Pd-Catalyzed Site-Selective Mono-allylic Substitution and Bis-arylation by Directed Allylic C-H Activation: Synthesis of anti-γ-(Aryl,Styryl)-β-hydroxy Acids and Highly Substituted Tetrahydrofurans

An efficient palladium-catalyzed site-selective arylation of γ-vinyl-γ-lactone by aryl boronic acid has been developed. γ-Vinyl-γ-lactone 1a has been contemplated as allyl electrophile donor for allylic arylation via π-allyl palladium intermediate using 1.5 equiv of aryl boronic acid 2. Using 3.0 equiv of the latter resulted in mono-arylation by allylic substitution and subsequent site-selective second arylation by directed allylic C-H activation giving stereoselectively anti-γ-(aryl,styryl)-β-hydroxy acids. Presence of O₂ was crucial for the second arylation via Pd(II) catalysis. Thus, a good synergy of dual catalysis by Pd(0) and Pd(II) was observed. This methodology has been elaborated to synthesize highly substituted tetrahydrofurans including aryl-Hagen's gland lactone analogues via intramolecular iodoetherification.