Revisiting the Synthesis and Nucleophilic Reactivity of an Anionic Copper Superoxide Complex.

The addition of 1 equiv of KO and Kryptofix222 (Krypt) in CHCN to a solution of LCu(CHCN) [L = N, N'-bis(2,6-diisopropylphenyl)-2,6-pyridinecarboxamide] in tetrahydrofuran at -80 °C yielded [K(Krypt)][LCuO], the enhanced stability of which enabled reexamination of its reactivity with 2-phenylpropionaldehyde (2-PPA). Mechanistic and product analysis studies revealed that [K(Krypt)][LCuO] reacts with wet 2-PPA to form [LCuOH], which then deprotonates 2-PPA to yield the copper(II) enolate complex [LCu(OC═C(Me)Ph)]. Acetophenone was observed upon workup of this complex or mixtures of KO and 2-PPA alone, in support of an alternative mechanism(s) to the one proposed previously involving an initial nucleophilic attack at the carbonyl group of 2-PPA.