High‐pressure [2 + 4]‐cycloaddition of dimethylmaleic anhydride to 3,4‐dimethoxyfuran; synthesis of dimethoxycantharidin preliminary communication

As an active diene (more active than furan itself), 3,4‐dimethoxyfuran ( 1 ) affords with many dienophiles the respective cycloadducts in a high yield [2]. It has recently been found that under thermal conditions 1 easily reacts with maleic anhydride and its monomethyl derivative, but not with dimethylmaleic anhydride ( 2 ) [3]. This is probably due to steric hindrance resulting from the location of two methyl groups on the double bond of the dienophile. Since all Diels‐Alder reactions in particular those with steric hindrance are pressure‐sensitive [4]. we resolved to perform the title reaction under conditions of static high pressure.