Selective Lewis Acid Catalyzed Transformation (γ-Butyrolactone versus Cyclopropane) of 2-Methoxy-4-benzyltetrahydrofuran Derivatives. Efficient Synthesis of Lignan Lactones

[reaction: see text]. A short synthesis of lactone lignans exploiting a three-component coupling strategy is presented using a new Lewis acid catalyzed ring-opening/cyclization reaction of 2-methoxytetrahydrofuran derivatives 4 leading to gamma-butyrolactones as a key step. By simply changing the reaction conditions, it was possible, from the same substrates 4, to obtain selectively cyclopropane derivatives.