A functionalized spiro[chlorin-porphyrin]-type 'dimer' dizinc complex from rapid [4+2] self-cycloaddition of a conjugated [β,β′- bis(methylene)porphyrinato]zinc

Article abstract of DOI:10.1002/hlca.201100385

Thermal extrusion of SO₂ from β,β′- sulfolenoporphyrins is an effective method for in situ generation of β,β′-bis(methylene)porphyrin which remained unobserved in typical synthetic applications but underwent quickly efficient [4+2]-cycloaddition reactions with dienophiles.We now report the thermal extrusion of SO₂ from the symmetrical (tetra-β,β′- sulfolenoporphyrinato)zinc 1·Zn in the absence of a dienophile (Scheme). In the event, the thermally in situ generated conjugated diene underwent a [4+2] self-cycloaddition, to give the {spirobi[tri-β,β′- sulfolenoporphyrinato]}dizinc 4·2Zn. This chiral (racemic) spirobiporphyrinoid dizinc complex represents the combination of the closely positioned and interacting chromophores of a (porphyrinato)zinc and of a (β-methylene-β,β′-dihydroporphyrinato)zinc. It carries six sulfoleno moieties that are still available for further SO₂ extrusion and cycloaddition reactions. Copyright