Oxidative Cyclization of 1,5-Dienes with Hydrogen Peroxide Catalyzed by an Osmium(III) Complex: Synthesis of <i>cis</i>-Tetrahydrofurans

Stereoselective oxidative cyclization of 1,5-dienes with hydrogen peroxide catalyzed by [OsIII(OH)­(H2O)­(L–N4Me2)]­(PF6)2 (1: L–N4Me2 = N,N′-dimethyl-2,11-diaza-[3,3]­(2,6)­pyridino­phane) is explored. 1,5-Dienes involving geraniol derivatives are converted to the corresponding tetrahydrofurans in modest to high yields. The products exclusively have the cis-conformation with respect to the substituents at the 2- and 5-positions of the tetrahydrofuran ring. The products also have a syn-conformation with respect to the furan oxygen atom and the hydroxyl groups. Mechanistic studies including a direct reaction of the oxo-hydroxo-osmium­(V) complex, 2, with a dihydroxylated geraniol derivative are performed.