Transition metal-free advanced synthetic approaches for isoindolinones and their fused analogues

The transition metal-free synthetic protocols of isoindolinone and its fused analogues are highlighted in this review since 2007 to 2021.

Excited-state palladium-catalysed reductive alkylation of imines: scope and mechanism

Palladium catalysis induced by visible-light irradiation is a promising tool for promoting unusual chemical reactivity. Here, the hybrid alkyl radical/Pd(i) species generated is used to promote the reductive alkylation of imines.

α-Chiral Amines via Thermally Promoted Deaminative Addition of Alkylpyridinium Salts to Sulfinimines

A deaminative reaction of Katritzky alkylpyridinium salts and sulfinimines has been developed to deliver enantiopure α-chiral amines. The success of this method relied on the discovery of a thermally promoted deamination via single-electron transfer of an anion-π complex of the alkylpyridinium cation with potassium carbonate. This method boasts excellent diastereoselectivity over the α-stereocenter as well as broad functional group and heterocycle tolerance.

Alkyl Radical Addition to Aliphatic and Aromatic N-Acylhydrazones Using an Organic Photoredox Catalyst

Increased versatility of intermolecular radical addition to imino acceptors via photoredox catalysis is reported. Primary and secondary radicals, generated via visible-light photocatalysis from alkyl biscatecholatosilicates with organocatalyst 4CzIPN, add successfully to both aromatic and aliphatic N-acylhydrazones in the presence of MgCl₂. With N-benzoylhydrazones, a simple reductive cleavage of the N-N bond of the hydrazine adduct furnishes the free amine. Synthetic utility is exemplified in a synthetic application toward repaglinide, a clinically important hypoglycemic agent.

Pd(OAc)2-catalyzed asymmetric hydrogenation of sterically hindered N-tosylimines

Asymmetric hydrogenation of sterically hindered substrates still constitutes a long-standing challenge in the area of asymmetric catalysis. Herein, an efficient palladium acetate (an inexpensive Pd salt with low toxicity) catalyzed asymmetric hydrogenation of sterically hindered N-tosylimines is realized with high catalytic activities (S/C up to 5000) and excellent enantioselectivities (ee up to 99.9%). Quantum chemical calculations suggest that uniformly high enantioselectivities are observed due to the structurally different S- and R-reaction pathways.

Sterically hindered unsaturated compounds are challenging substrates for asymmetric hydrogenation. Here, the authors report a palladium/chiral (bis)phosphine catalytic system that hydrogenates a number of hindered N-tosylimines with excellent enantioselectivitites.

A General Amino Acid Synthesis Enabled by Innate Radical Cross-Coupling

The direct union of primary, secondary, and tertiary carboxylic acids with a chiral glyoxylate-derived sulfinimine provides rapid access into a variety of enantiomerically pure α-amino acids (>85 examples). Characterized by operational simplicity, this radical-based reaction enables the modular assembly of exotic α-amino acids, including both unprecedented structures and those of established industrial value. The described method performs well in high-throughput library synthesis, and has already been implemented in three distinct medicinal chemistry campaigns.

Mild, Redox-Neutral Alkylation of Imines Enabled by an Organic Photocatalyst

An operationally simple, mild, redox-neutral method for the photoredox alkylation of imines is reported. Utilizing an inexpensive organic photoredox catalyst, alkyl radicals are readily generated from the single-electron oxidation of ammonium alkyl bis(catecholato)silicates and are subsequently engaged in a C–C bond-forming reaction with imines. The process is highly selective, metal-free, and does not require a large excess of the alkylating reagent or the use of acidic additives.