A diastereoselective approach to (2R, 5S)-and (2S, 5S)-2-methyl-1, 6-dioxaspiro [4.5] decane 1 and 1a is described. The route starts with an alkylation reaction among the cyclopentanone N, N-dimethylhydrazone 6 and the chiral iodides (R)-3 or (S)-3, derived from the enantiomers of ethyl β-hydroxybutyrate, controlling the estereocenter at C-2 of the molecules. The alkylated products 7 and 7a were easily transformed into the 1, 8-O-TBS-1 ...