Synthesis and Stereochemistry of Saturated and Partially Saturated 4‐Aryl‐4 H ‐3,1‐benzothiazine‐2(1 H )‐thiones

The reaction of 2‐arylidenecyclohexanones 1 with dithiocarbamic acid gave three of the four possible diastereomers of 4‐aryl‐4a,5,6,7,8,8a‐hexahydro‐8a‐hydroxy‐4 H ‐3,1‐benzothiazine‐2(1 H )‐thiones 2 – 4 . The isomeric composition of the reaction products was found to depend on the quantity of hydrochloric acid used as catalyst. 1 H‐NMR studies showed that the preferred conformation of the cis isomers 2 and 4 is controlled by the bulky 4‐aryl group, which always occupies the energetically more favourable quasiequatorial position. Dehydration of 2 – 4 afforded the corresponding 4‐aryl‐tetrahydro‐4 H ‐3,1‐benzothiazine‐2(1 H )‐thiones 5 and 6 . The orientation of the dehydration reactions depends on the configuration of the starting compounds 2 – 4 and the reaction conditions used.