Synthesis of Chroman-2-ones by Reduction of Coumarins

The scientific literature detailing the synthesis of chroman-2-onesby hydrogenation/reduction of the corresponding coumarinsis reviewed. The following methods are described: hydrogenationon palladium, platinum, nickel, catalytic transfer hydrogenation,homogeneous hydrogenation, reduction by complex hydrides, reductionby metals, and electrochemical reduction. For each appropriate reaction,the yield, duration and some additional information is given (ifavailable). Moreover, many exceptions and interesting transformationsare described. 1 Introduction 2 Hydrogenation of Coumarins 3 Transfer Hydrogenation of Coumarins 4 Reduction of Coumarins with Metals 5 Reduction of Coumarins with Complex Hydrides 6 Homogeneous Hydrogenation of Coumarins 7 Electrochemical Reduction 8 Other Methods of Coumarin Reduction 9 Conclusion