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Related Experiment Videos

Rules for ring closure.

J Baldwin

    Ciba Foundation Symposium
    |January 1, 1978
    PubMed
    Summary
    This summary is machine-generated.

    This study explores rules for cyclic structure formation, focusing on five-membered rings. It details how reaction conditions influence endocyclic versus exocyclic closure of nucleophiles to polarized double bonds.

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    Area of Science:

    • Organic Chemistry
    • Synthetic Chemistry
    • Reaction Mechanisms

    Background:

    • Cyclic structures are fundamental in organic chemistry and drug synthesis.
    • Understanding ring-closure rules aids in designing efficient synthetic pathways.
    • Previous studies hinted at predictable patterns in cyclic compound formation.

    Purpose of the Study:

    • To elucidate the rules governing the formation of cyclic structures, particularly five-membered rings.
    • To investigate the influence of reaction conditions (acidic vs. basic) on ring closure regioselectivity (endocyclic vs. exocyclic).
    • To analyze geometric restrictions in nucleophilic attack on polarized double bonds during cyclization.

    Main Methods:

    • Examined SN2 displacement reactions with linear transition states.

    Related Experiment Videos

  • Studied biogenetic-type synthesis of penicillin as an example.
  • Investigated cyclization of various enones and nucleophiles under acidic and basic conditions.

    • Main Results:

    • Base-catalyzed cyclization of 4-hydroxy- and 4-amino-2-methylenebutanoates favors exocyclic closure to lactones and lactams.
    • Hydroxymethyl vinyl ketones do not cyclize under basic conditions.
    • Acidic conditions promote endocyclic closure of hydroxy-enones, forming five-membered rings, and overcome geometric impediments via oxonium/protonated intermediates.

    Conclusions:

    • The regioselectivity of ring closure is predictable and dependent on substrate and reaction conditions.
    • Acid catalysis can overcome geometric constraints for endocyclic five-membered ring formation.
    • These findings provide a framework for controlling cyclic structure synthesis.