Bifunctional building blocks for glyco-architectures by TiCl4 -promoted ring opening of cyclodextrin derivatives

During our studies on the preparation of blocklike substituted 1,4-glucans by cationic ring-opening polymerization,1,2 we found that TiCl4 behaves differently from common initiators like Et3O+X- (X = PF6, SbCl6), BF3.Et2O, or methyl triflate, causing only ring opening under formation of alpha-maltooligosyl chlorides bearing one free hydroxyl group (4-OH) at the nonreducing end. These compounds are valuable building blocks for the preparation of new glyco-architectures since they are easily accessible starting materials for direct glycosylations or the preparation of a variety of oligomeric glycosyl donors like alkyl glycosides, thioglycosides, or azides. We successfully carried out and optimized the TiCl4-promoted ring opening with per-O-methylated, per-O-ethylated, and temporarily protected per-O-allylated cyclodextrins of various ring size. 1H NMR spectroscopy and high-pressure liquid chromatography-evaporative light-scattering detection (HPLC-ELSD) were used to characterize the products.