Syntheses of hepta-, hexa-, and penta-pivalates of trehalose by selective pivaloylation

The order of esterification of the eight hydroxyl groups of trehalose with pivaloyl chloride is HO-6,6′ > HO-2,2′ > HO-3,3′ > HO-4,4′. Under the appropriate conditions of pivaloylation, heptapivalates with either HO-4 or HO-3 free, hexapivalates with either HO-4,4′ or HO-3′,4 free, and pentapivalates with HO-3′,4,4′ free were obtained. In addition, selective pivaloyation of trehalose 2,2′,3,3′-tetrapivalate afforded the 4,4′-diol and the non-symmetrical 4,4′,6′-triol. The 4-ol, the major heptapivalate, was a convenient starting material for the syntheses of 4-azido-4-deoxy- and 4-amino-4-deoxy-trehalose, together with their 4-epimers, and 4-chloro-4-deoxy-α- d -galactopyranosyl α- d -glucopyranoside. The 4,4′,6′-triol was utilised as a synthetic precursor of 4,6-dichloro-4,6-dideoxy-α- d -galactopyranosyl 4-chloro-4-deoxy-α- d -galactopyranoside and its triazido and triamino analogues.