Concave 1,10-Phenanthrolines by Ring-Closing Metathesis

Ring-closing metathesis using Grubbs’ catalyst has been applied to the synthesis of the concave 1,10-phenanthrolines 5. Instead of a kinetically controlled double macrocyclization of the tetraphenol precursor 2 by two equivalents of ditosylates or diiodides, the new three step synthesis separates the alkylation of 2 from the macrocyclization. After the tetraalkylation of 2, the resulting tetraalkene 3 is cyclized by metathesis under thermodynamic control to give the bimacrocycles 4 in up to 92% yield. Hydrogenation of the alkene double bonds gave the bimacrocycles 5 in considerably improved overall yields (for instance for 5b from 19 to 79%).