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

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.