摘要:
In our previous studies, a mechanism for DIBAL-H promoted regioselective bis-de-O-methylation of per-O-methylated cyclodextrin (CD) was proposed based on per-O-methylated beta-CDs. As a further step to this work, four per-O-methylated alpha-CD derivatives (6, 7, 11, and 18) with mono functional group at the secondary rim have been designed and synthesized. Using DIBAL-H as a chemical 'scalpel', we found that (1) only the O-methyl at C-2(A) of 6 could be easily removed and (2) the O-methyl at C-3(B) could be firstly regioselectively removed slowly, followed by a rapid removal of the second O-methyl at C-2(A) to provide 3. Combined with our previous studies, we think that not only O-3(B)-methyl but also O-2(A) and O-3(B) are necessary for the formation of 'tweezers' during DIBAL-H promoted bis-de-O-methylation reaction of per-O-methylated CD. (C) 2013 Elsevier Ltd. All rights reserved.