1,8-Diazabicyclo(5.4.0)undec-7-ene → (R)-methyl 4-azido-3,4-dihydro-2H-chromene-7-carboxylate

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Reaction Steps

To a 3 L three-neck round-bottomed flask equipped with argon inlet/outlet, thermometer, and magnetic stirring was added (S)-methyl 4-hydroxychroman-7-carboxylate (71 g, 340 mmol) in 800 mL of toluene. The reaction vessel was cooled with a ice/salt bath, and treated with a solution of diphenylphosphoryl azide (88 mL, 407 mmol, Aldrich) in 200 mL toluene (internal temp.=−4° C.). After 10 min, a solution of 1,8-diazabicyclo[5.4.0]undec-7-ene (61 mL, 407 mmol, Aldrich) in toluene (350 mL) was added over 30 min (the internal temperature did not exceed 1° C.). The reaction mixture was warmed to room temp and stirred for 40 h. The reaction mixture was diluted with 800 mL EtOAc and washed with 1 M H3PO4, water, 5% NaHCO3, and brine. The organic layer was dried over Na2SO4, filtered and concentrated in vacuo. The residue was purified by silica gel chromatography (10:1 hexane-EtOAc) to provide the title compound. MS (+ion ESI) m/z=234 (MH+).

Provenance & Evidence