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|Title:||Inter- and intramolecular (4+2) cycloaddition reactions and tandem inter- and intramolecular (4+2)/intramolecular (3+2)cycloaddition reactions of nitroalkenes|
|Author(s):||Moon, Young Choon|
|Doctoral Committee Chair(s):||Denmark, Scott E.|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Both inter- and intramolecular cycloadditions of nitroalkenes with Lewis acid catalysis were investigated. The intramolecular cycloadditions of nitroalkenes were found to be completely stereoselective for trisubstituted nitroalkenes. Intermolecular cycloadditions of aromatic nitroalkenes were found to proceed with extremely high selectivity. It was found that E-nitroalkenes can be prepared from aldehydes using acetylation/dehydroacetylation method.
To evaluate the nitroalkene-olefin cycloadditions, many different types of olefins (mono-, di-, tri-, and tetra-substituted) were synthesized and cyclized. Regardless of the olefin geometries and substituents, all of the nitroalkene-olefin cycloadditions are completely stereoselective. The stereochemical course of cycloaddition of $\gamma$-substituted nitroalkenes is controlled by the allylic substituents and olefin geometries. Cyclization with the cis-olefin cyclized faster than with the trans-olefin (20 $>$ 1 selectivity). In the case of trisubstituted olefins, the cycloaddition occurred under thermal conditions (167$\sp\circ$C) as well as in the presence of tin tetrachloride. The nitroalkene-olefin cycloadditions are believed to have a very similar transition-state as the Diels-Alder cycloaddition reaction. The feasibility of performing subsequent (3+2) -dipolar cycloadditions with the nitronate products has been investigated. The two cycloadditions are electronically complementary which allows for the evaluation of tandem intramolecular cycloadditions. The nitronates reacted intramolecularly with tethered to $\alpha$,$\beta$-unsaturated nitrile or ester dipolarophiles to produce tricyclic nitroso acetals with high stereoselectivity. Intramolecular (3+2) cycloadditions with a Z-dipolarophile produced a single cycloadduct via an exo-transition state from the $\alpha$-face. The dipolarophile geometry was preserved in the cycloadduct. Therefore, the 1,3-dipolar cycloaddition was stereospecific. A tandem (4+2) / (3+2) cycloaddition of nitroalkenes was performed with a vinyl ether. Again nitroso acetals were produced stereoselectively in high yield.
|Rights Information:||Copyright 1991 Moon, Young Choon|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9210924|