Dichloromethane as C1 Synthon for the Photoredox Catalytic Cyclopropanation of Aromatic Olefins.

Dichloromethane, as a readily available and inexpensive C1 synthon is proposed as a powerful building block for cyclopropanation of alkenes under mild conditions. Herein, we report a highly efficient and versatile dual photoredox system, involving a nickel aminopyridine coordination complex and a photocatalyst, for the cyclopropanation of aromatic olefins using dichloromethane, under visible-light irradiation. The cyclopropanation protocol has been successfully applied at gram scale. Mechanistic studies suggest a Ni(II) pyridyl radical complex as the key intermediate for the homolytic cleavage of the Csp3-Cl bond, generating a chloromethyl radical that is captured by the olefin coupling partner. Our findings also highlight the versatility of this methodology. By directing the radical/polar crossover process, we were able to selectively drive the reaction towards either the formation of cyclopropyl derivatives or the corresponding non-cyclic alkyl chloride products. The methodology also successfully apply to geminal dichloroalkanes, including the formation of spiro[2,2] compounds. Moreover, our methodology extends to the synthesis of deuterium-labelled cyclopropanes, demonstrating its utility in isotopic labelling and broadening its applicability in chemical synthesis and drug development.

Light-driven reduction of aromatic olefins in aqueous media catalysed by aminopyridine cobalt complexes.

A catalytic system based on earth-abundant elements that efficiently hydrogenates aryl olefins using visible light as the driving-force and H2O as the sole hydrogen atom source is reported. The catalytic system involves a robust and well-defined aminopyridine cobalt complex and a heteroleptic Cu photoredox catalyst. The system shows the reduction of styrene in aqueous media with a remarkable selectivity (>20 000) versus water reduction (WR). Reactivity and mechanistic studies support the formation of a [Co-H] intermediate, which reacts with the olefin via a hydrogen atom transfer (HAT). Synthetically useful deuterium-labelled compounds can be straightforwardly obtained by replacing H2O with D2O. Moreover, the dual photocatalytic system and the photocatalytic conditions can be rationally designed to tune the selectivity for aryl olefin vs. aryl ketone reduction; not only by changing the structural and electronic properties of the cobalt catalysts, but also by modifying the reduction properties of the photoredox catalyst.

Photoredox Activation of Inert Alkyl Chlorides for the Reductive Cross-Coupling with Aromatic Alkenes.

The inertness of chloroalkanes has precluded them as coupling partners for cross-coupling reactions. Herein we disclose a general strategy for the activation of inert alkyl chlorides through photoredox catalysis and their use as coupling partners with alkenes. The catalytic system is formed by [Ni(OTf)(Py2 Ts tacn)](OTf) (1Ni ), which is responsible for the Csp3 -Cl bond activation, and [Ir(NMe2 bpy)(ppy)2 ]PF6, (PCIr NMe2 ), which is the photoredox catalyst. Combined experimental and theoretical studies show an in situ photogenerated NiI intermediate ([Ni(Py2 Ts tacn)]+ ) which is catalytically competent for the Csp3 -Cl bond cleavage via a SN 2 mechanism for primary alkyl chlorides, forming carbon-centered free radicals, which react with the olefin leading to the formation of the Csp3 -Csp3 bond. These results suggest inert alkyl chlorides can be electrophiles for developing new intermolecular strategies in which low-valent aminopyridine nickel complexes act as key catalytic species.

Gelatin/Maltodextrin Water-in-Water (W/W) Emulsions for the Preparation of Cross-Linked Enzyme-Loaded Microgels.

Cross-linked gelatin microgels were formed in gelatin-in-maltodextrin water-in-water (W/W) emulsions and evaluated as carriers of the enzyme ß-galactosidase (ß-Gal). The phase behavior of aqueous gelatin/maltodextrin mixtures was studied in detail, focusing on the multiphase region of the phase diagram that is constituted by three equilibrium phases: two immiscible aqueous phases plus one solid phase. The solid phase was analyzed by Raman spectroscopy, and water-in-water emulsions were formed within the multiphase region. Gelation of the dispersed gelatin droplets was induced by cooling and cross-linking with genipin, which is a natural cross-linking reagent of low toxicity, leading to the formation of gelatin microgel particles. These microgels were studied as delivery vehicles for the enzyme lactase, used as a model active component. Various incorporation methods of the enzyme were tested, to achieve highest encapsulation yield and activity recovery. Microgel particles, loaded with the enzyme, can be freeze-dried, and the enzyme remained active after a complete cycle of freeze-drying and rehydration. The stability of the enzyme at 37 °C under gastric and neutral pH conditions was tested and led to the conclusion that the cross-linked microgels could be suitable for use in food-industry, where ß-Gal carriers are of interest for hydrolyzing lactose in milk products.