Condensed bridgehead nitrogen heterocyclic systems;: Synthesis, stereochemistry and antimicrobial activity of 3,4-cis-8,8a-tetrahydro-2H,7H-pyrazolo[3′,4′ :4,5]thiazolo[3,2-b]-s tetrazines

7-Arylidene-3;3 -diethyl-3,4,6,7-tetrahydro-2H-thiazolo[3,2-b]-s-tetrazin-6-ones 2 have been synthesised in a single step by the condensation of 6,6-diethyl-1,2,4,5-tetrahydro-stetrazine-3-thione 1 with ethyl chloroacetate and aldehydes in I the presence of pyridine and piperidine. Condensation of 2 with hydrazine hydrate in the presence of anhyd. sodium acetate furnishes 8-aryl-3,3-diethyl-3,4-cis-8,8a-tetrahydro- 2H,7H-pryazolo[3',4':4,5]thiazolo[3,2-b]-s-tetrazines 3. The antibacterial and antifungal activities of some of the compounds have also been evaluated.