α,β-Unsaturated thioesters and selenoesters serve as dienophiles in Diels-Alder reactions with a variety of 1,3-dienes. Good levels of regioselectivity are obtained with unsymmetrical dienes when Lewis acid promoters are used. Thioesters and selenoesters are more reactive than the corresponding methyl esters based on competition experiments with cyclopentadiene.

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Reactions of cyclohexanone enamines with a,b-unsaturated thioesters and selenoesters provide bicyclo[3.3.1]nonane-2,9diones.

Diels-Alder Reactions of α,β-Unsaturated Thioesters and α,β-Unsaturated Selenoesters.-The regio-and exo/endo-selectivity of Diels-Alder reactions of thio-and selenoesters (II) with dienes is investigated. In general, thermal reactions show only low selectivities as expected. The selectivity improves upon use of soluble Lewis acid promotors such as EtAlCl 2 and TiCl 4 . -(BYEON, C.-H.; CHEN, C.-Y.; ELLIS, D. A.; HART, D. J.; LI, J.; Synlett (1998) 6, 596-598; Dep. Chem., Ohio State Univ., Columbus, OH 43210, USA; EN)

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