Lactam anionic epimerization

These compounds can be alkylated twice at the 6-position in a stereocontrolled fashion (eq 2). Treatment of the unsubstimted bicyclic lactam with Lithium Diisopropylamide and reaction of the enolate anion with an alkyl halide affords the monosubstimted product The epimeric mixture is treated again with LDA and a second alkyl halide to give the dialkylated bicyclic lactam. The... 

Verazine (37) has been the subject of a formal total synthesis (Scheme 1) based on the earlier reported versatile syntheses of solanidine and tomatidenol. As in the earlier work, Michael addition of the anion of the configurationally pure nitro-ester (30) to (29) gave the C-22 epimeric mixture (31), from which the individual diastereomers were isolated after acetylation. The (22S)-acetate (32) was converted via thioketal (34) and lactam (35) into the piperidine derivative (36). Base treatment of the N-chloro-derivative of (36) then gave verazine (37). 

After purification by recrystallization from toluene, monomer was polymerized hydrolytically. Polymerization of lactam 49, either cationically or anionically, might result in epimerization of the cis-tetrahydrofuran ring junction which would result in a polymer containing a mixture of cis and trans tetrahydrofuran rings (Fig. 22). The importance of tetrahydrofuran ring geometry has... 

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