Methanol → (1R,4S)-4-Aminocyclopent-2-ene-1-carboxylic acid

Methanol (300 ml) and 60 g (0.465 mol) (+)-cis-3-amino-4-cyclopentenecarboxylic acid (obtained from the bioresolution of 2-azabicyclo[2.2.1]hept-5-en-3-one) were stirred together, then 194 ml (1.39 mol) triethylamine slowly added. The reaction was cooled to 8° C. with ice, then 99 g (0.45 mol) di-t-butyl dicarbonate dissolved in 400 ml methanol was slowly added. After stirring for 48 hrs at ambient temperature the reaction was concentrated under reduced pressure to 100 ml and acidified to pH 3 with 1M KHSO4. The solution was extracted twice with an equal volume of methyl t-butyl ether, the organic layer dried with MgSO4, then evaporated under reduced pressure to give an off-white solid. This was recrystallised from a mixture of methyl t-butyl ether and heptane to give 90 g of N-Boc (+)-amino acid whose structure was verified by proton NMR.