Directed ortho metalation - cross coupling links. Carbamoyl rendition of the baker-venkataraman rearrangement. Regiospecific route to substituted 4-hydroxycoumarins
摘要:
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. (C) 1998 Elsevier Science Ltd. All rights reserved.