General Strategy for the Synthesis of Rare Sugars via Ru(II)-Catalyzed and Boron-Mediated Selective Epimerization of 1,2-trans-Diols to 1,2-cis-Diols

Key words

ruthenium catalysis - boronic acid - sugars - epimerization - hydrogenation

Significance

The Tang group reports a selective strategy for the conversion of sugars containing a trans-1,2-diol into the corresponding cis isomers. This method affords access to a wide host of rare sugars, with the OH group that flanks an axial OH group undergoing the epimerization each time. This approach was amenable to a variety of sugars, including complex disaccharides.

Comment

The formation of the boronate ester of the cis-1,2-diol drives the equilibrium toward the desired product. Shvo’s catalyst was better for substrates containing an axial γ-substituent, while Ru(PPh₃)₃Cl₂ was superior for equatorial groups in the same γ-position. The authors propose this selectivity could be due to the difference in H-abstraction mechanisms for each catalyst.

Publication History

Article published online:
20 April 2022