Carlotta Raviola

Acetalization allows the photoheterolysis of the Ar-Cl bond in chlorobenzaldehydes and chloroacetophenones.

The nonaccessibility of phenyl cations by irradiation of electron-poor aryl chlorides was circumvented by transforming the carbonyl group of aromatic ketones or aldehydes into the corresponding 1,3-dioxolanes and the carboxyl group of benzoate ester into an orthoester functionality. This transformation allowed the heterolytic photoactivation of the Ar-Cl bond in protic media and the generation of phenyl cations. In the presence of π-bond nucleophiles, arylated products were obtained in good to excellent yields.

Methoxy-Substituted α,n-Didehydrotoluenes. Photochemical Generation and Polar vs Diradical Reactivity

The photoreactivity of differently substituted (chloromethoxybenzyl)trimethylsilanes in alcohols and alcohol/water mixtures has been investigated by means of a combined computational and experimental approach. Subsequent elimination of the chloride anion and the trimethylsilyl cation gives the corresponding methoxy-substituted α,n-didehydrotoluenes (α,n-MeO-DHTs). The rate of desilylation is evaluated through the competition with arylation via phenyl cation (ca. 10(8) s(-1)). α,2-MeO- and α,4-MeO-DHTs show a purely radical behavior (H abstraction from the solvent, methanol), while α,3-MeO-DHT shows mainly a ionic chemistry, as when the parent α,3-DHT is thermally generated. This is likely due to triplet-singlet surfaces crossing occurring during desilylation.

Metal-free arylations via photochemical activation of the Ar–OSO2R bond in aryl nonaflates

The photolysis of electron-rich aryl nonaflates (ArONfs) in protic media was investigated and heterolysis of the Ar–OS bond (from 3ArONf) took place. The reaction generated a triplet phenyl cation that added to π-bond nucleophiles. This metal-free arylation method was made further useful by adopting in situ preparation of ArONf from the corresponding phenol.

On the Route to the Photogeneration of Heteroaryl Cations. The Case of Halothiophenes

2-Chloro-, 2-bromo-, and 2-iodothiophenes undergo photochemical dehalogenation via the triplet state. In the presence of suitable π-bond nucleophiles, thienylation occurs with modest yield from chloro and bromo derivatives (via photogenerated triplet 2-thienyl cation). Specific trapping by using oxygen along with computational analysis carried out by means of a density functional method support that, in the case of iodo derivatives, homolytic thienyl-I bond fragmentation occurs first and heteroaryl cations are formed by electron transfer within the triplet radical pair, thus opening an indirect access to such cations.