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

Abstract

Abstract The separate, radical denitration with Bu 3 SnH 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 4:1 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.