Mechanical trapping and in situ derivatization of the porphodimethene intermediate

Manipulation of the energy profile of a chemical reaction plays a crucial role in modulating its progress and selectivities. Porphodimethene and phlorin are two key isoelectronic intermediates during the stepwise oxidation process leading to the formation of porphyrin from calix[4]pyrrole. We report here the mechanical capture of porphodimethene instead of phlorin as well as its simultaneous derivatization by means of molecular-strain engineering (MSE). By tuning the linker between its 5- and 15- meso -positions, a constrained porphodimethene has been trapped which can be oxidized with 4,5-dichloro-3,6-dioxo-1,2-benzenedinitrile in the presence of a range of nucleophiles to afford a novel class of stable disubstituted porphodimethene derivatives. Their structures were characterized by NMR spectroscopies, mass spectrometry, and single-crystal X-ray crystallography. Theoretical calculations indicate that the enhanced strain energy resulted from the elongation of the bow-limb in the proposed porphyrin bow favors the formation of the configuration of the porphodimethene intermediate containing two sp 3 -hybridized meso -carbons rather than that of the phlorin consisting of one sp 3 - meso -carbon atom. This work demonstrates that MSE can steer the reaction trajectory through specific intermediates, providing the ability to control precisely the reaction progress and selectivity of desired products. • Selective trapping the porphodimethene intermediate without multistep synthesis or harsh reaction conditions. • Mechanical trapping of intermediates affords an alternative to conventional adding scavengers for investigating reaction mechanisms. • Reaction selectivity can be controlled by steering the reaction trajectory through specific intermediates. • In situ oxidation of porphodimethene in the presence of H 2 O and alcohols yields a series of novel disubstituted derivatives.