The osmium-catalyzed asymmetric dihydroxylation of cis-fused cyclopenteno-1,2,4-trioxanes

Abstract

Submission of racemic, cis-fused cyclopenteno-1,2,4-trioxanes ( 1 and 1-ent) to catalytic amounts of K 2OsO 4 and (DHQD) 2PHAL and 1.2 equivalents of N-methylmorpholine N-oxide in aqueous acetone at 20°C (hybrid AD-mix-β) for 2 h gave the (-)-enantiomer, 1-ent (ee 95%) in 30% yield. The same reaction, but with (DHQ) 2PHAL, (hybrid AD-mix-α) 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 reagents.