The first examples of 1,3,2-diazaphospholene-catalyzed imine reduction and conjugate reduction reactions are reported. This approach employs readily synthesized alkoxydiazaphospholene precatalysts that can be handled in open air. Reduction of substrates containing Lewis basic functionality, isolated unsaturation, and protic functional groups was accomplished. The synthetic utility of this approach is demonstrated by the synthesis of the important antiparkinson medicine rasagiline and the natural product zingerone.

We report here that addition of stoichiometric amounts of alcohols or water to mixtures of imines and pinacolborane promote reduction reactions.

Phosphorus‐sp3 or ‐sp2 carbon bonds are readily formed by the reaction of bis‐diazaphospholenes with several classes of electrophiles. These reactions result in cleavage of the phosphorus–phosphorus bond and formation of functionalized diazaphospholenes. The reactions proceed rapidly, without catalysis. Experimental evidence with aryl and alkyl halides suggests the intermediacy of radicals in some cases, however other evidence suggests either radical or polar mechanisms may be operative for certain substrates, with a dependence on reaction conditions. In three cases, the product aryl diazaphospholenes have been shown to transfer the aryl substituent to electrophiles. These results reveal that diazaphospholene dimers are potent participants in radical chemistry with organic substrates at room temperature without requiring chemical initiators.

No abstract

Diazaphospholenes are widely used as hydride transfer catalysts, however their use in radical reactions is a recently emerging area. Here, we show prior stoichiometric radical cyclizations of aryl iodides mediated by diazaphospholene hydrides are made catalytic by the combination of phenylsilane and alkali metal salts to regenerate the diazaphospholene hydride. The scope was expanded to include aryl bromides, which benefit from visible light irradiation. Twenty one substrates underwent cyclization, including a dearomative cyclization. Extension to six intermolecular radical hydroarylations with arenes, thiophenes, and a pyridine was also accomplished.