2,2′-Pyrromethene-5[1H]-one, its 1- and 1′-mono- and 1,1′-dimethyl homologues; Synthesis, thermal and photochemical reactivity

✍ Scribed by W. Onkenhout; J. A. van Koeveringe; J. Lugtenburg

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 434 KB
• Volume: 100
• Category: Article
• ISSN: 0165-0513
• DOI: 10.1002/recl.19811000307

✦ Synopsis

Abstract

2,2′‐Pyrromethene‐5[1__H__]‐one*, together with the 1‐ and 1′‐monomethyl and 1,1′‐dimethyl homologues are prepared in high yield.

2,2′‐Pyrromethene‐5[1__H__]‐one (1) and its 1′‐methyl homologue (2) are obtained in the Z form and the 1‐methyl (3) and 1,1′‐dimethyl homologue (4) in the E form. All four systems photoisomerize upon irradiation with light (λ > 360 nm) (Fig. 1). Separation of the photoisomeric mixtures provides the geometrical isomers that cannot be obtained via the thermal synthesis. The photoisomers do not isomerize thermally in refluxing methanol. Upon addition of sodium carbonate in methanol the photoisomers are converted back to the original isomers, demonstrating that Z**‐(1**), Z**‐(2**), E‐(3) and E‐(4) are thermodynamically more stable than E‐(1), E‐(2), Z‐(3) and Z‐(4), respectively. The presence of the 1‐methyl group in 2,2′‐pyrromethene‐5[1__H__]‐one systems is reflected in the thermodynamics and the photochemistry of these molecules.