A HIGH YIELD SYNTHESIS OF 1,2:5,6-DI-O-ISOPROPYLIDENE-D-MANNITOL: A great improvement in the synthesis of 1,2:5,6-di-O-isopropylidene-D-mannitol (2) using D-mannitol (1) as starting material, is described. The acetalation of (1) was performed in acetone in the presence of zinc chloride as catalyst to give (2) in 87% yield. Some studies on the acetal stability were carried out to explain the high yields. High field NMR spectra were obtained and assignment of all signals was accomplished with the aid of double irradiation, difference NOE and HETCOR spectra