A novel one-pot conversion of tetraacetal tetraoxa-cages to aza-cages mediated by iodotrimethylsilane in acetonitrile

Abstract

Treatment of the tetraacetal tetraoxa-cages la-f with excess of iodotrimethylsilane in acetonitrile at 25 °C gave the novel tetraacetal trioxamonoaza-cages 2a-f in 75-80% yields respectively, a novel one-pot conversion of oxa-cages to aza-cages. © 1997 Elsevier Science Ltd.The reaction chemistry of acetals has been greatly expanded by the use of Lewis acidic promoters particularly in conjunction with silicon-containing nucleophlies) '2 Usually, acyclic and monocyclic acetals, especially the acetal groups in monosaccharide derivatives, are the objects for study. 3 Recently, we accomplished the synthesis of novel oxa-cage compounds, such as tetraacetal tetraoxa-cages, 4 tetraacetal pentaoxa-cages, ~ triacetal trioxa-cages, ~ diacetal trioxa-cages, 7 and pentaacetal pentaoxa-cages (the pentaoxa[5]-peristylanes), s All these oxacages have acetal and ketal groups on the molecule. As part of a program that involves the synthesis, chemistry, and applications of new heterocyclic cages, we report here a novel one-step conversion of oxa-cages to aza-cages mediated by M%SiI, leading to formation of novel tetraacetal trioxamonoaza-cages. To our knowledge, a one-pot conversion of acetal group to monoazaacetal group mediated by Me3SiI has not yet been reported. ~,2Reaction of the tetraacetal tetraoxa-cages la-lf with three equivalents or more of iodotrimethylsilane in acetonitrile at 25 °C for 4 h gave the novel aza-cages 2a-2f in 80-85% yields (Scheme 1). This novel conversion takes place regioselectively on the C(3)-O(4) or 0(4)-C(5) bond. No detectable amount of the other regioisomers 3, 4, or 5 was obtained. We attribute the highly regioselective oxygen-nitrogen conversion reaction to the unusually large bond angle