[5,6-diamino-2,2-dimethyl-1,3-benzodioxole; dihydrochloride salt] (U.S. Pat. No. 4,904,775, Example 3D) (6.8 g, 0.02 mmol) was dissolved in a mixture of 25 ml water and 10 ml tetrahydrofuran and the pH of the solution was adjusted to 5.5 by the addition of 2N NaOH. After addition of the compound from Example 1 (3.8 g; 0.02 mol) the mixture was refluxed for 2 hours, concentrated in vacuo to remove the organic solvent tetrahydrofuran and then extracted with ethyl acetate. The combined organic phases were washed with brine, dried (Na2SO4) and then evaporated in vacuo to leave an oil which crystallized by the addition of petroleum ether.
