Stereostructure of condensed-skeleton cis- and trans-dihydro-1,3-thiazines and 1-thia-3-azaspiroalkenes

The stereostructures of some condensed-skeleton cis- and trans-dihydro-1,3-thiazines and 1-thia-2-phenyl-3-azaspiro[4n + 1]alk-2-enes (n = 3–6) were established by ¹H and ¹³C NMR spectroscopy. A comparative study indicated that the cis-thiazines have greater conformational mobility than the corresponding oxazines, although the preferred conformer of the two types of cis compounds is the same, with the sulphur axial and the 4-methylene group equatorial relative to the rings.