Benzyllithium compounds inversion

The HOMO of -3 TMEDA, showing a pyramidalized carbanionic unit, was visualized (Fig. 5) and compared with the HOMO of the benzyllithium compound (I ,S)-8, which displays a planar carbanionic unit. Whereas the planar system (R,S)-S reacts under inversion, in the case of the pyramidal system m-3-TMEDA retention of configuration should be expected. 

Since the stannylation proceeds with inversion and the Hthio-destannylation is a stereoretentative reaction, for the first time, the clean inversion of an enan-tioenriched benzyllithium compound could be accompHshed with a chirafity transmission of greater than 95% [Eq. (61)] [131,133]. 

The chiral benzyllithium compound generated by the reaction of the enan-tioenriched stannyl precursor with s-BuLi-(-)-sparteine was reacted with cyclohexanone to give the product with good enantioselectivity. Interestingly, this reaction proceeds with inversion of the configuration of the stannylated carbon [Eq.(43)j. 

Compound 20 (X = Cl) reacts with alkyllithiums with complete retention, in contrast to the inversion observed with R3Si-Cl allyllithium or benzyllithium and alkyl Grignard reagents also cleave the Si-F bond of 20 (X = F) with retention rather than inversion as observed with 1-NpPhMeSi-F. 

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