Methylamine → 4-Methyliminomethyl-9-phenyl-2,3,4,9-tetrahydrothiopyrano[2,3-b]indole

To a solution of 4-formyl-9-phenyl-2,3,4,9-tetrahydrothiopyrano[2,3-b]indole (1.4 g) in absolute benzene (20 ml) is added a 30% solution (1.5 ml) of methylamine in methanol. The mixture is stirred at room temperature for 3 hours and evaporated to give 4-methyliminomethyl-9-phenyl-2,3,4,9-tetrahydrothiopyrano[2,3-b]indole as orange solid. The product is dissolved in a mixture of methanol (20 ml) and tetrahydrofuran (20 ml) and sodium borohydride (274 mg) is added thereto. The mixture is stirred at room temperature for 1 hour and evaporated.