Formal transfers of hydride from carbon-hydrogen bonds. Attempted generation of H2 by intramolecular protonolyses of the activated carbon-hydrogen bonds of dihydrobenzimidazoles

Article abstract of DOI:10.1139/v96-074

Protonolyses of carbon-hydrogen bonds can occur under suitable conditions to produce carbocations and H₂. In an effort to accelerate these fundamental reactions, we have attempted to make them intramolecular by devising compounds in which carbon-hydrogen bonds designed to be particularly good formal donors of hydride are held in close proximity to acidic sites. Dihydrobenzimidazoles 4 and 11 are compounds of this type, since the carbon-hydrogen bonds at C2 are activated as formal donors of hydride by adjacent lone pairs in a dihydroaromatic ring, and acidic anilinium and carboxylic acid groups are held nearby. Unfortunately, this proximity does not lead to the formation of H₂ by protonolysis; instead, other reactions intervene when compounds 4 and 11 are subjected to pyrolysis.