Ruthenium(ii)-catalysed 1,2-selective hydroboration of aldazines.

Herein, an efficient and simple catalytic method for the selective and partial reduction of aldazines using ruthenium catalyst [Ru(p-cymene)Cl] (1) has been accomplished. Under mild conditions, aldazines undergo the addition of pinacolborane in the presence of a ruthenium catalyst, which delivered N-boryl-N-benzyl hydrazone products. Notably, the reaction is highly selective, and results in exclusive mono-hydroboration and desymmetrization of symmetrical aldazines. Mechanistic studies indicate the involvement of in situ formed intermediate [{(η-p-cymene)RuCl}2(μ-H-μ-Cl)] (1a) in this selective hydroboration.