A Carbohydrate to Cyclopentanol Conversion

There is much current interest in the development of simple and effective methods for the conversion of selectively functionalised carbohydrates into stereodefined cyclopentanols, and South African chemists have reported an excellent samarium diiodide-based process. Thus, dropwise addition of the iodoglucoside 1 to a refluxing solution of excess of samarium diiodide in THF/HMPA, and heating of the mixture under reflux for 2 hours followed by cooling, dilution with 1 1 hexane/ethyl acetate and quenching with 5% aqueous citric acid gave the pure cyclopentanol 2 in 70% yield after flash chromatography. 

Suggest a mechanism for the transformation of 1 into 2, which has been described as a Sml2-promoted Grob-fragmentation reaction. followed by an in situ, stereocontrolled Sml2-mediated cyclisation  

---