Yield:-

Reaction Conditions:

Stage #1: di-tert-butyl dicarbonate;ethyl (1S,5R)-2-azabicyclo[3.1.0]hexane-1-carboxylate hydrochloridewith triethylamine in tetrahydrofuran at 20; for 15 h;
Stage #2: with water;sodium hydroxide at 20; for 2 h;
Stage #3: with hydrogenchloride in water;Cooling with ice;

Steps:

157.C

C) Production of (1S,5R)-2-(tert-butoxycarbonyl)-2-azabicyclo[3.1.0]hexane-1-carboxylic acid A solution of ethyl (1S,5R)-2-azabicyclo[3.1.0]hexane-1-carboxylate hydrochloride (1.50 g), di-tert-butyl dicarbonate (1.91 mL) and triethylamine (2.18 mL) in tetrahydrofuran (15 mL) was stirred at room temperature for 15 hr. Water (10 mL) was added to the reaction mixture, and the mixture was extracted with ethyl acetate (20 mL). The organic layer was dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The residue was dissolved in ethanol (7 mL), 8M aqueous sodium hydroxide solution (1 mL) was added, and the mixture was stirred at room temperature for 2 hr. The reaction mixture was acidified with 6M hydrochloric acid (1.5 mL) under ice-cooling, and the precipitated solid was collected by filtration to give the title compound (1.20 g) as a colorless solid. ¹H-NMR(DMSO-d₆) δ 0.99(1H,t,J=5.3Hz), 1.40(9H,s), 1.72(1H,dd,J=8.9_,4.7Hz), 1.77-1.90(1H,m), 1.95-2.06(1H,m), 2.10-2.24(1H,m), 3.22-3.46(1H,m), 3.60(1H,ddd,J=11.0,9.4,6.2Hz), 12.35(1H,brs).

References:

EP2540728,2013,A1 Location in patent:Page/Page column 123-124