[CH:1]([C:3]1[N:8]=[N:7][C:6]2[O:9][CH2:10][CH2:11][O:12][C:5]=2[CH:4]=1)=C.I([O-])(=O)(=O)=[O:14].[Na+]>O1CCOCC1.O.[Os](=O)(=O)(=O)=O>[N:7]1[C:6]2[O:9][CH2:10][CH2:11][O:12][C:5]=2[CH:4]=[C:3]([CH:1]=[O:14])[N:8]=1A solution of 3-ethenyl-6,7-dihydro[1,4]dioxino[2,3-c]pyridazine (11.58 g) in 1,4-dioxane/water (600 ml/180 ml), cooled in ice, was treated with an aqueous solution of osmium tetroxide (4% w/v, 25 ml) and sodium periodate (43 g). This mixture was allowed to warm to room temperature and after 7 hours under stirring the mixture was evaporated to dryness and azeotroped with 1,4-dioxane. Silica gel, 1,4-dioxane and chloroform were added and the mixture was evaporated to dryness overnight, then added to a silica column (400 g) and chromatographed, eluting with chloroform then 0-100% ethyl acetate in hexane, to afford a white solid (7.55 g, 64%).
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