Scheme 1 Reagents and conditions: (i) NH2OH.HCl (1 equiv.), CH3COONa (anh. 0.41 equiv.), H2O, EtOH, 800C, 2.5 h; (ii) DMF (dry), NCS (1.4 equiv.) in portions during 1 h, N2, r.t. 30 min, 3 (1 equiv.), Et3N (1 equiv.), r.t. 24 h, for 4a-k; (iii) TFA (0.2 equiv.), 3 (1.1 equiv.), PIDA (1.1 equiv.) in MeOH, 2 (1 equiv.) in MeOH (dropwise during 1 h), r.t. 4 h, for 4k-o.