Sequential Norrish Type II photoelimination and intramolecular Aldol cyclization of alpha-diketones: synthesis of polyhydroxylated cyclopentitols by ring contraction of hexopyranose carbohydrate derivatives

Dimitri Alvarez-Dorta, E.I. Leon, Alan Kennedy, Angeles Martin, I. Perez-Martin, Concepcion Riesco-Fagundo, Ernesto Suarez

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish typeII photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enolexo)-exo-trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 degrees C).

Original languageEnglish
Pages (from-to)10312-10333
Number of pages22
JournalChemistry - A European Journal
Volume19
Issue number31
Early online date20 Jun 2013
DOIs
Publication statusPublished - 29 Jul 2013

Keywords

  • hydrogen abstraction reaction
  • photochemical reactions
  • effect-stereoselectivity relationship
  • photochemistry
  • ring contraction
  • aonomerical radical reactions
  • cyclopentitols
  • stereocontrolled photocyclization
  • ene reaction
  • diketones
  • conformational restriction strategy
  • transition-state
  • carbohydrates
  • alkoxy radicals

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