Allylation of (R)-2,3-O-Cyclohexylideneglyceraldehyde with Methyl 3-(Bromomethyl)but-3-enoate. Methyl 3-{(2S)-2-[(2R)-1,4-Dioxaspiro[4.5]dec-2-yl]-2-hydroxyethyl}but-3-enoate as a Convenient Universal Building Block for the Synthesis of Key Fragments of Bioactive Compounds