RESUMO
An efficient and high-yielding synthesis for [1,3,5-(13)C(3)]gallic acid from non-aromatic precursors is presented. [3,5-(13)C(2)]4H-Pyran-4-one was first prepared from the reaction between triethyl orthoformate and [1,3-(13)C(2)]acetone. The third (13)C-atom was introduced into the ring by reaction of the pyranone with diethyl [2-(13)C]malonate. The resulting ethyl 4-hydroxy-[1,3,5-(13)C(3)]benzoate was brominated in the 3- and 5-positions to give ethyl 3,5-dibromo-4-hydroxy-[1,3,5-(13)C(3)]benzoate. Subsequent hydrolysis of the ester and substitution of the bromine atoms with hydroxyl groups was achieved under basic conditions in a single step to yield the desired [1,3,5-(13)C(3)]gallic acid. The synthesis of [2,6-(13)C(2)]4H-pyran-4-one is also presented to demonstrate the potential of the methodology for the regioselective placement of (13)C-atoms into benzene rings.
