Stereospecific reactions bimolecular elimination

Munk and Kim22 described a new approach to the synthesis of stereoisomeric enamines of known configuration which takes advantage of the well-documented facility and stereospecificity of the bimolecular -elimination reaction. 

Mixtures of Z and E stereoisomers have been obtained in most syntheses. This undoubtedly holds in the presence of an acid catalyst. The tendency of the E-enamine to isomerize to the Z-enamine was readily observed on numerous occasions under unexpectedly mild conditions. Munk and Kim357 summarized the requirements for the stereospecific synthesis of enamines. First, if the introduction of the double bond is to be the final step of the synthesis, it must be stereospecific in character. Second, once the enamine is formed it must retain its stereochemical integrity under the conditions employed in the double-bond-forming step. The base-induced bimolecular -elimination reaction fulfills both these requirements. Indeed, treatment of the mesitoate esters of ( )-threo- (99) and ( )-erythro- (100) l-(4-morpholino)-l,2-diphenylethanol with... 

In the present case, alkaline solvolysis forms almost completely racemic product in contrast with that from the neutral hydrolysis which is stereospecific. It is clear that the alkaline solvolysis involves a symmetrical intermediate, a metaphosphorimidothioate. which reasonably may be expected to be planar (isoelectronic with S03). The close similarity in reactions of thiophosphoryl and phosphoryl centers is well established for bimolecular displacements on phosphorus and the resemblance apparently extends to the metaphosphate eliminations. 

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