Diastereoselectivity dissolving metal reductions

For the synthesis of cyclopropyl amino acids, Williams has used an oxazinone auxiliary (cf. Scheme 3.12) as an electrophilic component in a sulfur ylide cyclopropanation using Johnson s sulfoximines, as illustrated in Scheme 6.41 [148]. Surprisingly, the sulfur ylide approaches from the P face the authors speculate that there may be some sort of 7t-stacking between the phenyls on the oxazinone ring and the phenyl in the sulfoximine to account for this [149]. With Corey s [147] dimethylsulfonium methylide, the diastereoselectivity was only about 75%, but with Johnson s sulfoximines (used in racemic form), only one diastereomer could be detected for most substrates studied (with the exception of R = H, [149]). Dissolving metal reduction afforded moderate yields of the cyclopropyl amino acids. 

Electrochemical reductions of camphor oxime (R = Me) and norcamphor oxime (R = H) at a mercury cathode proceed with a high degree of diastereoselectivity (equation 3) . The products are in fact of opposite stereochemistry to those formed in dissolving metal (sodium-ethanol) reductions of the oximes. 

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