Dissertation/Thesis Abstract

Metal-catalyzed annulations of strained cycloalkanes
by Parsons, Andrew Thomas, Ph.D., The University of North Carolina at Chapel Hill, 2010, 230; 3402464
Abstract (Summary)

I. Lewis Acid-Catalyzed (3 + 2) Annulation of Malonate-Derived Donor-Acceptor Cyclopropanes and Aldehydes. An overview of the development, scope, and mechanism of the (3 + 2) annulation of malonate-derived donor-acceptor cyclopropanes and aldehydes is presented.*

II. Palladium(0)-Catalyzed Annulation of Dimethyl 2-Vinylcyclopropane-1,1-Dicarboxylate and Aldehydes: The Synthesis of Tetrahydrofurans through an Aldol–Allylic Etherification Sequence. The synthesis of tetrahydrofurans via palladium(0)-catalyzed annulation of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate and aldehydes is described. Carbon-carbon bond cleavage of the cyclopropane was achieved through π-allylpalladium formation. Aldol reaction with an aldehyde and subsequent ring-closure provides the desired 2,5-cis-disubstituted tetrahydrofurans with high diastereoselectivity.*

III. Enantioselective Synthesis of Tetrahydrofurans via Dynamic Kinetic Asymmetric (3 + 2) Annulation of Racemic Cyclopropanes and Aldehydes. The synthesis of enantioenriched 2,5-cis-disubstituted tetrahydrofurans was achieved through a dynamic kinetic asymmetric transformation (DyKAT) of racemic cyclopropanes. Use of a catalytic amount of 4-chloro- tert-butylpybox/MgI2 facilitated the enantioselective annulation of electron-rich donor-acceptor cyclopropanes and aldehydes. The electron-deficient 4-chloro-pybox ligand provided an increase in yield while maintaining high levels of stereoselectivity.*

IV. Dynamic Kinetic Asymmetric Synthesis of Pyrrolidines from Racemic Cyclopropanes and Aldimines: Reaction Development and Mechanistic Insights. The use of a (pybox)MgI2 catalyst for the dynamic kinetic asymmetric synthesis of pyrrolidines from donor-acceptor cyclopropanes and aldimines is described. The choice of N-protecting group and 4-substituted-tert-butyl-pybox ligand was essential to achieving high yields and selectivities. Mechanistic investigations suggest that the reaction occurs via annulation with the (E)-aldimine dipolarophile exclusively and minimal E—Z-isomerization occurs prior to annulation.*

V. Lewis Acid-Catalyzed (4 + 2) Annulation of Donor-Acceptor Cyclobutanes and Aldehydes. The diastereoselective synthesis of 2,6-cis -disubstituted tetrahydropyrans via (4 + 2) annulation of D–A cyclobutanes and aldehydes is described. Sc(OTf)3 and Hf(OTf) 4 catalyze the annulation with cinnamyl and aryl aldehydes. Extension of this methodology to alkyl aldehydes required the use of a bulky aluminum(III) Lewis acid. A one-pot cycloaddition/annulation cascade was achieved, providing access to tetrahydropyrans directly from an olefin, dimethyl 2-methylenemalonate, and an aldehyde.*

*Please refer to dissertation for diagrams.

Indexing (document details)
Advisor: Johnson, Jeffrey S.
Commitee: Brookhart, Maurice S., Gagne, Michel R., Templeton, Joseph L., Waters, Marcey L.
School: The University of North Carolina at Chapel Hill
Department: Chemistry
School Location: United States -- North Carolina
Source: DAI-B 71/05, Dissertation Abstracts International
Subjects: Organic chemistry
Keywords: Annulations, Asymmetric catalysis, Cycloaddition, Cycloalkanes, Heterocycles, Pyrrolidines, Tetrahydrofurans, Tetrahydropyrans
Publication Number: 3402464
ISBN: 9781109745788
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