Selective pivaloylation and diphenylacetylation of cyclomalto-oligosaccharides.

Regioselective acylation of cyclomalto-oligosaccharides was achieved using pivaloyl and diphenylacetyl chlorides. The reaction of cyclomaltohexaose (1) with pivaloyl chloride gave the hexakis(2,6-di-O-pivaloyl) derivative 19 in 66% yield. Similar reaction with cyclomalto-heptaose (2) led to the octakis(2I,6I,6II,6III,6IV,6V,6VI ,6VII-O-pivaloyl) 26 and the 17 heptakis(6-O-pivaloyl) derivatives in 34 and 26% yields, respectively. The octakis(6-O-pivaloyl) derivative 18 was the only compound isolated (72%) in the reaction of pivaloyl chloride with cyclomalto-octaose (3). Diphenylacetylation of 1-3 gave the symmetrical (20-22) and the non-symmetrical (27-29) per(6-O-diphenylacetyl) esters as major and minor products, respectively.