Diethyl 2-[cyano(toluene-4-sulfinyl)methylene]propanedioate and its Diels-Alder adduct with cyclopentadiene

The thermal Diels-Alder cycloaddition reaction of diethyl 2-[cyano(toluene- 4-sulfinyl)methylene]propanedioate, C16H17NO5S, with cyclopentadiene gave t he pure racemates of two of the four possible diastereomers, with a complet e pi -facial selectivity and a high (80:20) endo/exo-sulfinyl selectivity. X-ray diffraction studies of diethyl 2-[cyano(toluene-4-sulfinyl)methylene] propanedioate and the major isomer of the cycloaddition product, namely die thyl 3-cyano-3-(toluene-4-sulfinyl)bicyclo[2.2.1]hepta-5-ene-2,2-dicarboxyl ate, C21H23NO5S, reveal that the conformation of the substituents on the ac rylonitrile moiety produces both steric and electronic effects, which affec t the stereoselectivity of the reaction.