Direct Cross-Couplings of Propargylic Diols.

[Pd(PPh3 )4 ] catalyzes a Suzuki-Miyaura-like twofold cross-coupling sequence between underivatized propargylic diols and either aryl or alkenyl boronic acids to furnish highly substituted 1,3-dienes. Thus, 2,3-diaryl-1,3-butadienes and their dialkenic congeners ([4]dendralenes) are delivered in a (pseudo)halogen-free, single-step synthesis which supersedes existing methods. Allenols are also readily formed. Treatment of these single- and twofold cross-coupled products with acid leads to remarkably short syntheses of highly-substituted benzofulvenes and aryl indenes, respectively.