Abstract
Hydrogenation of p-tolil monoazine (1b) over palladium-on-charcoal gives as the major product 4,5-dihydro-5-(p-toluyl)-3,4,5-tri-(p-tolyl)-1H-pyrazol-4-ol (2b), which has previously been obtained by treatment of 1b with sodium methoxide. Several minor products are formed, which include p-tolualdehyde, p-toluic acid, and p-toluamide, p-tolunitrile, p-tolualazine, and 3,4,5-tri-(p-tolyl)-4H-pyrazo-4-ol (9). The structure of the last compound, which is also formed on reduction of 1b with sodium borohydride, was established by its independent synthesis from 1,2,3-tri-(p-tolyl)-1,3-propanedione by oxidation with lead tetraacetate followed by treatment with hydrazine. It is suggested that 2b arises via reduction of a C=N bond of 1b and aldol ring closure. The minor hydrogenation products are of interest in that their formation involves C—C hydrogenolysis; it is suggested that this is initiated by addition of a hydrogen atom to a carbonyl carbon atom of 1b.
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