(3aS)-1-methyl-3,3-diphenyl-hexahydropyrrolo(1,2-c)(1,3,2)oxazaborole → 2H-PYRAN-3-OL, TETRAHYDRO-4,4-DIMETHOXY-, (3R)-

Participants

Reaction Conditions

Reaction Steps

A 12-L 4-neck round bottom flask equipped with a overhead air stirrer, addition funnel with nitrogen inlet adapter, condenser, and thermocouple was charged with S-(−)-2-methyl-CBS-oxazaborolidine (40 g, 0.12 mol) and THF (2.2 L). The mixture was warmed under nitrogen to 40° C. then Me2S—BH3 (108 mL, 1.15 mol) was added to the THF-catalyst mixture via syringe. An addition funnel charged with 4,4-dimethoxydihydro-2H-pyran-3(4H)-one (as prepared in the previous step, 165 g, 0.59 mol) in THF (2.1 L) was added drop wise over a 7 h period. After the addition was complete, the reaction was allowed to stir for 18 h at 40° C. The reaction was chilled to 10° C. in an ice-acetone bath and quenched by slow addition of MeOH (1.1 L) over 1 h period. The cooling bath was removed and the mixture allowed to warm to room temperature for 3 h. After the gas evolution ceased, the mixture was concentrated on a rotary evaporator to give 188 g. Purification on silica gel using a mixture of EtOAc and heptanes afforded the title compound (166 g, 99%, chiral GC 93% ee) as a yellow oil.

Provenance & Evidence