
TY  - JOUR
A1  - Fraser-Reid, B. 
A1  - Lopez, J. C. 
A1  - Anilkumar, G. nair 
A1  - Lopez, J. C. 
A1  - Nair, L. G. 
A1  - Gomez, A. 
A1  - Uriel, C. 
A1  - Radhakrishnan, K. V. 
T1  - Evidence for Efficient Unpromoted Regioselective Reactions of Vicinal and Non-Vicinal Diols
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 2002
VL  - 55
IS  - 2
SP  - 123
EP  - 130
KW  - 
UR  - https://doi.org/10.1071/CH01146 
N2  - A 1965 publication from Angyal's laboratory reported that the cis-vicinal diol group of tetra-O-benzyl myo-inositol reacted regioselectively, sometimes exclusively, with acylating agents at the equatorial OH, but with alkylating agents at the axial OH. Recent reports by Fraser-Reid and coworkers showed that such selectivities were also found for the trans-1,3-diol of tetra-O-benzyl myo-inositol, as well as the C2-C4 hydroxyls of a di-O-allyl mannopyranoside. In addition, the latter workers reported that regioselectivities could be extended to glycosidation reactions. Thus, n-pentenyl ortho ester (NPOE) and 2-O-acyl n-pentenyl glycoside (NPGAC) donors reacted preferentially, if not exclusively, at the equatorial OH, whereas 2-O-alkyl counterparts (NPGALK) gave mixtures, usually with major glycosidation occuring at the axial OH. The present manuscript examines several vicinal diols, and reports that the NPOE and (NPGAC) donors frequently react at only one of the two hydroxy groups in good yield, whereas the corresponding benzylated donor (NPGALK) is less discriminating, and frequently gives lower yields. In a key experiment to examine the basis of the selectivity, it was found that the highly hindered C3 OH of 4,6-O-benzylidene methyl a-D-altropyranoside was selectively glycosylated with NPOE in 92% yield, thereby establishing that the glycosidation preference is not due to steric hindrance. 
ER  -

