Saad Shaaban

Metal-Free Synthesis of Highly Substituted Pyridines by Formal [2+2+2] Cycloaddition under Mild Conditions

The synthesis of pyridines through direct intermolecular cycloaddition of alkynes and nitriles is a contemporary challenge in organic synthesis. A Brønsted acid mediated formal [2+2+2] cycloaddition of heteroalkynes and nitriles was developed that proceeds under mild conditions. This constitutes a modular approach to highly substituted pyridine cores.

Metal‐Free Formal Oxidative C−C Coupling by In Situ Generation of an Enolonium Species

Much contemporary organic synthesis relies on transformations that are driven by the intrinsic, so-called natural, polarity of chemical bonds and reactive centers. The design of unconventionally polarized synthons is a highly desirable strategy, as it generally enables unprecedented retrosynthetic disconnections for the synthesis of complex substances. Whereas the umpolung of carbonyl centers is a well-known strategy, polarity reversal at the α-position of a carbonyl group is much rarer. Herein, we report the design of a novel electrophilic enolonium species and its application in efficient and chemoselective, metal-free oxidative C-C coupling.

Hydroxamic Acids as Chemoselective (ortho -Amino)arylation Reagents via Sigmatropic Rearrangement

The use of readily available hydroxamic acids as reagents for the chemoselective (ortho-amino)arylation of amides is described. This reaction proceeds under metal-free, mild conditions, displays a very broad scope, and constitutes a direct approach for the metal-free attachment of aniline residues to carbonyl derivatives.

Mechanistic Pathways in Amide Activation: Flexible Synthesis of Oxazoles and Imidazoles

The preparation of substituted aminooxazoles and aminoimidazoles from α-arylamides and α-aminoamides through triflic anhydride-mediated amide activation is reported. These reactions proceed via the intermediacy of nitrilium adducts and feature N-oxide-promoted umpolung of the α-position of amides as well as a mechanistically intriguing sequence that results in sulfonyl migration from nitrogen to carbon. Quantum-chemical mechanistic analysis sheds light on the intricacies of the process.

Redox-Neutral α-Amino C–H Functionalization: When the Catalyst Is Also the Nucleophile

A redox-neutral functionalization of cyclic amines that leads to acyclic products is presented. The reaction hinges on generation of transient aryl radical intermediates by catalytic activation with a simple hydrazine. Those aryl radicals subsequently undergo translocation and further oxidation prior to trapping with the same hydrazine, thus resulting in an overall process where the catalyst unusually also acts as the nucleophile.