Synthesis of Chroman-2-ones by Reduction of Coumarins

The scientific literature detailing the synthesis of chroman-2-ones by hydrogenation/reduction of the corresponding coumarins is reviewed. The following methods are described: hydrogenation on palladium, platinum, nickel, catalytic transfer hydrogenation, homogeneous hydrogenation, reduction by complex hydrides, reduction by metals, and electrochemical reduction. For each appropriate reaction, the yield, duration and some additional information is given (if available). Moreover, many exceptions and interesting transformations are 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