REGIOSELECTIVE REDUCTIVE ELECTROPHILIC SUBSTITUTION OF DERIVATIVES OF 3,4,5-TRIMETHOXYBENZALDEHYDE

The behavior of several protected derivatives of 3,4,5-trimethoxybenzaldehyde has been investigated under conditions of electron transfer from alkali metals in aprotic solvents. The 4-methoxy group can be regioselectively removed in good to high yield under such conditions, and an appropriate choice of the protecting group, metal, and solvent allows its substitution with a variety of electrophiles. 3,4,5-Trimethoxybenzaldehyde dimethyl acetal, 1, is the starting material of choice for a new general synthetic approach to several polysubstituted resorcinol dimethyl ethers. Investigation of the mechanism of demethoxylation, with the aid of labeling experiments, showed that reductive demethoxylation is strongly influenced by the nature of the aldehyde protective group employed.