A chiral thiourea catalyzed asymmetric 1,6-conjugate addition of para-quinone methides with dicyanoolefins has been developed. The reaction provided an efficient approach to the synthesis of chiral diarylmethine skeletons in good yields (up to 99% yield) with high diastereo- and enantioselectivity (>20:1 dr and up to 99.5:0.5 er), also on a gram scale. The preliminary mechanistic study showed that the remote stereocontrol was achieved through intermolecular hydrogen-bond interaction between the chiral thiourea catalyst and the para-quinone methides directly for the first time.
A 1,6‐addition arylation reaction of para‐quinone methides with α‐isocyanoacetamides and electron‐rich aromatic compounds under metal‐free conditions has been developed. BF3·Et2O plays two roles in the reaction: catalyzing the cyclization of α‐isocyanoacetamides to give oxazoles, and activating the para‐quinone methides to achieve the 1,6‐addition arylation process. The reaction shows good functional group tolerance, scalability, and regioselectivity. It is a consice protocol for the synthesis of diverse unsymmetrical triarylmethanes. Further transformation of the resulting triarylmethanes provides an efficient route to some functionalized molecules.
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