An Efficient Synthesis of Porphyrins with Different meso Substituents that Avoids Scrambling in Aqueous Media

Abstract

We have developed new conditions that afford regioisomerically pure trans-A2B2-, A3B-, and trans-AB2C-porphyrins bearing aryl and arylethynyl substituents. The porphyrins were prepared by the acid-catalyzed condensation of dipyrromethanes with aldehydes followed by oxidation with p-chloranil or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Optimal conditions for the condensation were identified after examining various reaction parameters such as solvent composition, acid concentration, and reaction time. The conditions identified (for aromatic aldehydes: EtOH/H2O 4:1, [DPM] = 4 mM, [aldehyde] = 4 mM, [HCl] = 38 mM, 16 h; for arylethynyl aldehydes: THF/H2O 2:1, [DPM] = 13 mM, [aldehyde] = 13 mM, [HCl] = 150 mM, 3 h) resulted in the formation of porphyrins in yields of 9-38% without detectable scrambling. This synthesis is compatible with diverse functionalities such as ester or nitrile. In total, 20 new trans-A2B2-, A3B-, and trans-AB2C-porphyrins were prepared. The scope and limitations of the two sets of reaction conditions have been explored. The methodological advantage of this approach is its straightforward access to building blocks and the formation of the porphyrin core in higher yields than by any other methodology and by using environmentally benign and nonhazardous chemicals.

Straightforward Syntheses That Avoid Scrambling of meso‐Substituted [28]Hexaphyrins

“…for C 37 H 18 F 15 N 4 [M + H] + 803.1286; found 803.1285. These analytical data are in accordance with the literature values , …”

Synthesis of Substituted 1‐Alkylidenephthalanes via Lithium‐Promoted 5‐exo‐dig Cyclization

“…At first, propynal dimethyl acetal 9a was synthesized in three steps from 1-bromo-2-iodobenzene (6) comprising a Sonogashira reaction [18] with propargyl alcohol, oxidation with TEMPO and (diacetoxyiodo)benzene [19] and acetalization with methanol. The diethyl acetal 9b was prepared by Sonogashira reaction of 1-bromo-2-iodobenzene (6) with propynal diethyl acetal, which are both commercially available Furthermore, the cyclic acetal 9c was synthesized by transacetalization of diethyl acetal 9b with 2,2-dimethylpropane-1,3-diol.…”

Synthesis and Studies of New Fluorescein‐Porphyrin Dyads: A Theoretical and Experimental Approach

“…Additional tries were made by microwave irradiations under milder conditions with similar yields (6‐8%) . The choice of the Little's method was preferred to that involving dipyrromethanes due to commercial availability of starting materials and well‐controlled procedures in laboratory. The synthesis of compound 9 was then achieved through a simple Williamson's reaction in the presence of 1,3‐dibromopropane (Scheme ).…”