1,2-Dibromopropane → 5,6-Dihydro-6-methyl-3-(2-thienyl)-1,4,2-oxadiazine

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Methyl-2-thiophenecarbodithioate (47 g, 0.27 mol) in methanol (250 ml) at 0-5° C., was stirred and treated with powdered hydroxylamine hydrochloride (20 g) and followed by dropwise addition of triethylamine (50 ml) in methanol (50 ml) over 2 hours, to prepare a reaction mixture. Additional hydroxylamine hydrochloride (5 g) and triethylamine (10 ml) was added consecutively to the reaction mixture and after 45 minutes, the reaction mixture turned yellow (from red). 1,2-Dibromopropane (26 ml) was then added to the yellow reaction mixture, followed by addition of triethylamine (75 ml). The resultant new reaction mixture was refluxed for 4 hours and then left overnight at ambient temperature. The methanol was removed from the reaction mixture to leave a residue. Water was added to the residue which was then extracted into ethyl acetate, washed with dilute hydrochloric acid (2N, 100 ml), water, and dried (MgSO4). The ethyl acetate was then removed to leave a brown oil which was crystallized with cyclohexane to produce two crops of 5,6-dihydro-6-methyl-3-(2-thienyl)-1,4,2-oxadiazine (11.7 g and 3.7 g, mp 70-72° C.) Found: C 48.90, H 4.66, N 7.17, C8H9NOS2 requires C 48.24, H 4.52, N 7.07

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