An unprecedented enantioselective intramolecular oxa-Michael reaction of enols has been described. A squaramide-containing tertiary amine based bifunctional organocatalyst efficiently activates the o-homoformyl chalcones to provide the chiral isochromenes in moderate yields and good to excellent enantioselectivities. Further, late-stage functionalizations of the vinyl ether moiety of the chiral isochromene products have also been exemplified.
A unified dynamic kinetic spiroketalization/enantioselective oxa-Michael addition cascade of an aromatic ketone tethered to an alkoxyboronate and an enone moiety has been developed using cinchona alkaloid based amino-thiourea/squaramide organocatalysts to provide isobenzofuran-based benzannulated spiroketals with high diastereoselectivities and excellent enantioselectivities. Further, a dynamic kinetic peroxy-hemiacetalization/dynamic kinetic spiroketalization/enantioselective oxa-Michael addition cascade of the above substrates provides the corresponding exo-peroxy-benzannulated spiroketals with outstanding enantio- and diastereoselectivities.
Disclosed here an amine‐catalyzed reductive aldol‐condensation followed by an intramolecular reductive Michael‐addition cascade employing Hantzsch ester as hydride source to a keto‐bis‐enone to provide enantio‐ and diastereoselective benzannulated diquinanes having three consecutive stereocenters, one of which is an all‐carbon quaternary formyl stereocenter. Interestingly, on changing a tether connecting the ketone and an enone moiety from an aliphatic to an aromatic, a change in reactivity is observed. In this case, instead of the above‐mentioned reductive aldol condensation, an asymmetric aldol reaction occurs, followed by an iminium/enamine isomerization and, finally diastereoselective Michael addition reaction occurs. As a result, a bis‐benzannulated diquinane is obtained with vicinal congested quaternary chiral centers.
The fruit extract of Ficus carica Linn (Dumur) is rich in different types of plant secondary metabolites such as terpenoids, polyphenols including flavanoids, etc. We have
demonstrated the use of the fruit extract for the synthesis of gold nanoparticles in water at room temperature under very mild conditions. There was no need of additional stabilizing or capping agents and the synthesis of the gold nanoparticles was complete in several minutes. The gold nanoparticles were characterized by HRTEM, EDX, SAED, Surface
Plasmon Resonance Spectroscopy and X-Ray diffraction studies. The freshly prepared gold nanoparticles have been used as an efficient catalyst for the sodium borohydride
reduction of 4-nitrophenol to 4-aminophenol in water at room temperature and the kinetics of the reduction reaction have been studied spectrophotometrically.
An enantioselective intramolecular oxa‐Michael reaction of enols catalyzed by a squaramide‐containing tertiary amine based bifunctional organocatalyst, which efficiently activates the o‐homoformyl chalcones, provides chiral isochromenes in moderate yields and good to excellent enantioselectivities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.