Reaction of Stereoisomers of 5-Isopropyl-4-methyl-1,3-dioxane with Esters of Monosubstituted Boric Acid

Gas-liquid chromatography was used to establish that the reactivity of the cis isomer in the reaction of 5-isopropyl-4-methyl-1,3-dioxane with the diisobutyl ester of isobutylboric acid leading to the corresponding 1,3,2-dioxaborinane is greater than for the trans isomer. An AM1 calculation for the energy of the intermediate ions in this reaction with model derivatives of boric acids: dioxyborane and the dimethyl ester of methylboric acid showed that one of the probable reasons for the observed behavior is the lower barrier for conversion of the intermediate bipolar structure of the cis derivative in the step involving formation of the endocyclic B-O bond.