REGIOSELECTIVE ACYLATIONS OF ALDONO-1,4-LACTONES

Partial benzoylation or pivaloylation of D-gulono-1,4-lactone (1) with 3.3-3.6 molar equivalents of the acyl chloride afforded 2,5,6-tri-O-benzoyl- (3) or 2,5,6-tri-O-pivaloyl-D-gulono-1,4-lactone (5), which were isolated crystalline from the reaction mixture in yields of 54% and 84.5 %, respectively. Similarly, partial pivaloylation of L-mannono-1,4-lactone (6) gave crystalline 2,5,6-tri-O-pivaloyl-L-mannono-1,4-lactone (9) in 50% yield. Under the same conditions of acylation, D-galactono-1,4-lactone (11) gave a mixture of products, which were separated by column chromatography. On benzoylation, 2,3,5,6-tetra-O-benzoyl- (12); 2,5,6-tri-O-benzoyl- (13); 2,3,6-tri-O-benzoyl- (14) and 2,6-di-O-benzoyl-D-galactono-1,4-lactone (15) were obtained in 47%, 16.4%, 8%, and 14% yield, respectively. Pivaloylation of 11 afforded 2,3,5,6-tetra-O-pivaloyl- (16), 2,5,6-tri-O-pivaloyl- (17), 2,3,6-tri-O-pivaloyl (18) and 2,6-di-O-pivaloyl-D-galactono-1,4-lactone (19) in 21.6%, 9.7%, 2.6%, and 30.0%, respectively.