β‐Alkyloxazolochlorins: Revisiting the Ozonation of Octaalkylporphyrins, and Beyond

Abstract

The reaction of β-octaalkylporphyrins (octaethylporphyrin and etioporphyrin I) with ozone generated the corresponding heptaalkyloxazolochlorinhemiacetals in which a pyrrolic subunit of the porphyrins was replaced by an oxazoline moiety. Thus, a pyrrolic β-carbon with its alkyl substituent was excised and replaced by an oxygen atom, and the neighboring β-carbon was hydroxylated. This work clarifies the nature of the products first described by Fischer and Deželić, in 1933, and verifies the work by Shulg'a and coworkers, from 1977. Furthermore, the chemistry of the oxazolochlorin hemiacetals was studied: They could be dehydroxylated or converted to alkyl acetals and gem-dialkyl derivatives, all possessing chlorin-type optical spectra. Their oxidative conversions generated a unique tetrahydrofuran-linked oxazolochlorin dimer and a hexaethylporpholactone. The work expands on the knowledge of converting porphyrins to porphyrinoids of potential utility containing nonpyrrolic building heterocycles.

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

“…This is because of their relative ease of synthesis in one step from T F PP using a number of different methodologies (see below Scheme 2 ) and the multiple possibilities to derivatize the C 6 F 5 -groups by means of nucleophilic aromatic substitution reactions to, for example, render them water-soluble [ 6 , 7 , 8 ]. The presence of a ß,ß’-lactone moiety in carbaporphyrins [ 9 ], thiaporphyrins [ 10 , 11 ], octaalkylporphyrins [ 12 ], or subporphyrins [ 13 ] is known but much more rare and the utility of these compounds has not yet been shown.…”

Conformational Landscapes of Metal(II) Porphyrinato, Chlorinato, and Morpholinochlorinato Complexes

“…Multiple examples of meso -arylporphyrinoids derived by the formal replacement of a pyrrole of a porphyrin by a nonpyrrolic moiety were reported. , One example containing a five-membered carbacycle in place of a pyrrole is the azuliporphyrin 1 , exclusively prepared by total synthesis . A formal replacement of a β,β′ bond by a lactone moiety results in the formation of the porpholactones 2 , generated by carefully calibrated oxidations of porphyrins or chlorins . The oxypyriporphyrin 3 containing a six-membered nonpyrrolic heterocycle can be accessed using either total synthesis or porphyrin modification methodologies .…”

Observations on the Mechanochemical Insertion of Zinc(II), Copper(II), Magnesium(II), and Select Other Metal(II) Ions into Porphyrins

“…T F PP degraded ∼30% faster than TPP , and OEP yet another ∼30% faster. Again, no products could be identified, although a number of direct oxidation products of TPP , T F PP , and OEP are known. The rates of degradation vary in the presence of the metal salts (not shown), likely reflecting the stability of the metalloporphyrins toward (oxidative) degradation. − On the upside, except for the reactions involving the chlorins (see below, Table , entries 4–11 and 4–12), the degradation products that formed did not interfere with the isolation or purity of the target products.…”