Reactions of 1,5-Dienes with Ruthenium Tetraoxide: Stereoselective Synthesis of Tetrahydrofurandiols

Abstract

An improved procedure for the ruthenium tetraoxide catalysed oxidation of 1,5-dienes, employing 0.05 equiv. of the catalyst RuO2·2H2O, 2.5 equiv. of NaIO4 as a stoichiometric oxidant, and a biphasic solvent system of AcOEt/(CH3)2CO/H2O (2:1:1, v/v/v), is presented. Reactions of 1,5-dienes 1, 3, and 5 furnished the new cis-tetrahydrofuran products 2, 4, 6, and 7 with total stereospecificity. The structures of the products have been established on the basis of NMR and MS data, as well as chemical evidence. Application of this procedure to geranyl acetate (8) and neryl acetate (12) afforded the cis-tetrahydrofuran derivatives 9, 10, and 13 in high yields, accompanied by small amounts of trans-tetrahydrofurandiols 11 and 14. These products are the same as those obtained by Sharpless et al. upon RuO4-catalysed oxidation of 8 and 12 in the biphasic solvent system CCl4/CH3CN/H2O (2:2:3, v/v/v), but our procedure has the advantages of higher stereospecificity, a greater material recovery (about 90%), and a more simple work-up. The oxidation of 1,5-dienes proceeds stereoselectively by syn oxygen addition to both double bonds. The formation of tetrahydrofuran derivatives is presumed to involve initial addition of RuO4 to one double bond of the 1,5-diene to give a ruthenium(VI) diester, which subsequently undergoes conversion into the cyclic ether with participation of the second double bond.