Gold‐Zinc Co‐Catalyzed Alkynoate Hydrocarboxylation with N‐Protected Amino Acids for Preparation of Storable Acylating Reagents and Racemization‐Free Peptide Synthesis

Abstract

Hydrocarboxylation of methyl 2‐octynoate, a chemical commercially available at a low cost, with <i>N</i>‐protected amino acids was developed with a gold‐zinc cooperative catalyst constructed with a 5‐[(2,2'‐bipyridin)‐5‐yl]imidazo[1,5‐<i>a</i>]pyridin‐3‐ylidene to prepare α‐methoxycarbonyl enol esters as acylating reagents. The α‐methoxycarbonyl enol esters were isolable through silica‐gel column chromatography and storable without precautions regarding moisture. Acylation of free amines with the α‐methoxycarbonyl enol esters smoothly proceeded without epimerization of the stereogenic center derived from the enol esters, affording analytically pure dipeptide compounds simply through filtration and hexane‐washing.