meso-Aryl-3-alkyl-2-oxachlorins

Abstract

The formal replacement of a pyrrole moiety of meso-tetraarylporphyrin 1 by an oxazole moiety is described. The key step is the conversion of porpholactones 4 (prepared by a known two-step oxidation procedure from 1) by addition of alkyl Grignard reagent to form meso-tetraaryl-3-alkyl-2-oxachlorins 9 (alkyloxazolochlorins; alkyl = Me, Et, iPr). Hemiacetal 9 can be converted to an acetal, reduced to an ether, or converted to bis-alkyloxazolochlorins 11. The optical properties (UV–visible and fluorescence spectroscopy) are described. The chlorin-like optical properties of the alkyloxazolochlorins are compared to regular chlorins, such as 2,3-dihydroxychlorins and nonalkylated oxazolochlorins made by reduction from porpholactone 4. The conformations of the mono- and bis-alkylated 2-oxachlorins, as determined by single crystal X-ray diffractometry, are essentially planar, thus proving that their optical properties are largely due to their intrinsic electronic properties and not affected by conformational effects. The mono- and bis-3-alkyl-2-oxachlorins are a class of readily prepared and oxidatively stable chlorins.

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

“…While the porpholactones described are of broad utility, access to the free base porpholactones also enables entry to a number of other metalloporpholactones. Moreover, closely related porphyrins of utility can be derived, like the thionolactones used as hypochlorite sensors [ 18 ], the porpholactone reduction products porpholactols [ 4 , 55 , 56 , 57 ] useful as photosensitizers [ 58 ] or hydrogen evolution catalysts [ 28 ], as well as chlorolactones and chlorolactams [ 59 , 60 ], porpholactams [ 59 , 60 ], and imidazoloporphyrins [ 60 ], even if alternative synthetic pathways for the latter porphyrinoid were developed that circumvent the intermediate porpholactone [ 61 ]. The method described also allow direct access to the meso -pentafluorophenyl-substituted porphodilactone isomers of broad utility [ 17 ], though longer but more rational syntheses might be desirable when more than 10 −5 mol quantities are desired of either the fluorinated or non-fluorinated series [ 17 , 62 ].…”

Effects of Substituents on Synthetic Analogs of Chlorophylls. Part 4: How Formyl Group Location Dictates the Spectral Properties of Chlorophylls b, d and f

“…The studies have encompassed analysis of the photophysical characteristics and electronic structure of sets of chlorins and 13 1 ‐oxophorbines bearing a formyl (or other substituent) at the 7‐position (relevant to Chl b ) and at the 3‐ and/or 13‐position (relevant to Chl d ). Understanding the effects of such auxochromes on the spectral properties is of fundamental interest and underlies numerous applications in the photochemical arena .…”

Siamese‐Twin Porphyrin: A Pyrazole‐Based Expanded Porphyrin of Persistent Helical Conformation

“…[17] In these complexes, the pyrazoles are monoanionic donors supporting a range of metalmetal distances. [18] The integration of pyrazole moieties (or other heterocycles such as imidazoles, [19] oxazoles, [20] thiadiazoles, or triazoles [21] ) in porphyrinoid macrocyclic compounds is, however, little developed. Only one family of porphyrin analogues incorporating a pyrazole, carbaporphyrins 4, recently introduced by the group of Lash, is known.…”