A novel and unusual reaction of 1,2,3,4,5,6,7-hepta(methoxycarbonyl)-cyclohepta-2,4,6-trien-1-yl potassium with organic azides

A new type of rearrangement of an unsaturated seven-membered cycle into substituted ethenylcyclopentadienyl derivatives is described. This process proceeds via a cascade reaction of 1,2,3,4,5,6,7-hepta(methoxycarbonyl)cycloheptatrienyl potassium with organic azides (sulfonyl and carbonyl azides), and affords in one experimental step, N-substituted Z-1-[1,2-bis(methoxycarbonyl)-2-(methoxycarbonylamino)ethen-1-yl]-2,3,4,5-tetrakis(methoxycarbonyl)cyclopentadienyl anions, which represent a new type of chelating ligands.