Methanol as a formylating agent in nitrogen heterocycles

Accessing Rare α-Heterocyclic Aziridines via Brønsted Acid-catalyzed Michael Addition/Annulation: Scope, Limitations, and Mechanism

We report an approach to the diastereoselective synthesis of 1,2-disubstituted heterocyclic aziridines. A Brønsted acid-catalyzed conjugate addition of anilines to trisubstituted heterocyclic chloroalkenes provides an intermediate 1,2-chloroamine. Diastereocontrol was found to vary significantly with solvent selection, with computational modelling confirming selective, spontaneous fragmentation in the presence of trace acids, proceeding through a pseudo-cyclic, protonated intermediate and transition state. These chloroamines can then be converted to the aziridine by treatment with LiHMDS with high stereochemical fidelity. This solvent-induced stereochemical enrichment thereby enables an efficient route to rare cis-aziridines with high dr. The scope, limitations, and mechanistic origins of selectivity are also presented.

A Fenton Approach to Aromatic Radical Cations and Diarylmethane Synthesis

Manipulating carbon-centered radicals to add to electron-deficient systems is a well-precedented process. By coupling the Fe(II)-mediated Fenton reaction with the Fe(III)-mediated single-electron oxidation of anisolic compounds, we demonstrate how electron-rich carbon-centered radicals can react with electron-rich arenes through a radical-polar cascade pathway. This bioinspired approach produces diarylmethane derivatives from simple unfunctionalized precursors.

HAT-Mediated Electrochemical C(sp2)-H Acylation of Quinolines with Alcohols

Herein, an electrochemical hydrogen atom transfer (HAT) strategy for C(sp2)-H formylation of electron-deficient quinolines and isoquinolines is described. The cheap methanol acts as a formyl source with a catalytic amount of N-hydroxyphthalimide (NHPI) as the hydrogen atom transfer (HAT) catalyst. The advantages of this reaction are transition-metal-catalyst- and chemical-oxidant-free conditions, and the protocol could also be applied to the direct C(sp2)-H acetylation or propionylation of quinolines.