Triethylamine → Thiomorpholinecarboxylic acid ethyl ester

Participants

Reaction Steps

4-Boc-thiomorpholine-3-carboxylic acid can also be substituted for the compound of formula (XXIV) in Reaction Scheme 7 and can be prepared in the following manner: To THF was added cysteine ethyl ester hydrochloride (1.15 g, 6.18 mmol), triethylamine (4.17 mL, 30 mmol) and dibromoethane (2.51 mL, 6.2 mmol). After stirring for 1 hour and refluxing for 16 hours, the solids were removed by filtration. The solvent was removed in vacuo and the residue was chromatographed on silica to give thiomorpholinecarboxylic acid ethyl ester (0.94 g, 87%). The ester (15.3 g, 95 mmol) was dissolved in dioxane/water (1/1) and di-t-butyldicarbonate (24 g, 110 mmol) and LiOH were added. After stirring for 3 hours, the solvent was removed in vacuo and the pH was adjusted to 3 with KHSO3 and extracted with ethyl acetate. The organic layer was separated, washed with brine, dried (MgSO4), and the solvent was removed in vacuo to give 17.4 g (78%) 4-Boc-thiomorpholine-3-carboxylic acid: 1H NMR (CDCl3) δ 1.45 (m, 9), 2.45 (m, 1), 2.71 (m, 1). 2.93(m, 1), 3.10 (m. 1), 3.29 (m, 1), 4.11 (m, 1), 4.19 (m, 1), 5.20 (m, 1). 4-Boc-thiomorpholine-3-acetic acid can also be substituted for the compound of formula (XXIV) in Reaction Scheme 7 and can be prepared in the following manner: To THF (50 mL) was added methyl bromocrotonate (1.0 mL, 8.6 mmol), Hünig's base (1.5 mL, 8.6 mmol), and N-Boc-2-aminoethanethiol (1.5 g, 8.6 mmol). After stirring for 3 hours, the reaction was poured into saturated NH4Cl and extracted with ethyl acetate. The organic layer was washed with brine, dried (MgSO4), and the solvent was removed in vacuo. Chromatography (hexane/ethyl acetate, 6/1) gave N-Boc-2-aminoethanethiocrotonic acid methyl ester. The ester was dissolved in CH2Cl2 (80 mL) and TFA (20 mL) was added. After stirring for 1 hour, the solvent was removed in vacuo. The residue was added to a solution of toluene and TEA (2.5 ml). After stirring for 16 hours, the solvent was removed in vacuo and the residue was chromatographed to give the thiomorpholine. The ester (18.0 g, 95 mmol) was dissolved in dioxane/water (1/1) and di-t-butyldicarbonate (19.6 g, 90 mmol) and LiOH were added. After stirring for 12 hours, the solvent was removed in vacuo and the pH was adjusted to 3 with KHSO3 and extracted with ethyl acetate. The organic layer was separated, washed with brine, dried (MgSO4), and the solvent was removed in vacuo to give 20.3 g (86%) 4-Boc-thiomorpholine-3-acetic acid: 1H NMR (CDCl3) δ 1.45 (m, 9), 2.45 (m, 1), 2.51 (m, 1), 2.68 (m, 1), 2.82 (m, 1), 3.05 (m. 4), 4.24 (s, 1), 4.93 (s, 1).

Provenance & Evidence