𝔖 Bobbio Scriptorium
✦   LIBER   ✦

A survey of acid catalysts in dipyrromethanecarbinol condensations leading to meso-substituted porphyrins

✍ Scribed by G. Richard Geier III; Jennifer B. Callinan; Polisetti Dharma Rao; Jonathan S. Lindsey


Publisher
John Wiley and Sons
Year
2001
Tongue
English
Weight
204 KB
Volume
05
Category
Article
ISSN
1088-4246

No coin nor oath required. For personal study only.

✦ Synopsis


The successful use of dipyrromethanecarbinols in rational routes to porphyrinic macrocycles requires catalysis conditions that enable irreversible condensation, thereby avoiding substituent scrambling and formation of undesired porphyrin products. Previously, successful conditions of trifluoroacetic acid (TFA) (30 mM) in acetonitrile were identified following a lengthy survey of TFA and BF~3~-etherate catalysis in diverse solvents. In this study, focus was placed on the acid catalyst by examining 17 acids in CH ~2~ Cl ~2~, the traditional solvent for two-step, one-flask porphyrin syntheses. In the self-condensation of the carbinol derived from 1-(4-methylbenzoyl)-5-phenyldipyrromethane, porphyrin yields of 9–55% were obtained from the various acids, compared to 20% under TFA catalysis in acetonitrile. A number of catalytic conditions that produce little to no porphyrin in reactions of pyrrole + benzaldehyde afforded good yields of porphyrin and the suppression of scrambling in reactions of dipyrromethanecarbinols. The four best acid catalysts ( InCl ~3~, Sc ( OTf )~3~, Yb ( OTf )~3~, and Dy ( OTf )~3~) initially identified were then examined with dipyrromethanecarbinols bearing challenging substituents (alkyl, pyridyl, or no substituent). The greatest improvement was obtained with the pyridyl substrates. Selected reactions performed on a preparative scale (115 to 460 mg of isolated porphyrin) verified the results of the analytical-scale experiments and revealed the more facile isolation of the porphyrin from reactions performed in CH ~2~ Cl ~2~ rather than acetonitrile. This study provides alternatives to the use of TFA/acetonitrile that offer advantages in terms of yield and isolation of the porphyrin without sacrificing suppression of scrambling. Furthermore, the finding that poor catalysts for the benzaldehyde + pyrrole reaction can be excellent catalysts for dipyrromethanecarbinols provides guidance for the identification of other catalysts for use with reactive precursors in porphyrin-forming reactions.


πŸ“œ SIMILAR VOLUMES


ChemInform Abstract: Synthesis of meso-S
✍ A. SRINIVASAN; S. MAHAJAN; S. K. PUSHPAN; M. RAVIKUMAR; T. K. CHANDRASHEKAR πŸ“‚ Article πŸ“… 2010 πŸ› John Wiley and Sons βš– 31 KB πŸ‘ 2 views

## Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a β€œFull Text” option. The original article is trackable v