Diels-Alder Reactions of Protoporphyrin IX Dimethyl Ester with Electron-Deficient Alkynes

Article abstract of DOI:10.1021/jo00357a029

The vinyl and cross-conjugated porphyrin β,β' double bonds of either ring A or B of protoporphyrin IX dimethyl ester react in a <4 + 2> cycloaddition with electron-deficient acetylenes.The methyl and ethyl esters of acetylenedicarboxylic acid and β-(phenylsulfonyl)propiolic acid react to give the corresponding chlorins with the ring A and B isomers being readily separable by chromatography.The initial products are rearranged by treatment with base.Reaction with triethylamine or 1,5-diazabicyclo<5.4.0>undec-5-ene gave, in every case, two diastereomers, where theformer rearrangement led to the kinetically controlled and the latter the thermodynamically controlled products.The Diels-Alder reaction with the unsymmetric acetylenes is both regio- and stereospecific.