Synthesis of unstable 4-benzoyl-1,6-anhydro-3-keto-β-D-mannopyranose via stereoselective photobromination of 2,3-isopropylidene-4-benzoyl-1,6-anhydro-β-D-mannopyranose

Abstract

Stereoselective photobromination of 1,6-anhydro-β-D-glucopyranose derivatives occurs at exo-H6. However, photobromination of 4-benzoyl-2,3-isopropylidene-1,6-anhydro-β-D-mannopyranose 6 produced unstable 4-benzoyl-1,6-anhydro-3-keto-β-D-mannopyranose 7. The mechanism of stereoselective oxidation at C-3 could be attributed to the facile radical proton abstraction at C-3, followed by the subsequent bromination of the isopropylidene group, which was subsequently eliminated during the aqueous workup. Thus, the aim of this article is to identify the molecular structure of the unstable compound 7.

Graphical Abstract

KEYWORDS:

• 1,6-anhydro-3-keto-β-D-mannopyranose
• 6-bromo-1,6-anhydroglycopyranose
• photobromination
• synthesis

Acknowledgment

We thank Dr Dai Hibbs, Department of Chemistry, Cardiff University, Cardiff, UK, for running the X-ray diffraction. Also, we thank the EPSRC for time allocations at the Mass Spectrometry Center in Swansea, Wales, UK.