Asymmetric conjugate addition

Article Abstract:

The synthetic strategies for conjugate 1,4-addition of organometallic reagents to alpha,beta-olefins are described. Research in this area has taken two general routes. Majority of high-yielding and highly enantiomeric successes are scored in the diastereoeselective conjugate addition to scalemic substrates. Experimental results point to an ideal reagent as a scalemic catalyst, still hypothetical, that can promote enantioselective conjugate addition of readily available Grignards and organolithiums to cyclic and acyclic alpha,beta-ene substrates.

Organometallic compounds, Grignard reagents

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Asymmetric hydroxylation of enolates with N-sulfonyloxaziridines

Article Abstract:

Easy access to, and use of, enantiopure N-sulfonyloxaziridines make possible effective stereocontrol in the asymmetric hydroxylation of enolates. These reagents are prepared by the biphasic basic oxidation of a sulfonimine with m-chloroperbenzoic acid or Oxone. The hydroxylation mechanism involves a bimolecular nucleophilic substitution process, where the enolate anion attacks the oxaziridine oxygen atom, giving a hemiaminal intermediate in a subsequent equilibrium step. The use of this process in natural synthesis is stressed.

Methods, Organosulfur compounds, Organic sulfur compounds, Hydroxylation, Alcohols, Substitution reactions

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The concept of transient chirality in the stereoselective synthesis of functionalized cycloalkenes applying the retro-Diels-Alder methodology

Article Abstract:

The concept of transient chirality in stereoselective synthesis of functionalized cycloalkenes was examined using the Diels-Alder/retro-Diels-Alder methodology. The earliest example was observed in the synthesis of cyclopentanoids wherein the parent endo-tricyclodecadienone was applied for the synthesis of vicinal dialkylated methylcyclopentenones. Another group of transient chiral intermediates may be found among the five-membered hydrofuran and pyrrolidine systems present in pharmaceutical compounds.

Usage, Cyclic compounds, Diels-Alder reaction

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