The palladium-catalysed copper-free Sonogashira coupling of isoindoline nitroxides: a convenient route to robust profluorescent carbon-carbon frameworks.
A series of novel acetylene-substituted isoindoline nitroxides were synthesised via palladium-catalysed copper-free Sonogashira coupling. These results demonstrate that the Sonogashira reaction is suitable for the generation of a wide range of aryl nitroxides of expanded structural variety. The novel aryl-iodide containing nitroxide, 5-iodo-1,1,3,3-tetramethylisoindolin-2-yloxyl, 3, was a key intermediate for this coupling, giving acetylene-substituted isoindoline nitroxides in high yield. Subsequent reaction of the deprotected ethynyl nitroxide 12 with iodinated polyaromatics furnished novel aromatic nitroxides with extended-conjugation. Such nitroxides have been described as profluorescent, as their quantum yields are significantly lower than those of the corresponding diamagnetic derivatives. The quantum yields of the naphthyl- and phenanthryl-acetylene isoindoline nitroxides (13 and 14) were found to be 200-fold and 65-fold less than the non-radical methoxyamine derivatives (23 and 24). Ethyne- and butadiyne-linked nitroxide dimers could also be synthesised by this cross coupling methodology.
Keddie
Daniel J
DJ
ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, Queensland University of Technology, Brisbane 4001, Australia.
Fairfull-Smith
Kathryn E
KE
Bottle
Steven E
SE
D000114:Acetylene / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D007211:Indoles / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry; D009589:Nitrogen Oxides / Q000138:chemical synthesis / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010616:Phenanthrenes / Q000737:chemistry
D005456:Fluorescent Dyes; D007211:Indoles; D009281:Naphthalenes; D009589:Nitrogen Oxides; D010616:Phenanthrenes; C031721:naphthalene; C031181:phenanthrene; D010165:Palladium; D002244:Carbon; D003300:Copper; D000114:Acetylene