A new synthesis of 6-O-acylsucroses and of mixed 6,6′-di-O-acylsucroses

Various 6-O-acylsucroses were synthesized in good yields from unprotected sucrose in N,N-dimethylformamide and the appropriate 3-acylthiazolidine-2-thiones 6 or 3-acyl-5-methyl-1,3,4-thiadiazole-2(3H)-thiones 7. A selective ionization of the free sugar by sodium hydride or triethylamine, followed by acylation with 6, gave 2-O-acylsucroses which were subjected in situ to intramolecular isomerizations using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or an aqueous solution of triethylamine to yield 6-O-acylsucroses. The later were otherwise obtained directly when sucrose was acylated with 6 or 7 in the presence of DBU. Moreover, mixed 6,6′-di-O-acylsucroses were readily obtained from 6′-monoacylates by using a Mitsunobu reaction without involving the concomitant formation of the 3′,4′-epoxide.