A Functionalized Spiro[chlorin‐porphyrin]‐Type ‘Dimer’ Dizinc Complex from Rapid [4+2] Self‐cycloaddition of a Conjugated [ β , β′ ‐Bis(methylene)porphyrinato]zinc

Thermal extrusion of SO 2 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 SO 2 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 SO 2 extrusion and cycloaddition reactions.