Reactive Intermediates Iron and Copper Species

Most of the metal-dioxygen adducts previously discussed have limited stability and therefore serve as the starting point in our discussion of reactive intermediates. Although many of the complexes are difficult to work with under ambient 

---

O2 activation is a key step in enzymatic oxidation catalysis. Interaction with metals like copper or iron generates high valent metal species with high oxidizing power. Some bioinspired systems can carry out such an activation to yield reactive intermediates. Nevertheless, these can also be formed by shunt pathways using other chemical oxidizing compounds, and such examples will also be presented in this section. 

Copper(II), iron(III), and other silver(I) salts displayed no reactivity, apart from AgqO, which produced inferior yields (63%). The reaction was unaffected by acidic or basic additives, and moiecuiar oxygen was inoperabie as a terminal oxidant consequentiy, 2.0 equiv of Ag2C03 was required for optimal yields. Various 2-aminopyridines were viabie, exhibiting minimal substituent effects. Additionaiiy, 1-aminoisoquinoiine and 2-aminoquinoline couid be cyciized however, imidazoie dispiayed diminished reactivity (40% yieid). A diversity of terminai aryi alkynes could also be employed. A silver acetylide species was postulated to serve as a key intermediate. Notably, zolimidine, a marketed antiulcer drug, could be efficiently obtained via this process (eq 36). 

A formal [2+1+1] cycloaddition is achieved by reaction of alkynes with an iron carbonyl species that is prepared in situ from dodecacarbonyltriiron Fe3(CO)i2 in the presence of certain amines. This procedure provides cyclobutenediones in moderate to good yields after demetalation with copper(II) chloride (Scheme 4-14). Instead of amines and dodecacarbonyltriiron, alkoxides such as ter/-BuOK can be reacted with pentacarbonyliron to give reactive carbonyliron intermediates that undergo cyclization... 

---