A Reinvestigation of the α‐Alkylation of 4‐Monosubstituted 2‐phenyloxazol‐5(4 H )‐ones (‘azlactones’): A general entry into highly functionalized α,α‐disubstituted α‐amino acids

Novel, more reliable and general reaction conditions for the α‐alkylation of 4‐monosubstituted 2‐phenyloxazol‐5(4 H )‐ones ( = 4‐monosubstituted 2‐phenyl‐azlactones) rac ‐ 2 to 4,4‐disubstituted 2‐phenyloxazol‐5(4 H )‐ones rac ‐ 1 were found ( Scheme 2 ). Thus, a whole range of highly functionalized rac ‐ 1 were prepared in medium‐to‐good overall yields (40‐90%, see Table ). Azlactones rac ‐ 1 are ideal precursors for the synthesis of optically pure α,α ‐disubstituted ( R )‐ and ( S )‐α‐amino acids.