Chemistry of Diazocarbonyl Compounds: XVIII. Synthesis and Spectral Parameters of 1,3-Dialkyl- 3-hydroxy-2-diazoketones

Reduction of the carbonyl groups in cyclic and acyclic 2-diazo-1,3-diketones with sodium tetrahydridoborate in aqueous–alcoholic medium, followed by hydrolysis of the reaction mixture over wet silica gel and chromatographic purification on neutral aluminum oxide, afforded 1,3-dialkyl-3-hydroxy-2-diazoketones in 58–87% yield. Bulky substituents at the carbonyl group considerably reduce the efficiency of the process, and the reduction of cis- and trans-4,6-di-tert-butyl-2-diazocyclohexane-1,3-diones is characterized by low stereoselectivity (de 40–49%). In the IR spectra of 3-hydroxy-2-diazocyclohexanes, absorption bands corresponding to stretching vibrations of free axial hydroxy groups are located at higher frequencies (by 20-45 cm^-1) than those belonging to equatorial hydroxy groups. These parameters may be useful for conformational analysis of cyclic hydroxy diazo ketones. Stabilization of the E conformation of acyclic hydroxy diazo ketones via intramolecular hydrogen bonding is likely to occur only in nonpolar solvents (CCl₄, cyclohexane).