Stereoselectivity control in Diels-Alder reactions of 4-thiosubstituted 5-alkoxyfuranones: synthesis and reactivity of enantiopure 4-sulfinyl and sulfonyl 5-(l-menthyloxy)furan-2(5H)-ones

The synthesis of enantiomerically pure (S)-4-phenylsulfinyl- and 4-phenylsu lfonyl-(5S)-5-(l-menthyloxy)furan-2(5H)-ones 5a and 6 and (SR)-5-(l-menthyl oxy)-4-phenylsulfonylfuran-2(5H)-one 8 and the study of their reactions wit h cyclopentadiene are described. The sulfur substituents at C-4 modify (sul fone 8, anti/syn=78/22) and invert (sulfoxide 5a and sulfone 6, anti/syn ap proximate to 27/73) the trend imposed by C-5 on the pi -facial selectivity and the syn-adducts become the favoured ones. The endo or exo approach mode is favoured for anti (endo/exo ratio ranging between 26 and 5) or syn (exo /edno ratio ranging between 4.5 and 2.3) attack, respectively. (C) 2001 Pub lished by Elsevier Science Ltd.