1.3- Dimethyl-2-imidazolidinone/lithium

A solution of 20 mmol of a .s-3-(2-alkyl-l-oxoalkyl)-l, 5-dimethyl-4-phenyl-2-imidazolidinone 5 in 40 mL of dry THF is slowly added at 0 3C to a stirred suspension of lithium aluminum hydride in 30 mL of THF under argon. The mixture is stirred for 1 h, then the reaction is quenched by the cautious addition of methanol, followed by 2M aq hydrochloric acid. Extraction with ethyl acetate is followed by concentration under vacuum and flash chromatography (cyclohexane/ethyl acetate). For specific examples, see Table 12. 

Of special importance is a mixed lithium-magnesium complex, since the individual metal enolates show much lower enantiofacial discrimination. (2/l,3/ )-Dipivaloyltartaric acid is not a useful proton source, however, tert-butyl alcohol, 3,4-dimethyl-5-phenyl-2-imidazolidinone and 2-(Ar-isopropyl-Ar-methylamino)-l-phenylpropanoI (9-H) yield highly enantiomerically enriched (R)- or (S )-oc-damascone (11), especially in the presence of lithium (+)- or (-)-2-(Ar-iso-propyl-A -methylamino)-1 -phenylpropanolate (9-Li) as an auxiliary. 

Iminic derivatives of (4R,55)-l,5-dimethyl-4-phenyhmidazolidin-2-one have been dia-stereoselectively alkylated with activated alkyl halides or electrophilic olefins either under phase transfer catalysis (PTC) conditions or in the presence of the phosphazene base BEMP at —20°C in the presence of lithium chloride (LiCl). Hydrolysis of the alkylated imino imides gave (5)-a-amino acids with recovery of the imidazolidinone chiral auxihary [18]. 

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