1,8-Diazabicyclo(5.4.0)undec-7-ene → (R)-3-((S)-1-(4-bromophenyl)ethyl)-6-(2-methylallyl)-6-phenyl-1,3-oxazinan-2-one

Participants

Reaction Conditions

Reaction Steps

To a dried 10 L jacketed reactor under a nitrogen atmosphere was charged 1-chloro-5-methyl-3-phenyl-hex-5-en-3-ol (167 g, 81.7 wt %, 610 mmol, 1.00 equiv), 1-bromo-4-((S)-1-isocyanato-ethyl)-benzene (219 g, 93.7 wt %, 911 mmol, 1.50 equiv), anhydrous tetrahydrofuran (3.00 L), and then 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 409 mL, 2.73 mol, 4.50 equiv). The resulting solution was agitated and refluxed (Tint=67-69° C., Text=75° C.) for 19 h, at which point HPLC analysis indicated ˜1A % (220 nm) of the 1-chloro-5-methyl-3-phenyl-hex-5-en-3-ol remained. The dark solution was cooled to Tint=20-25° C. Two liters of tetrahydrofuran were removed by distillation under reduced pressure. The remaining dark solution was diluted with 4.0 L of ethyl acetate and 1.0 L of hexanes. The resulting solution was washed with 4.0 L of a 1.0 M aqueous solution of hydrogen chloride (note: the wash is slightly exothermic). The aqueous solution was cut and the remaining organic solution was dried with anhydrous sodium sulfate, filtered and then concentrated to an oil via reduced pressure. The resulting material was subjected to flash silica chromatography (5-30% ethyl acetate/hexanes, 1.74 kg of silica) to produce 137.8 g of material (59 wt %, 3.1:1 diastereomeric ratio favoring the desired diastereomer

Provenance & Evidence