To reduce the possibility of meeting of the enolate with another molecule to form a dimer by the intermolecular reaction. You don't have to consider the collision probability or frequency for an intramolecular reaction whose reaction rate is rather controlled by the favored angles between nucleophilic and electrophilic orbitals (Baldwin's rule).
Dear Bishnu Neupane thank you for your interesting technical question. I think that Kohei Torikai already mentioned the key point. Low concentrations generally favor cyclization reactions instead of dimerization or even polymerization. For enolates please have a look at the following relevant articles:
1. Rules for ring closure: application to intramolecular aldol condensations in polyketonic substrates
Article Rules for ring closure: application to intramolecular aldol ...
2. Rules for ring closure. Stereoelectronic control in the endocyclic alkylation of ketone enolates
Article Rules for ring closure. Stereoelectronic control in the endo...
Also please have a look the the Wikipedia entry on "Baldwin's rules" at
https://en.wikipedia.org/wiki/Baldwin%27s_rules#cite_note-8
See this link
https://www.sciencedirect.com/topics/chemistry/enolates
Thanks to you all for clear and logical answers. Definitely, I will check those papers and link for the depth knowledge.
Bishnu Neupane, enolate chemistry is very popular and thus in any textbooks, but it is really difficult indeed, when you carry out. Addition direction, addition speed, concentration, etc there are many factors you have to take care of. Good luck!
Kohei Torikai, absolutely I agreed with you. Enolates are smart and hard to predict their game. I am trying to learning their rules and reaction paths. Thanks a lot.
Enolates are smart in reaction and thus careful monitoring of the reaction conditions is required. One such is the dilution factor which minimize the side products formation.
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