S(N)2' reactions of chiral allylic carbamates with organocopper reagents. Asymmetric synthesis of tertiary and quarternary carbon centers
Marble, Lyndon Kenneth
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https://hdl.handle.net/2142/22879
Description
Title
S(N)2' reactions of chiral allylic carbamates with organocopper reagents. Asymmetric synthesis of tertiary and quarternary carbon centers
Author(s)
Marble, Lyndon Kenneth
Issue Date
1991
Doctoral Committee Chair(s)
Denmark, Scott E.
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
Language
eng
Abstract
The chiral auxiliary-based, asymmetric S$\sb{\rm N}2\sp\prime$ cuprate reactions of allylic carbamates were examined. The amine and amino ether auxiliaries were evaluated based on the enantioselectivities each provided in the reactions of the carbamates with methylcopper. The effects of varying the geometry and substitution pattern of the olefin in the carbamates were also studied.
The reactions of E-disubstituted chiral allylic carbamates bearing amine and amino ether auxiliaries with methylcopper gave varying degrees of enantiomeric enrichment in the product alkene. The auxiliaries derived from aromatic amino acids gave good enantioselectivities whereas those derived from aliphatic amino acids provided modest enantioselectivities. The amino ether (S)-$\alpha$-methoxymethyl-1-naphthlenemethanamine gave the highest enantioselectivity (95%). The size of the 1-naphthyl substituent was determined to be the most important feature of the auxiliary, based on size and electronic character comparisons with other auxiliaries and by analysis of Taft Steric parameters.
The effects of varying solvent, temperature, time profile, additive, and number of equivalents of copper reagent were studied. The reactions of the E-disubstituted carbamate bearing the 1-naphthyl auxiliary gave alkenes in good yield in the reactions with two equivalents of n-butylcopper and phenylcopper. The enantioselectivities were 88% and 91%, respectively.
Five carbamates with two substituents at the allylic terminus were allowed to react with phenylcopper of n-butylcopper to provide alkenes in moderate to good yields and with moderate to high enantiomeric excesses (60% ee to 99% ee) at the newly created quarternary center. The E-carbamate with methyl and cyclohexyl substituents at the $\gamma$-terminus provided the highest yield (87%) and enantioselectivity (99%) of all the substitution patterns tested. The corresponding Z-carbamate gave the lowest enantioselectivity observed (60%). Carbamates with other substituents (n-butyl and t-butyl) at the E-terminal position gave moderate yields and enantioselectivities of alkenes. Cinnamyl substrates also provided good yields of alkenes with moderate enantioselectivities.
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