A novel and simple method for the preparation of iminium salts

Expedient Synthesis of Thermally Stable Acyclic Amino(haloaryl)carbenes: Experimental and Theoretical Evidence of "Push-Pull" Stabilized Carbenes

A library of novel structurally related singlet carbenes, namely, acyclic amino(haloaryl)carbenes, was designed by a high-yielding two-step procedure, and their chemical stability explored both experimentally and theoretically. Thanks to a careful selection of both the amino and the aryl substitution pattern, these carbenes exhibit a wide range of stability and reactivity, spanning from rapid self-dimerization for carbenes featuring ortho-F substituents to very high chemical stability as bare carbenes, up to 60 °C for several hours for compounds carrying ortho-Br substituents. Their structure was determined through NMR and X-ray diffraction studies, and their reactivity evaluated in benchmark reactions, highlighting the ambiphilic character of this novel class of singlet carbenes. In contrast with previously reported aryl substituents incorporating o-CF3 and t-Bu groups, which were considered "spectator", the high chemical stability of some of these carbenes relates to the stabilization of the σ-orbital of the carbene center by the π-accepting haloaryl substituent through delocalization. Kinetic protection of the carbene center is also provided by the ortho-halogen atoms, as demonstrated computationally. This push-pull stabilization effect makes acyclic amino(haloaryl) carbenes among the most ambiphilic stable carbenes reported to date, holding promise for a variety of applications.

Enzyme Grafting with a Cofactor-Decorated Metal-Organic Capsule for Solar-to-Chemical Conversion

Semi-artificial approaches to solar-to-chemical conversion can achieve chemical transformations that are beyond the capability of natural enzymes, but face marked challenges to facilitate in vivo cascades, due to their inevitable need for cofactor shuttling and regeneration. Here, we report on an enzyme grafting strategy to build a metal-organic capsule-docking artificial enzyme (metal-organic-enzyme, MOE) that comprised the self-assembly of a cofactor-decorated capsule and the supramolecular enzyme-recognition features between the enzyme scaffold and the capsule to bypass cofactor shuttling and regeneration. The incorporated NADH mimics within the metal-organic capsule interacted with the imine intermediate that formed from the condensation of the amines and the dehydrogenation of alcohol substrates in the microenvironment to form complexes within the capsule and subsequently served as an in situ-generated photoresponsive cofactor. Upon illumination, the photoresponsive cofactor facilitates efficient proton/electron transport between the inner space (supramolecular hydrogenation) and outer space (enzymatic dehydrogenation) of the capsule to dehydrogenize the alcohols and hydrogenize the imine intermediates, respectively, circumventing the conventionally complex multistep cofactor shuttling and regeneration. The semi-artificial enzyme endows the conversion of diverse types of alcohol to amine products in both aqueous/organic solutions and Escherichia coli with high efficiency, offering a wide range of opportunities for sustainable and environmentally friendly biomanufacturing of commodity and fine chemicals.

Stable dicationic dioxoliums and fate of their dioxolyl radicals

A glimpse into uncharted territory: the synthesis and study of dicationic dioxolium salts allow for assessing the fate of the corresponding elusive dioxolyl radicals.

A new approach to the asymmetric Mannich reaction catalyzed by chiral N,N'-dioxide-metal complexes

An efficient asymmetric Mannich-type reaction between α-tetralone-derived β-keto esters/amides and 1,3,5-triaryl-1,3,5-triazinanes was realized catalyzed by chiral N,N'–dioxide-Ni(ii)/Mg(ii) complexes.

A highly efficient asymmetric Mannich-type reaction between α-tetralone-derived β-keto esters/amides and 1,3,5-triaryl-1,3,5-triazinanes was realized in the presence of chiral N,N′-dioxide–Ni(ii) or Mg(ii) complex. A variety of optically active β-amino compounds with all-carbon quaternary stereocenters were obtained in good yields with excellent enantioselectivities. A possible transition state was proposed based on these experiments and previous reports.