Synthesis and asymmetric Diels-Alder reactions of enantiopure 3-(alkylsulfinyl)-1-methoxy-1,3-butadienes

Simple syntheses of enantiopure (E)- and (Z)-3-(alkylsulfinyl)-1-methoxy-1,3-butadienes 2 and 3 were provided by the addition of (1S)-isobornel-10-sulfenic and (S)-phenyl-2-hydroxyethanesulfenic acid 8 to (E)- and (Z)-1-methoxybut-1-en-3-ynes (9) and (10). These additions proceeded with asymmetric induction, the extent of which depended upon the nature of the chiral hydroxyalkyl group. Cycloadditions of methyl acrylate to the enantiopure dienes proceeded with complete regioselectivity and very high stereoselectivity when catalyzed by lithium perchlorate or zinc chloride in dichloromethane. The chirality at sulfur controlled the diastereofacial selectivity in these Diels-Alder cycloadditions.