A 5 mL round-bottom flask equipped with a magnetic stirrer and an inert gas supply was charged with 436.3 mg of 12 and 0.83 mL DMSO. To the clear colorless solution at RT was added 71.5 mg sodium azide and the reaction mixture was stirred for 2.5 h, then an additional 13.7 mg of sodium azide were added and stirring continued at RT for 19 h. The reaction mixture was diluted with 5 mL of EtOAc and extracted three times with a 1 M solution of NaHCO3. The organic phase was separated, dried (Na2SO4), filtered and evaporated at 20° C./140-10 mbar to obtain 0.33 g of the crude product as light yellow oil. The crude product was purified by SiO2 column chromatography eluting with a ½ mixture of EtOAc and n-hexane. The combined fractions were evaporated and dried on a rotary evaporator to obtain 0.27 g of 14 as a colorless oil
