p-, m- and o-bromophenols were first protected by t-butyldimethylchlorosilane, and then treated with Mg to form Grignard reagents. After reaction with tributylborate and selective hydrolysis, three t-butyldimethylsiloxy phenylboronic acids were ob-tained in yields 51% (p), 44% (m) and 40% (o), respectively. If dibutyl p- or m-siloxyphenylborate intermediates were hydrolyzed in strong acid, p or m-hydroxy- phenylboronic acids were achieved with yields of 14% and 65% respectively. But these hydroxyphenylbo-ronic acids were difficult to purify because the impurity hydroxyphenol was always formed spontaneously.

Key words: t-butyldimethylsiloxyphenylboronic acid, Grignard reagent, preparation, hydroxyphenylboronic acid