Base compounds Betti reaction

Since the Betti reaction results in a product with a benzylic chiral centre, several studies have been reported whereby the product enantiomers are resolved. Betti reported in 1906 that his base 10 could be classically resolved following separation of the corresponding tartaric acid salts. More recently Hu and co-workers have reported a high yielding and scaleable modification to this procedure by using tartaric acid in acetone. In acetone, two different compounds were formed, the (/ )-enantiomer giving the aminal 19 and the (iS)-enantiomer giving the tartaric acid salt 20. 

The importance of this reaction relies on the fact that the Betti bases can function as both excellent ligands and auxiliaries in asymmetric synthesis. The racemic Betti amines can be separated into their optical antipodes. In this respect, among the Betti bases from monochlorobenzaldehydes, only the dextro form of the ortho and meta chloro compounds could be resolved with satisfaction, while the levo antipodes are extremely difficult to obtain due to their higher solubilities. ... 

The marked temperature dependence of the enantioselective addition of diethylz-inc to aryl aldehydes catalysed by (S)-2-(3-methyl-2-pyridyl)-3,5-di-r-butylphenol displays an inversion temperature which is affected by the para-substituent of the aldehyde. Enantioselectivities of up to 78% ee for addition of diethylzinc to ben-zaldehyde have been achieved using (15, 45)-2,5-diazabicyclo[2.2.1]heptane derivatives as catalysts however, a study of chiral compounds related to the Betti base (51a) has identified r-aminonaphthol (51b) as a much more effective catalyst (99% ee) for this reaction. The catalytic efficiency of chiral pyrrolidine derivatives and (25)-3-eJt -(dimethylamino)isobomeol have also been explored. 

Naphthol is another electron-rich aromatic compound which can also lead to sp -sp CDC-type products. Thus, a new type of Betti base was formed via the CDC reaction of N-phenyl-THIQ with 2-naphthol derivatives under our CuBr/TBHP system with a small amount of homocoupled 2,2-binaphthol (BINOL) (Scheme 1.10). Subsequently, the scope of cross-dehydrogenative Friedel-Crafts type aiylations was significantly improved by the development of highly efficient catalyst systems, and an intramolecular Cu-catalyzed aerobic synthesis of functionalized cinnolines via a Friedel-Crafts-type CDC aiylation was reported by Zhang et al. ... 

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