Syntheses of all eight stereoisomers of conidendrin.

All eight stereoisomers of conidendrin were synthesized from (1  R ,2  S ,3  S )-1-(4-benzyloxy-3-methoxyphenyl)-3-(4-benzyloxy-3-methoxybenzyl)-2- hydroxymethyl-1,4-butanediol ((+)- 4 ) and its enantiomer with high optical purity. The configurations at 4-positions of the conidendrin stereoisomers were constructed by intramolecular Friedel-Crafts reaction of protected 4 . After conversion to tetrahydronaphthalene intermediate 7a , the 2- and 3-position of tetrahydronaphthalene structure 7a were converted to 3a- and 9a-position of (+)-α-conidendrin ( 3a ), respectively. By the epimerization process of 2- or 3-position of 7a , the other diastereomers were obtained. All enantiomers were also synthesized from (-)- 4 .