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-metho xy-1,3-butadienes 2 and 3 were provided by the addition of (1S)-isobor nel-10-sulfenic and (S)-phenyl-2-hydroxyethanesulfenic acid 8 to (E)- and (Z)-1-methoxybut-1-en-3-ynes (9) and (10). These additions proceed ed with asymmetric induction, the extent of which depended upon the na ture of the chiral hydroxyalkyl group. Cycloadditions of methyl acryla te 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 controlle d the diastereofacial selectivity in these Diels-Alder cycloadditions.