1979
DOI: 10.1002/anie.197908641
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Enantioselective Oxidation by a Chiral Acylaminyl Oxide

Abstract: of the alkylation can be determined, either 'H-NMR spectroscopically at the stage of the alkylation product (6) or polarimetrically or NMR spectroscopically with chiral shift reagents at the stage of the a-methyl-a-aminocarboxylate (7) or a-methyl-a-amino acid.We obtained 3,6-dihydropyrazine (3) by reaction of cyclo-(L-Ala-L-Ala) (2)I2I with trimethyloxonium tetrafluoroborate. This reaction proceeds without racemization. The lithiation of (3) to (4) can be smoothly performed at -70 "C (in tetrahydrofuran) wit… Show more

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Cited by 28 publications
(11 citation statements)
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“…To the best of our knowledge, isolation and direct identification of a pure optically active radical has not been heretofore achieved. A few of the previous studies have involved optically active radical intermediates (23)(24)(25)(26) by inferring from product analysis or by observing different optical rotation values for the solution containing both the presumed chiral radical and the parent optically active reactant.…”
mentioning
confidence: 99%
“…To the best of our knowledge, isolation and direct identification of a pure optically active radical has not been heretofore achieved. A few of the previous studies have involved optically active radical intermediates (23)(24)(25)(26) by inferring from product analysis or by observing different optical rotation values for the solution containing both the presumed chiral radical and the parent optically active reactant.…”
mentioning
confidence: 99%
“…The failure to obtain data for the N-hydroxycarbamates is puzzling. Analogy with the discussion so far would tend to suggest that the strengths of the 0 -H bonds in (10) and (1 1) might have been found to be between those of (4a) and (12). Whether intramolecular hydrogen bonding might be especially important in these hydroxy-compounds, and impede atom transfer to (l), is not clear.…”
Section: Discussionmentioning
confidence: 80%
“…Because of the rather wide error limits in these experiments, no attempt has been made to study the temperature dependence of K for any of the equilibria. In any case, it might reasonably be expected that hydrogen bonding effects will be similar in 0- (14) most of the systems studied, and from the high reactivity of the acyl nitroxides in hydrogen abstraction reactions [9][10][11][12] it is at least clear that we are dealing with nitroxides which have an unusually high affinity for hydrogen, Hydrogen bonding in the hydroxamic acids will be discussed further below, but with the above reservation in mind, Table 4 has been prepared as a summary of the hydroxamic acid 0-H bond dissociation energies obtained from the experimental AG (CCI,) values by addition to the 0-H bond strength (71.8 kcal mol-I) for One problem, removed as the investigation developed, was the original choice of benzene as solvent. Weak radical sohation by benzene has often been and at least one specific instance concerns nitroxides.…”
Section: Discussionmentioning
confidence: 99%
“…Other oxidations may be effected often in high yield [18,19]. Especially interesting are those of allylic and benzylic alcohols; here, the near quantitative oxidations of vitamin A alcohol 9 to retinal [20], and of hydrobenzoin to benzil without cleavage to benzoic acid, are good examples. the interesting result that reaction via an eight-membered ring transition state (n = 2) was found to be more favourable than that via the more familiar 6-membered ring.…”
Section: Acyl T-alkyl Nitroxidesmentioning
confidence: 99%
“…Indeed, no intramolecular radical processes appear to show the enormous rate enhancements frequently encountered in intramolecular ionic reactions [22]. In our [~]2SICHCl3 )= -1.9" 8% enantiorner~ excess |opf~colly pure) benzil [20]. Although the selectivity was small, and substantial improvements seemed unlikely in view of the relative remoteness of X and Y in a linear hydrogen atom transfer X-H + Y" ~ X" + HY, consideration was given to means of This brief paper has concentrated on the structure and chemistry of acyl nitroxides.…”
Section: Acyl T-alkyl Nitroxidesmentioning
confidence: 99%