Highly Efficient and Selective Procedures for the Synthesis of γ-Alkylidenebutenolides via Palladium-Catalyzed Ene-Yne Coupling and Palladium- or Silver Catalyzed Lactonization of (Z)-2-En-4-ynoic Acids. Synthesis of Rubrolides A, C, D, and E
The Pd(0)-catalyzed cross coupling between 4-bromo-2(5H)-furanones and arylboronic acids provides the corresponding 4-aryl-2(5H)-furanones in yields of 61-85%. By using this method in conjunction with furanolate chemistry, the marine antibiotics rubrolide C and E have been synthesized in highly efficient fashion (4 steps, overall yield = 61 and 56% respectively) from beta-tetronic acid. (C) 1998 Elsevier Science Ltd. All rights reserved.