A Reinvestigation of the α‐Alkylation of 4‐Monosubstituted 2‐phenyloxazol‐5(4H)‐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(4H)‐ones ( = 4‐monosubstituted 2‐phenyl‐azlactones) rac‐2 to 4,4‐disubstituted 2‐phenyloxazol‐5(4H)‐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.