“…To date, various methods have been developed to access unnatural α-amino derivatives (Scheme ). The selected existing approaches toward such privilege structures involve: (i) N -alkylation of anilines with α-bromophenylesters; (ii) transfer hydrogenation of imino esters with Hantzsch dihydropyridine by Co-phosphoric acid or Bro̷nsted acid and carboxyl-tailed benzothiazoline using a trifluoroacetic acid (TFA) catalyst; (iii) amination of aryl azides with methyl phenylacetates by Ru(TPP)CO or Ru(TPP)(py) 2 ; (iv) oxidative dehydrogenative cross-coupling of N -arylglycine esters with phenols by transition-metal catalysts (Cu, Rh, or Ru), N -substituted anilines under CuCl, and α-alkylation of N -arylglycine esters with diacyl peroxides, respectively; (v) reductive coupling of alkyl and arylglyoxylate esters with anilines using Cu/BINAP or HFIP as a catalyst; (vi) N–H insertion of sulfoxonium ylides with anilines in the presence of a catalytic amount of [Ir(COD)Cl] 2 or AuCl(SMe 2 ); (vii) phosphoric acid-catalyzed C–N bond formation of sulfonium ylide esters with p -methoxyphenyl; (viii) urea-catalyzed N–H insertion–arylation of α-nitrodiazoesters with anilines; and (ix) N–H insertion of α-aryl-α-diazoacetates with anilines by transition-metal catalysts (Cu, Rh, Ru, Pd, Ir, or Fe). Despite notable progress in this area, however, among all of these methods, the use of air-sensitive metal reagents or transition-metal catalysts, harsh reaction conditions, and functional group incompatibility all have limitations; consequently, the development of a general methodology for the synthesis of unnatural α-amino esters without the use of metal reagents or transition-metal catalysts using diazo chemistry under mild reaction conditions presents a fundamental and practical challenge yet not resolved.…”