6 research outputs found
Enantioselective Desymmetrization of <i>para</i>-Quinamines through an Aminocatalyzed Aza-Michael/Cyclization Cascade Reaction
An unprecedented organocatalytic
asymmetric desymmetrization of <i>para</i>-quinamines leading
to functionalized hydroindoles,
a common motif in many alkaloids, has been reported. The ability of
diarylprolinol silyl ethers to promote iminium and enamine activation
of α,β-unsaturated aldehydes in one catalytic cycle is
the centerpiece of the strategy involving a challenging aza-Michael/intramolecular
cyclization cascade reaction. A range of prochiral <i>para</i>-quinamines and α,β-unsaturated aldehydes were investigated
to afford 16 examples of hydroindoles possessing four contiguous stereocenters
including one quaternary carbon. The hydroindole structures include
multiple orthogonal functionalities, which underwent various transformations
Synthesis of Enantioenriched Aza-Proline Derivatives through Gold(I)-Catalyzed Cyclization of Chiral α‑Hydrazino Esters
A selective gold(I)-catalyzed synthesis of chiral aza-proline
derivatives
has been developed by ring closure of enantioenriched α-hydrazino
esters bearing an alkyne group. These are easily prepared through
a synthetic strategy involving two key steps: organocatalyzed electrophilic
amination of pent-4-ynal with dialkyl azodicarboxylate promoted by l-proline and functionalization of the triple bond by Sonogashira
cross-coupling. This strategy allowed the preparation of a range of
enantioenriched α-hydrazino esters that underwent ring closure
by using Ph<sub>3</sub>PAuCl/AgBF<sub>4</sub> as a catalytic system.
Under these conditions, 5-<i>exo</i>-<i>dig</i> cyclization was favored over 6-<i>endo</i><i>-dig</i> and aza-proline derivatives were obtained in good yields without
epimerization at the stereogenic center. Influence of the catalytic
system, hydrazine protecting group and alkyne substitution on the
cyclization step has also been investigated
Asymmetric Synthesis of Fused Polycyclic Indazoles through Aminocatalyzed Aza-Michael Addition/Intramolecular Cyclization
The first example
of an asymmetric aminocatalyzed aza-Michael addition
of 1<i>H</i>-indazole derivatives to α,β-unsaturated
aldehydes is described. The iminium/enamine cascade process lies at
the heart of our strategy, leading to enantioenriched fused polycyclic
indazole architectures. Variations on both the α,β-unsaturated
aldehydes and the indazole-7-carbaldehyde heterocycles were studied
in order to broaden the scope of the transformation in synthetically
interesting directions. The fused polycyclic indazoles exhibit fluorescence
properties and can undergo synthetic transformations
Asymmetric Synthesis of Fused Polycyclic Indazoles through Aminocatalyzed Aza-Michael Addition/Intramolecular Cyclization
The first example
of an asymmetric aminocatalyzed aza-Michael addition
of 1<i>H</i>-indazole derivatives to α,β-unsaturated
aldehydes is described. The iminium/enamine cascade process lies at
the heart of our strategy, leading to enantioenriched fused polycyclic
indazole architectures. Variations on both the α,β-unsaturated
aldehydes and the indazole-7-carbaldehyde heterocycles were studied
in order to broaden the scope of the transformation in synthetically
interesting directions. The fused polycyclic indazoles exhibit fluorescence
properties and can undergo synthetic transformations
Merging Oxidative Dearomatization and Aminocatalysis: One-Pot Enantioselective Synthesis of Tricyclic Architectures
The combination of oxidative dearomatization and trienamine/enamine activation in a single vessel is described. Under these conditions, a three-bond forming process generates functionalized tricyclic architectures with up to six contiguous stereocenters with excellent stereoselectivities from readily available planar substrates
Solvent- and Catalyst-Free Synthesis of Nitrogen-Containing Bicycles through Hemiaminal Formation/Diastereoselective Hetero-Diels–Alder Reaction with Diazenes
A solvent-
and catalyst-free synthesis of nitrogen-containing bicyclic
derivatives through a three-bond forming process is reported. Starting
from dienals and readily available diazenes, the strategy involving
the hemiaminal formation/hetero-Diels–Alder reaction affords
the bicyclic products in a highly diastereoselective manner. This
simple and green procedure has been applied to a selection of substrates,
giving rise to 12 examples of nitrogen-containing bicyclic architectures.
These products underwent various synthetic transformations. A sequence
involving the cleavage of the hydrazine allowed the preparation of
a hydantoin motif bearing an aminopropyl side chain, which is a structure
found in natural products. A mechanism has also been suggested to
explain the observed selectivities