1-O-tert-butyl 2-O-methyl 6-methoxypiperidine-1,2-dicarboxylate

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

Procedure: To a solution of 6-methoxy-piperidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester, 37, (5.0 g, 18.3 mmol) and allyltrimethylsilane (5.8 mL, 36.6 mmol) in CH2Cl2 (125 mL) at −78° C. is added dropwise boron trifluoride etherate (2.5 mL, 19.7 mmol). After 1 h, the solution is poured into water and extracted with EtOAc. The extracts are washed with brine, dried (MgSO4), and concentrated in vacuo. The resulting residue is used in the next step without purification. extracted with EtOAc The extracts are washed with brine dried (MgSO4) concentrated in vacuo The resulting residue is used in the next step without purification

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

Procedure: The crude 6-hydroxy-piperidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester, 36, obtained in the previous step is dissolved in methanol (500 mL) and treated with Dowex-50 (1.0 g). After stirring at rt for 3 hr, the solution is filtered and concentrated in vacuo, and the residue is purified over silica (hexanes/ethyl acetate, 5:1) to afford 2.1 g of the desired product. 1H NMR (CDCl3) δ 5.43 (br s, 0.5H), 5.28 (br s, 0.5H), 4.88 (br s, 0.5H), 4.66 (br s, 0.5H), 3.73 (s, 3H), 3.33 (s, 3H), 2.32 (m, 1H), 1.87 (m, 2H), 1.70–1.40 (m, 3H), 1.51 (s, 9H). treated with Dowex-50 (1.0 g) the solution is filtered concentrated in vacuo the residue is purified over silica (hexanes/ethyl acetate, 5:1)

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

Procedure: To a solution of 6-methoxy-piperidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester, 37, (5.0 g, 18.3 mmol) and allyltrimethylsilane (5.8 mL, 36.6 mmol) in CH2Cl2 (125 mL) at −78° C. is added dropwise boron trifluoride etherate (2.5 mL, 19.7 mmol). After 1 h, the solution is poured into water and extracted with EtOAc. The extracts are washed with brine, dried (MgSO4), and concentrated in vacuo. The resulting residue is used in the next step without purification. extracted with EtOAc The extracts are washed with brine dried (MgSO4) concentrated in vacuo The resulting residue is used in the next step without purification

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

Procedure: The crude 6-hydroxy-piperidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester, 36, obtained in the previous step is dissolved in methanol (500 mL) and treated with Dowex-50 (1.0 g). After stirring at rt for 3 hr, the solution is filtered and concentrated in vacuo, and the residue is purified over silica (hexanes/ethyl acetate, 5:1) to afford 2.1 g of the desired product. 1H NMR (CDCl3) δ 5.43 (br s, 0.5H), 5.28 (br s, 0.5H), 4.88 (br s, 0.5H), 4.66 (br s, 0.5H), 3.73 (s, 3H), 3.33 (s, 3H), 2.32 (m, 1H), 1.87 (m, 2H), 1.70–1.40 (m, 3H), 1.51 (s, 9H). treated with Dowex-50 (1.0 g) the solution is filtered concentrated in vacuo the residue is purified over silica (hexanes/ethyl acetate, 5:1)