Organocatalytic Atroposelective Intramolecular [4+2] Cycloaddition: Synthesis of Axially Chiral Heterobiaryls

The enantioselective construction of axially chiral aryl-naphthopyran skeletons was realized by organocatalytic atroposelective intramolecular [4+2] cycloaddition of in situ generated vinylidene ortho-quinone methides, from 2-ethynylphenol derivatives, with alkynes. Through this method, the heteroatropisomers were obtained with excellent yields and enantioselectivities. Moreover, a speculative model of the stereochemical outcome is proposed based on preliminary mechanistic studies. The products having various functional groups can be easily transformed into valuable intermediates as either potential ligands or organocatalysts.