroacetate, and an olefin
readily delivers an aromatic nitrile. A variety of aryl iodides/bromides
have been converted into the corresponding cyanoarenes in fair to
excellent yields. The reaction likely involves the following steps:
(a) Pd-catalyzed α-arylation of ethyl nitroacetate; (b) nitrile
oxide formation; (c) [3 + 2]-cycloaddition with an olefin to provide
an isoxazoline; (d) isoxazoline cleavage to benzonitrile formation
Synthesis of Carbolines via Palladium/Carboxylic Acid Joint Catalysis
The combination of
a Pd(0) complex with benzoic acid converts propargylic
tryptamines to the corresponding tetrahydro-ÎČ-carbolines. The
method uses unprotected indoles and affords the desired products with
ample functional group tolerance. Detailed modeling studies reveal
a close synergy between the organic and metal catalysts, which enables
sequential alkyne isomerization, indole CâH activation, and
eventual CâC reductive elimination to afford the target heterocycles