O-benzoyl-~-~-ribofuranosyl)-1, 4-thiazine-2, 3-dione (9) in 32% yield and 4-(2, 3, 5-tri-O- benzoyl-P-~-ribofuranosyl)-1, 4-thiazin-3-one 1-oxide (10) in 16% yield as shown in Scheme 11. The formation of compound 9 was unexpected but was rationalized as the result of two consecutive Pummerer reactions, as discussed below. An alternate route to the thiazine 1- oxides via 2-[(2, 2-diethoxyethy1) sulfinyljacetamide (12) or 2-[(2, 2-dieth-oxyethyl) ...