Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on March 17, 2020, 06:24:25 AM

Title: alcoholate RO- direct or conjugated addition
Post by: xshadow on March 17, 2020, 06:24:25 AM

Hi

 In a α-β insaturated  carbonyl compound  I know that usually alcohol"ROH" give the   conjugated addiction    to the  " -C=C-C=O" system because the direct addiction is reversible while the conjugated one it isn't!!

So after a bit of time the direct product formed is re-converted in the reagent and sometime it reacts again to form   the conjugated product instead
The reaction that forms conjugated product is  "always" irreversible so I have the final product
NOW this is how it works for ROH, a weak base.


My question is now about the RO^-,the alcoholate (NB: a simply alcoholate,not an enolate,which is a weak base-resonance stabilization). RO^- is a strong base and perhaps  this time also the direct addition to C=O is irreversible...so  if  the direct product is formed faster than the conjugated one (and usually the direct addition is the kinetic product) ,the direct product can't be reconverted in the reagent latet, to give the other product( the conjugated one)

SO I should get the  direct addiction if I use a strong base like RO-  (not enolate but alcoholate)


Is it correct?
Thanks!!!

Title: Re: alcoholate RO- direct or conjugated addition
Post by: pgk on March 18, 2020, 02:42:26 PM

According to an attached file in a reply to a previous post of yours, both RO- and ROH can give the 1,4-conjugated addition to the "-C=C-C=O" system, depending on the particular catalysis.
Besides, 1-addition leads to acetals and ketals that can easily be obtained by condensation with ROH under dehydrative conditions (azeotropy, molecular sieves, etc.). In general, RO- does not conviently form acetals and ketals.

Does alcohol give conjugated addition?-Chemical Forums
https://www.chemicalforums.com/index.php?topic=102224.0