Reductive dehalogenation Subject

Perhalogenated aliphatic compounds such as hexachloroethane and perchloro-ethene (PCE) are highly oxidized compounds that are subject to reductive dehalogenation... 

One of the earliest reported preparations of the requisite glycosidation precursor 5-deoxy-l,2,3-tri-0-acetyl-p-D-ribofuranoside (17) was published by Kissman and Baker in 1957.23 D-Ribose was heated at reflux in a methanol/acetone mixture in the presence of concentrated HCI to provide methyl 2,3-O-isopropylidene-D-ribofuranosidc (21), which was in turn converted to the corresponding 5-O-mesyl ribofuranoside 22 with methanesulfonyl chloride in pyridine in 63% yield. The sulfonate moiety of 22 was then displaced with sodium iodide in refluxing DMF to provide 5-deoxy-5-iodo derivative 23 in 76% yield on a multigram scale. Reductive dehalogenation of 23 was accomplished under heterogeneous catalytic hydrogenation conditions to provide the reduced 2,3-0-protected intermediate 24 in 56% yield, which was subjected to hydrolysis conditions in... 

The free-radical chemistry of this class of compound has been the subject of study by radiation chemists (c/. [11, 27-29]) ever since it was observed that they are reductively dehalogenated by electron attachment. 

Having developed an efficient route to the common intermediate 91, we next turned our attention to the further transformation of 91 into quinolizidine-type alkaloids (Scheme 18). The amido group in 91 was reduced with BH3 THF in THF under reflux to give amine 100. Without purification, 100 was treated with SOCI2 to yield chloride 101, which was subjected to the next reaction without purification because of instability on SiOa gel. Reductive dehalogenation of chloride 101 with LiAlH4 afforded cermizine C (87) [51]. 

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