Investigation of Complementary Reactions of a Dipyrromethane with a Dipyrromethanemonocarbinol Leading to a 5-Isocorrole

Abstract

Two complementary dipyrromethane + dipyrromethanemonocarbinol routes to a meso-substituted 5-isocorrole were investigated. While both routes could afford the identical 5-isocorrole, self-condensation of the different dipyrromethanemonocarbinol precursors could potentially lead to a second porphyrinoid of different structure (a porphyrin or a porphodimethene). The two reaction routes were examined to compare the distribution of porphyrinoid products, probe the effect of key reaction parameters on the product distribution, and identify conditions for the efficient preparation of the 5-isocorrole so that its spectral properties and stability toward light and air could be assessed. For each route, a systematic survey of reaction parameters was performed via analytical-scale reactions monitored for the yields of the 5-isocorrole and self-condensation product by HPLC. The two reaction routes were found to afford very different product distributions in accordance with the anticipated nucleophilicity of the dipyrromethane and dipyrromethanemonocarbinol precursors. The most promising reaction condition (InCl(3), 0.32 mM) was performed on a preparative-scale providing the 5-isocorrole in an isolated yield of 31% (102 mg). Spectroscopic analysis was consistent with the 5-isocorrole structure. The stability of the 5-isocorrole in dilute solution upon exposure to light and air was assessed by UV-vis spectroscopy and HPLC and was found to be excellent.

Mechanical Trapping of the Phlorin Intermediate

“…In principle, phlorins can be prepared by two major strategies: (1) starting from porphyrin, which can be attacked by nucleophiles-for example, alkyl lithium reagents or hydride-at its meso-position [13][14][15][16] and (2) starting from acyclic (oligo)pyrrole building blocks and aldehydes or ketones employing an acid-catalyzed condensation followed by the oxidative dehydrogenation of intermediates. 1,[17][18][19][20][21] However, native phlorins with unmodified core-structures are highly unstable and readily oxidized, 9,19,22,23 making it difficult to isolate them. To stabilize phlorins during their synthesis, chemists have proposed five methods: (1) introducing bulky substituents, for example, mesityl and phenyl, at the meso-sp 3 -carbon atom to hinder oxidation 1,13,18,19,22,[24][25][26][27] and electron-withdrawing substituents, for example, pentafluorophenyl, 1,19,24,27 to enhance the oxidation potential of the phlorin; (2) N-substitution 16,28,29 so as to distort its conformation; (3) metalation with metal ions in the core of the phlorin 30 ; (4) replacing pyrrole with thiophene 31 ; and (5) introducing electron-withdrawing groups at the β-position of these pyrroles.…”

One-pot synthesis of meso-alkyl substituted isocorroles: the reaction of a triarylcorrole with Grignard reagent

“…More recently, the synthesis of the free-base isocorroles has been reported. In 2006, Setsune et al [10] described the isolation of 10,10-dimethylisocorrole in 28% yield, and more recently Geier and co-workers investigated two complementary routes leading to the formation of 5,5-dimethylisocorroles (31%) [11]. …”

An Easily Prepared Monomeric Cobalt(II) Tetrapyrrole Complex that Efficiently Promotes the 4e–/4H+ Peractivation of O2 to Water

“…[18][19][20]24,48 Recent work has been aimed at development of nonaromatic tetrapyrrole scaffolds (e.g. phlorins, [49][50][51][52][53][54][55][56] biladienes, [57][58][59][60] and isocorroles [61][62][63][64][65][66][67] ) that include an sp 3 -hybridized meso-carbon and which support unique photophysical and multielectron redox properties. These nontraditional tetrapyrroles provide alternate platforms to consider for ORR and other small molecule activation processes and may offer distinct reactivity profiles and catalytic activities.…”