Porpholactones are porphyrinoids in which one or more β,β′-bonds of the parent chromophore were replaced by lactone moieties. Accessible to varying degrees by direct and nonselective oxidations of porphyrins, the rational syntheses of all five dilactone isomers along stepwise, controlled, and high-yielding routes via porphyrin → tetrahydroxyisobacteriochlorin metal complexes → isobacteriochlorindilactone metal complexes or porphyrin → tetrahydroxybacteriochlorin → bacteriochlorindilactone (and related) pathways, respectively, are described. A major benefit of these complementary routes over established methods is the simplicity of the isolation of the dilactones because of the reduced number of side products formed. In an alternative approach we report the direct and selective conversion of free base meso-tetrakis(pentafluorophenyl)porphyrin to all isomers of free base isobacteriodilactones using the oxidant cetyltrimethylN+MnO4 –. The solid-state structures of some of the isomers and their precursors are reported, providing data on the conformational modulation induced by the derivatizations. We also rationalize computationally their differing thermodynamic stability and electronic properties. In making new efficient routes toward these dilactone isomers available, we enable the further study of this diverse class of porphyrinoids.
Syntheses and optical properties of mono- and bis-chromene-annulated bacteriochlorins are described. Known monochromene-annulated meso-(pentafluorophenyl)chlorin is susceptible to a regioselective OsO4-mediated dihydroxylation, generating two monochromene-annulated trihydroxybacteriochlorin stereoisomers: either the newly introduced vic-cis-diol functionality is on the same side as the vic-cis-diol moiety the chromene-annulation was based on or on the opposite side. Treatment of the two isomers with heat or base generates different sets of bis-chromene-annulated bacteriochlorin stereo- and regioisomers. Detailed 1D and 2D (1)H and (19)F NMR spectroscopic investigations allowed the characterization of the isomers that formed. The regioselectivity of the second annulation reaction was rationalized computationally on steric grounds. The bacteriochlorin-type optical spectra of the mono- and bis-chromene-annulated bacteriochlorins are modulated as a result of the annulation, with each isomer possessing a unique spectrum, attributed to the effects the regiochemically distinct annulations have on the conformation of the chromophore. The formation of a bis-chromene-annulated chlorin from the bacteriochlorins is also described, including its X-ray crystal structure, revealing some details of the metrics of the chromene-annulated moiety. The vic-diol functionality of monochromene-annulated trihydroxybacteriochlorins is also susceptible to oxidation and ring-expansion reactions, generating chromene-annulated pyrrole-modified chlorins incorporating oxazolone and morpholine moieties. The work expands the body of work on the synthesis and optical fine-tuning of meso-aryl-substituted bacteriochlorins.
A chromene-annulated chlorin is a meso-pentafluorophenyl-2,3-dihydroxychlorin in which one of the hydroxy groups is linked to the ortho-position of a flanking meso-aryl group, thereby forming an annulated chromene moiety; the second hydroxy group is unprotected. This report illustrates the oxidation chemistry of the chromene-annulated chlorin under a number of different oxidation conditions. In some reactions, chromene annulation is retained and the non-protected alcohol is oxidized, generating chlorin-like chromophores carrying pyrroline β-carbons in oxidation states between those found in typical porphyrins and chlorins. Other products have lost the chromene moiety. The reactivity of the pyrroline carbon with respect to undergoing radical chemistry is shown with the formation of a number of products following a Swern oxidation, including the formation of two directly linked pyrroline-pyrroline and pyrroline-pyrrole chlorin dimers. This work contributes to the further understanding of the chemistry of chlorins. Selected compounds possess functionalities at their periphery susceptible to nucleophilic attack by MeOH, suggesting their use as chemosensors.
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