Synthesis of Cyclobutene-Fused Eight-Membered Carbocycles through Gold-Catalyzed Intramolecular Enyne [2+2] Cycloaddition

Article abstract of DOI:10.1002/adsc.201701193

Cationic gold(I) complexes with hollow-shaped triethynylphosphine ligands efficiently catalyzed intramolecular [2+2] cycloaddition of 1,9-enynes to afford cyclobutene-fused eight-membered carbocycles that were difficult to synthesize by other catalytic systems. Various 1,9-enynes with carbon linkers with or without a fused ring underwent efficient [2+2] cycloaddition with 5 mol% of the Au catalyst bearing the triarylmethyl-end-capped triethynylphosphine in CH₂Cl₂ at rt in the presence of MS 4A as an additive. More challenging 1,9-enyne substrates with fully saturated acyclic carbon linkers underwent eight-membered ring formation at 60 °C in ClCH₂CH₂Cl in the absence of MS 4A, forming monocyclic 1,3-dienes as major products. (Figure presented.).