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Synthetic Approaches to Phosphasugars (2-oxo-1,2-oxaphosphacyclanes) Using the Anomeric Alkoxyl Radical β‑Fragmentation Reaction as the Key Step
journal contribution
posted on 2020-03-24, 21:03 authored by Daniel Hernández-Guerra, Alan R. Kennedy, Elisa I. León, Ángeles Martín, Inés Pérez-Martín, María S. Rodríguez, Ernesto SuárezThe
anomeric alkoxyl radical β-fragmentation (ARF) of carbohydrates
possessing an electron-withdrawing group (EWG) at C2, promoted by
PhI(OAc)2/I2, gives rise to an acyclic iodide
through which a pentavalent atom of phosphorus can be introduced via
the Arbuzov reaction. After selective hydrolysis and subsequent cyclization,
the phosphonate or phosphinate intermediates can be converted into
2-deoxy-1-phosphahexopyranose and 2-deoxy-1-phosphapentopyranose sugars.
The ARF of carbohydrates with an electron-donor group (EDG) at C2
proceeds by a radical-polar crossover mechanism, and the cyclization
occurs by nucleophilic attack of a conveniently positioned phosphonate
or phosphinate group to the transient oxocarbenium ion. This alternative
methodology leads to 5-phosphasugars with a 4-deoxy-5-phosphapentopyranose
framework. The structure and conformation of the 2-oxo-1,2-oxaphosphinane
and 2-oxo-1,2-oxaphospholane ring systems in different carbohydrate
models have been studied by NMR and X-ray crystallography.
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radical-polar crossover mechanismphosphinate intermediates2- deoxy -1-phosphahexopyranoseelectron-withdrawing groupalternative methodologycarbohydrate modelsEWGphosphonateKey Step2- deoxy -1-phosphapentopyranose sugarsacyclic iodide5- phosphasugarspentavalent atomSynthetic Approachesanomeric alkoxylβ- fragmentationX-ray crystallographyNMREDGoxocarbenium ionC 2 proceedsArbuzov reaction4- deoxy -5-phosphapentopyranose frameworkphosphinate groupcyclizationelectron-donor groupnucleophilic attackARF
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