Deoxy‐nitrosugars. 6th communication. Stereoelectronic control in the reductive denitration of tertiary nitro ethers. A synthesis of ‘C‐glycosides’

Abstract

SummaryThe separate, radical denitration with Bu3SnH of the pyranose derivatives 3, 4, 9, and 10 gave in good yields exclusively the 'C-glycosides' 5 and 11, respectively (Scheme 1). Similar reduction of the cyclohexyl derivatives 15, 16, 19 and 20 gave 4:l mixtures of 17, 18, 21 and 22, respectively, always with predominant formation of an axial C,H-bond. In the furanose series a divergent behaviour was observed for the D-mannose-derived nitro ethers 25 and 27 and the D-ribose-derived nitro ethers 30 and 31, respectively, in that the former two gave isomerically homogeneous reduction products (26 and 28, respectively; Scheme 3) and the latter a 1 : 1 mixture of the diastereoisomers 32 and 33 (Scheme 4). The stereochemical results were explained on the basis of the stereoelectronic effect of the ring O-atom, the preferred conformation of the intermediate, pyramidal alkoxyalkyl radicals and steric effects in the trioxabicyclo [3.3.0]octane ring system. As far as it is known, these reactions follow a radical-chain mechanism and proceed via planar radical intermediates. As expected, the few stereochemically relevant reductions so far studied occur without stereospecificity [2] and with a variable diastereoselectivity [7] which is difficult to predict2).In the case of conformationally biased n-nitro ethers, however, the analogous reductive denitrations are expected to occur with a high degree of diastereoselectivi ty .

The synthesis of d-C-mannopyranosides

“…This procedure was shown to be very efficient, giving the b-C-mannopyranoside in both cases (Scheme 60) [207].…”

Recent Advances in the Synthesis of C‐Oligosaccharides

“…Anomeric nitro derivative 32 was treated with TBAF and exposed to aldehyde 33 to give the adduct 34 in 78% yield. Acetylation of 34 followed by reductive denitration afforded 35 (Scheme 8) [16].…”

Synthesis of glycosyl dipyrromethanes

“…[1][2][3][4][5][6][7][8][9][10][11][12] In the course of our research, fluorophores that are suitable for labeling biomolecules such as carbohydrates and nucleic acids are required. These fluorophores should be relatively insensitive to pH and polarity changes, stable in physiological conditions, and emit intense fluorescence.…”