The Diels-Alder reaction of chiral 1-p-tolylsulfinyl-3,5-heptadien-2-ols (1a, 1b) with 8,8-dimethylnaphtalene-l,4,5(8H)-trione (2) and N-ethylmaleimide (3) were studied (Scheme 1). The reactions with dienophile 2 take place with high regioselectivity in accord with published results about regioselective reaction with hexadienol [1]. At room temperature these reactions also show high pi-facial selectivity. Instead the cycloaddition with dienophile 3 is unselective in absence of catalyst. However, high yield and high π-facial selectivity was obtained using basic alumina. The structures of transition states of dienophile 2 with both dienols were calculated, the energy differences between them are in good agreement with experimental ratio of products. Interestingly, intermolecular hydrogen bonding is the responsible of the selectivity in one case and intramolecular hydrogen bonding in the other.

[1] R. Araya-Maturana, B. K. Cassels, T. Delgado-Castro, J. A. Valderrama, B. Weiss-López, Tetrahedron 1999, 55, 637-648.

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