Synthesis of Amide Enol Carbamates and Carbonates through Cu(OTf)₂-Catalyzed Reactions of Ynamides with t-Butyl Carbamates/Carbonates

Abstract

A highly regioselective approach to access amide enol carbamates and carbonates 5a−5c′, 7a−7h, and 9 was developed through Cu(OTf) 2catalyzed reactions of ynamides 4 with t-butyl carbamates 2 and 8 and t-butyl carbonates 6. Moreover, this strategy was successfully applied to generate amide enol carbamates 11a−11s and 14a−14f from imides 10 and 13 with ynamides through an N-Boc cleavage−addition ring-opening process. A range of substituents was amenable to this transformation, and the desired amide enol carbamates and carbonates were obtained in moderate to good yields.

Gold-Catalyzed Addition–N-Boc Cleavage–Cyclization of N,O-Acetal with Ynamides for Construction of 6-(tert-Butyldimethylsilyl)oxy-tetrahydropyrrolo[1,2-c][1,3]oxazin-1-ones

“…In the past decade, gold catalysis in alkyne-involved reactions has undoubtedly become one of the most attractive fields in modern organic synthesis owing to its high selectivity and high atom economy. , The ynamides, as special alkynes bearing an electron-withdrawing group on the nitrogen group, have become versatile building blocks to generate important N -heterocyclic scaffolds typically through transition-metal catalysis or acid catalysis . In this context, gold-catalyzed transformations of ynamides with various precursors were givenspecial attention .…”

Metal-free stereoselective addition of propiolic acids to ynamides: a concise synthetic route to highly substituted enediyne/dienyne-(E)-N,O-acetals

“…1b). 7 Despite this progress, developing an atom-efficient chemo-, regio- and stereoselective 1,2-addition of carboxylate species to internal ynamides attracts attention.…”

Synthesis of Amide Enol 2-Iodobenzoates by the Regio- and Stereoselective Gold-Catalyzed Acyloxyalkynylation of Ynamides with Hypervalent Iodine Reagents

“…13 Recently, Wei and co-workers reported a highly regioselective Cu(OTf) 2 -catalyzed route providing amide enol carbonates when starting from ynamides and tert-butyl carbonates. 14 Notably, the nitrogen atom's lone pair readily assists the functionalization of the α-position of ynamides. However, a simultaneous difunctionalization of ynamides with electrophilic as well as nucleophilic groups at the αand the β-position still presents a challenge to the modern organic chemist.…”

“…After that, Bi’s, Gillaizeau’s, and Zhao’s groups reported a metal-free, acid-catalyzed hydroacyloxylation reaction of ynamides to afford amide enol benzoates . Recently, Wei and co-workers reported a highly regioselective Cu­(OTf) 2 -catalyzed route providing amide enol carbonates when starting from ynamides and tert -butyl carbonates . Notably, the nitrogen atom’s lone pair readily assists the functionalization of the α-position of ynamides.…”