Direct Catalytic Asymmetric Mannich-Type Reaction of Benzyl Isocyanide: Stereoselective Synthesis of 1,2-Diarylethylenediamines

Responsive photonic hydrogel for colorimetric detection of formaldehyde

Formaldehyde (FA) can damage DNA, cause liver and kidney dysfunction, and ultimately lead to malignant tumors. Therefore, it is essential to develop a method that can conveniently detect FA with high detection sensitivity. Here, a responsive photonic hydrogel was prepared by embedding three-dimensional photonic crystal (PC) into amino-functionalized hydrogel to construct a colorimetric sensing film for FA. The amino groups on the polymer chains of the photonic hydrogel reacts with FA to increase the crosslinking density of the hydrogel, resulting in its volume shrinkage and a decrease in microsphere spacing of the PC. That causes the reflectance spectra blue-shift of more than 160 nm and color change from red to cyan for the optimized photonic hydrogel, achieving the sensitive, selective and colorimetric detection of FA. The constructed photonic hydrogel shows good accuracy and reliability for practical determination of FA in air and aquatic products, providing a new strategy for designing other target analytes responsive photonic hydrogels.

Ring opening and skeletal reconstruction of 3-vinyl benzofuranone-chromone synthons: catalyst-free access to skeletally-diverse 2-pyridone and optically active imidazoline derivatives

Herein is reported the first example of ring opening and skeletal reconstruction of 3-vinyl benzofuranone-chromones 1 as versatile synthons, which can react with ammonia or primary aliphatic amines as binucleophiles, for the eco-friendly and atom-economical synthesis of diverse and functionalized 2-pyridones 3 with potential biological activity in good to excellent yields (77-93%). When using optically active 1,2-diphenylethylenediamine 2 as the binucleophile, the in situ generated 2-pyridone intermediates are successfully transformed to novel optically active functionalized imidazoline derivatives 4 with high efficiency (up to 87% yield). In particular, this is the first report on the catalyst-free intramolecular cyclization occurring between an amide and a primary aliphatic amine for the construction of imidazoline molecules.

Catalytic Enantioselective Isocyanide-Based Reactions: Beyond Passerini and Ugi Multicomponent Reactions

The development of catalytic enantioselective isocyanide-based reactions is currently of great interest because the resulting products are valuable in organic synthesis, pharmacological chemistry, and materials science. This review assembles and comprehensively summarizes the recent achievements in this rapidly growing area according to the reaction types. Special attention is paid to the advantages, limitations, possible mechanisms, and synthetic applications of each reaction. In addition, a personal outlook on the opportunities for further exploration is given at the end.

Synthesis of chiral anti-1,2-diamine derivatives through copper(I)-catalyzed asymmetric α-addition of ketimines to aldimines

Chiral 1,2-diamines serve as not only common structure units in bioactive molecules but also useful ligands for a range of catalytic asymmetric reactions. Here, we report a method to access anti-1,2-diamine derivatives. By means of the electron-withdrawing nature of 2- or 4-nitro-phenyl group, a copper(I)-catalyzed asymmetric α-addition of ketimines derived from trifluoroacetophenone and 2- or 4-NO₂-benzylamines to aldimines is achieved, which affords a series of chiral anti-1,2-diamine derivatives in moderate to high yields with moderate to high diastereoselectivity and high to excellent enantioselectivity. Aromatic aldimines, heteroaromatic aldimines, and aliphatic aldimines serve as suitable substrates. The nitro group is demonstrated as a synthetical handle by several transformations, including a particularly interesting Fe(acac)₃-catalyzed radical hydroamination with a trisubstituted olefin. Moreover, the aryl amine moiety obtained by the reduction of the nitro group serves as a synthetically versatile group, which leads to the generation of several functional groups by the powerful Sandmeyer reaction, such as -OH, -Br, -CF₃, and -BPin.

Chiral 1,2-diamines are useful chemicals used as ligands in asymmetric catalysis. Here, the authors report a copper(I)-catalyzed asymmetric α-addition of ketimines derived from trifluoroacetophenone and 2- or 4-NO2-benzylamines to aldimines, affording a series of chiral anti-1,2-diamine derivatives.

Asmic Isocyanide [3 + 2] Cascade to Dihydrooxazoles and Dihydroimidazoles

The versatile isocyanide building block Asmic, anisylsulfanylmethylisocyanide, reacts with aldehydes and ketones in a BF₃·OEt₂-mediated condensation to afford thioimidoyl-substituted 2,5-dihydrooxazoles. The condensation is distinguished from related base and transition-metal-catalyzed [3 + 2] processes in proceeding via the condensation of aldehydes and ketones with 2 equiv of an isocyanide followed by a molecular rearrangement that installs four new bonds. BF₃·OEt₂ mediates an analogous condensation of Asmic with imines to generate N-substituted dihydroimidazoles. Mechanistically, BF₃·OEt₂ activates the isocyanide to facilitate deprotonation evolving to a zwitterion that traps π-electrophiles in a formal [3 + 2] process. A second deprotonation-condensation with Asmic initiates a structural rearrangement involving a sulfanyl elimination-addition transposition sequence. The resulting dihydrooxazoles and dihydroimidazoles contain a thioimidate that serves as a diversification point for further elaboration.

To each his own: isonitriles for all flavors. Functionalized isocyanides as valuable tools in organic synthesis

The term functionalized isocyanides refers to all those isocyanides in which a neighbouring functional group can finely tune the reactivity of the isocyano group or can be exploited in post-functionalization processes. In this manuscript, we have reviewed all the isocyanides in which the pendant functional group causes either deviation from or reinforces the normal reactivity of the isocyano group and categorized them to highlight their common features and differences. An analysis of their synthetic potential and the possible unexplored directions for future research studies is also addressed.

Isocyanide-based multicomponent reactions in the synthesis of heterocycles

In this review, we update our previous presentation, underscoring the recent applications of isocyanides as privileged synthons in the synthesis of various heterocyclic compounds, especially focused on those synthesizedviamulticomponent reactions.