2-Mercaptobenzoic Acid → 4-((alpha-s)-alpha-((2s,5r)-2,5-Dimethyl-1-piperazinyl)benzyl)-n,n-diethylbenzamide

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Reaction Steps

The compound of Example 1 was de-allylated by the method of Genet [J. P. Genet, S. Lemaire-Audoire, M. Savignac, Tetrahedron Letters, 36, 1267-1270 (1995)] as follows. A solution of 4-((alpha-S)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)benzyl)-N,N-diethylbenzamide (Example 1, 8.392 g, 20 mmol) and thiosalicylic acid (3.70 g, 24 mmol) in anhydrous tetrahydrofuran (50 mL) was stirred under nitrogen for 3 h at room temperature with a catalyst solution prepared by dissolution of bis(dibenzylidineacetone)palladium (575 mg, 1.0 mmol) and 1,4-bis(diphenylphosphino)butane (426 mg, 1.0 mmol) in tetrahydrofuran (10 mL). The reaction mixture was evaporated to dryness, the residue dissolved in a mixture of ethyl acetate/ether (1:3, 300 mL) and extracted with 5% sodium carbonate solution (2×300 mL). The organic layer was diluted with two volumes of pentane and extracted with 3M-hydrochloric acid (6×50 mL). The aqueous solution was filtered to remove suspended solid and the pH adjusted to 12 with 5-MNaOH. The resulting oily suspension was extracted with methylene chloride (2×125 mL) and the combined organic extracts dried over anhydrous sodium sulfate and evaporated to dryness. The residue was crystallized from ethyl acetate to yield fine white needles of 4-((alpha-S)-alpha-((2S,5R)-2,5-dimethyl-1-piperazinyl)benzyl)-N,N-diethylbenzamide (3.46 g). The product showed a single spot on thin layer chromatography (silica gel, EM60F264, 4% NH4OH/10% EtOH in ethyl acetate, Rf=0.47). 1H NMR (CDCl3, 600 MHz); δ 0.93 (d, J=6.3 Hz, 3H); 1.12 (br m, 3H); 1.20 (d, J=6.1 Hz, 3H); 1.24 (br m, 3H); 1.55 (dd, J=9.7, 11.3 Hz, 1H, partially obscured by br m, 2H); 2.33 (m, 1H); 2.68 (m, 2H); 2.89 (m, 1H); 2.92 (dd, J=12.1, 3.1 Hz, 1H); 3.29 (br m, 2H); 3.54 (br m, 2H); 5.38 (s, 1H); 7.14 (m, 2H); 7.30 (m, 3H); 7.35 (m, 2H); 7.46 (d, J=7.8 Hz, 2H).

Provenance & Evidence