Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: OrganicH2O on May 27, 2020, 04:56:16 PM
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I have a question about how the number of alpha hydrogens effects the ease or Robinson Annulation. I attached a picture which illustrates my question.
In reaction 1 in the picture, the 1,3-diketone has two alpha hydrogens. Following Michael addition, the ground state would be the doubly stabilize enolate ion shown. I hypothesize that this stable enolate will slow down subsequent aldol cyclization. This aldol cyclization is possible, but might require harsher conditions like higher temperature and longer reaction times.
In reaction 2, the 1,3-diketone has only one alpha hydrogen. Therefore, formation fo the an especially stable enolate is not possible. Subsequent aldol cyclization would therefore be much faster. It might even be impossible to stop the aldol cyclization.
Is this speculation logical and correct?