RESUMO
An unprecedented enantioselective organocatalytic spirocyclization strategy is presented by inâ situ generation of aminoisobezofulvenes. The reaction sequence involves a reductive Michael/aldol-condensation/Michael addition cascade by iminium-enamine catalysis. The key success of this spirocyclization was the formation of intermediatory nucleophilic aminoisobenzofuvenes accountable for intramolecular Michael addition. Benzospirononanes featuring an all carbon qauternary spirocenter were obtained using proline-derived amino-organocatalyst in moderate to good yields and excellent diastereo- and enantioselectivities (up to >20 : 1 dr, and 99 % ee). Post-methodological manipulation of benzospirononanes was also demonstrated.
RESUMO
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.
RESUMO
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.