A NEW HETEROANNULATION METHOD TO 2-CYCLOHEXENONE, MEDIATED BY PHOSPHONATE AUXILIARIES - SYNTHESIS OF 4,5,6,7-TETRAHYDROBENZOTHIAZOLE DERIVATIVES

Dimethyl (1,2-epoxy-3-oxocyclohex-1-yl)phosphonate 7, easily available from 2-cyclohexen-1-one, affords the new (tetrahydrobenzothiazolyl)ph osphonates 10 upon reaction with thiocarboxamides 8. This cyclocondens ation proceeds with regioselective conjunction of the bis-nucleophile 8 to carbonyl group and adjacent oxirane carbon of the epoxide precurs or. On treatment with alkali the 5,6-dihydro-7(4H)benzothiazolones 12 are obtained from compounds 10, or from the intermediately formed bicy clic dihydroxy derivatives 9. Reaction of the corresponding cyclopenty lphosphonate 14 with thiobenzamide (8b) yields the cyclopentathiazole derivative 15 as a single isomer, the dihydro-thiazole moiety being no w annulated regio- and cis-stereoselectively to both oxirane carbons o f the epoxyphosphonate.