The chlorobenzodioxole acid 5.00g (24.93mmol) and triethylamine 4.9mL solution in anh. THF (220mL) was cooled to 0C and ethyl chloroformate 2.9mL (30mmol) was added dropwise over 5 min. The mixture was stirred at 0C for 90 min, ice-cooled solution of sodium azide 8.2g in water 80mL was added, followed by ice-cold water 120mL. The cooling bath was removed and the mixture was stirred at ambient temperature for 10 hours (overnight). The reaction mixture was extracted twice with ether (2x250mL), the extracts were washed with brine (250mL), combined, dried (MgSO4) and evaporated. The crude product (yellow solid, 3.89g) was applied onto a column of silica (80g) in hexane, and eluted with EtOAc gradient, 0 to 30% (in hexane). Y= 3.278g (76.5%) of a pale-yellow crystalline solid.
1H(d6-DMSO, 400MHz): 6.739(d, 8.4Hz, 1H), 6.241(d, 8.4Hz, 1H), 5.976(s, 2H), 5.117(very br s, 2H); 13C(d6-DMSO, 100MHz): 146.03, 133.79, 129.28, 121.60, 111.80, 106.96, 101.04. 97.79