One-pot synthesis of 4-substituted 3,4-dihydro-3-methoxyisocoumarins via carboxylation of α-substituted 2-lithio-β-methoxystyrenes with carbon dioxide

摘要

A new type of isocoumarins (=1H-isochromen-1-ones=1H-2-benzopyran-1-ones), 4-substituted 3,4-dihydro-3-methoxyisocoumarins 2, can be obtained by a one-pot process from α-substituted 2-bromo-β-methoxystyrenes 1. Thus, lithium 2-(1-aryl(or methyl)-2-methoxyethenyl)benzoates are conveniently generated via the Br/Li exchange between 1 and BuLi, followed by the action of CO _2 on the resulting α-substituted 2-lithio-β-methoxystyrenes. Upon treating with concentrated HCl at room temperature, these lithium benzoates undergo lactonization to provide the desired 3,4-dihydroisocoumarins 2 in relatively good yields.