Synthesis
Step 5: Compound 5 (260 mg) was dissolved in a 1,4-dioxane solution (7 mL) of 4 M HCl and the reaction was stirred at 25°C for 18 hours. Upon completion of the reaction, the reaction mixture was concentrated by nitrogen bubbling for 7 hours to remove excess HCl. Toluene (2 mL) was added to the residue for azeotropic removal of water and then mixed with hexane (2 mL) and stirred for 10 minutes. The hexane layer was removed by decantation and this operation was repeated once using hexane (1 mL). The residue was stirred with toluene (1.5 mL) for 2 hours at 25°C to promote crystallization. The solid product was collected by filtration, washed with a 1:1 solvent mixture of toluene/hexane (10 mL) and finally dried under vacuum to give the target compound 6 (160 mg, 80% yield) as a light brown solid.
