Bisoxazoline–copper(I)-catalyzed aziridination of diazoacetate with imines — A DFT study

Density functional theory (DFT) has been used to study bisoxazoline–copper(I)-catalyzed aziridination of diazoacetate with syn-imines or anti-imines. All the intermediates and transition states were optimized completely at the B3LYP/6-31G(d) level. Calculation results confirm that Cu(I)-catalyzed aziridination goes mainly through the catalyst–diazoacetate complex (M1), the copper(I)–carbene intermediate (M2), the copper–carbene–imine complex (M3), and the catalyst–aziridine carboxylate complex (M4). For syn-imines, the reaction mode I (C3–N5 bond attacking the Cu–C1 bond of M2) is more dominant than the reaction mode II (C3–N5 bond attacking the carbene–carbon C1 of M2), and the attack from the si-surface of M2 is prior to the re-surface. For anti-imines, the reaction modes and attacks from the si- or re-surface coexist. The reactivity of syn-imines is stronger than anti-imines. The favorable reaction channel is CA2 → M1b → TS1b → M2 → syn-TS2b → syn-M3b → syn-TS3b → syn-M4b → syn-P2. The dominant product theoretically predicted is of (S,S)-chirality. On the whole, the solvent effect decreases the free energies of the species.