The Synthesis of Substituted Benzo[c]chromen‐6‐ones by a Suzuki Coupling and Lactonization Sequence Using Ionic Liquids – from Laboratory Scale to Multi‐Kilogram Synthesis

A series of benzo[c]chromen‐6‐ones are prepared by a Suzuki coupling and lactonization sequence starting with 2‐methoxyphenylboronic acids and methyl 2‐bromobenzoate derivatives. The use of ionic liquids in this synthesis has been explored. It was found that the Suzuki coupling proceeds much faster when a catalytic amount of the ionic liquid [BMIM][PF6] is used. By using the Lewis acidic ionic liquids [BMIM][Al2Cl7] or [TMAH][Al2Cl7] the methyl 2‐(2‐methoxyphenyl)benzoate product obtained from the Suzuki coupling can be converted to benzo[c]chromen‐6‐ones in one step, while the conventional route involves three steps. The use of ionic liquids is demonstrated in the synthesis of a variety of benzo[c]chromen‐6‐ones. It is also shown that the application of ionic liquids is not limited to laboratory scale experiments, as a process was developed and performed on a multi‐kilogram scale. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)