Dries De Vos

A visible-light-driven, metal-free catalyzed switchable chemo-selective transformation of aromatic aldehydes and ketones into pinacols and benzyl alcohols is reported.

Abstract

We report a versatile and efficient organophotoredox-catalyzed (4CzIPN) chemo-selective conversion of aromatic aldehydes and ketones into pinacols and benzyl alcohols. Hantzsch ester and thiophenol were used as the electron, proton and hydrogen atom donors. Product selectivity can be switched from pinacols to benzyl alcohols simply by adding a stoichiometric amount of thiophenol to the reaction system. The operationally simple protocol tolerates a variety of functional groups and selectively converts aromatic aldehyde into pinacol or benzyl alcohol in the presence of both aromatic ketone and aliphatic aldehyde.

Abstract

Selenols react with isocyanates under mild catalyst-free conditions to generate selenocarbamates in good yield and with high selectivity over potentially competing nucleophilic additions. The methodology enables the incorporation of a wide variety of functional groups providing access to a broad array of densely functionalised selenocarbamates. In the presence of competing heteroatom-centered nucleophiles, isocyanates selectively couple with selenols. Selenocarbamates exhibited thiol-peroxidase-like properties, enabling the reduction of hydrogen peroxide at the expense of thiols, which are converted into the corresponding disulfides. A series of control experiments suggested that the catalytic mechanism proceeds through a pathway, involving a H₂O₂-promoted transcarbamoylation reaction leading to a thiocarbamate with concomitant releasing of catalytically active selenolate anions. By undergoing peroxide-driven thiol-selenol exchange, selenocarbamates behave as equivalents of selenolate anions with thiol-peroxidase-like activity.

The anodic generation of symmetrical and unsymmetrical thiosulfonates is presented. The principle of the oxidation of symmetrical disulfides was expanded to the conversion of in situ generated unsymmetrical disulfides yielding the respective thiosulfonates. A strong dependency of the regioselectivity for the formation of the unsymmetrical thiosulfonates was encountered and allows their regioselective formation in the future.

Abstract

The anodic generation of symmetrical and unsymmetrical thiosulfonates is presented. First, the oxidation of disulfides yielding symmetrical thiosulfonates was realized. The direct synthesis is performed using a simple quasi-divided cell design, whereby using a supporting electrolyte is unnecessary. Its principle was then expanded to the conversion of unsymmetrical disulfides that were generated in situ through metathesis of two symmetrical disulfides. This enables a direct access to unsymmetrical thiosulfonates without any pre-functionalization or elaborate synthesis of the starting materials for the first time. The reaction scope was investigated by converting differently functionalized aliphatic and aromatic disulfides in moderate to very good yields. Furthermore, a sensitivity assessment for an improved reproducibility and a robustness screen to determine the compatibility of the reaction against functional groups were performed.