Aldehydes, Ketones, and Derivatives

Most aldehyde-based chiral auxiliaries come from carbohydrates [248]. For example, aldehyde 1.97 is transformed into a-aminoester imines 1.98, which undergo stereoselective alkylations in basic media. After acidic hydrolysis, the dural 

Charette and coworkers [366] found that the reactions of 1.103 and 1.104 (R = CH2CHO) with BU3 SnCH2CH=CH2 in the presence of MgBr2 are highly stereoselective and either stereoisomer can be obtained, depending upon whether or not the R-substituent (PhCH2 or /-P Si) promotes chelation control. 1-Pen-ten-4,5-diols are obtained after treatment of the products of these reactions with ally alcohol under slightly acidic conditions. From nitrosochloride 1.105, chiral allylamines are obtained via ene-reactions [370] and chiral heterocycles are obtained via asymmetric [4+2] cycloaddition reactions on the N=0 bond [241, 371, 372]. 

Naturally occurring ketones and their readily prepared derivatives have also been used as chiral auxiliaries. Menthone ketals have been the subject of some study [373, 374], For example, enolates of compound 1.106, obtained from 8-phenylmenthone, are alkylated with a good stereoselectivity [375]. Cleavage of the chiral auxiliary is accomplished by hydrolysis. Enolates of tert-butylglycine camphor imine 1.107 are alkylated [154, 159] or suffer Michael additions [376] with a high stereoselectivity, and the auxiliary is cleaved by treatment of the prod- 

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