192636-83-2Relevant academic research and scientific papers
α- And β-hydrogen eliminations in the reactions of some 3-O-triflylglycosides with (t)BuOK and pyridine
El Nemr, Ahmed,Tsuchiya, Tsutomu
, p. 267 - 281 (1997)
Previous papers [10-12] reported new reactions that occur when some carbohydrate triflates are treated with MeLi (or BuLi) in Et2O to give the C-methyl(butyl) or unsaturated compounds through elimination of the CH-hydrogen bearing a CF3SO3 group ( α-elimination) as a proton. This paper extends the previous work and describes the reactions for some 3-O-triflyl-D-gluco- and -allo-furanosides and -pyranosides with (t)BuOK and pyridine [instead of Me(Bu)Li], utilizing the corresponding 2- and 3-deuterated analogs. It was found that, when (t)BuOK was used, the 3-O-triflyl-D-glucopyranosides gave 2,3- and 3,4-unsaturated compounds through a-hydrogen elimination (a-elimination) followed by (possibly) C-3 carbene formation, while the 3-O-triflyl-D-allopyranosides gave mainly 2,3-unsaturated compounds through p-elimination. When pyridine was used, most of the compounds gave the corresponding 3-pyridinium derivatives through an SN2 process.
α-Hydrogen elimination in some 3- and 4-triflates of α-D- glycopyranosides
El Nemr, Ahmed,Tsuchiya, Tsutomu
, p. 77 - 87 (2007/10/03)
In previous papers [A. El Nemr and T. Tsuchiya, Tetrahedron Lett., 36 (1995) 7665-7668; A. El Nemr, T. Tsuchiya, and Y. Kobayashi, Carbohydr. Res., 293 (1996) 31-59] we reported new reactions that occur when some carbohydrate triflates are treated with MeLi (or BuLi) in ether, giving C-methyl (or butyl) or unsaturated compounds. Both reactions may be explained by α-hydrogen elimination in the triflates. This paper is an extension of the previous work and describes the mechanism of unsaturation of some 3- or 4-triflylates of α-D-glycopyranosides. By using deuterated analogs, it was found that methyl 2-O-benzyl-4,6-O-benzylidene-3-O-triflyl-α-D-glucopyranoside gives the 2,3- and 3,4-unsaturated compounds through a-hydrogen elimination, and the corresponding allopyranoside gives the 2,3-unsaturated compound through α- and β- (for 14) and α-hydrogen eliminations (for 19). Carbene formation is proposed as the key intermediate for the former eliminations, and a 1 → 2 proton-shift is proposed as the key reaction for the latter.
