THE OSMIUM-CATALYZED ASYMMETRIC DIHYDROXYLATION OF CIS-FUSED CYCLOPENTENO-1,2,4-TRIOXANES

Submission of racemic, cis-fused cyclopenteno-1,2,4-trioxanes (1 and 1 -ent) to catalytic amounts of K2OsO4 and (DHQD)(2)PHAL and 1.2 equival ents of N-methylmorpholine N-oxide in aqueous acetone at 20 degrees C (hybrid AD-mix-beta) for 2 h gave the (-)-enantiomer, 1-ent (ee 95%) i n 30% yield. The same reaction, but with (DHQ)(2)PHAL, (hybrid AD-mix- alpha) afforded the (+)-enantiomer, 1 (ee 95%) in 25% yield after 2.7 h reaction. Similar, efficient kinetic resolution of the racemic di-p- fluoro analogues (2 and 2-ent) was also achieved with the same reagent s.