Diastereo- and enantioselective routes to some 2,8-dimethyl-1,7-dioxaspiro[5.5]undecanols. Absolute stereochemistry of (E,E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecan-3-ol and of (E,E)-8-methyl-1,7-dioxaspiro[5.5]undecan-2-yl)methanol present in Bactrocera cucumis