Protodefluorinated Selectfluor Aggregatively Activates Selectfluor for Efficient Radical C(sp)-H Fluorination Reactions.

Efficient fluorination reactions are key in the late-stage functionalization of complex molecules in medicinal chemistry, in upgrading chemical feedstocks, and in materials science. Radical C(sp)-H fluorinations using Selectfluor - one of the most popular fluorination agents - allow to directly engage unactivated precursors under mild photochemical or thermal catalytic conditions. However, H-TEDA(BF) to date is overlooked and discarded as waste, despite comprising 95% of the molecular weight of Selectfluor.

Azotriptycenes: Photoswitchable Molecular Brakes.

The control of molecular motions is a central topic of molecular machine research. Molecular brakes are fundamental building blocks towards such goal as they allow deliberately decelerating specific motions after an outside stimulus is applied. Here we present azotriptycenes as structural framework for light-controlled molecular brakes.

Photo enhancement reveals (,) and (,) configurations as additional intermediates in iminium ion catalysis.

Imidazolidinone-based α,β-unsaturated iminium ions are the reactive species within countless synthetic protocols in asymmetric organocatalysis. However, (,) and (,) imidazolidinone iminium ions, ()-CC configurations, have been elusive so far. Herein we describe how photoisomerization enables the observation and assignment of high energetic ()-configured intermediates below the detection limit of NMR spectroscopy for (,) and (,) iminium perchlorate complexes derived from MacMillan's 1st generation catalyst and cinnamaldehyde.

Benzoates as photosensitization catalysts and auxiliaries in efficient, practical, light-powered direct C(sp)-H fluorinations.

Of the methods for direct fluorination of unactivated C(sp)-H bonds, photosensitization of SelectFluor is a promising approach. Although many substrates can be activated with photosensitizing catalysts, issues remain that hamper fluorination of complex molecules. Alcohol- or amine-containing functional groups are not tolerated, fluorination regioselectivity follows factors endogenous to the substrate and cannot be influenced by the catalyst, and reactions are highly air-sensitive.