Chiral Multifunctional Isoprene Units by Ring-Contraction of Riboside Oxiranes

Article abstract of DOI:10.1021/jo00371a002

Lithium bromide induced ring-contraction of benzyl 2,3- and 3,4-anhydro-β-D(and L)-ribopyranoside (1 and 4) in HMPA/toluene or tetramethylurea (TMU)/toluene gave (R)(and S)-2-(benzyloxy)-2,5-dihydrofufan-4-carboxaldehyde (2 and 5) together with a small amount of benzyl 4-bromo-4-deoxy-β-L(and D)-lyxopyranoside (3 and 6).The latter compound was formed with lithium bromide in 1,1,1-trichloroethane.Benzyl 2,3- and 3,4-anhydro-2-deuterio-β-L-ribopyranoside (4d and 8d) gave the deuterated aldehyde 5d, which carried a vinylic deuterium atom, wheraes benzyl 2,3-anhydro-4-deuterio-β-L-ribopyranoside (4d' ) gave the nondeuterated aldehyde 5.On the basis of these experiments, the mechanism of the ring-contraction as postulated.