methyl (2S)-4-hydroxy-2-[(2-methylpropan-2-yl)oxycarbonylamino]butanoate

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A solution of triphenylphosphine (2.20 g, 8.39 mmol) in dry CH2Cl2 (20 mL) was added dropwise via syringe to a solution of N-Boc homoserine methyl ester 80 (8.39 mmol) and carbon tetrabromide (4.18 g, 12.60 mmol) in dry CH2Cl2 (20 mL). The resulting dark solution was stirred at room temperature for 16 h. Hexanes was added and precipitates were removed by suction filtration. The filtrate was concentrated under reduced pressure and subject to flash silica gel column chromatography using ethyl acetate/hexanes (1:10, v/v then 1:6, v/v) to give the desired product 90 as a yellow oil (501 mg, 20% overall yield from homoserine). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 2.12-2.48 (m, 2H), 3.39-3.47 (m, 2H), 3.78 (s, 3H), 4.33-4.48 (m, 1H), 5.10-5.22 (m, 1H). m/z (ESI) 296 [C10H18BrNO4+H]+. precipitates were removed by suction filtration The filtrate was concentrated under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A solution of triphenylphosphine (2.20 g, 8.39 mmol) in dry CH2Cl2 (20 mL) was added dropwise via syringe to a solution of N-Boc homoserine methyl ester 80 (8.39 mmol) and carbon tetrabromide (4.18 g, 12.60 mmol) in dry CH2Cl2 (20 mL). The resulting dark solution was stirred at room temperature for 16 h. Hexanes was added and precipitates were removed by suction filtration. The filtrate was concentrated under reduced pressure and subject to flash silica gel column chromatography using ethyl acetate/hexanes (1:10, v/v then 1:6, v/v) to give the desired product 90 as a yellow oil (501 mg, 20% overall yield from homoserine). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 2.12-2.48 (m, 2H), 3.39-3.47 (m, 2H), 3.78 (s, 3H), 4.33-4.48 (m, 1H), 5.10-5.22 (m, 1H). m/z (ESI) 296 [C10H18BrNO4+H]+. precipitates were removed by suction filtration The filtrate was concentrated under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a stirred solution of (S)-(tert-butoxycarbonylamino)-4-hydroxybutyric acid methyl ester (1.43 g; CAS 120042-11-7) in THF (4 ml) were added phenol (692 mg), triphenylphosphine (1.77 g) and diisopropyl azodicarboxylate (1.36 g). The resulting yellow solution was stirred at room temperature overnight. The reaction mixture was evaporated and purified by column chromatography (SiO2; gradient: heptane/EtOAc 100:0->90:10) to give (S)-2-tert-butoxycarbonylamino-4-phenoxy-butyric acid methyl ester (1.16 g, 61%) as a light yellow oil. MS (ISP): 210.1 ([M+H-BOC]+)). The reaction mixture was evaporated purified by column chromatography (SiO2; gradient: heptane/EtOAc 100:0->90:10)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A solution of triphenylphosphine (2.20 g, 8.39 mmol) in dry CH2Cl2 (20 mL) was added dropwise via syringe to a solution of N-Boc homoserine methyl ester 29 (8.39 mmol) and carbon tetrabromide (4.18 g, 12.60 mmol) in dry CH2Cl2 (20 mL). The resulting dark solution was stirred at room temperature for 16 h. Hexanes was added and precipitates were removed by suction filtration. The filtrate was concentrated under reduced pressure and subject to flash silica gel column chromatography using ethyl acetate/hexanes (1:10, v/v then 1:6, v/v) to give the desired product 30 as a yellow oil (501 mg, 20% overall yield from homoserine). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 2.12-2.48 (m, 2H), 3.39-3.47 (m, 2H), 3.78 (s, 3H), 4.33-4.48 (m, 1H), 5.10-5.22 (m, 1H). m/z (ESI) 296 [C10H18BrNO4+H]+. precipitates were removed by suction filtration The filtrate was concentrated under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A solution of triphenylphosphine (2.20 g, 8.39 mmol) in dry CH2Cl2 (20 mL) was added dropwise via syringe to a solution of N-Boc homoserine methyl ester 18 (8.39 mmol) and carbon tetrabromide (4.18 g, 12.60 mmol) in dry CH2Cl2 (20 mL). The resulting dark solution was stirred at room temperature for 16 h. Hexanes was added and precipitates were removed by suction filtration. The filtrate was concentrated under reduced pressure and subject to flash silica gel column chromatography using ethyl acetate/hexanes (1:10, v/v then 1:6, v/v) to give the desired product 19 as a yellow oil (501 mg, 20% overall yield from homoserine). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 2.12-2.48 (m, 2H), 3.39-3.47 (m, 2H), 3.78 (s, 3H), 4.33-4.48 (m, 1H), 5.10-5.22 (m, 1H). m/z (ESI) 296 [C10H18BrNO4+H]+. precipitates were removed by suction filtration The filtrate was concentrated under reduced pressure

Conditions: temp:0.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a cooled (0° C.) solution of (S)-2-tert-butoxycarbonylamino-4-hydroxy-butyric acid methyl ester (28.7 g, 123 mmol) in dichloromethane (500 mL) was added CBr4 (51.0 g, 154 mmol). The mixture was stirred for 5 minutes before the portion-wise addition of triphenylphosphine (48.41 g, 185 mmol). The mixture continued to stir at 0° C. for 1 hour and was then allowed to warm to room temperature. The solvent was removed under reduced pressure and was then diluted with ether (500 mL) and stirred for 30 minutes. The mixture was filtered, and the filtrate was concentrated under reduced pressure. The residue was chromatographed eluting with ether/hexanes (1:2) to afford 27.5 g of white solid (76% yield). to warm to room temperature The solvent was removed under reduced pressure was then diluted with ether (500 mL) stirred for 30 minutes The mixture was filtered the filtrate was concentrated under reduced pressure The residue was chromatographed eluting with ether/hexanes (1:2)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a stirred solution of (S)-(tert-butoxycarbonylamino)-4-hydroxybutyric acid methyl ester (1.43 g; CAS 120042-11-7) in THF (4 ml) were added phenol (692 mg), triphenylphosphine (1.77 g) and diisopropyl azodicarboxylate (1.36 g). The resulting yellow solution was stirred at room temperature overnight. The reaction mixture was evaporated and purified by column chromatography (SiO2; gradient: heptane/EtOAc 100:0→90:10) to give (S)-2-tert-butoxycarbonylamino-4-phenoxy-butyric acid methyl ester (1.16 g, 61%) as a light yellow oil. MS (ISP): 210.1 ([M+H-BOC]+)). The reaction mixture was evaporated purified by column chromatography (SiO2; gradient: heptane/EtOAc 100:0→90:10)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A solution of triphenylphosphine (2.20 g, 8.39 mmol) in dry CH2Cl2 (20 mL) was added dropwise via syringe to a solution of N-Boc homoserine methyl ester 29 (8.39 mmol) and carbon tetrabromide (4.18 g, 12.60 mmol) in dry CH2Cl2 (20 mL). The resulting dark solution was stirred at room temperature for 16 h. Hexanes was added and precipitates were removed by suction filtration. The filtrate was concentrated under reduced pressure and subject to flash silica gel column chromatography using ethyl acetate/hexanes (1:10, v/v then 1:6, v/v) to give the desired product 30 as a yellow oil (501 mg, 20% overall yield from homoserine). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 2.12-2.48 (m, 2H), 3.39-3.47 (m, 2H), 3.78 (s, 3H), 4.33-4.48 (m, 1H), 5.10-5.22 (m, 1H). m/z (ESI) 296 [C10H18BrNO4+H]+. precipitates were removed by suction filtration The filtrate was concentrated under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A solution of triphenylphosphine (2.20 g, 8.39 mmol) in dry CH2Cl2 (20 mL) was added dropwise via syringe to a solution of N-Boc homoserine methyl ester 18 (8.39 mmol) and carbon tetrabromide (4.18 g, 12.60 mmol) in dry CH2Cl2 (20 mL). The resulting dark solution was stirred at room temperature for 16 h. Hexanes was added and precipitates were removed by suction filtration. The filtrate was concentrated under reduced pressure and subject to flash silica gel column chromatography using ethyl acetate/hexanes (1:10, v/v then 1:6, v/v) to give the desired product 19 as a yellow oil (501 mg, 20% overall yield from homoserine). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 2.12-2.48 (m, 2H), 3.39-3.47 (m, 2H), 3.78 (s, 3H), 4.33-4.48 (m, 1H), 5.10-5.22 (m, 1H). m/z (ESI) 296 [C10H18BrNO4+H]+. precipitates were removed by suction filtration The filtrate was concentrated under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A solution of triphenylphosphine (2.20 g, 8.39 mmol) in dry CH2Cl2 (20 mL) was added dropwise via syringe to a solution of N-Boc homoserine methyl ester 80 (8.39 mmol) and carbon tetrabromide (4.18 g, 12.60 mmol) in dry CH2Cl2 (20 mL). The resulting dark solution was stirred at room temperature for 16 h. Hexanes was added and precipitates were removed by suction filtration. The filtrate was concentrated under reduced pressure and subject to flash silica gel column chromatography using ethyl acetate/hexanes (1:10, v/v then 1:6, v/v) to give the desired product 90 as a yellow oil (501 mg, 20% overall yield from homoserine). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 2.12-2.48 (m, 2H), 3.39-3.47 (m, 2H), 3.78 (s, 3H), 4.33-4.48 (m, 1H), 5.10-5.22 (m, 1H). m/z (ESI) 296 [C10H18BrNO4+H]+. precipitates were removed by suction filtration The filtrate was concentrated under reduced pressure

Conditions: temp:0.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a cooled (0° C.) solution of (S)-2-tert-butoxycarbonylamino-4-hydroxy-butyric acid methyl ester (28.7 g, 123 mmol) in dichloromethane (500 mL) was added CBr4 (51.0 g, 154 mmol). The mixture was stirred for 5 minutes before the portion-wise addition of triphenylphosphine (48.41 g, 185 mmol). The mixture continued to stir at 0° C. for 1 hour and was then allowed to warm to room temperature. The solvent was removed under reduced pressure and was then diluted with ether (500 mL) and stirred for 30 minutes. The mixture was filtered, and the filtrate was concentrated under reduced pressure. The residue was chromatographed eluting with ether/hexanes (1:2) to afford 27.5 g of white solid (76% yield). to warm to room temperature The solvent was removed under reduced pressure was then diluted with ether (500 mL) stirred for 30 minutes The mixture was filtered the filtrate was concentrated under reduced pressure The residue was chromatographed eluting with ether/hexanes (1:2)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a stirred solution of (S)-(tert-butoxycarbonylamino)-4-hydroxybutyric acid methyl ester (1.43 g; CAS 120042-11-7) in THF (4 ml) were added phenol (692 mg), triphenylphosphine (1.77 g) and diisopropyl azodicarboxylate (1.36 g). The resulting yellow solution was stirred at room temperature overnight. The reaction mixture was evaporated and purified by column chromatography (SiO2; gradient: heptane/EtOAc 100:0->90:10) to give (S)-2-tert-butoxycarbonylamino-4-phenoxy-butyric acid methyl ester (1.16 g, 61%) as a light yellow oil. MS (ISP): 210.1 ([M+H-BOC]+)). The reaction mixture was evaporated purified by column chromatography (SiO2; gradient: heptane/EtOAc 100:0->90:10)