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|Title:||Chiral phosphonyl and thiophosphonyl carbanions in asymmetric alkylation and olefination reactions|
|Doctoral Committee Chair(s):||Denmark, Scott E.|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||A series of 3-substituted 2-benzyl-6-methyl-1,3,2-oxazaphosphorinane-2-oxides, derived from (S)-N-alkyl-4-amino-2-butanols, was prepared. The alkylation behavior of the derived lithium anions was examined as a function of the N-substituents and electrophiles. In the l-series, the methylation proceeded with high diastereoselectivity (90/10-97/3) and the benzylation selectivity ranged from 80/20 to 94/6. In the u-series, little steric influence on the methyl selectivity (83/17-85/15) was observed except in the case of sterically demanding group (R = $\rm C(C\sb2H\sb5)\sb3)$ where high diastereoselectivity (95/5) could be accomplished. An extremely high level of asymmetric induction was achieved in the alkylation of (l)-N-isopropyloxazaphosphorinane-2-oxide with a diverse array of electrophiles. Further extensions to other P-alkyl-N-isopropylphosphonamidates were also examined. Anions derived from enantiomerically enriched N-isopropyloxazaphosphorinane-2-sulfides underwent smooth electrophilic substitution with excellent diastereoselectivity in both l- and u-stereoisomers, which allowed the preparation of scalemic phosphonic acids and phosphonates with three $\alpha$-substitution patterns (aryl, alkyl, and alkoxy). Synthesis of $\alpha$-hydroxyphosphonates in either antipodal form could be achieved by the highly diastereoselective alkylation of anions derived from the corresponding P-methoxymethyl analog in the presence of HMPA or PMDTA.
The anion derived from scalemic P-benzyl-N-isopropylphosphonamidate added to 4-substituted cyclohexanones with excellent diastereoselectivity. The $\beta$-hydroxyphosphonamidates were decomposed to alkylidenes with excellent stereospecificity (94%) using a novel electrophile-promoted olefination that employed trityl triflate and 2,6-lutidine in warm acetonitrile. An asymmetric phenylthiomethylidenation also proceeded with high overall selectivity. The alkylidene sulfide underwent highly stereospecific nickel-catalyzed coupling with Grignard and dialkylzinc reagents to produce a variety of dissymmetric olefins.
|Rights Information:||Copyright 1994 Chen, Chien-Tien|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9512324|