Perruthenate ion. Another metal oxo species able to promote the oxidative cyclisation of 1,5-dienes to 2,5-disubstituted cis-tetrahydrofurans

Perruthenate ion, from tetrapropylammonium perruthenate (TPAP), in the presence of tetrabutylammonium periodate (TBAPI) as reoxidant catalyses the stereospecific and stereoselective oxidative cyclisation of 1,5-dienes to cis-2,5-disubstituted tetrahydrofurans in good to moderate yields. NMO also works as co-oxidant in the process but is less effective and at least 0.7 equiv TPAP are required. Acidic conditions promote the formation of THF diols. 1,5-Dienes with two terminal double bonds give poor yields of THF’s or cleavage products.