KO(CH&OH RR'CXCH(0CHs)x - I /O\ t-C4H*OK /O\ ... \O/ RR'CXCH (CHa), RR'C=C ... 11 111, n = 2 or 3 ene glycol acetals from the methyl rather than the ethyl acetals (I) because of the proximity of the boiling points of the latter to those of the cyclic acetals (11, n is 2). The trimethylene glycol ace- tals, because of their higher boiling points, could be prepared from either the methyl or ethyl ace- tals. Chloral diethyl acetal did not undergo this type of alcohol exchange; ...