A process for preparing the compound of formula I comprising: a) coupling a compound of formula 2 wherein a leaving group O—SO2—R is selected from the triflate group, the tosylate group, the mesylate group, the besylate group, the nosylate group or the brosylate group, with a suitable boronic acid, a trifluoroborate or a boronic acid ester under argon condition and in the presence of a catalyst and a base in a suitable solvent and then isolating the product as an acid addition salt to afford the compound of formula Ia and b) converting the acid addition salt of formula Ia wherein the acid HX comprises suitable organic or inorganic acids into the compound of formula I by treatment with at least a stoichiometric equivalent of a suitable base.