Directed ortho metalation-cross coupling links. Carbamoyl rendition of the Baker-Venkataraman rearrangement. Regiospecific route to substituted 4- hydroxycoumarins

Article abstract of DOI:10.1016/S0040-4039(98)00977-0

A new carbamoyl Baker-Venkataraman rearrangement (4) which allows a general synthesis of substituted 4-hydroxycoumarins 8 in 43-82% overall yields is described; the intermediate arylketones 6 are efficiently prepared (59-91% yields) via a Directed ortho Metalation - Negishi cross coupling protocol from arylcarbamates 5 and the overall sequence provides a regiospecific anionic Friedel-Crafts complement for the construction of ortho-acyl phenols and coumarins.