Synthesis of conjugation-expanded porphyrins based on the retro diels-alder reaction

摘要

Bicyclo-, benzobicyclo-, and naphthobicyclo-[2.2.2]octadiene-fused porphyrins were prepared from ethano-bridged isoindole derivatives via the common methods such as cyclic tetramerization, MacDonald [2+2], and [3+1] porphyrin syntheses. Heating these porphyrins over 200 deg C caused the retro Diels-Alder reaction leading to quantitative extrusion of ethylene to give the corresponding benzo-, naphtho-, and anthra-fused porphyrins, UV absorption of which showed efficient red-shift compared to those of the starting porphyrins. Upon the thermal treatment, the very bulky bicyclic-ring-fused porphyrins readily soluble in common solvents were converted to the flat, insoluble, conjugation-expanded porphyrins, purification of which often encountered difficulty. This methodology provides not only an easy access to highly conjugated porphyrins and related chromophores in very high quality, but also a significant conversion of soluble dyestuffs of insoluble pigments.