Steroids and related products. XXIV. The synthesis of 17α-amino 20-keto steroids. Part I

α-Azido ketones, Part 6. Reduction of acyclic and cyclic α-azido ketones into α-amino ketones: old problems and new solutions

“…Next, we tested the synthetic value of the catalytic hydrogenation by using Lindlar's catalyst instead of the previously reported Pd-charcoal, 4 Pd-calcium carbonate 5 or platinum oxide. 6 This catalyst was found effective in the reduction of azido group 28 but has never been tried in the case of α-azido ketones. The 2-Azidoacetophenones 5a,b, 2-azidopropiophenone (5e), and the heterocyclic α-azido ketones 12a,d were hydrogenated at atmospheric pressure in the presence of Lindlar's catalyst.…”

“…Suzuki and his co-workers 2 have also reported the formation of symmetrical 2,5-substituted-or 2,3,5,6-tetrasubstituted-pyrazines 4 by treating α-azido ketones 2 with sodium hydrogen telluride in ethanol. The reaction could be performed in a "crossed" manner to synthesize complex pyrazines such as the naturally occurring cephalostatin 7, cephalostatin 12, and ritterazin K. 3 In some cases the catalytic reduction over Pd-charcoal, 4 Pd-calcium carbonate 5 or platinum oxide 6 was reported to give stable α-amino ketones but usually the products should be protected by their immediate transformation into a salt or an acylated / alkoxycarbonylated derivative to avoid the pyrazine formation. Hydrogen chloride or perchloric acid was added to the solution of the substrate prior to the hydrogenation [7][8][9][10][11] , or as an alternative, concentrated hydrochloric acid or dry hydrogen chloride was added to the reaction mixture just after filtering the catalyst off.…”

Synthesis and in silico evaluation of 16?-azido pregnenolone analogue as a clickable substrate for steroid-converting enzymes

“…The employed method was adopted from Winternitz and Engel with minor modifications [7]. To the solution of 16α,17α-epoxypregn-5-en-3-ol-21-one (50.5 mg, 1.53·10 -4 mol) and sodium azide (64 mg, 1.01·10 -3 mol) in a mixture of ethanol (2.2 ml) and dimethylsulfoxide (0.9 ml) were added 0.3 ml of ethanol containing 3 μl of acetic acid.…”