One-Pot Synthesis of 4-Substituted 3,4-Dihydro-3-methoxyisocoumarins via Carboxylation of alpha-Substituted 2-Lithio-beta-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 a-substituted 2-bromo-beta-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 CO2 on the resulting a-substituted 2-lithio-beta-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.

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