Oxidations of chromene-annulated chlorins

Abstract

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.

Oxazolochlorins 21. Most Efficient Access to meso-Tetraphenyl- and meso-Tetrakis(pentafluorophenyl)porpholactones, and Their Zinc(II) and Platinum(II) Complexes

“…Among the possible multi-step processes toward TPL ( Scheme 1 ), one process stands out as particularly suitable for its simplicity and high yields: We have reported in detail [ 51 , 52 ], both the OsO 4 -mediated cis-vic -dihydroxylation, followed by a diol oxidation of the intermediate dihydroxychlorin [ 4 , 17 , 53 , 54 ]. However, there a number of variabilities in these processes: The intermediate osmate ester can be isolated and oxidized, or the osmate ester is reduced to a diol and is then oxidized, with a number of possible oxidants for either step (MnO 4 – with the counter cations cetyltrimethyl ammonium (CTAP) or [18-C-6]·K + [ 4 , 53 ]; CrO 3 [ 17 , 54 ]).…”

“…The most simple, scalable and highest yielding process we find is the osmylation of TPP (performed in up to a 5 g scales), the isolation of osmate ester 4 , followed by its reductive cleavage using gaseous H 2 S, to form chlorin diol 2 [ 51 ], and finally a CrO 3 -mediated oxidation of the diol (performed in up to 300 mg scales) ( Scheme 4 ) [ 17 , 54 ]. The overall yield of 45% of TPL over all three steps from TPP is good (even without considering that ~20% of TPP is recovered after the first step), the reaction is scalable, straight-forward, and well-controlled.…”

β‐meso‐Annulated meso‐Tetraarylchlorins: A Study of the Effect of Ring Fusion on Chlorin Conformation and Optical Spectra

“…were further interested to study the reactivity of the chromene‐annulated chlorin under different conditions to yield new and interesting derivatives. Hence, chemistry of the mono‐chromene‐annulated chlorin under different oxidation conditions was explored and it was discovered that, upon using KMnO 4 − /H + the non‐protected β’‐alcohol in 57 was oxidized whereas chromene annulation was retained (compound 59 , Scheme ) . Swern oxidation of the same chromene‐annulated chlorin yielded α‐thiomethyl‐ether ketone 60 as a minor product, which could be considered as a thio‐analogue of 59 (Scheme ).…”

“…In these examples the linker chromene ring allowed for some degree of conformational flexibility to the molecules. This fact is clearly seen in the crystal structure of the thiomethyl ether which has some waving type deformations . Product 59 displayed a chlorin‐type UV‐visible spectrum which had a ∼10 nm red‐shifted Q y band compared to that of parent chromene‐chlorin 57 (Q y =663 nm) and also a red‐shifted Soret band (432 nm) .…”

“…This fact is clearly seen in the crystal structure of the thiomethyl ether which has some waving type deformations . Product 59 displayed a chlorin‐type UV‐visible spectrum which had a ∼10 nm red‐shifted Q y band compared to that of parent chromene‐chlorin 57 (Q y =663 nm) and also a red‐shifted Soret band (432 nm) . The UV‐Visible spectra of α‐thiomethyl‐ether ketone 60 was very similar to the spectrum α‐hydroxy ketone 59 .…”