Palladium-catalyzed alkynylative lactonization of unsaturated bicyclic carboxylic acids: Synthesis of fused polycyclic γ-lactone compounds

Abstract

Unsaturated bicyclic carboxylic acids undergo palladium-catalyzed coupling with bromoalkynes to produce γ-alkynyl lactones in moderate to good yields with excellent chemo- and regioselectivity. The reaction conditions were extremely mild, and functional groups such as methyl, methoxy, chloro, and bromo were tolerated under the optimized reaction conditions. Moreover, γ-chloroalkenyl lactones were facilely synthesized through chloropalladation/carboesterification of electron-deficient C≡C bonds by using molecular oxygen as the sole oxidant. Facile and tandem Pd-catalyzed synthesis of γ-alkynyl lactone and γ-chloroalkenyl lactone derivatives by using readily accessible bromoalkynes and unsaturated bicyclic carboxylic acids is reported. Two subsequent steps, namely, C(sp or sp 2)-C(sp3) bond formation and C-O bond formation, are catalyzed by a single Pd catalyst. The reactions proceed with good yields of the products. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.