Enantioselective Radical Addition toN-Acyl Hydrazones Mediated by Chiral Lewis Acids

Visible-Light Photoredox-Catalyzed C-H Difluoroalkylation of Hydrazones through an Aminyl Radical/Polar Mechanism

An unprecedented visible-light-induced direct C-H bond difluoroalkylation of aldehyde-derived hydrazones was developed. This reaction represents a new way to synthesize substituted hydrazones. The salient features of this reaction include difluorinated hydrazone synthesis rather than classical amine synthesis, extremely mild reaction conditions, high efficiency, wide substrate scope, ease in further transformations of the products, and one-pot syntheses. Mechanistic analyses and theoretical calculations indicate that this reaction is enabled by a novel aminyl radical/polar crossover mechanism, with the aminyl radical being oxidized into the corresponding aminyl cation through a single electron transfer (SET) process.

Enantioselective Radical Cyclizations: A New Approach to Stereocontrol of Cascade Reactions

Stereocontrol in a cascade radical addition-cyclization-trapping reaction was achieved by a new approach, which utilizes a hydroxamate ester moiety as a coordinating chiral Lewis acid tether between two radical acceptors. A remarkable feature of this reaction is the construction of three bonds and tertiary and quaternary stereogenic centers through both inter- and intramolecular carbon-carbon bond-forming processes. The chiral Lewis acid mediated reaction of oxime ethers also proceeded smoothly with good enantio- and diastereoselectivities, indicating the usefulness of the cascade approach for the asymmetric synthesis of various gamma-lactams.

N-Acylhydrazones as Versatile Electrophiles for the Synthesis of Nitrogen-Containing Compounds

The use of N-acylhydrazones as electrophiles in reactions with nucleophiles has recently made some important advances. N-Acylhydrazones, which can be readily prepared and stored, act as stable imine surrogates in these reactions. The hydrazide products are useful, often chiral building blocks which can be transformed into various nitrogen-containing compounds by cleavage of the N--N bond. The N-acyl groups often play important roles as templates for metal catalysis in controlling stereochemistry. This Minireview summarizes the most recent results of N-acylhydrazone chemistry, and provides an overview of current developments in this field.