A Perspective of One‐Pot Pyrrole–Aldehyde Condensations as Versatile Self‐Assembly Processes

Abstract

Regarded as the classic one-pot synthetic route to symmetrical porphyrins for well over half a century, pyrrole-aldehyde cyclocondensations have yielded a cornucopia of nonporphyrin macrocycles, such as N-confused porphyrins, corroles, sapphyrins, and expanded porphyrins, and have thus emerged as versatile self-assembly processes. A highlight in this field is the remarkably general one-pot corrole synthesis. The manifold of intermediates generated in the anaerobic phase of a Lindsey-type synthesis have been viewed as a dynamic covalent self-assembly system. This raises the possibility that the addition of a suitable host may alter the equilibrium concentrations of these intermediates by molecular recognition and related phenomena and thus determine the major product formed after oxidative quenching.

Synthesis, Characterization, and Electrochemistry of Open‐Chain Pentapyrroles and Sapphyrins with Highly Electron‐Withdrawing meso‐Tetraaryl Substituents

“…The oxidative conversiono fp entapyrroles to sapphyrins in a non-aqueous solvent containing I 2 and TFAh as been reported and was proposed to proceed through abis-protonated pentapyrrole intermediate, that is, [(Ar) 4 PPyH 5 ] 2 + ,a ss hown in Scheme 3f or derivatives with stericallyh indered meso-aryl substituents. [61] We wished to know if ap entapyrrole-to-sapphyrinc onversion could also occur for the newly synthesized pentapyrroles after protonation in CH 2 Cl 2 and if so, we wished to elucidate the mechanism and possibly evaluatet he kinetics of this conversion.…”

“…The knownp rotonation reactions of corroles, sapphyrins, and pentapyrroles are schematically shown in Scheme2.T wo protons can be added stepwise to the neutral sapphyrins to give [(Ar) 4 SapH 4 ] + and [(Ar) 4 SapH 5 ] 2 + ,r espectively,w hereas the open-chain pentapyrroles can add two protons in as ingle step to give [(Ar) 4 PPyH 5 ] 2 + as shown in Scheme 2.…”

“…The protonation of (Ar) 4 PPyH 3 to [(Ar) 4 PPyH 5 ] 2 + is showni n Figure 4f or the CF 3 derivative. The protonation of (Ar) 4 PPyH 3 to [(Ar) 4 PPyH 5 ] 2 + is showni n Figure 4f or the CF 3 derivative.…”

“…[1] This macrocycle is an early member of the group of "expanded porphyrins" [2][3][4][5][6][7][8][9][10][11] and was first discovered in the early 1960s as ab yproduct in the synthesis of corroles. [1] This macrocycle is an early member of the group of "expanded porphyrins" [2][3][4][5][6][7][8][9][10][11] and was first discovered in the early 1960s as ab yproduct in the synthesis of corroles.…”

Oxidative Metalation as a Route to Size‐Mismatched Macrocyclic Complexes: Osmium Corroles

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Heavy-element corroles are of great interest as optical sensors, near-IR dyes, phosphors, organic light-emitting diodes, and anticancer compounds. [2,3] Since then, the field has grown exponentially and, in many ways, has begun to rival the breadth and excitement of porphyrin chemistry. Against this backdrop, oxidative metalation of meso triarylcorroles with [Os 3 (CO) 12 ]/NaN 3 in refluxing 1:2 diethylene glycol monomethyl ether/glycol has provided a convenient and relatively high-yielding route to nitridoosmium(VI) corroles, three of which could be characterized with single-crystal X-ray structure analysis.

Although corroles were discovered as long ago as 1964 by Johnson and Kay, [1] the chemistry of corroles started in earnest only some 15 years ago, with reports of convenient one-pot syntheses of meso triarylcorroles.

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