The allyl group for protection in carbohydrate chemistry. Part 21. (±)-1,2 : 5.6- and (±)-1,2 : 3,4-di-O-isopropylidene-myo-inositol. The unusual behaviour of crystals of (±)-3,4-di-O-acetyl-1,2,5,6-tetra-O-benzyl-myo-inositol on heating and cooling: a ‘thermosalient solid’

Racemic 1,2-O-isopropylidene-myo-inositol was converted into a mixture of 1,2 : 5,6-, 1,2 : 3,4-, and 1,2 : 4,5-di-O-isopropylidene-myo-inositols which were resolved by g.l.c. The 1,2 : 4,5- and 1,2 : 5,6- isomers were isolated from the mixture as benzoate derivatives. Allylation of the mixed isomers allowed the separation of all three allyl ethers by column chromatography and these were converted into the corresponding di-O-allyl-myo-inositols. 1,4-Di-O-allyl-myo-inositol was converted into 1,4-di-O-allyl-5,6-O-isopropylidene-myo-inositol on kinetic acetonation. Removal of the allyl groups from 5,6-di-O-allyl-1,2 : 3,4-di-O-isopropylidene-myo-inositol gave pure 1,2 : 3,4-di-O-isopropylidene-myoinositol which gave the known 1,2,3,4-tetra-O-benzyl-myo-inositol. Crystals of the diacetate of 1,2,5,6 tetra-O-benzyl-myo-inositol showed interesting ‘jumping’ behaviour on heating and cooling.