3.6- Dihydro-27/-thiin, conformations

Table 1 shows the two dihydrothiopyrans, and the two corresponding benzo fused systems. The monocycles (5,6-dihydro-2//- thiin and 3,4-dihydro-2iT-thiin) are quite clearly from their chemistry an allylic sulfide and an enol sulfide respectively, and in many of the reactions they exhibit they are perfectly comparable with acyclic counterparts. Once again, as for the tetrahydrothiopyrans, in many cases the principal chemical interest is related to the effects of preferred conformations on the stereochemistry of particular conversions, but this will not be discussed in great length as it is entirely predictable from classical alicyclic work. Where differences exist they may be attributed to the interaction of the heteroatom with the neighbouring alkene, which is not too considerable, and more importantly the reactivity of the sulfur atom in its own right. The benzo fused compounds, of course, have their own particular chemistry which has received considerable attention over many years, some of which will be discussed. 

Hetero-substituted cyclohexenes, e.g., 3,6-dihydro-2/7-pyran, 3,6-dihydro-2//-thiin, and 3,6-dihydro-l,2-dioxin, exist in half-chair conformations (see Section 2.2.3.2). 

Thiin, cw-3,5-di-t-butyItetrahydro-conformation, 3, 888 Thiin, dihydro-derivatives synthesis, 3, 931, 933... 

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