Chiral C2-Symmetric Bronsted Bases Guanidines

To overcome the difficulty associated with the design of chiral guanidines as a catalyst, the binaphthyl-derived 22 was initially developed with the expectation that substituents at the 3,3 -positions of the binaphthyl backbone would break the planar symmetry of the guanidine skeleton to create an attractive chiral environment. This type of axially chiral organic base catalyst, particularly 22a, could indeed 

G-substituent of the catalyst and the aldehyde would approach from the far side of this diarylmethyl group, while keeping away from the phenyl substituent of the binaphthyl backbone. Since the enolate would be oriented to nhriiinize the steric repulsion of C4 halogen atom with aldehyde substituent, it was most likely that the Si face of the aldehyde was attacked by the Si face of the furanone enolate to give the I R-configured syn product as experimentally observed. 

By installing aromatic substituents of suitable steric and electronic properties, this type of chiral guanidine catalyst could find numerous applications in asymmetric synthesis [67]. 

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