Reduction Stereoisomerism alcohol derivative article carbonyl derivative iodine priority journal stereochemistry unclassified drug 1,3 butadiene 1,5 anhydro 2,3,4 tri o acetyl dextro threo pent 1 enitol 1,5 anhydro 2,3,4 tri s phenyl 2,3,4 trithio dextro,levo threo pent 1 enitol 2 benzyl 2h pyran 3(6h) one 2 benzylthio 2h pyran 3(6h) one 2 phenylthio 2h pyran pyran 3(6h) one Alcohols Betulaceae Biochemistry CARBON Carbohydrate Conformation Carbohydrate Sequence Carbon Catalysis Chromatography Chromatography, Thin Layer Cyclizations Cycloadducts Cyclopentanes Diastereoselection Diels Alder reaction