Summary
Dimethyl (1,2-epoxy-3-oxocyclohex-1-yl)phosphonate7, easily available from 2-cyclohexen-1-one, affords the new (tetrahydrobenzothiazolyl)phosphonates10 upon reaction with thiocarboxamides8. This cyclocondensation proceeds with regioselective conjunction of the bisnucleophile8 to carbonyl group and adjacent oxirane carbon of the epoxide precursor. On treatment with alkali the 5,6-dihydro-7(4H)benzothiazolones12 are obtained from compounds10, or from the intermediately formed bicyclic dihydroxy derivatives9. Reaction of the corresponding cyclopentylphosphonate14 with thiobenzamide (8b) yields the cyclopentathiazole derivative15 as a single isomer, the dihydro-thiazole moiety being now annulated regio- andcis-stereoselectively to both oxirane carbons of the epoxyphosphonate.
Zusammenfassung
Umsetzung des aus 2-Cyclohexen-1-on leicht zugänglichen (1,2-Epoxy-3-oxocyclohex-1-yl)phosphonats7 mit den Thioamiden8 liefert die neuen (Tetrahydrobenzthiazolyl)phosphonate10. Dabei wird der Thiazolring regioselektiv an Carbonylgruppe und benachbarten Oxirankohlenstoff des Epoxyphosphonats anelliert. Mit Alkali werden sowohl die α-Hydroxyphosphonate10 als auch die intermediär gebildeten Dihydroxyverbindungen9 zu den 5,6-Dihydro-7(4H)benzthiazolonen12 gespalten. Im Gegensatz dazu reagiert das Cyclopentylphosphonat14 mit Thiobenzamid8b zu einem Cyclopentathiazol-Derivat15, bei dem der Dihydrothiazolring regioundcis-stereoselektiv mit den beiden früheren Oxiran-Kohlenstoffen verknüpft ist.
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Öhler, E. A new heteroannulation method to 2-cyclohexenone, mediated by phosphonate auxiliaries. Synthesis of 4,5,6,7-tetrahydrobenzothiazole derivatives. Monatsh Chem 124, 763–773 (1993). https://doi.org/10.1007/BF00817312
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DOI: https://doi.org/10.1007/BF00817312