Synthesis of Highly Functionalized Chiral Nitriles by Radical Fragmentation of β-Hydroxy Azides. Convenient Transformation of Aldononitriles into 1,4- and 1,5-Iminoalditols

The synthesis of highly functionalized nitriles by an alkoxyl radical fragmentation of cyclic β-hydroxy azides is described. The alkoxyl radicals were generated by reaction of the alcohols with (diacetoxyiodo)benzene and iodine under mild conditions compatible with the presence of sensitive substituents and the protective groups most frequently used in carbohydrate chemistry. To explore the scope and limitations of this methodology, experiments were carried out using a variety of β-hydroxy azides of the carbohydrate (1 − 6, 33, and 41), monoterpenoid (21 and 22), and steroid (23 − 25) families of natural products. Of special interest are the aldopentonitriles (15 − 18, 34, and 42) and aldotetrononitriles (19 and 20) synthesized from the corresponding 2-azido-2-deoxycarbohydrates. To demonstrate the versatility of these aldononitriles as chiral synthons, 1,4-imino-1-deoxysugar (37) and 1,5-imino-1-deoxysugar (43) analogues of the polyhydroxypyrrolidine and -piperidine types were prepared.