Water → ethyl 5-(aminothioxomethyl)tetrahydro-2H-1,2-oxazine-2-carboxylate

A mixture of ethyl 5-cyanotetrahydro-2H-1,2-oxazine-2-carboxylate (i.e. the product of Step H) (0.63 g, 0.0034 mol) and thioacetamide (0.72 g, 0.0096 mol) in trifluoroacetic acid (about 2 mL) was stirred at 50° C. for 20 h. The reaction mixture was poured into water (10 mL) and extracted with diethyl ether (3×10 mL). The combined organic extracts were washed with water (10 mL), dried over magnesium sulfate, filtered and concentrated to provide an orange oil (about 0.76 g). The resulting oil was adsorbed onto Celite® (diatomaceous filter aid), and then purified by silica gel column chromatography (25% to 50% gradient of ethyl acetate in petroleum ether as eluant) to provide the title compound (0.19 g).