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Planar chirality found tremendous use in many fields, such as chemistry, optics, and materials science. In particular, planar chiral 2.2paracyclophanes (PCPs) are a type of structurally interesting and practically useful chiral compounds bearing unique electronic and photophysical properties and thus have been widely used in π-stacking polymers, organic luminescent materials, and as a valuable toolbox for developing chiral ligands or organocatalysts. However, the synthesis of chiral PCP derivatives remains a longstanding challenge. Current synthetic methods primarily rely on chiral preparative liquid chromatography separation or chemical and kinetic resolution reactions. Here, we report an enantioconvergent alkynylation of an in situ-formed dehydro-2,2-paracyclophane intermediate by asymmetric copper(I) catalysis. This approach enables the efficient synthesis of valuable planar chiral PCP building blocks and heterocycles with good yields and excellent enantioselectivity. The success of this reaction lies in the development of a practical route to access strained dehydro-2,2-paracyclophane intermediates, which can also be utilized in various strain-release nucleophilic or cycloaddition reactions to synthesize diverse functionalized PCPs. DFT calculations of this reaction suggest that the enantioselectivity is determined by the aryne complexation with chiral copper(I) acetylide and the subsequent insertion reaction.
Zhang et al. (Mon,) studied this question.