Improved RuO4-catalysed oxidative cyclisation of geraniol-type 1,5-dienes to cis-2,5-bis(hydroxymethyl)tetrahydrofuranyldiols

The oxidation of some representative 1,5-dienes based on the geraniol and nerol carbon skeletons, namely geranyl acetate (1), geranic acid methyl ester (5), trans,trans-2,6-dimethyl-2,6-octadiene-1,8-diol diacetate (9), neryl acetate (13) and neroic acid methyl ester (16), has been performed using catalytic amounts of RuO4 (from RuO2·2H2O, 4%) in the presence of NaIO4 (4 equiv.) as co-oxidant in the solvent mixture EtOAc/CH3CN/H2O (3:3:1) at 0°C for 4 min. These conditions assure a degree of stereoselectivity for the geraniol-type dienes higher than that obtained under the Sharpless conditions [RuCl3·(H2O)n (2.2%), NaIO4 (3.1 equiv.), CCl4/CH3CN/H2O (2:2:3), 0°C], furnishing the cis- and trans-THF diol products in 62–70 and 6–9% yields, respectively. In addition, the amount of the cis-THF, C-2 overoxidised, product is strongly reduced (2–7%). A comparison with the related MnO4−-induced process, tested on the same substrates, was made.