Efficient access to β-amino acid ester/β-amino ketone derivatives via photocatalytic radical alkoxycabonylimidation/carbonylimidation of alkenes

Abstract

A photocatalytic protocol for the synthesis of β-amino acid ester and β-amino ketone derivatives is developed by using simple and easy-to-synthesize oxime oxalate and oxime phenylglyoxylate as difunctionalization reagents. These...

Metal-Free Photochemical Imino-Alkylation of Alkenes with Bifunctional Oxime Esters

“…For the construction of fluorinated alkyl- and nitrogen-based chemical bonds across an alkene, several photochemically mediated amino-trifluoromethylation strategies have been developed to assemble the two vicinal functional groups (e.g., NR 2 and CF 3 ) in a single step. ,, However, the synthetic utility of these approaches is often limited because of the requirement for activated alkenes (e.g., styrene), transition-metal catalysts, and the circumscribed use of electrophilic CF 3 sources such as Togni’s ($102.0/g) and Umemoto’s reagents ($124.0/g). Alternatively, alkyl oxime esters provide a tactical advantage as they are capable of generating both alkyl- and nitrogen-based radicals simultaneously via a fragmentation/decarboxylation process (Figure b). − However, the use of oxime esters is limited because the solitary adoption of either nitrogen- or carbon-based radicals in the chemical synthesis leads to poor atom economy. ,− As a result, the use of bifunctional oxime esters in organic synthesis remains underdeveloped.…”

N–O Bond Activation by Energy Transfer Photocatalysis

“…Careful selection of the substrate and photocatalyst in terms of compatible triplet energies and mismatched redox potentials is a prerequisite for the success of the EnT process. Figure shows substrates and photocatalysts used in N–O bond activation by selective EnT, including oximes (aryl oximes, − oxime esters, ,− oxime carbonates, , and oxime (gly)­oxalates), 1,2,4-oxadiazolines, , phthalimide enolates, N -indolyl carbonates, N -benzoyloxy carbamates, and N -enoxybenzotriazoles, with a disclosure of their triplet excited state energies. Our laboratory (often in collaboration with the You and Shin groups) utilized a diverse range of substrates such as 1,2,4-oxadiazolines, oxime esters, N -indolyl carbonates, and N -enoxybenzotriazoles.…”

“…In the presence of a suitable photocatalyst ([Ir­(dF­(CF 3 )­ppy) 2 (dtbbpy)] + ([Ir–F] + ) or thioxanthone) with high triplet excited state energy, various oxime derivatives, including oxime ester (X = COR), carbonate (X = CO 2 R), glyoxalate [X= (CO) 2 R], and oxalate [X = (CO)­CO 2 R], followed the EnT process to provide key radical species, including iminyl and oxy radicals as well as alkyl/aryl radicals (if decarboxylation followed) for C–N coupling processes (Scheme a and Scheme d) or coupling with external reactant (Scheme b). The addition of radicals to external alkenes was also realized during carboimination (Scheme c and Scheme i), oxyimination (Scheme f, Scheme g, and Scheme h-i)), and hydrooxygenation (Scheme h-ii)) reactions. In other efforts, dual catalytic strategies involving copper complexes (Scheme j and Scheme k) facilitated intramolecular cyclization of N-centered radicals generated from N -aryl- N -alkoxy oximes (X = Ar).…”

Synthesis of γ-amino acids via photocatalyzed intermolecular carboimination of alkenes

“…8 Schiff bases may offer the possibility of addressing this issue via an additional hydrolysis pathway. 9 Based on recent works from the groups of Glorius, 10 Cho, 11 Han 12 and Xia 13 on the use of oxime esters as the source of N-centred diaryliminyl radicals, we hypothesized whether or not such a method could be used to synthesize γ-amino acid Schiff bases (Fig. 1c).…”