Stereoselective functionalisation of cis- and trans-2-ferrocenyl-3-pivaloyl-4-alkyl-1,3-oxazolidin-5-ones: asymmetric synthesis of (R)- and (S)-2-alkyl-2-aminopent-4-enoic acids and (2R,3S)-2-amino-2-methyl-3-hydroxy-3-phenylpropanoic acid.
Alonso F., Davies SG., Elend AS., Leech MA., Roberts PM., Smith AD., Thomson JE.
Treatment of a range of cis- and trans-2-ferrocenyl-3-pivaloyl-4-alkyl-1,3-oxazolidin-5-ones with LDA followed by the addition of allyl bromide promotes highly stereoselective allylation (>98% de) at the 4-position of the oxazolidinone ring anti to the stereodirecting 2-ferrocenyl group. Hydrolysis of the resultant 4,4-disubstituted oxazolidinones (>98% de) yields enantiomeric (R)- and (S)-2-alkyl-2-aminopent-4-enoic acids in high ee. Furthermore, the aldol reaction of the lithium enolate of cis-2-ferrocenyl-3-pivaloyl-4-methyl-1,3-oxazolidin-5-one with benzaldehyde followed by in situ O-protection affords O-protected aldol products in >98% de, with hydrolysis affording (2R,3S)-2-amino-2-methyl-3-hydroxy-3-phenylpropanoic acid in >98% de.