A process for preparing -3-amino-4-(difluoromethylenyl)cyclopent-1-ene-1-carboxylic acid or salt thereof comprising: converting (1 R,4 S)-2-azabicyclo[2.2.1]hept-5-en-3-one to (1 R,4 R,6 S,7 R)-7-bromo-2-(4-methoxybenzyl)-3-oxo-2-azabicyclo[2.2.1]heptan-6-yl acetate; converting (1 R,4 R,6 S,7 R)-7-bromo-2-(4-methoxybenzyl)-3-oxo-2-azabicyclo[2.2.1]heptan-6-yl acetate to (1 R,4 R,7 R)-7-bromo-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptane-3,6-dione, preferably by reacting with a. K 2 CO 3, alcohol; and either b. 2-iodoxybenzoic acid, MeCN; or b. tetrapropylammonium perruthenate (TPAP), N-methylmorpholine N-oxide; converting (1 R,4 R,7 R)-7-bromo-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptane-3,6-dione to (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptan-3-one, preferably by reacting either with 2-((difluoromethyl)sulfinyl)pyridine, KO t Bu, DMF, NH 4 Cl, HCl; or with tert-BuLi and F 2 CHP (OEt) 2; converting (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptan-3-one to (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-azabicyclo[2.2.1]heptan-3-one, preferably by reacting with ceric ammonium nitrite, MeCN, H 2 O; converting (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-azabicyclo[2.2.1]heptan-3-one to (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(tert-butoxycarbonyl)-2-azabicyclo[2.2.1]heptan-3-one, preferably by reacting with Boc 2 O, N,N-dimethylaminopyridine (DMAP), Et 3 N, CH 2 Cl 2; converting (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(tert-butoxycarbonyl)-2-azabicyclo[2.2.1]heptan-3-one to methyl -3-((tert-butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylate or -3-(( tert -butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylic acid; and converting methyl -3-((tert-butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylate or -3-(( tert -butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylic acid to -3-amino-4-(difluoromethylenyl)cyclopent-1-ene-1-carboxylic acid, optionally followed by acidification to provide the hydrochloride salt thereof. converting (1 R,4 S)-2-azabicyclo[2.2.1]hept-5-en-3-one to (1 R,4 R,6 S,7 R)-7-bromo-2-(4-methoxybenzyl)-3-oxo-2-azabicyclo[2.2.1]heptan-6-yl acetate; converting (1 R,4 R,6 S,7 R)-7-bromo-2-(4-methoxybenzyl)-3-oxo-2-azabicyclo[2.2.1]heptan-6-yl acetate to (1 R,4 R,7 R)-7-bromo-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptane-3,6-dione, preferably by reacting with a. K 2 CO 3, alcohol; and either b. 2-iodoxybenzoic acid, MeCN; or b. tetrapropylammonium perruthenate (TPAP), N-methylmorpholine N-oxide; converting (1 R,4 R,7 R)-7-bromo-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptane-3,6-dione to (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptan-3-one, preferably by reacting either with 2-((difluoromethyl)sulfinyl)pyridine, KO t Bu, DMF, NH 4 Cl, HCl; or with tert-BuLi and F 2 CHP (OEt) 2; converting (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(4-methoxybenzyl)-2-azabicyclo[2.2.1]heptan-3-one to (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-azabicyclo[2.2.1]heptan-3-one, preferably by reacting with ceric ammonium nitrite, MeCN, H 2 O; converting (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-azabicyclo[2.2.1]heptan-3-one to (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(tert-butoxycarbonyl)-2-azabicyclo[2.2.1]heptan-3-one, preferably by reacting with Boc 2 O, N,N-dimethylaminopyridine (DMAP), Et 3 N, CH 2 Cl 2; converting (1 R,4 R,7 R)-7-bromo-6-(difluoromethylene)-2-(tert-butoxycarbonyl)-2-azabicyclo[2.2.1]heptan-3-one to methyl -3-((tert-butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylate or -3-(( tert -butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylic acid; and converting methyl -3-((tert-butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylate or -3-(( tert -butoxycarbonyl)amino)-4-(difluoromethylene)cyclopent-1-ene-1-carboxylic acid to -3-amino-4-(difluoromethylenyl)cyclopent-1-ene-1-carboxylic acid, optionally followed by acidification to provide the hydrochloride salt thereof.