Synthesis of porphyryl boronates with (un)saturated side-chains

Porphyrins with (un)saturated side–chains containing boron residues were developed as synthons for porphyrin functionalisation. Porphyrins with mono and bis-substituted unsaturated boronyl residues were prepared in good yields (52–66%) using a cross-metathesis approach in the presence of Grubbs I-generation catalysts. In all cases complete E-stereoselectivity (100%) was observed. Furthermore, formal cross-metathesis products with α,β-unsaturated chains smoothly underwent addition with bis(pinacolato)diboron [(Me4C2O2)B-B(O2C2Me4)] to yield the corresponding saturated boron compounds in 60–70% yields.