Concave 1,10-phenanthrolines by ring-closing metathesis

Ring-closing metathesis using Grubbs' catalyst has been applied to the synt hesis of the concave 1,10-phenanthrolines 5. Instead of a kinetically contr olled double macrocyclization of the tetraphenol precursor 2 by two equival ents of ditosylates or diiodides, the new three step synthesis separates th e 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 t he alkene double bonds gave the bimacrocycles 5 in considerably improved ov erall yields (for instance for 5b from 19 to 79%).