No abstract

No abstract

2‐Pyrones are compounds present in several natural products and represent interesting building blocks for the preparation of intermediates in organic syntheses. For these reasons, many different preparation protocols have been developed for the synthesis of pyrone moieties. In this work, a green approach toward the synthesis of those compounds starting from C6 aldaric acids has been investigated. These products are an interesting and versatile class of poly functional C6 units coming from renewable sources. In this paper, we report a green procedure based on a reaction with acetic anhydride under different pH conditions to convert mucic acid and glucaric acid salts into the 3‐acetoxy‐2‐oxo‐2H‐pyran‐6‐carboxylic acid salts and their derivatives. The salts, in the presence of hydrochloric acid, are quantitatively converted into the corresponding 3‐hydroxy‐2‐oxo‐2H‐pyran‐6‐carboxylic acid, which afforded 3‐hydroxy‐2H‐pyran‐2‐one in very high yield by further thermal decarboxylation. Crystal structure of the five membered ring lactone intermediate is reported.

No abstract

Nowadays, the use of biomass derived synthons as precursors of aromatic products is an important research topic in green chemistry. In particular, the Diels−Alder protocol has been applied in the construction of valuable aromatic derivatives such as terephthalic acid and esters using muconic acid and 2-pyrones as diene components. In this context, we now propose the use of 3hydroxy-2-pyrones, prepared from galactaric acid, as building block for the synthesis of functionalized aromatic carboxylic acids. Our protocol consists in a base-promoted domino reaction in which 2-pyrones and electron-poor alkenes lead directly to the aromatic derivatives preserving all the carbon atoms. High yields are obtained by using small amounts of solvent, in neat conditions and in a water biphasic system, typically at 50 °C. The reaction proceeds through a Diels−Alder cycloaddition followed by aromatization reaction with elimination of water. The aromatization represents a key step and a possible reaction mechanism is proposed.