[14077-15-7] · C20H24CuN2O2 · Bis(N-propylsalicylideneaminato)copper(II) · (MW 387.97)
Alternate Name: bis[2-(N-propylformimidoyl)phenolato]copper.
Physical Data: green or greenish-brown needles; mp 127-128 °C.
Solubility: sol alcohol, dioxane, chloroform, and benzene; insol water, pet ether.
Preparative Method: by one-pot reaction of n-propylamine with the bis(salicylaldehato)copper complex prepared from copper(II) acetate and salicylaldehyde.1
Purification: recrystallization from cyclohexane or chloroform-ethanol.1
Handling, Storage, and Precautions: irritant. The copper chelate can be stored at rt in the absence of moisture.
In the synthesis of the natural sesquiterpene (±)-a-chamigrene, construction of the spirocyclic skeleton involved an intramolecular ketocarbenoid addition via thermal copper-catalyzed diazo ketone decomposition, followed by dissolving-metal reduction of the cyclopropane ring in the product (eq 1).2,3
It was discovered that insoluble copper salts typically employed for such decompositions, e.g. Copper(II) Acetate and Copper(I) Chloride, reacted instead with the acetal protecting group. Use of the more soluble copper chelate avoided this problem, giving the tricycloketone intermediate in 66% yield.3 With relatively nonfunctionalized systems (eq 3), the more traditional copper salt catalysts are as effective as the title reagent; thus Copper powder could be employed in a similar diazo ketone decomposition which ultimately led to the spirocyclic (-)-acorenone B (eq 2).3,5
The reagent, and other similar chelated copper(II) complexes, catalyzes the oxidation of 3,5-di-t-butylcatechol by O2. The catalytic behavior is related to the electron transfer reactions between the complex and two-electron donors such as catechols and ascorbic acid (eq 4).4
Edward J. Parish & Shengrong Li
Auburn University, AL, USA