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Steven A Raw

Publications and source records attributed to Steven A Raw.

9 recordsLinked to original sources
PubMed2005

Improved methodologies for the preparation of highly substituted pyridines.

[reaction: see text] Two separate strategies have been developed for the preparation of highly substituted pyridines from 1,2,4-triazines via the inverse-electron-demand Diels-Alder reaction: a microwave-promoted, solvent-free procedure and a tethered imine-enamine (TIE) approach. Both routes avoid the need for a discrete aromatization step and offer significant advantages over the classical methods, giving a wide variety of tri-, tetra-, and penta-substituted pyridines in high, optimized yields.

Molecular Structure↗
PubMed2005

Tandem oxidation processes using manganese dioxide: discovery, applications, and current studies.

"One-pot" processes in which alcohol oxidations are combined with further elaboration of the carbonyl intermediate are reviewed. Sequential processes are briefly discussed, but most attention is centered on tandem processes; that is, oxidations carried out in the presence of a nucleophilic trapping agent, rather than those in which the trapping agent is added after the oxidation is complete. As part of this Account, a comprehensive review of the discovery of tandem oxidation processes (TOP) will be given together with applications in alkene-forming reactions, cyclopropanations, and imine, oxime, amine, and heterocycle formation.

Journal Article↗
PubMed2004

Tandem oxidation processes for the preparation of functionalized cyclopropanes.

[reaction: see text] A novel manganese dioxide-mediated tandem oxidation process (TOP) has been developed which allows the direct conversion of allylic alcohols into cyclopropanes, the intermediate aldehydes being trapped in situ with a stabilized sulfur-ylide. This methodology has been applied successfully to a variety of allylic alcohols and to a formal synthesis of the simple, naturally occurring lignan, (+/-)-picropodophyllone.

Journal Article↗
PubMed2004

A versatile and stereocontrolled route to pyranose and furanose C-glycosides.

[reaction: see text] The alpha,beta-unsaturated-gamma,delta-epoxyester 1 is a novel and versatile precursor to a wide variety of C-glycosides. For instance, treatment of Z-1 or E-1 with palladium(0) affords, stereospecifically, beta- or alpha-C-furanosides, respectively. In contrast, reaction of Z-1 or E-1 with base gives, stereoselectively, the beta- or alpha-C-pyranosides, respectively.

Catalysis↗
PubMed2004

Tandem oxidation processes for the preparation of nitrogen-containing heteroaromatic and heterocyclic compounds.

alpha-hydroxy ketones undergo manganese dioxide-mediated oxidation followed by in situ trapping with aromatic or aliphatic 1,2-diamines to give quinoxalines or dihydropyrazines, respectively, in a one-pot procedure which avoids the need to isolate the highly reactive dicarbonyl intermediates. The scope and limitations of these procedures are outlined and modifications to this procedure are discussed in which reduction is carried out in the same reaction vessel, generating piperazines, or oxidation, leading to pyrazines.

Journal Article↗
PubMed2004

Highly substituted pyridines via tethered imine-enamine (TIE) methodology.

A tethered imine-enamine methodology has been developed for the direct conversion of 1,2,4-triazines into highly substituted pyridines via the inverse electron demand Diels-Alder reaction which avoids the need for a discrete aromatisation step. This TIE methodology has also been applied in one pot reaction cascades involving 1,2,4-triazines and utilising MnO(2)-mediated tandem oxidation processes (TOPs).

Journal Article↗