Free-Radical Ring Contraction of Six-, Seven-, and Eight-Membered Lactones by a 1,2-Shift Mechanism. A Kinetic and (17)O NMR Spectroscopic Study.
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Biomedical subjects
David Crich
Publications and source records attributed to David Crich.
Stannane-Mediated Radical Addition to Arenes. Generation of Cyclohexadienyl Radicals and Increased Propagation Efficiency in the Presence of Catalytic Benzeneselenol.
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Chemistry of beta-(Acyloxy)alkyl and beta-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbonminus signOxygen Bonds.
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A Practical Method for the Removal of Organotin Residues from Reaction Mixtures.
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Chemistry of 1-Alkoxy-1-glycosyl Radicals: Formation of beta-Mannopyranosides by Radical Decarboxylation and Decarbonylation of manno-Heptulosonic Acid Glycoside Derivatives.
A method for the preparation of highly enriched beta-mannopyranosides is described. A glycosyl donor 28 is prepared from tetraallyl mannonolactone by standard means and coupled to a number of primary carbohydrate alcohols, resulting in the isolation in excellent yields of axial disaccharides. Following exchange of the allyl groups for acetyl esters, the furan is oxidatively cleaved with catalytic RuO(2) and NaIO(4) and the resulting acid subjected to the Barton decarboxylation. Coupling of 28 to a secondary alcohol, methyl 2,3-isopropylidene-alpha-L-rhamnopyranoside, resulted in an apparent inversion of anomeric stereochemistry and isolation of an equatorial disaccharide.
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Formation of beta-Mannopyranosides of Primary Alcohols Using the Sulfoxide Method.
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Diastereoselective Cyclizations of 1,3-Dioxan-2-yl Radicals: Chiral Acyl Radical Equivalents.
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Chemistry of 1-Alkoxy-1-glycosyl Radicals: The Manno- and Rhamnopyranosyl Series. Inversion of alpha- to beta-Pyranosides and the Fragmentation of Anomeric Radicals.
The formation and stereoselective quenching of 1-mannopyranosyl radicals by a tributyltin hydride-mediated intramolecular 1,5-hydrogen abstraction sequence is described. A competing process is 1,4-hydrogen atom abstraction leading principally to glucopyran-2-ulosides. Fragmentation of the anomeric radical resulting in the formation of ring opened products is a problem in certain series. The chemistry is dictated to a considerable extent by the nature of the protecting groups employed with the 4,6-benzylidene series and, for rhamnose, the Ley 3,4-dispiroketal, being particularly susceptible to the 1,4-hydrogen atom abstraction but less to the fragmentation. Photochemical conditions are described, in which these side reactions are practically eliminated, and applied to the inversion of an alpha- to a beta-mannoside in a disaccharide.
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