Ligand effect of bulky 2,2-dialkyl-1-phosphaethenes on Au-catalyzed cycloisomerization of 1,6-enynes and lactonization of pent-4-ynoic acids

2,2-Dimethyl- and 2-benzyl-2-methyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaethenes were employed as ligand of mononuclear chlorogold(I) complexes, which catalyzed cycloisomerization of 1,6-enyne affording vinylcyclopentene exclusively in the absence of silver co-catalyst. The reaction mechanisms are discussed based on DFT calculations. In addition to the cycloisomerization, the phosphaalkene–chlorogold(I) complexes catalyzed cyclization of pent-4-ynoic acids providing γ-methylene-γ-lactones under basic conditions.

Mononuclear phosphaalkene–chlorogold(I) complexes [Mes∗PCRR′][AuCl] (R, R′ = Me, CH2Ph; Mes∗ = 2,4,6-tBu3C6H2) catalyzed cyclizations of 1,6-enynes and pent-4-ynoic acids affording vinylcyclopentenes and methylenelactones, respectively, in the absence of co-catalyst.Figure optionsDownload as PowerPoint slide