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Alkylation Step (alkylation + step)

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Chemistry100%

Selected Abstracts

Enantioselective Synthesis of the Originally Proposed Usneoidone Structure: Evidence for a Structural Revision

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2004
Michèle Danet
Abstract The enantioselective synthesis of the initially proposed structure of usneoidone has been completed according to a convergent strategy in which the key steps were an enantioselective Michael addition involving chiral imines to set up the C12 quaternary center, and the final assembly of the chiral pyran moiety with the aromatic subunit through a cyanohydrin anion alkylation step. The obtained product displays spectroscopic data that significantly differ from the reported values. A putative revised structure in which the pyran ring is opened is proposed for usneoidones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Cover Picture: (Adv. Synth.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010
Catal.
The cover picture, provided by David W.,C. MacMillan, shows a dual-catalytic aldehyde alkylation via photoredox organocatalysis in which electrophilic radicals (derived from the photoredox cycle; above) combine with facially biased enamine intermediates (derived from the organocatalytic cycle; below). The photoredox catalyst, Ru(bpy)32+ readily accepts a photon from a visible light source to populate the *Ru(bpy)32+ metal-to-ligand charge transfer (MLCT) excited state, eventually enabling single-electron transfer (SET) with an alkyl halide to furnish the electron-deficient alkyl radical. Simultaneously, the organocatalytic cycle is initiated upon condensation of the imidazolidinone catalyst (inset) exclusively with a non-substituted aldehyde to form a stereochemically-defined enamine. The two activation pathways merge in the key alkylation step via rapid addition of the electrophilic radical to the ,-rich olefin followed by a series of concerted steps which return the organocatalyst and photocatalyst to their respective cycles and render the optically enriched ,-alkyl aldehyde. [source]

Analysis of urinary biomarkers for exposure to alkyl benzenes by isotope dilution gas chromatography-mass spectrometry

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2005
Adriaan A. S. Marais
Abstract A validated GC-MS method for the analysis of urinary metabolites of alkyl benzenes is reported. Metabolites for exposure to toluene, xylene and ethylbenzene were analyzed simultaneously using stable isotope substituted internal standards. The method entailed acidic deconjugation of urine samples followed by extractive alkylation with pentafluorobenzyl bromide as alkylating agent. The resulting pentafluorobenzyl derivatives of ortho -, meta -, para -cresol, mandelic acid (MA), hippuric acid (HA) and ortho -, meta -, para -methylhippuric acid (MHA) were then quantified by SIM. Optimized reaction conditions for the extractive alkylation step are reported. The derivatives were found to be sufficiently stable for overnight batch analysis. The LODs were below 0.1 ,mol/L for the cresols and below 1 ,mol/L for MA and the HAs. Within-batch precision for o -MHA was 7%, for m -MHA 5%, for p -MHA 5.2% and below 5% for the rest of the analytes. [source]