It can be prepared in two different ways: 1) The condensation of 2,4-di-tert-butylphenol (I) with dimethyl acetylenedicarboxylate (II) by means of benzyltrimethylammonium hydroxyde (III) gives 2,4-di-tert-butylphenoxyfumaric acid dimethyl ester (VI), which is hydrolyzed with NaOH in refluxing methanol - water yielding the corresponding acid (V). Finally this acid is cyclized by treatment with chlorosulfonic acid.
2) The Friedel-Crafts reaction of 2,4-di-tert-butylphenol (I) with acetic anhydride (VI) by means of BF3 gives 3,5-di-tert-butyl-2-hydroxyacetophenone (VII), which is cyclized with diethyl oxalate (VIII) by means of NaOEt in a refluxing mixture ethanol - ethyl ether to afford ethyl 6,8-di-tert-butyl-4-oxo-4H-1-benzopyran-2-carboxylate (IX) (1,2). Finally this compound is hydrolyzed with NaOH in ethanol (1).