hydrogen and according to a preferred embodiment said acidic workup takes place at a temperature comprised between u2212 50 u00b0 c and 30 u00b0 c using a mineral acid such as hydrochloric or sulfuric acid the compound ia can be isolated as free base or in a salified form depending on the ph of the reaction mixture preferably in a salified form more preferably in form of a hydrogen sulfate or hydrogen chloride salt it has to be pointed out that when isolating the compound ia or the corresponding addition salts thereof it has also been possible to recover the starting ketone of formula r 5 r 6 c u2550 o as by product of the above described reaction which represents a further advantage of the process of the present invention if desired the boronic acid derivative of formula ia can be converted directly from the reaction mixture into the corresponding ester of formula i by esterification with an alcohol of formula r u2014 oh wherein r is as defined above typically the boronic ester of formula i is prepared by reaction of the boronic acid of formula ia with an alcohol of formula r u2014 oh preferably pinacol 1 2 ethanediol and 1 4 butanediol at a ph comprised between 7 0 and 8 5 said alcohol is preferably used in a molar ratio comprised between 0 8 and 1 5.