Near-infrared photocatalysis with cyanines: synthesis, applications and perspectives.

Cyanines are organic dyes bearing two aza-heterocycles linked by a polymethine chain. Excited states, fluorescence, redox activity, and energy transfer are interesting properties of cyanines which have been used by chemists. Moreover, they are easily accessible and highly tunable. For all these reasons, cyanines are often selected for applications like fluorescent probes, phototherapy and photovoltaics. However, considering cyanines as photocatalysts is a new field of investigation and has been sparsely reported in the literature. This field of research has been launched on the basis of near-infrared light photocatalysis. With a deeper NIR light penetration, the irradiation is compatible with biological tissues. Due to the longer wavelengths that are involved, the safety of the operator can be guaranteed. In this perspective review, the photophysical/redox properties of cyanines are reported as well as their preparations and applications in modern synthetic approaches. Finally, recent examples of cyanine-based NIR-photocatalysis are discussed including photopolymerization and organic synthesis.

Ruthenaelectro-catalyzed C-H acyloxylation for late-stage tyrosine and oligopeptide diversification.

Ruthenaelectro(ii/iv)-catalyzed intermolecular C-H acyloxylations of phenols have been developed by guidance of experimental, CV and computational insights. The use of electricity bypassed the need for stoichiometric chemical oxidants. The sustainable electrocatalysis strategy was characterized by ample scope, and its unique robustness enabled the late-stage C-H diversification of tyrosine-derived peptides.

Atropoenantioselective palladaelectro-catalyzed anilide C-H olefinations viable with natural sunlight as sustainable power source.

Enantioselective electrocatalyzed transformations represent a major challenge. We herein achieved atropoenantioselective pallada-electrocatalyzed C-H olefinations and C-H allylations with high efficacy and enantioselectivity under exceedingly mild reaction conditions. With (S)-5-oxoproline as the chiral ligand, activated and non-activated olefins were suitable substrates for the electro-C-H activations. Dual catalysis was devised in terms of electro-C-H olefination, along with catalytic hydrogenation. Challenging enantiomerically-enriched chiral anilide scaffolds were thereby obtained with high levels of enantio-control in the absence of toxic and cost-intensive silver salts. The resource-economy of the transformation was even improved by directly employing renewable solar energy.

Rhoda-Electrocatalyzed Bimetallic C-H Oxygenation by Weak O-Coordination.

Rhodium-electrocatalyzed arene C-H oxygenation by weakly O-coordinating amides and ketones have been established by bimetallic electrocatalysis. Likewise, diverse dihydrooxazinones were selectively accessed by the judicious choice of current, enabling twofold C-H functionalization. Detailed mechanistic studies by experiment, mass spectroscopy and cyclovoltammetric analysis provided support for an unprecedented electrooxidation-induced C-H activation by a bimetallic rhodium catalysis manifold.

Towards Atropoenantiopure N-C Axially Chiral Compounds via Stereoselective C-N Bond Formation.

N-C axial chirality, although disregarded for decades, is an interesting type of chirality with appealing applications in medicinal chemistry and agrochemistry. However, atroposelective synthesis of optically pure compounds is extremely challenging and only a limited number of synthetic routes have been designed. In particular, asymmetric N-arylation reactions allowing atroposelective N-C bond forming events remain scarce, although great advances have been achieved recently. In this minireview we summarize the synthetic approaches towards synthesis of N-C axially chiral compounds via stereocontrolled N-C bond forming events. Both organo-catalyzed and metal-catalyzed transformations are described, thus illustrating the diversity and specificity of both strategies.

Enantioselective Synthesis of N-C Axially Chiral Compounds by Cu-Catalyzed Atroposelective Aryl Amination.

N-C axially chiral compounds have emerged recently as appealing motifs for drug design. However, the enantioselective synthesis of such molecules is still poorly developed and surprisingly no metal-catalyzed atroposelective N-arylations have been described. Herein, we disclose an unprecedented Cu-catalyzed atroposelective N-C coupling that proceeds at room temperature. Such mild reaction conditions, which are a crucial parameter for atropostability of the newly generated products, are operative thanks to the use of hypervalent iodine reagents as a highly reactive coupling partners. A large panel of the N-C axially chiral compounds was afforded with very high enantioselectivity (up to >99 % ee) and good yields (up to 76 %). Post-modifications of thus accessed atropisomeric compounds allows further expansion of the diversity of these appealing compounds.