Cyclizations of γ-Hydroxyallenes Mediated by Organopalladium Halides: A Convergent Synthetic Route to Substituted 5-Alkenyl-2-furanones and 2-Alkenyltetrahydrofurans

Abstract

When a γ-hydroxyallene (various β-allenylcarbinols or 4,5-hexadienoic acid) is allowed to react with aryl or alkenyl halides in the presence of (Ph3P)4Pd and base, cyclization and coupling to form the title compounds in 14 - 78 (average 50)% yields occurs. A mechanism in which an aryl- or alkenylpalladium(II) halide initiates the cyclization by intramolecular oxypalladation is discussed.