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Intramolecular reductive coupling of enones bearing an unsaturated ketone, ester or nitrile was carried out under radical conditions. Upon exposure of these enone derivatives to tri-n-butyltin hydride in presence of AIBN, tin enolates were generated via 1,4-hydrostannation and then added to the internal activated alkenes in a Michael fashion to produce 1,2-disubstituted cyclopentane products. The reaction of bisenones smoothly produced the desired products in good to excellent yields under optimized conditions using 1.3 equivalents of n-Bu3SnH in benzene solution. On the other hand, the coupling of enones to a,b-unsaturated esters or nitriles, which is a thermodynamically disfavorable process, was accomplished by addition of a catalytic amount of tetrabutylammonium bromide after 1,4-hydrostannation. Coordination of the bromide ion to the tin enolate enhanced its nucleophilicity and promoted the reaction. This work represents the first examples of intramolecular reductive head-to-tail coupling of enones bearing a,b-unsaturated esters or nitriles as a Michael acceptor.
tin enolate, o-stannyl ketyl, enone, Michael addition, 1, 4-addition, tributyltin hydride, tin hydride, radical process, reductive coupling, cyclization, tetrabutylammonium bromide, unsaturated ester, bisenone, unsaturated nitrile, Michael cyclization
Date of Defense
April 5, 2006.
A Thesis Submitted to the Department of Chemistry and Biochemistry in Partial Fulfillment of the Requirements for the Degree of Master of Science.
Includes bibliographical references.
Florida State University
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