ABC‐Type meso‐Triaryl‐Substituted Subporphyrins

Abstract

Abstract ABC‐Type subporphyrins 5a – 5h, which bear three different meso ‐aryl substituents, were rationally synthesized by condensation of AB‐type tripyrranes and aroyl chlorides. ABC‐Type subporphyrins 5i and 5j were synthesized by Pd‐catalyzed amination reaction of 4‐bromophenyl subporphyrins 5e and 5h , respectively. Comparative studies on these ABC‐type subporphyrins with A 3 ‐type subporphyrins and A 2 B‐type subporphyrins revealed that substituent effects are mostly simple superpositions of individual substituents but cooperative effects are recognized for subporphyrins which bear both electron‐donating and electron‐withdrawing substituents. Despite extensive attempts, enantiomeric separation of B‐methoxy ABC‐type subporphyrins was unsuccessful, whereas B‐phenylated ABC‐type subporphyrins were separated to pure enantiomers. Separated enantiomers showed weak but distinct CD signals reflecting the chiral clockwise/anticlockwise arrangements of the meso ‐aryl substituents. These results suggest facile racemization through S N 1‐type heterolysis of the B–OMe bond in solution.