A synthesis and the determination of the absolute configuration of (−)-( 1S, 3R′ 6R, 8R)-2, 7-dioxa-isotwistane ( 13) and (−)-( 1R, 3R, 6R, 8R)-2, 7-dioxa-twistane ( 14) is described. The results for 14 are compared with those for carboeyclic (+)-twistane ( 2) of known chirality.