James P. Hagen

Bio: James P. Hagen is an academic researcher from University of Nebraska–Lincoln. The author has contributed to research in topics: Allylic rearrangement & Nucleophilic substitution. The author has an hindex of 8, co-authored 12 publications receiving 344 citations.

Acyclic stereoselection. 25. Stereoselective synthesis of the C-1 to C-7 moiety of erythronolide A

Abstract: A partir de dimethyl-2,4 pentene-3al, synthese de benzyloxy-6 dimethyl-2,4 formyl-6 isopropylidenedioxy-3,5 œnanthate de methyle

Acyclic stereoselection. 6. A reagent for achieving high 1,2-diastereoselection in the aldol conversion of chiral aldehydes into 3-hydroxy-2-methylcarboxylic acids

Abstract: Durch Erhitzen des ausgehend vom Enon (I) erhaltlichen Hydroxyketons (IIIa) mit Bis-trimethylsilylacetamid wird die Verbindung (IIIb) dargestellt, die als wirksames Reagenz fur stereoselektive Aldolkondensationen eingesetzt werden kann.

Acyclic stereoselection. 23. Lactaldehyde enolate equivalents

Abstract: On etudie la stereochimie de l'addition d'enolates d'esters d'acide O-alkyllactique aux aldehydes

Double Asymmetric Synthesis and a New Strategy for Stereochemical Control in Organic Synthesis

Abstract: This account examines double asymmetric induction from theoretical and practical viewpoints. In the context of four major organic reactions-the aldol, Diels-Alder, catalytic hydrogenation, and epoxidation-it is shown that a double asymmetric induction can be analyzed in terms of the single asymmetric reactions of each of the two chiral reactants. A rule which qualitatively relates the results of these single asymmetric reactions with the outcome of the double asymmetric reaction is proposed. A powerful new strategy based on this rule for the predictable creation of new chiral centers is discussed and the use of this strategy for the synthesis of sugars and macrolides is presented.

Structure and Reactivity of Lithium Enolates. From Pinacolone to Selective C‐Alkylations of Peptides. Difficulties and Opportunities Afforded by Complex Structures

Abstract: The chemistry of lithium enolates is used to demonstrate that complex structures held together by noncovalent bonds (“supramolecules”) may dramatically influence the result of seemingly simple standard reactions of organic synthesis. Detailed structural data have been obtained by crystallographic investigations of numerous Li enolates and analogous derivatives. The most remarkable features of these structures are aggregation to give dimers, tetramers, and higher oligomers, complexation of the metal centers by solvent molecules and chelating ligands, and hydrogen-bond formation of weak acids such as secondary amines with the anionoid part of the enolates. The presence in nonpolar solvents of the same supramolecules has been established by NMR-spectroscopic, by osmometric, and by calorimetric measurements. The structures and the order of magnitude of the interactions have also been reproduced by ab-initio calculations. Most importantly, supramolecules may be product-forming species in synthetic reactions of Li enolates. A knowledge of the complex structures of Li enolates also improves our understanding of their reactivity. Thus, simple procedures have been developed to avoid complications caused by secondary amines, formed concomitantly with Li enolates by the common methods. Mixtures of achiral Li enolates and chiral Li amides can give rise to enantioselective reactions. Solubilization by LiX is observed, especially of multiply lithiated compounds. This effect is exploited for alkylations of N-methylglycine (sarcosine) CH2 groups in open-chain oligopeptides. Thus, the cyclic undecapeptide cyclosporine, a potent immunosuppressant, is converted into a THF-soluble hexalithio derivative (without epimerization of stereogenic centers) and alkylated by a variety of electrophiles in the presence of either excess lithiumdiisopropyl amide or of up to 30 equivalents of lithium chloride. Depending on the nature of the LiX additive, a new stereogenic center of (R) or (S) configuration is created in the peptide chain by this process. A structure-activity correlation in the series of cyclosporine derivatives thus available is discussed.

Scandium Trifluoromethanesulfonate as an Extremely Active Lewis Acid Catalyst in Acylation of Alcohols with Acid Anhydrides and Mixed Anhydrides.

Abstract: Scandium trifluoromethanesulfonate (triflate), which is commercially available, is a practical and useful Lewis acid catalyst for acylation of alcohols with acid anhydrides or the esterification of alcohols by carboxylic acids in the presence of p-nitrobenzoic anhydrides. The remarkably high catalytic activity of scandium triflate can be used for assisting the acylation by acid anhydrides of not only primary alcohols but also sterically-hindered secondary or tertiary alcohols. The method presented is especially effective for selective macrolactonization of ω-hydroxy carboxylic acids.

Synthesis of Open-Chain 2,3-Disubstituted 4-nitroketones by Diastereoselective Michael-addition of (E)-Enamines to (E)-Nitroolefins. A topological rule for C, C-bond forming processes between prochiral centres. Preliminary communication

Abstract: The Michael-additions of aliphatic, alicyclic, and arylsubstituted nitroolefins and enamines lead to γ-nitroketones 3 in good chemical and excellent (> 90%) diastereomeric yields (see Table 1). The known threo-configuration of one type of adducts 3 (entries 8, 10, and 11 of Table 1) can be arrived at by assuming the approach 8 of the Michael-acceptor and -donor; the reaction follows a topological rule, which is formulated and which is applicable to such diverse reactions as the diene synthesis, cyclopropanations, carbonyl olefinations and methylenations, aldol- and nitroaldol-type additions, as well as additions of lithium, boron, and chromium derivatives to aldehydes (see 9, 10, 11, and Table 2).