Synthesis of 3,6-substituted 2-methylthio-4-pyrones by acylation of ketene dithioacetals via soft enolization

The tandem acylation-heterocyclization of ketene dithioacetals was performed via soft enolization in MgBr2·OEt2/NEt3 system. A series of 3,6-substituted 2-methylthio-4-pyrones were obtained with a wide functional group tolerance. The reaction showed a good scalability, and the isolation of the products was performed by crystallization without the use of chromatography. Some transformations of the obtained 2-methylthio-4-pyrones, including substitution of the SMe group with N-nucleophiles, have been demonstrated for the preparation of functionalized 4-pyrones as analogs of several bioactive molecules.