The condensation of hydroxybenzoic acids and their methyl esters with isoprene in the presence of orthophosphoric acid gives corresponding 2, 2-dimethylchromans, which can be dehydrogenated with DDQ or NBS to give the corresponding 6-carboxy-2, 2- dimethylchromenes. The synthesis of β-tubaic acid, a natural compound, has also been achieved.
