p-Toluenesulfonic acid (200 mg) is added to a solution of 2-(4'-benzyloxybutyl)-2-methyl-oxepan-6-one (5.9 g, 0.021 mol), ethylene glycol (30 ml) and dry benzene (200 ml) and the mixture is refluxed for 17 hours in a nitrogen atmosphere with a Dean-Stark apparatus. The solution is cooled and poured into a satd. NaHCO3 solution. The benzene layer is separated and the aqueous phase is extracted with ether (3×50 ml). The organic layers are combined, dried (MgSO4) and the solvents removed at reduced pressure. The crude product is chromatographed on SilicAR CC-7 (125 g) in hexane. Elution with 10% ethyl acetate/hexane gives 2-(4'-benzyloxybutyl)-6,6-ethylenedioxy-2-methyloxepane as a clear colorless oil (6.7 g, 99%): nmr (CDCl3) δ1.10 (s., 3H, CH3), 3.5 (m, 4H, O--CH2 --and O--CH2 --CH2), 3.96 (s, 4H, ketal) 4.48 (s, 2H, O--CH2 --Ph), 730 (s, 5H, aromatic).
