(3) The methods for generating these compounds are outlined in ref If.(4)(a) For example, the we of 2, 2-dimethoxypropane to prepare acetonides from diols (Tanabe, M.; Bigley, BJJ Am. Chem. SOC. 1961, 83, 756) or the conversion of hydroxy acetals into tetrahydrofurans (Eaton, PE; Cooper, GF; Johnson, RC; Mueller, RHJ Org. Chem. 1972, 37, 1947).(b) There are examples of the conversion of bicyclic acetals into polymeric acetals: Hall, HK, Jr.; Can ...