Experimental and theoretical assessment of the mechanism involved in the reaction of steroidal ketone semicarbazone with hydrogen peroxide

3β-Acetoxy-5α-cholestan-6-one semicarbazone 1 on reaction with hydrogen peroxide affords selectively 3β-acetoxy-5α-cholestan-6-spiro-1′,2′,4′-triazolidine-3′-one 2. The structural assignment of the product was confirmed by spectral data and elemental analysis. A free radical mechanism of the present reaction was described successfully by calculating theoretical models of 1, A, B and 2, using DFT with B3LYP/6-31G* basis set. It was found that the reaction undergoes through the formation of two radical intermediates and the only one isomer of the product in which –NH–CO– group is cis with respect C5α-H, was selectively obtained. Frontier molecular orbital, spin electronic density, electrostatic potential and atomic charges were discussed.

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► Preparation of 3β-acetoxy-5α-cholestan-6-spiro-1′,2′,4′-triazolidine-3′-one.
► Triazolidinone ring closes at C-6 carbon atom.
► Reaction mechanism is described by using density functional theoretical models.