Synthesis of Concave 1,10-Phenanthrolines by a Combination of Suzuki Coupling, Ring Closing Metathesis and Hydrogenation
A wide variety of saturated and unsaturated concave 1,10-phenanthrolines 2 and 4 have been synthesized in good yields starting from dichloro-1,10-phenanthroline 14. In the three step synthesis, Suzuki couplings of bis-ortho-substituted boronic acids were used to introduce two different or two identical aryl bridgeheads into the 2- and 9-positions of the 1,10-phenanthroline (yields ⩾70%). The resulting diaryl-1,10-phenanthrolines 3, substituted with alkenyloxy groups of different lengths, underwent ring closing metathesis reactions giving (bi)macrocyclic 1,10-phenanthrolines 4 in yields between 73 and 96%. The alkene chains of 4 were saturated using hydrogen and Pd/C giving the concave 1,10-phenanthrolines 2 in yields between 75 and 99%. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)