Scheme 2 Reagents and conditions: (i) Anh. K2CO3 (1 equiv.), DMF (dry), 2-bromo-1,1-diethoxyethane (1 equiv.), 90°C, 24 h; (ii) 1N HCl, reflux, 1 h; (iii) NH2OH.HCl (1 equiv.), CH3COONa (anh. 0.41 equiv.), H2O, EtOH, 800C, 1.5 h; (iv) DMF (dry), NCS (1.4 equiv.) in portions during 1 h, N2, r.t. 30 min, 10 (1 equiv.), Et3N (1 equiv.), r.t. 24 h.