In recent years, dihydrogen activation at non-metallic centers has received increasing attention. A system in which dihydrogen is trapped by a pyridylidene intermediate that is generated from a pyridinium salt and a base is now reported. The dihydropyridine formed in this process can act as reducing agent towards organic electrophiles. By coupling the hydrogen-activation step with subsequent hydride transfer from the dihydropyridine to an imine, a catalytic process was established. Treatment of the N-phenylimine of phenyl trifluoromethyl ketone with 5-20 mol% of N-mesityl-3,5-bis(2,6-dimethylphenyl)pyridinium triflate and 0.3-1.0 equivalents of LiN(SiMe3)2 under 50 bar of hydrogen gas resulted in high conversion into the corresponding amine.

Tetrasubstituted N-methylpyridinium salts bearing a free tertiary amino group have been synthesized by a straightforward procedure starting from inexpensive starting materials. The key feature of the synthesis is the use of a proton as a simple effective protecting group to achieve selective N-methylation of the pyridine ring without attacking the amino group.

In recent years, dihydrogen activation at non‐metallic centers has received increasing attention. A system in which dihydrogen is trapped by a pyridylidene intermediate that is generated from a pyridinium salt and a base is now reported. The dihydropyridine formed in this process can act as reducing agent towards organic electrophiles. By coupling the hydrogen‐activation step with subsequent hydride transfer from the dihydropyridine to an imine, a catalytic process was established. Treatment of the N‐phenylimine of phenyl trifluoromethyl ketone with 5–20 mol % of N‐mesityl‐3,5‐bis(2,6‐dimethylphenyl)pyridinium triflate and 0.3–1.0 equivalents of LiN(SiMe3)2 under 50 bar of hydrogen gas resulted in high conversion into the corresponding amine.

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