Lithium diisopropylamide reaction with epoxides

Eliminations of epoxides lead to allyl alcohols. For this reaction to take place, the strongly basic bulky lithium dialkylamides LDA (lithium diisopropylamide), LTMP (lithium tetramethylpiperidide) or LiHMDS (lithium hexamethyldisilazide) shown in Figure 4.18 are used. As for the amidine bases shown in Figure 4.17, the hulkiness of these amides guarantees that they are nonnucleophilic. They react, for example, with epoxides in chemoselective E2 reactions even when the epoxide contains a primary C atom that easily reacts with nucleophiles (see, e.g., Figure 4.18). 

The a-protons of iron acyl complexes are acidic and these can be deprotonated with Lithium diisopropylamide (LDA) or with n-butyllithimn. Thus the corresponding enolates are readily functionalized and undergo reaction with alkyl halides, aldehydes, disulfides, trimethylsilyl chloride, and epoxides to afford the corresponding a-derivatized products. " Early work on racemic complexes revealed that these transformations occur in a highly diastereoselective fashion,... 

The stereochemical information is introduced by (J )-methyl p-toluenesulfoxide 110. This compound is deprotonated with lithium diisopropylamide and reacted with a-chloro methylacetate 109 to give a-chloroketone 111. This ketone when reacted with diisobutylaluminum hydride at —78°C gives (J )-chlorohydrine 112, whereas reaction of ketone 111 with diisobutylaluminum hydride and zinc chloride gives the corresponding (S)-chlorohydrine 113. Treatment of both chlorohydrines with potassium carbonate resulted in the formation of epoxides 114 and 116. These can now be reacted with either (Z)- or (T)-vinyl cuprates to give the desired homoallylic alcohols 115 and 117 in diastereomeric excesses around 90%. 

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