A highly diastereo- and enantioselective
methodology for the asymmetric
synthesis of vicinal diaxial styrenes and multiaxis system was achieved
by organocatalysis. Various vicinal diaxial styrenes and multiaxis
systems were obtained in excellent enantioselective manners. The mechanism
studies revealed that a new tetra-substituted vinylidene ortho-quinone methide (VQM) intermediate was likely involved
and accounted for the excellent enantioselectivity.
The applications of a newly designed chiral naphthyl-C2-indole bifunctional phosphine organocatalyst in stereoselective formal [4 + 2] cycloaddition reactions were reported. The chiral naphthyl-C2-indole skeleton was introduced to bifunctional phosphine organocatalysis for the first time, and excellent stereocontrol was achieved in two types of formal [4 + 2] cycloaddition reactions. With the optimal catalyst, a series of chiral spirooxindole and hydrodibenzofuran architectures were produced in moderate to good yields with excellent stereoselectivities (up to >99% ee, >20:1 dr).
An efficient organocatalytic construction of enantioenriched axially chiral 1,4-distyrene 2,3-naphthalene diols through the nucleophilic addition of α-amido sulfone to in situ generated vinylidene o-quinone methide is described. The reaction pathway was investigated by isolating reaction intermediates and performing a kinetic resolution process. Axially chiral 1,4-distyrene 2,3-naphthalene diol was used as the chiral ligand for the enantioselective addition of diethylzinc to naphthalene formaldehyde. The preliminary results revealed that these adducts could be potentially used as ligands in asymmetric synthesis.
A metal-free protocol for difunctionalization of alkynes through spontaneous selenosulfonylation of vinylidene ortho-quinone methide (VQM) was developed with good yields and excellent stereoselectivities.
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