Production of Quaternary α-Aminonitriles by Means of Indium-Catalyzed Three-Component Reaction of Alkynes, Amines, and Trimethylsilyl Cyanide

Triggering Lewis Acidic Nature through the Variation of Coordination Environment of Cd-Centers in 2D-Coordination Polymers

The rational design and successful synthesis of novel functional metal-organic frameworks relies on careful selection of metals and versatile organic ligands. A newly designed pyrazole-based dicarboxylate ligand, 5-(3,5-dimethyl-1H-pyrazol-1-yl) 1,3-benzenedicarboxylic acid (H₂L), was utilized to obtain two new Cd-based coordination polymers I [Cd(L)(H₂O)]·H₂O and II [Cd(L)] under similar reaction conditions via solvothermal strategy. Single-crystal X-ray data confirmed that compound I exhibits a two-dimensional (2D) skeleton comprising pentagonal bipyramidal Cd-ions and an organic ligand moiety. Compound II has also formed a two-dimensional layer arrangement with the connectivity between trigonal bipyramidal Cd-ions and the organic ligand. Topological analysis revealed that compound I has formed unique 4³.6³ net topology while compound II has displayed a 4⁴.6² sql net topology with 2D frameworks. The Lewis acidic nature of both I and II containing a Cd²⁺ metal center has been correlated with the coordination number through dye adsorption-desorption and catalysis studies. The selective adsorption of anionic dye and the extent of adsorption are interrelated with the Cd-ion geometry. For the first time, the role of coordinated water molecule has been analyzed through heterogeneous catalysis reaction (i.e., cyanosilylation) with Cd-based 2D-coordination polymers (CPs). The plausible mechanisms have been proposed to explain the subsequent role of coordination number and environment in CPs.

Cyano-borrowing: titanium-catalyzed direct amination of cyanohydrins with amines and enantioselective examples

The direct amination of cyanohydrins with amines via a catalytic cyano-borrowing reaction was developed. The transformation features broad substrate scope, excellent functional group compatibility, and very mild and simple operations. Moreover, a titanium catalyst supported by quinine and (S)-BINOL ligands enabled an asymmetric cyano-borrowing reaction with moderate to high enantioselectivity.

Cu(OAc)2-Mediated benzimidazole-directed C–H cyanation using 2-(4-methylpiperazin-1-yl)acetonitrile as the cyano source

The C–H activation catalytic system was originally applied to the C(sp²)–H cyanation of aryls/heteroaryls to synthesize 2-(1H-benzo[d]imidazol-2-yl)aryl nitriles.

Indium-Catalyzed Annulation of o-Acylanilines with Alkoxyheteroarenes: Synthesis of Heteroaryl[b]quinolines and Subsequent Transformation to Cryptolepine Derivatives

We disclose herein the first synthetic method that is capable of offering heteroaryl[b]quinolines (HA[b]Qs) with structural diversity, which include tricyclic and tetracyclic structures with (benzo)thienyl, (benzo)furanyl, and indolyl rings. The target HA[b]Q is addressed by the annulation of o-acylanilines and MeO–heteroarenes with the aid of an indium Lewis acid that effectively works to make two different types of the N–C and C–C bonds in one batch. A series of indolo[3,2-b]quinolines prepared here can be subsequently transformed to structurally unprecedented cryptolepine derivatives. Mechanistic studies showed that the N–C bond formation is followed by the C–C bond formation. The indium-catalyzed annulation reaction thus starts with the nucleophilic attack of the NH₂ group of o-acylanilines to the MeO-connected carbon atom of the heteroaryl ring in an S_NAr fashion, and thereby the N–C bond is formed. The resulting intermediate then cyclizes to make the C–C bond through the nucleophilic attack of the heteroaryl-ring-based carbon atom to the carbonyl carbon atom, providing the HA[b]Q after aromatizing dehydration.

Indium(iii) as π-acid catalyst for the electrophilic activation of carbon–carbon unsaturated systems

This review focuses on indium(iii) as a π-acid for the activation of C–C unsaturated systems (alkynes, alkenes, and allenes) in organic synthesis.

Indium-Catalyzed Regioselective β-Alkylation of Pyrroles with Carbonyl Compounds and Hydrosilanes and Its Application to Construction of a Quaternary Carbon Center with a β-Pyrrolyl Group

Treatment of N-substituted pyrroles with carbonyl compounds and nucleophiles under indium catalysis was found to be a promising method for preparing β-alkylpyrroles without contamination by α-alkylpyrroles. With this methodology, a variety of alkyl groups, which are primary, secondary, and tertiary as well as cyclic and functionalized types, can be introduced in place onto the pyrrole ring. The simplicity performable as a catalytic one-step process is one of the important features of this reaction. The substituent on the nitrogen atom of the product β-alkylpyrrole can be removed easily by literature procedures. Therefore, the indium-catalyzed β-alkylation plus the N-deprotection is a powerful system for all six variations, which are N-substituted and N-unsubstituted β-alkylpyrroles having primary, secondary, and tertiary alkyl groups. Our method is applicable to synthesizing, albeit in two steps, β-pyrrolyl-group-connected unsymmetrical tetraarylmethanes that have not been addressed thus far. Mechanistic studies showed the following three aspects: (1) dipyrrolylalkanes produced in situ from the pyrrole and carbonyl compound are key intermediates, (2) the selective β-alkylation is attributed to the selective elimination of an α-pyrrolyl group from the dipyrrolylalkane intermediates, and (3) the indium Lewis acid catalyst is indispensable for the progress of both stages.