Lanthanoid-BINOL complexes nitroaldol reaction

A. Catalytic, asymmetric nitroaldol reaction promoted by the lanthanoid-lithium-BINOL complex (LnLB)... 

In 1992, Shibasaki et al. reported for the time an application of chiral heterobimetallic lanthanoid complexes (LnLB) as chiral catalysts in asymmetric catalysis, namely the catalytic asymmetric nitroaldol reaction (Henry reaction), which is one of the most classical C-C bond forming processes [11]. Additionally, this work represents the first enantioselective synthesis of (3-nitroalcohol compounds by the way of enantioselective addition of nitroalkanes to aldehydes in the presence of a chiral catalyst. The chiral BINOL based catalyst was prepared starting from anhydrous LaCl3 and an equimolar amount of the dialkali metal salt of BINOL in the presence of a small amount of water [9]. 

Shibasaki and coworkers have developed lanthanoid-lithium-BINOL complexes (LLB catalysts) as efficient catalysts for the asymmetric nitroaldol (Henry) reaction (59-46). The heterobimetallic asymmetric catalysts effectively mediate the reaction of a variety of aldehydes with nitroalkanes to afford the corresponding desired nitroaldols with high enantioselectivity (Scheme 4). We examined the capability of the LLB complexes as asymmetric catalysts for the nitroaldol reaction of 2,2-difluoroaldehydes with nitromethane (47). 

In the lanthanoid-lithium-( )-BINOL-catalyzed nitroaldol reaction of 2,2-difluoroaldehydes, the nitronates were found to preferentially react on the Si face of the aldehydes. On the contrary, (/1)-LLB generdly causes attack with the Re facial selection as ahown in Figure 2 (39,40,42). Therefore, the enantiotopic face selection for 2,2-difluoroaldehydes is opposite to that for nonfluorinated aldehydes. This stereoselectivity is identical with that of jS-oxaaldehydes, suggesting that fluorine atoms at the a position exert a significant influence on the enantioface selection. The fluorine atoms may coordinate with the rare earth or the lithium of LLB complexes. 

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