Barbiturates are we ll -known for their CNS activities l 4 . The introduction of spiro nuc leus is known to enhance the antimicrobial activity of the compound. We now report the synthesis of some new fused pyrimidino [4 ,5-e] thiadi azines and spiro compounds containing 1,3,4-thiadiazine and thiazolidine moieties. The reaction of thiocarbohydrazide 1 with 5bromo-barbituric acid (2a, X=O, R=H) in the presence of pyridine afforded 6,8-dioxo-2-hydrazino4H, 5,6, 7, 8-tetrahydropyrimido[ 4,5-e][ 1,3 ,4 ]-thiadiazine 3a (cf Scheme I). IR (KBr): 3350 and 33 17 (-NH2)' 3203, 3187 (2 x -NH), 1694 and 1674 (2 x C=O) and 1585 cm· 1 (C=N); IHNMR (300MHz in DMSO-d6) : 8 2 .35 (t, J = 9.5 Hz, lH , exocyclic -NH-N), 4.8 (d , J = 9.5 Hz, 2H, -N-NH2)' 6.95 (s, I H, ring -NH at positi on 4 ), 9 .5 (s, I H, -NHCO), 9.9 (s, I H,-NHCO), 11 .0 (s, I H, -N=C(OH) ) and I 1. 1 (s, I H, -N=C(OH» . Compound 3 on treatment with different a ldehydes afforded the corresponding Schiff' s bases 4 . An alternate unamb iguous synthes is of 4 was also achieved by the interacti on of 2a with I-a lky lidene/arylidene thiocarbohydrazide5 (cf. Scheme I ). The compounds thus obtained were identifi ed through undepressed mmps', superimposable IR spec tra and coTLC. The react ion was ex tended to 5-bromo-I,3di substituted-2-thiobarbituric ac ids 2b/c (cf. Scheme I). The interaction of 2-a lkyl/arylimino-5-bromo-5carbethoxy-thiazolidin-4-one 6 with 4-ary l substituted thiosemicarbazides 7 in the presence of sodium acetate yielded 4-aryl-3S-(5'-carbethoxy-2'-a lkyllaryl-