An Anionic 3 + 2 Cyclization-Elimination Route to Cyclopentenes
Burg, Douglas Alan
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https://hdl.handle.net/2142/70419
Description
Title
An Anionic 3 + 2 Cyclization-Elimination Route to Cyclopentenes
Author(s)
Burg, Douglas Alan
Issue Date
1988
Doctoral Committee Chair(s)
Beak, Peter
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Abstract
Recently there has been considerable interest in the synthesis of five-membered carbocycles. In this thesis we discuss our work on the development and use of 1-benzenesulfonyl-2-carbamoylallyllithium reagents in an anionic 3+2 cyclization-elimination route to cyclopentenes.
Treatment of N,N -diisopropyl-3-benzenesulfonyl-2-methylenepropanamide with lithium 2,2,6,6-tetramethylpiperidide in tetrahydrofuran at $-$78$\sp\circ$C produces the stable N,N-diisopropyl- ((1-benzenesulfonyl)-2-carbamoylallyl) lithium reagent which when allowed to react with electron-deficient olefins produces 4-substituted-N,N-diisopropylcyclopent-1-ene carboxamides in 89% to 22% yields. Similarly, allyllithium reagents have also been formed from the less hindered tertiary amide, N,N-dimethyl-3-benzenesulfonyl-2-methylenepropanamide, and the secondary amide, N-phenyl-3-benzenesulfonyl-2-methylenepropanamide, and then allowed to react with cyclohexyl methacrylate to produce the N,N-dimethyl- and N-phenyl-4-cyclohexyloxycarbonyl-4-methylcyclopent-1-ene carboxamides in 49% and 19% yields respectively. Acid hydrolysis of these two cyclopentenes produces 4-methylcyclopent-1-ene-1,4-dicarboxylic acid in 62% and 77% yields respectively. Studies with allyllithium reagents derived from N,N-diisopropyl-3-benzenesulfonyl-2-methylenebutanamide and N,N-diisopropyl-2-(benzenesulfonylmethyl)but-2-enamide show that alkyl substitution on either end of the allyllithium reagent can be tolerated and cyclopentenes are produced even though decreased yields are obtained. This allows for the synthesis of cyclopentene products which are substituted in the two or five positions.
The formation of the cyclopentenes is believed to occur by a stepwise, rather than concerted, reaction as evidenced by three results. First, the formation of a cycloheptene side product is best explained by a stepwise mechanism. Second, there was a net loss of stereochemistry in the cyclopentene products when (E)- and (Z)-$\beta$-deuteriomethacrylamides were used as the electron-deficient olefins. Finally, acyclic addition products have been isolated when $\beta$-substituted electron-deficient olefins were used in the cyclization-elimination reaction. These observations are most consistent with a stepwise mechanism which proceeds by an initial highly regioselective Michael addition of the allyllithium reagent to the electron-deficient olefin followed by cyclization and elimination to produce the substituted cyclopentenes.
The 1-benzenesulfonyl-2-carbamoylallyllithium reagents provide cyclopentenes in higher yield, higher regioselectivity, and with a wider range of substituents than the previously reported 1-phenylthio-2-carbamoylallyllithium reagent. This appears to be the most versatile anionic 3+2 route to five-membered carbocycles.
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