4 + 2] -Photocycloaddition eines Organoeisendienophils mit 1.3-Dienen/ [4 + 2]-Photocycloaddition of an Organoiron Dienophile with 1,3-Dienes

Abstract

Abstract A tricyclic 1,1,1-tricarbonyl-2,3,1-diazaferrole derivative (1) reacts photochemically with 1,3-dienes with formation of [4 + 2]-cycloadducts. Introduction of substituents in the 1- or 1,4-positions of the diene or of electron releasing groups in the dienophile results in an inhibition of the cycloaddition. The reaction proceeds stepwise via photodissociation of carbon monoxide, coordination of the diene to iron, intramolecular photocycloaddition, and re-uptake of carbon monoxide. No cycloaddition occurs if the complexed diene is allowed to react thermally. X-ray structural analyses of 1 and its cycloadduct with 2,3-dimethylbutadiene (3d) reveal the presence of a novel type of three electron metal - diazene bond for both compounds and delocalized bonding for the diazaferrole 1.