Synthesis of non-anomeric C-glycosyl pyrazolidinone derivatives via visible-light photoredox catalysis.

C-Glycosyl compounds have gained considerable attention over the last few decades due to their high chemical stability and promising applications in drug discovery. Herein we disclose an operationally simple, metal-free, photocatalytic approach for the glycosylation of azomethine imines using 4-glycosyl-1,4-dihydropyridines (DHPs) as radical precursors. The protocol features mild reaction conditions, scalability, broad substrate scope, and good functional group tolerance. Moreover, the resulting pyrazolidinone moiety can be easily deprotected, acylated or reduced into a glycosyl ß-alanine analog.

Visible-Light Mediated Carbamoylation of Nitrones under a Continuous Flow Regime.

Herein, we report a rapid and scalable continuous-flow photocatalytic approach for the carbamoylation of nitrones. This protocol makes use of readily available 4-amido-1,4 dihydropyridines as carbamoyl radical precursors. The scope of this transformation exhibits high compatibility with complex structures containing amino acids, peptides, and glycosides. Importantly, the developed method allows a photocatalytic synthetic strategy in combination with flow conditions, maximizing the potential and efficiency for the synthesis of valuable α-(N-hydroxy)amino amides.

Photoinduced carbamoylation reactions: unlocking new reactivities towards amide synthesis.

The preparation of amide-containing compounds is among the most interesting and challenging topics for the synthetic community. Such relevance is given by their reactive aspects explored in the context of organic synthesis and by the direct application of these compounds as pharmaceuticals and useful materials, and their key roles in biological structures. A simple and straightforward strategy for the amide moiety installation is the use of carbamoyl radicals - this nucleophilic one-electron intermediate is prone to undergo a series of transformations, providing a range of structurally relevant derivatives. In this review, we summarize the latest advances in the field from the perspective of photoinduced protocols. To this end, their synthetic applications are organized accordingly to the nature of the radical precursor (formamides through HAT, 4-substituted-1,4-dihydropyridines, oxamic acids, and N-hydroxyphthalimido esters), the mechanistic aspects also being highlighted. The discussion also includes a recent approach proceeding via photolytic C-S cleavage of dithiocarbamate-carbamoyl intermediates. By exploring fundamental concepts, this material aims to offer an understanding of the topic, which will encourage and facilitate the design of new synthetic strategies applying the carbamoyl radical.

Carbamoylation of Azomethine Imines via Visible-Light Photoredox Catalysis.

A versatile and robust photocatalytic methodology to install the amide functional group into azomethine imine ions is described. This protocol is distinguished by its broad scope and mild reaction conditions, which are well suited for the preparation of structurally complex compounds in the form of amino acids, peptides, and small drug-like molecules. Moreover, the generated pyrazolidinone core could be easily converted into ß-alanine analogues.