Borane-tetrahydrofuran complex (1M in tetrahydrofuran, 1 ml, 1 mMol) was added dropwise to a solution of (R)-tetrahydro-1-methyl-3,3-diphenyl-1H,3H-pyrrolo [1,2-c][1,3,2]oxazaborole (0.1 equiv, 30 mg, 0.1 mMol) in tetrahydrofuran (6 ml) at ambient temperature under an argon atmosphere. After 5 minutes, 8-benzyloxy-5-chloroacetylcarbostyril (328 mg, 1 mMol) was added and the reaction mixture was stirred for a further 15 minutes. The reaction mixture was cooled to 5° C. and quenched by the dropwise addition of methanol (2 ml). The quenched reaction mixture was stirred for 15 minutes at 5° C. and for 30 minutes at ambient temperature. The solvent was evaporated and the residue was purified by chromatography on silica gel eluting with 10% methanol in ethyl acetate to afford the title compound as a pale yellow solid; m.p. 148°-149° C.; [α]D25 -9.0° (c=1, methanol).
