, [a] Nikolaos F. Nikitas, [a] Errika Voutyritsa, [a] Dimitrios I. Tzaras, [a] Nikolaos Kaplaneris, [a] and Christoforos G. Kokotos* [a] CÀ H functionalization at the α-position of heterocycles has become a rapidly growing area of research. Herein, a cheap and efficient photochemical method was developed for the CÀ H functionalization of heterocycles. Phenylglyoxylic acid (PhCO-COOH) could behave as an alternative to metal-based catalysts and organic dyes and provided a very general and wide array of photochemical CÀ H alkylation, alkenylation, and alkynylation, as well as CÀ N bond forming reaction methodologies. This novel, mild, and metal-free protocol was successfully employed in the functionalization of a wide range of CÀ H bonds, utilizing not only O-or N-heterocycles, but also the less studied S-heterocycles.

Schreiner's thiourea activating aldehydes in photochemical reactions.

Phenylglyoxylic acid-mediated photochemical synthesis of symmetrical and non-symmetrical disulfides.

Although the use of light stimulating organic transformations has been known for more than a century, there is an increasing research interest on expanding the established knowledge. While [2 + 2] cycloadditions are promoted photochemically, literature precedent on the reaction between alkynes and maleimides is limited and only a handful of examples exist, focusing mainly on N-aliphatic maleimides. Herein, the differences in reactivity between N-alkyl and N-aryl maleimides were identified, and the use of hexafluoroisopropanol (HFIP) or trifluoroacetic acid (TFA) as viable solutions was proposed in order to achieve high yields. In the case of N-alkyl maleimides, both HFIP-mediated or TFA-promoted reactions were established using LED 370 nm irradiation, without the use of an external photocatalyst. In the case of N-aryl maleimides, thioxanthone (THX) was employed as the energy transfer photocatalyst along with LED 427 nm irradiation and HFIP. Mechanistic studies were performed, supporting the pivotal role of HFIP or TFA, in acquiring good to high yields in both classes of maleimides.

Organocatalysis and photoorganocatalysis are two areas of synthetic methodology that have been successfully combined.