[bhkuk]

 

i want to synthesise S(R)-1-Deoxy-1-(p-tolylsulfinyl)-2-O-(benzyl)-3,4-O-isopropylidene-D-erythritol and i have question on the procedure so i will give details about it:
1. to asolution of S(R)-1-Deoxy-1-(p-tolylsulfinyl)-3,4-O-isopropylidene-D-erythritol in THF asuspension of NaH in THF is add at room temperature and the mixture should stirred at reflux for 30 minutes.
2. after cooling to room temperature i should add Tetrabutyl ammonium iodide and benzyl bromide at equivalent amount and i should mix the reaction for 20 hours.
3. after it the solvent remove under reduced pressure  and the residue treats with aqueous sodiumbicarbonate and extracted with dichloromethane
4. the combine organic extracts were drying by sodium sulfate and the solvent was removed under reduced pressure and the residue was purified by flash chromatography.
so my question is:
1.why should i add NaH- is it take proton out off my hydroxy group?
2. why should i add Tetrabutyl ammonium iodide what is the mechnism to its  reaction?  what reaction accure with him? and why should i mix the reaction for such long time (20 hours!!)
3.why should i add  sodiumbicarbonate at the end of the reaction?

[miraculix]

Hello bhkuk,

concerning your questions:

for 1) The sodiumhydride will deprotonate the Hydroxyl-group in your molecule. This is necessary, because it will create a much better nucleophile.

for 2) This is a common protocol. You generate benzyl-iodide in situ, wihich is far more reactive than the corresponding bromide.
Regarding the reaction time: Check a TLC after some hours. Perhaps the one reporting this protocol just didn't want to stay in the lab for too long, so he decided to go home and let stirr overnight? ;-)

for 3) You should avoid acidic conditions during the work up in any case. The acetonide protecting group would not be stable under these conditions. So, just a use a base for work-up.


kind regards

miraculix