On the peculiar reactivity of a C,N-annelated isoindole core

Abstract

C-, N-, and/or O-methylation products were generated from 11 H -isoindolo[2,1-a]quinazoline-5-one upon treatment with NaH followed by iodomethane under air, and possible recrystallization from methanol. Two products were fully characterized by NMR and X-ray diffraction analysis. In accordance with the HSAB principle, this soft methylating agent (MeI) leads mainly to the C,C-dimethylated product 11,11-dimethyl-11 H -isoindolo[2,1-a]quinazoline-5-one, which was previously not observed, beside the N-methylated product, in a procedure using methyl tosylate as a hard methylating agent of the same substrate in the initial absence of a base. A mechanism is finally proposed for the formation of methyl 2-(3-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)benzoate as an oxidation side product.

A difluorenyl-carbo-cyclohexadiene: prospective chromophore for two-photon absorption

“…substituted carbo-cyclohexadiene 3 were found to display a weak emission at = 533 nm upon excitation at 470 nm. This result meets previous observations of poor emission properties of carbo-chromophores, even those bearing fluorophore substituents, the fluorescence quenching being correlated with their high absorbance[18].…”

Steric/π‐Electronic Insulation of the carbo‐Benzene Ring: Dramatic Effects of tert‐Butyl versus Phenyl Crowns on Geometric, Chromophoric, Redox, and Magnetic Properties

“…The emission properties of 5 – 8 in the UV/Vis region were measured to be very weak, with quantum yields below 1 %, lifetimes shorter than 2 ns, and Stoke shifts above 70 nm (Table ; calculated data are given in Supporting Information). This is in line with trends reported for most of the carbo ‐benzenes, even those bearing fluorophoric substituents: to date, the sole example of significant fluorescence has been reported for a bis‐indolyl derivative and explained by an exceptionally low molar extinction coefficient . The high extinction coefficients of 5 – 8 ( ϵ =260 000–400 000 L mol −1 cm −1 ) and extremely low fluorescence are in accordance therewith.…”

“…The high extinction coefficients of 5 – 8 ( ϵ =260 000–400 000 L mol −1 cm −1 ) and extremely low fluorescence are in accordance therewith. It was indeed proposed that the very weak fluorescence of carbo ‐benzenes was due to their very high ϵ values, any emitted photons being instantly reabsorbed by the medium …”

Difluorenyl carbo‐Benzenes: Synthesis, Electronic Structure, and Two‐Photon Absorption Properties of Hydrocarbon Quadrupolar Chromophores

“…Finally, the fluorenyl‐substituted carbo ‐benzenes 3 a and 3 b were found to exhibit very weak fluorescence at about 650 nm on excitation at 532 nm (Supporting Information, Figure S2) 22…”

“…Because of their very poor fluorescence,22 the 2PA cross‐sections of carbo ‐chromophores 3 a and 3 b were measured by the Z ‐scan technique. The Z ‐scan method indeed allows convenient investigations of third‐order NLO properties,17b not only nonlinear refraction (self‐focusing or self‐defocusing phenomena), but also nonlinear absorption of materials.…”