New methods to synthesize phthalaldehyde and its diacetals

Abstract

A new synthesis of phthalaldehyde that avoided formation of HBr involved treatment of 1,2-bis(dibromomethyl)benzene with trimethyl orthoformate (1: 6, 90 °C, 10 mol.% ZnCl₂) to obtain acyclic diacetal without admixture of cyclic one (1,3-dimethoxy-1,3-dihydrobenzo-[c]furan) followed by hydrolysis to give the target dialdehyde. Phthalaldehyde reacted with CH(OMe)₃ in the presence of trifluoroacetic acid to yield exclusively cyclic diacetal. Acyclic diacetal was phosphorylated by treatment with secondary chlorophosphines and by the reaction with PCl₃ followed by treatment with P^III acid ester.