Conversion of pentynol to pentanone catalysed by Pd(II) metal centres

The cyclization of 3- or 4-pentyn-1-ol is catalysed by PdCl2 or trans-[PdCl2L2] (L = R-camphorimine; R = Ph; Pri; NMe2) complexes at room temperature affording heterocyclic compounds, respectively, 2-methyl-2-pent-3-ynyloxy-tetrahydrofuran or 2-methyl-2-pent-4-ynyloxy-tetrahydrofuran which subsequently add water to give selectively 5-(2-methyl-tetrahydrofuran-2-yloxy)-pentan-2-one from both starting materials. By hydrolysis 5-(2-methyl-tetrahydrofuran-2-yloxy)-pentan-2-one undergoes ring cleavage to form 5-hydroxy-2-pentanone. The catalytic activity and selectivity of complexes trans-[PdCl2L2] (L = R-camphorimine) depend on the characteristics of the R group (NMe2 > Pri > Ph). The catalytic activity of PdCl2 is comparable to that of trans-[PdCl2L2] (L = Ph-camphorimine) which is the less efficient catalyst.