NEW ORGANIC NITRATES .2. SYNTHESIS OF 2H-PYRIDO[2,3-E]-1,3-OXAZINE-2,4(3H)-DIONES, 2H-PYRIDO[4,3-E]-1,3-OXAZINE-2,4(3H)-DIONES, 2H-PYRIDO[4,3-E]-1,3-OXAZIN-4(3H)-ONES, 2H-THIENO[2,3-E]-1,3-OXAZIN-4(3H)-ONES AND 2H-THIENO[3,4-E]-1,3-OXAZIN-2,4(3H)-DIONES Journal Article