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Actually i want to protect one -OH group using using 1.1Eq of TBDMSCl and 1.5 Eq of Imidazole. Is is possible to protect one OH group using these condition. Even if i get mixture of Products ( one protected OH and Both OH protected compounds), separation by column would be easy and what would be approximate yield of both products.

any suggestions.?

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  • $\begingroup$ Welcome to Chemistry.SE! Take the tour to get familiar with this site. Mathematical expressions and equations can be formatted using $\LaTeX$ syntax. This appears to be a homework question, please share your thoughts and attempts towards the solution. If you have a procedure you are working on, please provide a citation to it. Possibly the context of it might already explain the selectivity of such a reaction. $\endgroup$ – Martin - マーチン Jul 20 '16 at 8:07
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The product is symmetrical so it doesn't really matter which alcohol gets protected, you'll end up with the same product.

There are many examples of doing this kind of mono protection of simple substrates. Quite often a fairly large excess of the diol is added to try and ensure no bis protection takes place. In your case the starting material should be easily separable from product by column chromatography.

A potentially better method is to formally deprotonate the diol with 1 eq of a base such as sodium hydride or butyl lithium then trapping with a solution of the silyl chloride. This often works well in cases where bis protection may occur, as energetically its unfavourable for both oxygens on the molecule where there's molecules that are neutral

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  • $\begingroup$ Actually I tried Mitsunobu reaction of 1,4-benenedimehtanol (1eq) with Imidazole (1eq) using Ph3P and DIAD 2 eq each. I was expecting to get mixture of Products ( one Imidazole group replace OH group of diol or both OH are replaced by imidazole). when i performed the experiment I only able to get product in which both OH group are replaced by Imidazole. what would be the reason for that, Due to this i thought better to protect one OH group to successfully carried out Mitsunobu reaction. $\endgroup$ – Khan Jul 20 '16 at 7:42
  • $\begingroup$ If all of the hydroxyl groups have reacted then you must have added too much reagent. Maybe try looking on Reaxys for your specific reaction but I've did the silyl protection on many similar sunstrates and never had an issue as long as I was careful with weighing $\endgroup$ – NotEvans. Jul 20 '16 at 7:45

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