Table 1.

Optimization of cyclization of the thiosemicarbazide.

Entry	Oxidant	Solvent	Temp. (°C)	Yield (%)
1	K2S2O8	Water	100	N.O. a,c
2	(NH4)2S2O8	Water	100	N.O. a,c
3	IBX	Water	100	<30 a
4	Oxone	Water	100	<40 a
5	KIO3	Water	100	53 b
6	KIO3	Water	80	83 b
7	KIO3	Water	40	46 b
8	KIO3	Water	60	90 b
9	KIO3	DCM	60	5 a
10	KIO3	Acetone	60	N.O. a,c

All the reaction were carried out on a 0.4 mmol scale with 1.5 equiv. oxidants within 2 h; ^a the reaction conversions were monitored by LC-MS; ^b Isolated yield; ^c N.O.: No observation.