An efficient asymmetric catalytic hydrogenation of 4-aryl coumarins, preparation of a key intermediate in the synthesis of a class of endothelin receptor antagonists

The 4-aryl-3,4-dihydrocoumarin 1 is a critical intermediate in the synthesi s of two endothelin receptor antagonists. Asymmetry is introduced by the ch iral catalytic hydrogenation of 2. Reduction occurs only if the lactone is open (3). A number of chiral ruthenium and rhodium organometallic species a re evaluated as catalysts. The reaction is optimized to produce 1 in high y ield and ee. (C) 1999 Elsevier Science Ltd. All rights reserved.