277-Thiins, Diels-Alder reactions

The synthesis and Diels-Alder reactions of enantiopure (-)-tra s-benzo[d]thiin-S,S -dioxide 7 were described. Whereas with cyclopentadiene and 1,3-cyclohexadiene a high endolexo ratio (> 99/1) was obtained, with fiiran these values are lower depending on the reaction conditions... 

Dihydropyridines are isomerized photochemically to 2-azabicyclohexenes (520). 2/7-Thiins behave as dienes in Diels-Alder reactions (Scheme 59). 

Figure 2.3.14 (a) Schematic representation of the SCSC Diels-Alder reaction (b) a wireframe representation of a thiine and an anthracene molecule in the reactant co-crystal. 

It is quite likely that 2H- thiin is very similar in structure to the dioxide though perhaps with a widened C(6)—S(l)—C(2) angle and consequently less twisted dialkene this is supported by the Diels-Alder reactivity it displays (albeit with difficulty), while the sulfone (34) is inert to similar reactions. Structures (36) and (37) are tentatively suggested as possible pseudo chair and pseudo boat conformations for the AH-thiin system. 

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