C(alkenyl)–H Activation via Six-Membered Palladacycles: Catalytic 1,3-Diene Synthesis

A catalytic method to prepare highly substituted 1,3-dienes from two different alkenes is described using a directed, palladium­(II)-mediated C­(alkenyl)–H activation strategy. The transformation exhibits broad scope across three synthetically useful substrate classes masked with suitable bidentate auxiliaries (4-pentenoic acids, allylic alcohols, and bishomoallylic amines) and tolerates internal nonconjugated alkenes, which have traditionally been a challenging class of substrates in this type of chemistry. Catalytic turnover is enabled by either MnO₂ as the stoichiometric oxidant or co-catalytic Co­(OAc)₂ and O₂ (1 atm). Experimental and computational studies were performed to elucidate the preference for C­(alkenyl)–H activation over other potential pathways. As part of this effort, a structurally unique alkenylpalladium­(II) dimer was isolated and characterized