Regio- and stereoselective cyclizations of dianhydro sugar alcohols catalyzed by a chiral (salen)CoIII complex

The (salen)CoIIIOAc ((R,R)-1 and (S,S)-1) catalyzed cyclizations of the chiral dianhydro sugars, 1,2:5,6-dianhydro-3,4-di-O-methyl-d-glucitol (2), 1,2:5,6-dianhydro-3,4-di-O-methyl-d-mannitol (3), 1,2:5,6-dianhydro-3,4-di-O-methyl-l-iditol (4), and 1,2:4,5-dianhydro-3-O-methyl-l-arabinitol (5), is a facile method for the synthesis of anhydroalditol alcohols. Cyclization of 2 using (R,R)-1 and (S,S)-1 proceeded diastereoselectively to form 2,5-anhydro-3,4-di-O-methyl-d-mannitol (6) and 2,5-anhydro-3,4-di-O-methyl-l-iditol (7), respectively. The cyclization of 3 and 5 is a novel method for obtaining 1,6-anhydro-3,4-di-O-methyl-d-mannitol (11) and a stereoselective route to 1,5-anhydro-3-O-methyl-l-arabinitol (13). It is proposed that the reaction occurs via endo-selective cyclization of an epoxy alcohol produced by the endo-selective ring-opening of one of the two epoxide moieties in the starting material.