Here we report a new type of chiral all-carbon tetrasubstituted VQMs generated via chiral phosphoric acids catalyzed nucleophilic addition of 2-alkynylnaphthols to o-quinone methides or imines, which can be captured intramolecularly as a result of cycloaddition reaction. A new class of naphthyl-2H-chromenes bearing axially and centrally chiral elements and axially chiral quinone-naphthols were prepared efficiently with good to excellent yields, diastereoselectivities and enantioselectivities. Noteworthy, the enantioselective cycloaddition of alkynylnaphthols with o-quinone methides proceeded via a [2+2] cycloaddition, followed by a retro-4π-electrocyclization and a 6π re-cyclization. While the cycloaddition of alkynylnaphthols with imines proceeded via a sequential [2+4] cycloaddition and an auto oxidation reaction. Moreover, the obtained axially chiral naphthols can be converted into valuable phosphine ligands and other functional molecules.
The first highly enantioselective [3 + 2] formal cycloaddition of 1-styrylnaphthols (or phenol) with quinones catalyzed by a chiral phosphoric acid has been reported. A class of trans-2,3-diarylbenzofurans were prepared efficiently (up to 99% yield, >20:1 dr, 99% ee). This organocatalytic procedure allows lowering of the catalyst loading to 0.5 mol % without considerable loss in reactivity and enantioselectivity.
Asymmetric Prins cyclization of in
situ generated quinone methides and o-aminobenzaldehyde
has been developed with chiral phosphoric acid as an efficient catalyst.
This unconventional method provides a facile access to diverse functionalized
trans-fused pyrano-/furo-tetrahydroquinoline derivatives in excellent
yield and with excellent diastereo- and enantioselectivities (up to
99% yield and 99% ee). Mechanistic studies suggested that the three
adjacent tertiary stereocenters were constructed through the sequential
formation of C–O, C–C, and C–N bonds.
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