Asymmetric Induction from Cp Stereogenic Centers

Effect 0 -Stereoaenic center Effect of p-Stereoaenic center  

Ab initio calculations [3] are consistent with X-ray findings [25] and indicate the preference for the anti benzaldehyde - BF3 complex. The unusually short H-F bond distance led Corey to propose a H-bond as a conformational lock [32] 

As part of extensive studies of carbonyl additions in the presence of Lewis acidic catalysts, Reetz found that both TiCb and SnClj produced stereoselective allylations of aldehyde 94 to afford 95 in dr = 95 5, consistently with chelation control (Equation 5) [6]. The use of BFj OEtj furnished 95 with only slightly diminished preference for the same diastereomer (dr=85 15). The results are surprising, given that BF3-OEt2 possesses only a single free coordination site and is incapable of participating in chelation. This study underscores the concepts delineated earlier namely, that the observed diastereo- 

In an early example of 1,3-chelation control. White reported in 1976 that the diastereoselective reduction of methyl ketone 96 with L-selectride proceeds in 9 1 dr (Equation 6) [74]. The isolated product, nonactic acid (98), is the repeating subunit of the tetrameric nactin macrolide antibiotics. 

The stereoselective reduction of hydroxy ketones to the 1,3-syn diol products can be effected with dialkylmethoxyborane and NaBH4, a process known as the Prasad reduction (79, 80], It has been proposed that these reactions proceed through a chelate 112 formed upon exchange of the methoxy substituent on boron by the substrate alcohol. It is hypothesized that subse- 

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