Synthesis, transformations, and comparative studies of porphyryl acrylic acids and their homologues

The reactivity of porphyryl acrylates and their homologues was studied systematically and to establish their potential as building blocks for the synthesis of novel tetrapyrroles. A new synthetic approach for multifunctional porphyrins was developed using alpha,beta-unsaturated acyl porphyrins as versatile building blocks with yields of 44-95%. The reaction of acyl chlorides generated in situ with ethyl diazoacetate in the presence of PPh(3) led to the corresponding phosphazine, which was quickly self-transformed into a novel porphyrin beta-keto ester system in up to 78% yield. Comparative studies of the next homologue of acrylic porphyrins, i.e., those bearing an additional CH(2) group next to the double bond of the alpha,beta-unsaturated fragment, showed that these can undergo rearrangement reactions via vinylketenes to yield both regioisomers. Depending on the reaction conditions, this method gives regioselectively access to either a rearrangement product or the product of esterification reactions in yields of 81% or 57%, respectively. Enyne metathesis of novel propargyl esters with allyl porphyrins provided an easy access to 1,3-disubstituted butadienes in up to 76% yield.