A modular approach to α,β-unsaturated N-aryl ketonitrones

Copper‐Catalyzed Rearrangement of N‐Aryl Nitrones into Epoxyketimines

“…Both electron‐rich and electron‐poor aryl groups were also screened for the imine substituent, and were observed to undergo equally efficient transformations (Table 2, entries 8–11). Alkyl‐substituted α,β‐unsaturated nitrones such as 1 m were unreactive under the optimized reaction conditions, but this stark change in reactivity does not appear to be due to the fact that these substrates favor the opposite imine isomer to the chalcone‐derived nitrones 8. A control experiment showed that a 1:1 E / Z mixture of 1 a gave the desired product in high yield.…”

Copper‐Catalyzed Rearrangement of N‐Aryl Nitrones into Epoxyketimines

“…Several copper(I) and copper(II) salts were observed to catalyze the oxygen transfer in the presence of phenanthroline, but CuCl was shown to be the optimal (Table 1 entries 8-12). [8] A control experiment showed that a 1:1 E/ Z mixture of 1 a gave the desired product in high yield. The conversion of 1 a into 2 a can be achieved at 25-80 8C under the conditions shown in Table 1, entry 8; however, 80 8C was chosen as the preferred reaction temperature, as lower temperatures required longer reaction times.…”

“…The yield of this transformation was dependent upon the choice of reaction medium, copper salt, and N-donor ligand. Benzene, THF, and dimethylsulfoxide (DMSO) were tolerated as solvents, but the most efficient transformation was observed in acetonitrile (Table 1, entries [4][5][6][7][8]. Several copper(I) and copper(II) salts were observed to catalyze the oxygen transfer in the presence of phenanthroline, but CuCl was shown to be the optimal (Table 1 entries [8][9][10][11][12].…”

“…Benzene, THF, and dimethylsulfoxide (DMSO) were tolerated as solvents, but the most efficient transformation was observed in acetonitrile (Table 1, entries [4][5][6][7][8]. Several copper(I) and copper(II) salts were observed to catalyze the oxygen transfer in the presence of phenanthroline, but CuCl was shown to be the optimal (Table 1 entries [8][9][10][11][12]. The copper catalyst required the presence of a N-donor ligand for an efficient process and 1,10-phenanthroline was shown to provide the highest yield ( Table 1, entries 8 and 13-15).…”

“…Alkyl-substituted a,b-unsaturated nitrones such as 1 m were unreactive under the optimized reaction conditions, but this stark change in reactivity does not appear to be due to the fact that these substrates favor the opposite imine isomer to the chalconederived nitrones. [8] A control experiment showed that a 1:1 E/ Z mixture of 1 a gave the desired product in high yield. Finally, dibenzylidene acetone substrates were shown to be tolerated by the copper-catalyzed transformation, but unsymmetrical examples did not exhibit an electronic preference for oxygen transfer ( Table 2, entries [13][14].…”