Deoxygenative [1,2]-Hydride Shift Rearrangements in Nucleoside and Sugar Chemistry:  Analogy with the [1,2]-Electron Shift in the Deoxygenation of Ribonucleotides by Ribonucleotide Reductases1

• Published in: Journal of organic chemistry 2007-10, Vol.72 (22), p.8216-8221
• Main Authors: Robins, Morris J, Nowak, Ireneusz, Wnuk, Stanislaw F, Hansske, Fritz, Madej, Danuta
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo071102b

A variant of the semipinacol rearrangement that was observed in our laboratory has been applied to the synthesis of several furanose and pyranose derivatives. The process consists of an “orchestrated” [1,2]-hydride shift with departure of a leaving group from the opposite face. Transient formation of a CO group is followed by rapid transfer of a hydride-equivalent from the same face from which the leaving group departed, which results in double inversion of stereochemistry at the two vicinal carbon atoms. Treatment of 2‘-O- and 3‘-O-tosyladenosine with lithium triethylborohydride in DMSO/THF gave the respective 2‘- and 3‘-deoxynucleoside analogues with β-d-threo configurations. Identical treatment of 5‘-O-TPS-2‘-O-tosyladenosine gave 9-(5-O-TPS-2-deoxy-β-d-threo-pentofuranosyl)adenine. The same [1,2]-hydride shift and stereochemistry with the 5‘-OH and 5‘-O-TPS compounds demonstrated the absence of remote hydroxyl-group participation. Application of this process to other nucleoside 2‘-O-tosyl derivatives gave the 2‘-deoxy-threo compounds in good yields. The reaction-rate order was OTs ≈ Br ≫ Cl for 2‘-O-tosyladenosine, 2‘-bromo-2‘-deoxyadenosine, and 2‘-chloro-2‘-deoxyadenosine (all with β-d-ribo configurations). Analogous results were obtained with mannopyranoside derivatives with either 4,6-O-benzylidene protection or a free OH group at C4. Deuterium labeling clearly defined the stereochemical course as a cis-vicinal [1,2]-hydride shift on the face opposite to the original cis OH and OTs groups followed by hydride transfer from the face opposite to the [1,2]-hydride shift. Synthetic and mechanistic considerations are discussed.