The formation of isopropylidene acetals of erythritol and ribitol under conditions of kinetic control

The isopropylidenation of erythritol, under conditions of kinetic control, employing 2-methoxypropene, yielded the 1,2:3,4- (1, 50%), the 1,4:2,3- (2, 18%), and the novel 1,3:2,4-diacetal (3, 5%). Under similar conditions, ribitol gave the known 1,2:4,5- (4, 36%) and 1,4:2,3-diacetal (7, 3%) together with the new 1,3:4,5- (8, 12%) and 1,3:2,5- diacetal (11, 5%), a further example of a dioxepane ring. ¹³C-N.m.r. and ¹H-n.m.r. spectroscopy showed that the 1,3-dioxane rings in 3, 8, and 11 adopt chair conformations. In 9, the p-nitrobenzoate of 8, the dioxane chair is flattened. The product composition is compared with that from the equilibrated system. © 1990.