Synthesis of (+)‐1,3:2,5‐dianhydroviburnitol ((+)‐(1 R ,2 R ,3 S ,5 R ,6 S )‐4,7‐dioxatricyclo[3.2.1.0 3,6 ]octan‐2‐ol)

Epoxidation of (−)‐(1 R ,2 R ,4 R )‐2‐ endo ‐cyano‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐ exo ‐yl acetate ((−)‐5) followed by saponification afforded (+)‐(1 R ,4 R ,5 R ,6 R )‐5,6‐ exo ‐epoxy‐7‐oxabicyclo[2.2.1]heptan‐2‐one ((+)‐7). Reduction of (+)‐7 with diisobutylaluminium hydride (DIBAH) gave (+)‐1,3:2,5‐dianhydroviburnitol ( = (+)‐(1 R ,2 R ,3 S ,4 R ,6 S )‐4,7‐dioxatricyclo[3.2.1.0 3,6 ]octan‐2‐ol; (+)‐3). Hydride reductions of (±)‐7 were less exo ‐face selective than reductions of bicyclo[2.2.1]heptan‐2‐one and its derivatives with NaBH 4 , AlH 3 , and LiAlH 4 probably because of smaller steric hindrance to endo ‐face hydride attack when C(5) and C(6) of the bicyclo‐[2.2.1]heptan‐2‐one are part of an exo oxirane ring.