Benzyl Bromide → 1,3-Diphenylmethyl-2-piperidinone

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1-Phenylmethyl-2-piperidinone (See: Yamaguchi M, Hirao I (1985) "A direct synthesis of [(tert-butoxycarbonyl)methylidene]-azacycloalkanes from N-alkyllactams" J. Org. Chem., 50, 1975-1977) (3.40 g, 18 mmol) was reacted with benzyl bromide (4.84 g, 28.3 mmol) in the presence of lithium diisopropylamide (prepared by treating diisopropylamine (2.73 g, 27 mmol) with butyllithium in hexanes (2.5M, 10.3 mL, 25.7 mmol)) in THF (45 mL) and HMPA (2.7 mL, 15.5 mmol) as described above in the preparation of Example 7. After the addition of benzyl bromide, the reaction mixture was stirred for 2 h at -78° C., and then quenched with saturated NH4Cl (50 mL). The reaction mixture was extracted with ether (3×40 mL) and the combined ether extract washed with brine (40 mL) and dried over MgSO4. The solvent was removed in vacuo, and the residue (8.40 g) thus obtained, was chromatographed over silica gel (hexanes-CHCl3 -EtOAC, 15:4:1 and then 7:2:1) to give the product lactam (3.14 g, 63%) as a colorless solid: mp 94°-95° C. (CH2Cl2 -hexanes).

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