An entry to 1,6-dioxaspiro[4.6]undecanes and 1,7-dioxaspiro[5.6]dodecanes

Ketones 11a–c obtained by iterative alkylation of acetone N,N-dimethylhydrazone with iodides 6 and 8a,b or epoxide 9 followed by SiO2/H2O-induced cleavage of the hydrazone were quantitatively transformed into 1,6-dioxaspiro[4.6]undecanes 12a,c and 1,7-dioxaspiro[5.6]dodecanes 12b using Yb(OTf)3 in CH3CN.